I have to say, this article is exceptionally disappointing. As someone who works in this space, there are numerous misleading depictions about the state of the field. Almost any respectable simulation shows that disk galaxies are widely present at very early times. This is simply an argument of angular momentum conservation and these rotational states are simply more transient at early times compared to the local Universe.
"Yan found 87 distant galaxies behind the galaxy cluster SMACS 0723" --> this is not true. They found 87 galaxy candidates. To be fair to the article, they do note that these await spectroscopic confirmation but experts only believe those with spectroscopic confirmation. Everything else is tentative and we don't yet have good numbers on confirmation rates. Finally, the Yan et al candidates are wildly inconsistent with almost every other estimate of high-redshift galaxy samples. You can see a comparison in Table 4 here: https://arxiv.org/pdf/2212.06683.pdf. They claim more than double the number of high-redshift sources compared to everyone else. JWST data is still very new and hard to both reduce and analyze. One particular problem is correlated hot pixels which can appear as very high-redshift sources. I don't know if this impacts the Yan et al paper but just an example of something that is not 100% straightforward to deal with. I highly recommend people take this with a healthy amount of skepticism until everything has a spectrum.
Honestly, thank you very much for this comment. As a lay person, I very often fall into taking such news as solid, as am kind of hoping for some great breakthroughs in cosmology (broadly speaking). Thanks for providing details. "One particular problem is correlated hot pixels" has a nice, cooling effect on me and I get the idea that it is an unsolved issue (kind of get it). Same with "experts only believe those with spectroscopic confirmation" - fair enough. An antidote for getting fooled in this way by such articles (or YT video beating some popular notions over and over) is to read core material (like books) and seek some actual lectures, I think. That's a pity you can't skim some topic and have it right. You just can't and it only fills you with fake knowledge.
The need of counterpoints and different views are important especially in academic field. But some debates got us lost as well. I would not say bad against YT but more about lack of quality one. Hope that will come.
Take an example of MONO discussed below. One claimed it is right but wrong in other prediction.
“ So MOND does predict more galaxies at high redshift however it also predicts earlier reionization than LCDM which it turns out not to be true and the mass function of clusters is not what we see purely based on X-ray temperatures. So getting one thing right at the expense of many others doesn't make this particularly viable.”
But the major discussion shifted to dark energy and refracted … and totally ignored that wrong predictions by mono … it is just hard to follow the threads.
McGaugh came to support MOND over dark matter reluctantly for just such reasons—MOND routinely predicts things in advance that dark matter struggles to justify ex post facto, usually by adding additional moving parts to the model.
Whether or not you find the evidence persuasive, McGaugh's blog is worth a deep dive just to appreciate the subtleties and complexities of this kind of observational astronomy.
Any publications indicate whether Refracted Gravity (RG) predicts the same thing?
RG has always fascinated me, since it neatly explains flat rotation curves[1] without messing up the equations for gravity too much. If some refractory effect (TBD) causes gravity to bend toward mass concentrations, then this effectively "confines" gravity into a plane. Then the propagation law becomes 1/r rather than 1/r^2.
In effect it becomes a galactic analog of the SOFAR layer in the ocean.[2]
Intuitively the "self feeding" effect on disk formation should accelerate the process, but I'd be interested to see a full treatment.
>without messing up the equations for gravity too much. If some refractory effect (TBD) causes gravity to bend toward mass concentrations, then this effectively "confines" gravity into a plane. Then the propagation law becomes 1/r rather than 1/r^2.
There are objects like globular clusters and dwarf galaxies that lie outside the galactic plane, but are not that far away. If our galaxy's gravity was confined to its plane, you would expect nearby external objects to move differently from how they are observed to move. See illustration:
I was hoping someone would mention globular clusters! I couldn't find a way to integrate it naturally in my post.
I don't see any information about globular cluster movement in that image. Naturally the confinement wouldn't be 100%, and some amount of gravity would still "leak out,"[1] so the mere existence of globular clusters isn't proof one way or another.
Surveying globular clusters offers a good test. RG might (or might not) explain why globular clusters are mysteriously 1) preferentially orbiting perpendicular to the primary galaxy's rotation, perhaps due to stability, and 2) preferentially aligned with each-other in their own plane, perhaps due to mutual (lensed) gravitation. Both of these observations are otherwise unexplained (or require numerous free parameters) under dark matter.
We won't know until someone does a survey, and probably some simulation work. Sadly MOND soaks up most of the oxygen in the Modified Gravity field, leaving almost none for RG.
So MOND does predict more galaxies at high redshift however it also predicts earlier reionization than LCDM which it turns out not to be true and the mass function of clusters is not what we see purely based on X-ray temperatures. So getting one thing right at the expense of many others doesn't make this particularly viable.
It seems to me, as a layperson, if MOND was hypothesized first, it would be the dominant theory. It’s so elegant and simple with so much explanatory power. However, because it was hypothesized much later, the fact it matches past predictions is given no weight, despite its simplicity.
I think this is a bit of a mistake. I believe that simplicity itself is evidence. Dark matter theory is starting to feel like the epicycles of Copernicus.
If MOND completely described observable phenomenon it would supplant dark matter, but it doesn't. MOND still requires dark matter, just less of it. Or, to quote Milgrom, "some standard matter in some form that has not been detected"[1]. Which, IMHO, is nearly isomorphic to DM as far as statements go.
So until we figure out what the missing mass is, MOND is widely viewed as an unnecessary complication. There is missing mass, if we figure out the nature of DM or discover this hitherto unknown "standard matter" then we can talk about modifying universal gravitation.
The explanatory power of dark matter is so weak though. With the right clumping of LCDM you could probably also explain various reports of poltergeists around the world.
Then you could claim that reports of poltergeists are evidence of LCDM over MOND because it's another phenomenon that MOND can't explain.
However, there is plenty of evidence to suggest that it does exist.
The distribution of dark matter being uneven is evidence that something functioning like dark matter has to exist as MOND doesn't easily replicate that. Colliding galaxy clusters show a distribution of matter that differs from the distribution of visible matter, so the simplest explanation is that there is invisible matter that reacts gravitationally.
The simplest explanation is that there is regular matter which we fail to detect. Not weird, given the huge distances involved - there almost assuredly is mass that we didn't detect (e.g. planets).
The point where fairy matter comes in, is that we can guess how bad we could be at not detecting matter. Basically, regular matter that we didn't observe can't explain everything - we would've observed it otherwise.
Sorry, There are currently hard constraints on the lumpiness and size on that matter which basically exclude all reasonable possibilities for "normal matter we fail to detect". It's certainly possible something strange is happening though, or our statistics could be wrong.
That's not the simplest explanation as our current theories limit the amount of normal matter that can exist and galaxies behave gravitationally as though there must be a lot more than normal matter. Normal matter that is invisible to us is not a viable solution to the evidence.
> The simplest explanation is that there is regular matter which we fail to detect. Not weird, given the huge distances involved - there almost assuredly is mass that we didn't detect (e.g. planets).
What is the difference between that and dark matter?
> there almost assuredly is mass that we didn't detect (e.g. planets).
Don’t planets give off light and thus contribute to the distribution of light observed?
The GP is talking about MACHOs; MAssive Compact Halo Objects. They used to be a valid DM candidate but have been ruled out 20-30 years ago. Planets don't give off any non-negligible amount of light. However, they do consist of baryons (read: atoms) which would contribute to the baryonic accoustic oscillations in the CMB power spectrum, so that's a good probe to set upper limits on baryonic matter in general.
Primordial black holes are a somewhat related candidate; but those are mostly considered ruled out as well. They are not considered baryonic matter.
The evidence that it exists boils down to: gravitational anomalies. It's not multimodal, which is a problem because you're saying "it must exist because of x therefore it must exist" versus "it must exist because of x, which has a side effect of y, which aha also we see". That's why it's weak.
> the simplest explanation is that there is invisible matter that reacts gravitationally.
That's the whole point of the poltergeist example. If someone said: "Oh, that urn on your mantle just fell over? Must have gotten knocked over by a rogue ball of dark matter. The simplest explanation is that dark matter must exist". You would think they are insane.
You can think of dark matter as gravitational anomalies that aren't distributed uniformly. If we assume that physical laws are constant throughout the universe, then it becomes difficult to account for those anomalies without saying that there is "something" there that is influencing gravity. Obviously, we've labelled that "something" as dark matter and figured out what properties it can and can't have.
With your poltergeist example - if it was relatively common for urns on mantle to be knocked over, then it would make sense to come up with a hypothesis. If objects around the urn were affected gravitationally just before the urn falls over, then dark matter would appear to be a rational hypothesis.
This argument seems to pop up on HN every time dark matter is discussed. Unfortunately, it stems from a fundamental misunderstanding of how modern cosmology works.
The exact spatial DM distribution is not a parameter of the cosmological standard model. Instead, you assume an initial condition (pretty much a smooth distribution with only quantum fluctuations, which are parameterized by one or two parameters), apply the laws of physics to evolve this state some 14 billion years and compare the statistics of the theoretical and observed distribution.
In fact, DM suffers from the dwarf galaxy problem. Our theory predicts more than we observe. It's a bit of a challenge for DM, and considering how fuzzy our knowledge of galaxy formation is and how much other evidence for DM there is, it's not falsifying it yet. But if this is cemented by future observations it might very well be a blow to DM.
Besides, DM was hypothesized after measuring the famous rotation curves of galaxies. DM could have been easily falsified if we made gravitational lensing measurements afterwards and didn't see any DM. But we saw DM. Same thing with baryionic accoustic oscillations in the cosmic microwave background angular power spectrum. We looked there after we already thought that DM should be there, and the power spectrum looks just like if there is DM. It could have easily falsified DM, but didn't. The list goes on. DM could have been falsified may times, but passed almost all tests so far. Well, except for the ones in the lab, unfortunately.
It's not as if dark matter doesn't follow any rules at all - hypothetically, it obeys gravity like any other matter. So you can't have arbitrary amounts in arbitrary positions - you have to explain what attracted the dark matter to that position.
MOND mispredicts many, many past discoveries. This would have people scrambling for alternative explanations immediately. Dark matter is simply a better fit for what we see.
Second, I don't know why MOND seems simpler and more elegant to you than literally something that doesn't modify the laws of physics at all but just increases the mass you use in computations.
Two clusters collided, with most of the observable objects being just past the middle point right now, however most of the mass seems have already shot way out to the edges, as if it passed right through everything. It's pretty hard to explain with anything else other than that there's something there that has mass yet can't interact with anything else that passed through everything when the collision happened. Adjusting equations doesn't really work in this case, there must be something physically there.
I'm not sure why this isn't mentioned first thing every time in dark matter discussions because it's literally the only thing that's pretty hard evidence imo.
> however most of the mass seems have already shot way out to the edges, as if it passed right through everything. It's pretty hard to explain with anything else other than that there's something there that has mass yet can't interact with anything else that passed through everything when the collision happened.
It is my understanding that dark matter does interact gravitationally, so I am confused by this.
I should've been clearer there, "has mass" would mean that it interacts gravitationally and has inertia while moving. But that's about it, from what I understand.
I am too ignorant to weigh in on MOND vs dark matter, but this seems entirely possible.
In all domains - not only physics - there are many possible models that seem to match our observations. They’re continually adapted over time in order to meet to perceived needs and reality (see: the medieval European church).
Paradigm shifts can happen incremental or explosively. With the enormous sunk cost in our existing models - not least the millions of people educated in them - incremental change becomes harder. If MOND or any alternative theory is “true”, it faces a distinct challenge: there are decades of experiments and observations that have been fit to our existing model. To take over, it needs to answer _all_ of it - or provide so much utility that the incentives shift.
Success can be paralysing. In tech, a new idea can come along and shake everything up by showing results and solving a problem. The only way a new model of physics can do that is by generating a practical breakthrough. I hope I’m wrong!
Epicycles is what Copernicus fought against. Have he also have some I am not aware of ?!
Epicircle come about if one consider earth is the Center and some planets sometimes move backwards and then start to move forward again. You do not have that issues with Copernicus.
But he made a mistake of using circle. The observation guy using everything rotate around the sun and sun around the earth … a wrong model but the key is not the model but the observation he made. His record keeper Kepler finally found some other patterns and Newton get the … the rest is history.
I do not go to wiki or internet to check out the phrase. But epicircle …not of Copernicus.
I don't know if this instance qualifies as one, but I think its fair to say that cosmology is the one domain of "fundamental" physics where "discrepancies" or question marks keep piling up and not really resolving.
It the pattern of previous science revolutions repeats, there could come a point where reinterpreting the large existing body of knowledge using a different paradigm would explain an number of "oddities" in a more economical way.
I don't know if this generation of telescopes will get us there but it feels that this is a plausible outcome over the next 1-2 decades. Which would be very exciting :-)
I think this says less about cosmology and more about the incredibly effectiveness of the standard model in the regime we can test directly on earth.
If we compare ΛCDM to most other scientific theories it doesn't look so bad in terms of discrepancies. Certainly there are many unexplained effects in solid state physics, there isn't even an accepted explanation for why rubbing a balloon on your head makes it stick to a wall and that's an experiment you probably did as a child.
I had to look that up. Here's research[1][2] from 2019 about "why ice is so slippery", including some of the apparent surprises. I dunno. I'm not a physicist so some of the surprises seem like very minor things to me.
Spoiler: According to this research, ice is slippery because of a thin layer of water. (As we expected, no?) But the water layer is 1) thinner than expected, 2) more viscous than expected, and 3) contains bits of ice which help make it extra slippery.
> "Usual explanation is completely incorrect."
Only for an unusual definition of "completely" IMO. Again, IANAP.
Exactly, this it’s the new research. Standard (incorrect) explanation is because ice melts because of the pressure from the object put on it. Robert Wood showed it to be untrue at the beginning of the twentieth century, but “popular scientists” didn’t get the memo.
> Only for an unusual definition of "completely" IMO.
Agreed. While the "usual explanation" may lack the details that actual testing provided, deduction and logic in this case were pretty much harmonious with the findings. The water layer being thinner or more viscous than expected doesn't invalidate the basic assumption, and that's where all science starts, right? Some basic, yet to be disproved* assumption.
Maybe the ice molecules move through the water with less resistance, since the ice molecules are already 'tied up' in a lattice structure and therefore do not form as strong of hydrogen bonds with the neighboring water molecules.
That's just because your skin has water molecules that freeze on contact with the ice cube. If you use tongs to put an ice cube on your desk, it doesn't stick at all, right? And the friction is very low so it's easy to kick away -- things like a leather wallet stick much better to your desk.
I remember listening to joe rogan when he interviewed neil degrasse tyson and he had some fascinating insights into the behavior of water with relation to pressure and temperature.
I can imagine ice on an iceskate wanting to be solid, but because that takes up too much space it becomes a liquid instead.
The usual hypothesis is that a microscopic layer of the surface melts, not because your shoes are warm, but because of the pressure. But the pressure is not enough to do that.
That said, as anyone who has been in icy conditions can attest, it is clear that ice at ~0° C is vastly more slippery than at, say, -20°C.
My understanding is that, at the borders, master is constantly changing between its states. A boiling pot has water molecules turning to steam, as well as vice versa. It just has more of the first probabilistically.
That's more or less it, as far as I understand. There's the hexagonal lattice of solid water ice, where hydrogen bonds form a 3D tetrahedral structure which is very stable. At the boundary, there are no molecules "above" the solid latice, so those water molecules are held less tightly. The exact dynamics are challenging to predict because we can't exactly see what's going on (most simulation based).
The pressure from well distributed static load divided by area is not, but on the tiny scale where the difference between grippy and less grippy surfaces happens there isn't so much "well distributed" going on. And once you add lateral force to the mix all bets are off: there will always be a point getting better grip (is surface interference the correct term?) than others, see a local force concentration and when that causes a tiny spot of phase transition there will very soon be a new point of least local slippyness getting all the attention of lateral force.
", it is clear that ice at ~0° C is vastly more slippery than at, say, -20°C."
There is nothing more slippery in my experience, than rain on the street, that just turned frozen. But ice at -20°C is usually older and has not such a smooth surface anymore, so hard to compare in non lab settings.
If that were the case, then cold things wouldn't slip on ice, but they do (for a demonstration, pick up a rock that's been sitting out in the cold and note that it still slides on ice)
I'm not sure a cold rock sliding across very cold ice will slide any better than if the ice was another very large smooth rock. Ice is hard and smooth. Hard smooth things have low friction.
My favourite example of the intractabilities of some theories is that magnetohydronamics apparently can't predict the formation of streamer jets when you put your finger on a kid's plasma ball – i.e. the main point of the toy is beyond the most advanced theory that lies behind NIF, JET, ITER, etc...
I don't think I've ever, out of all my physics classes up to grad seminars, been given the impression we have everything figured out. In fact, it was hammered into us that all we have are "effective" theories, at least when it comes to high energy physics, and that's not even talking about grand unification (electroweak + strong force unification), let alone Theory of Everything (electroweak + strong + gravity).
Maybe not where you studied, or at the level you studied, but in upper division undergrad physics at a top tier California school I definitely was given the impression that I should just crunch the numbers and not think too much about how it might be working.
Was this a quantum mechanics class? Thinking about how it might be working leads to strange things like the Many-Worlds Theory[1] and other very weird ideas. "Shut up and calculate" is the usual method of dealing with these deeper questions.
So much this! There’s surely a huge argument that all of scientific education is a massive disservice.
The point should be to learn and appreciate the method or process of scientific investigation of uncertain and mysterious or hard to understand phenomena.
Instead we get dogma as a proxy of measuring intelligence with little regard for what the fundamental tools are of being a scientist.
I’ve gone all the way through to Grad School and came out astounded at just how little commitment to or a sense of the essence of scientific investigation and what’s expected of the investigator there is in the system. They don’t prepare you for it because they themselves weren’t prepared. You can try to leverage some meta understanding of the “process” in conversation or debate, but so often the conversation falls flat because few are prepared or accustomed to it. Research is often done, IMO, in philosophical poverty by people eking out a living in the gutters of novelty and paradigmatic safety, averting their gazes from the sky (flourishes aside, you get my point).
Putting aside the health of actual research. If the general public is to benefit from education and pass that benefit into their society (that’s the point right), it needs to be more than soon to be forgotten and often useless fallacies.
> There’s surely a huge argument that all of scientific education is a massive disservice.
> If the general public is to benefit from education and pass that benefit into their society (that’s the point right), it needs to be more than soon to be forgotten and often useless fallacies.
I realize this is hyperbole, but still I think it's obvious that there is more than soon to be
forgotten and often useless fallacies.
I do generally agree though that current models/paradigms are usually presented more as "the final word" vs "a useful mental model".
Esp. when paradigms are challenged by, or conflict with untestable traditional explanations, ppl tend to get irritated and overstate the confidence of their own understanding
Agree. I’m guilty of descending to hyperbole at times!
Nonetheless, while I agree with your pushback, I do wonder how much utility there is in the “dogma” approach. There’s a lot of “facts” being thrown around in education, from what I’ve seen, that are often forgotten or become vague memories. How much better would it be to focus on skills and practice and concepts? Especially in the digital age where a fact is easily discoverable, provided one has the appropriate research skills.
Who do you think makes it appear we have it all figured out? That is not my impression at all. All the scientists I know are extremely aware of the limitations of their field.
It is easy for children to come up with questions for biologists that none can answer, and that none has even tried to answer.
Biologists are almost unique among scientists in being happy to say how little they still know about their subject. Up until last year nobody had thought to see whether anything eats viruses! Turns out some do.
To be more precise, viruses are just made up of proteins and DNA / RNA. Your normal digestion that can handle proteins and DNA/RNA from animals, plants etc doesn't have any more problem breaking down virus proteins into amino acids and absorbing them.
I think the OP was talking about the bacteria that derive non-negligible sustenance from viruses.
>Moreover, our foraging trials demonstrated robust growth in the Halteria population with only chloroviruses as food (rint = 0.66 ± 0.26 [SD], black lines, Fig. 1A), with minimal to no growth in the controls (with chloroviruses filtered out; rint = 0.22 ± 0.12 [SD], blue lines, Fig. 1C). The abundance of the larger Paramecium did not increase in treatment or control trials (Fig. 1D), indicating that not all ciliates can grow on chloroviruses in these conditions, even when they consume them.
How could you possible find a citation for that? It’s not even pretending to be a scientific or totally objective claim. Asking for a citation for this type of statement is no way to have a discussion. Do you not see why?
Eh, 'Citation needed.' was my admittedly somewhat snarky way of calling bullshit.
Most any scientist will happily babble all about the stuff they don't know yet in their discipline, because that's exactly where the excitement lies for them.
> Much of Wikipedia is "curated" by retired professors carefully scrubbing mention of anything new that makes their graduate thesis look ill-conceived.
What makes you think so? What evidence do you have?
Magnetohydrodynamics is, specifically, the "easy part" carved out of plasma fluid dynamics. It is inadequate to almost all applications, with only rare, precious exceptions, mostly manufactured. Devices that rely on plasma fluid dynamics to work are carefully designed to keep the plasma in the domain where MHD can be used to model them.
Astrophysicists, as a rule, hate to be obliged to consider phenomena that involve plasma fluid dynamics, even what can be shoehorned into MHD. Such phenomena are thus orphaned, and you won't find anybody talking about them.
The exception is solar physics, where nothing can be done at all without fully general plasma fluid dynamics. Solar physicists have the largest gonads in science, on par with rocket propellant chemists.
I think most consider it "somebody else's problem". I know some don't like to think there is anything to it beyond MHD, so they call anything involving plasma "MHD".
Are there other phenomena they see but don't like to talk about? Maybe?
It has several commonly unphysical assumptions, including infinite conductance, "freezing" the magnetic field in a chosen frame, and assumptions about time and length scales.
"Effects which are essentially kinetic and not captured by fluid models include double layers, Landau damping, a wide range of instabilities, chemical separation in space plasmas and electron runaway."
That electrons are 1836 times less massive than the lightest positive charge carrier is neglected. Accelerated, they strike positive and neutral particles and knock loose more electrons.
> The triboelectric effect is very unpredictable, and only broad generalizations can be made.
> The mechanisms of triboelectrification (or contact-electrification) have been debated for many years, with possible mechanisms including electron transfer, ion transfer or the material's species transfer.
> Recent studies in 2018 using Kelvin probe microscopy and triboelectric nanogenerators revealed that electron transfer is the dominant mechanism for triboelectrification between solid and solid.
> For a general case, since triboelectrification occurs for any material, a generic model has been proposed by Wang, in which the electron transfer is caused by a strong electron cloud overlap between two atoms for the lowered interatomic potential barrier by shortening the bonding length.
So, still very much misunderstood. There is an experiment showing the dominant mechanism (so still only explaining a part!) between solid-solid and a generic model proposed that can be used to explain other interactions (solid-liquid, liquid-liquid, etc).
Unless there's a tested model with predictable results, I'd say we're not really understanding it properly.
> So, still very much misunderstood. There is an experiment showing the dominant mechanism (so still only explaining a part!) between solid-solid and a generic model proposed that can be used to explain other interactions (solid-liquid, liquid-liquid, etc).
This seems like a very large part, no?
I mean, we know it works, we get the majority of it, and it doesn’t seem super necessary to spend a lot of dollars and brain power to satisfy an internet debate on a theory of rubbing a balloon on one’s head.
I get your point. However, this is worked on by researchers who get paid to work on unsolved problems. This is one of them. It's a surprising one, since it looks like such a simple and obvious effect governed by physics we've (seemingly) understood for centuries. Gauss's Laws are from 1773 and much of the work on static electricity is from that era.
So, it's not just an internet debate. Knowing how things work _exactly_ is what scientists do. Getting the majority is not good enough.
And yes, that will often surpass the scale of "Is what we're doing useful?". However, won't know until we find out. Most likely understanding this effect will not bring any revolutionary insight but we should understand it nonetheless. Maybe our understanding will help someone else solve a problem, that solves another problem, that solved another problem, that gives someone a brilliant idea.
Maybe there are researchers who want to study the discrepancies of static electricity but if they don’t get funding, then they won’t be paid and have to take other priorities.
Seeming to demand these problems are resolved is a road to cynicism, in my opinion.
Clearly you've never recalibrated the thermal interferometery scanner so you can reverse the polarity of the neutron flow in the isoneutronic pulse wave carrier.
We do not call it witchcraft, because that is the end of the discussion and the answer. We call it unknown because it is knowable and is the beginning of the experiments.
>We do not call it witchcraft, because that is the end of the discussion and the answer.
Also, we'd have to eliminate the practitioners for clearly being witches. We've had that period and history, but it seems some modern day people are content to bring that very time period back.
"Friction-driven static electrification is familiar and fundamental in daily life, industry, and technology, but its basics have long been unknown and have continually perplexed scientists from ancient Greece to the high-tech era. [...] To date, no single theory can satisfactorily explain this mysterious but fundamental phenomenon." --Eui-Cheol Shin et. al. (2022)
My understanding is that the standard model likely does predict static electricity, but since it's a phenomenon bigger than a few molecules, we have no way to actually run the simulation. The physics is willing but the computers are weak.
My favorite poorly understood phenomenon in basic physics is the Mpemba effect, where hot water can freeze faster than cold water under certain circumstances. It's just phase changes of water in a simple experiment you can do at home, and I think there's still no widely accepted explanation.
> the actual occurrence of the Mpemba effect is a matter of controversy
> In 2016, Burridge and Linden defined the criterion as the time to reach 0 °C (32 °F; 273 K), carried out experiments, and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers: "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect."
> In controlled experiments the effect can entirely be explained by undercooling [water may cool below the freezing point without actually solidifying] and the time of freezing was determined by what container was used.
That's because nobody's replicated that effect in a real lab. People who claimed to observe effect didn't even bother to bypass the freezer thermostat and force the compressor to stay on, nor did they measure power consumption. It's just shoddy science.
> there isn't even an accepted explanation for why rubbing a balloon on your head makes it stick to a wall
You mean dielectric moments and static electricity? Electromagnetism is the one thing we know the most about. It's that spooky gravity junk that makes us scratch our heads. It never seems to behave quite right and doesn't mesh with all the other forces.
> You mean dielectric moments and static electricity?
You're confusing what with why. My understanding is that everyone knows it has something to do with electrons collecting on the balloon; but nobody quite knows why rubbing rubber against hair causes the electrons to do that.
Often the gap between what and why is enormous. Humanity began curing meats to protect against microorganisms around 3000BC. The effect of what was going on was immediately observable, but it wasn't until 4500 years or so later that we discovered the why of microorganisms.
I think I got confused because I was thinking about why it stuck to the wall, rather than why it accumulated charge. I know why electrically charged objects stick to things. The why of how they got like that is a bit different as you mentioned. Triboelectric effect is spooky, but there are some theories. It's one of those non-linear messy quantum things that's a pain in the neck to solve.
> That is exactly equivalent to "dunno, maybe something".
Yup! It's like understanding the why of weather and people. They are messy and have so many factors you can't account for. It's like saying, why are the clouds shaped like that. You can why your way down, but it's turtles all the way!
When it comes to non-linear junk, the why becomes mixed up because the causes are so numerous. There are so many tiny interactions you can't really say there is one individual cause. Often times you have phenomena that occur at specific energy levels that aren't really caused by any one thing. Even something as simple as a double pendulum is unpredictable.
One thing that is kind of mind blowing is strange attractors. Systems that are so random you cannot predict them even a few moments later can exhibit seemingly ordered patterns. They seem to have a cause, but they are literally just statistical mechanics. A slightly more likely outcome out of un-countable numbers of other outcomes.
It is entirely possible that global warming could tip us into the next ice age, though probably not in our lifetimes.
First you would need a world-wide cloud layer reflecting insolation back without conversion to IR. As the temperature drops, ice forms. When the clouds dissipate, the ice takes over reflecting sunlight out.
Or it could return us back to the hothouse earth of the cretaceous era. Or it could turn our entire planet into a second Venus with a runaway effect from all the methane. Or it could do almost nothing at all. There is just no way to know because it's never really happened before. We are playing with fire for sure.
There's a joke that calling Computer Science Computer Science is like calling Astronomy Telescope Science, but part of what makes it funny is the ring of truth to it. Our instruments really do limit our observations. The advantage Computer Scientists have is that we can glimpse a world of Platonic Forms[1], where Functions, and Sets, and Information exist, or something close enough for government work, merely through the intellect. Astronomers have no such luxury.
[1] Or whatever circumlocution you prefer to express the same general concept.
Astronomers probably should go on the quest for immortality since otherwise you are basically condemned to look at a still image. Even if that image contains a story from the earliest universe until now. It is a million states, but no real process.
What I find so fascinating is that the observations are still quite precise. How do you know the outer rims are rotating too fast? Couldn't this be some gravitational lensing and stars are actually much closer to the core than they appear?
How do you even begin to estimate the mass of a galaxy? How do you weight the behavior of a disc and combine it with keplers law to even see that something is wrong here? As a layman I would be perfectly happy with how galaxy are rotating... I find it fascinating that much is so precisely determined that we have to miss something.
Computer Science doesn’t get the pass, unfortunately. First of all because it’s a branch of maths, so in reality it doesn’t have any instruments to worry about.
Secondly, applied CS relies on an incredibly simple instrument: binary logic gates. The computers we have today are just a mesh of stuff that flips on and off with no intermediate states. That’s pretty primitive as a means of expression and computation compared with the rest of the universe
A lot of people think that computer science is just a branch of maths. But when I was doing my doctorate, I was a computer scientist, and my three supervisors were a mathematician, an engineer, and a meteorologist. The difference between us was much more than the stuff we knew - it was the way that we thought, and therefore approached a problem. Supervision meetings were interesting - it very much felt like four people speaking four different languages.
On a very broad level (and I'll get loads of people disagreeing with this, because both mathematics and computer science divide further into different specialities), mathematics is primarily about proving logical truths, whereas computer science is about managing complexity. That's a massive cognitive difference, even if many of the problems the two fields tackle are the same.
> The computers we have today are just a mesh of stuff that flips on and off with no intermediate states.
Only when things are working properly and there isn't too much cosmic radiation, interference, strange patterns accessing memory, someone turning on a light…
I feel for the Weather pattern folk. All of the one I have spoken to over the years are pretty cool. They are trying to model an insanely complex system - oh but thanks to global warming they are struggling to make models that work for longer than a few years because it all keeps changing!
If “it all keeps changing”, which thwarts their attempts to “model an insanely complex system”, then wouldn’t that mean any claim about “global warming” is actually a claim to possessing a priori knowledge?
No. That the planet is warming is incontrovertible. What this might mean for highly interdependent, chaotic systems is harder to predict. Will the Greenland ice sheet melt? Looks like yes. Will that affect the Gulf Stream? Probably. Will that make Spain colder? again, probably, but the error bars are bigger, and so on.
It just sounds like global warming is giving them good test data. A comprehensively accurate model should be able to take e.g. a Greenland ice sheet melting in stride.
It's a lot of factors that they didn't even consider in the first place; decades ago, the Greenland ice sheet melting wasn't a consideration. Similar things: The north pole ice cap melting causes less sunlight to be reflected back into space, adding to the warming effect. Or the huge areas of permafrost melting (not so perma now, but for earlier models they would have considered permafrost not an issue), which causes sequestered biomatter to start decomposing and releasing tons of methane.
Forest fires were probably in the model, but they seem to be intensifying due to (mis)management and droughts. The Amazon rainforest probably has a significant impact on weather and weather models, but under Bolsenaro a lot of it was cut down and burned. And it goes on.
No as has already been answered. The example I can directly think of is modelling of specific weather patterns across Australia. A model that works in predicting weather 2 weeks out may work today but not work so well in 5 years.
Global Warming is happening, that is not just a realm of modelling but is directly observable today. The models on a broad scale look to be working very well, specific locations and reactions not so much.
It is possible to make broad engines that work but also get the finer details wrong. Signal : Noise ratio and all of that.
We know very well how carbon dioxide interacts with infrared radiation (easily tested with an IR spectrometer), and we know human activity releases enormous quantities of carbon dioxide into the atmosphere, which does not magically disappear.
Precise predictions are hard, but the general direction of travel cannot be seriously disputed without arguing against the above simple facts.
Carbon dioxide is actually a relatively weak greenhouse gas. At least compared to water vapour, or even methane.
Btw, CO2 does 'magically' disappear. Into the oceans. Alas, from what I've read it'll take about 2,000 years to do so.
> [...], but the general direction of travel cannot be seriously disputed without arguing against the above simple facts.
I don't want to argue against global warming, but I want to argue that can't argue against global warming without arguing against your 'simple facts'.
Your 'simple fact' about CO2 could be true, but global warming could still be a myth. (I don't think it is; but your argument is far from sufficient. It's a complex system. Eg from time to time volcanic eruptions produce a lot of CO2, but they are typically associated with a cooling of the climate, because of other factors.
Similarly, burning coal releases a lot of CO2, but it also used to release a lot of SO2. Locally, SO2 is pretty bad (ever heard of acid rain?), but SO2 converts to sulfuric acid aerosols that can block solar radiation. These days most coal fired power plants have measure to avoid spewing so much SO2.
It's conceivable someone could find a coal so 'dirty' with sulphur, that burning it would decrease temperatures. I don't think it's very likely, but it's conceivable. So you need more empirical observations, than just your simple facts to make your argument.)
I understood their point to be that that based on our understanding of basic physics and chemistry, the energy balance is such that the Earth system is gaining energy, and that this will lead to increased temperatures among other things. Certainly there are all kinds of complexities about how that energy will be distributed and what the effects will be, but just in terms of a simple energy balance model based on well understood physics, it would be difficult to make the case that warming won't happen.
> Certainly there are all kinds of complexities about how that energy will be distributed and what the effects will be, but just in terms of a simple energy balance model based on well understood physics, it would be difficult to make the case that warming won't happen.
There are lots more effects. When lots of volcanoes erupt, we also see more CO2, but we see the climate cool down.
That's because the effect of the CO2 is outweighed by other factors. But exactly that there are lots of factors is my point.
Not in the long run. If CO2 levels are increasing and the energy balance into the Earth system is positive, then the basic physics that the original poster referred to will result in warming. The net energy increase of the system will result in a higher equilibrium temperature.
> Precise predictions are hard, but the general direction of travel cannot be seriously disputed without arguing against the above simple facts.
To add, the predictions re: global warming seem to have been too optimistic, and they were already gloom and doomsaying enough decades ago. I scoffed when I read a headline saying something about a specific glacier being gone in 100 years - I'm sure it'll be much sooner than that.
I don't think it is fair to characterize cosmology as not making progress no. Stuff is far away and occluded and hard to measure and see. Each improvement in observation causes a need to refine previous ideas, as expected. There are of course the two big mysteries that have lingered for a long time: Dark Matter and Dark Energy, but other areas of physics have lingering mysteries as well.
I almost had the same reaction, but technically they didn't say anything about cosmology not making progress. It's entirely reasonable to assume a scientifically minded person describing a field as "piling up question marks" means they think it's making a LOT of progress. Imagine a field that answers questions more often than it finds new ones; that'd be a pretty stagnant field to be in.
This is how I understood OP, too. Last time we had a "crisis in physics", it was the early transition from classical physics to quantum mechanics, when some good new ideas had been coinceived of, but trying to reconcile them with the classical way of thinking and with experimental evidence required increasingly convoluted hacks in the models to make it all work - until folks like Heisenberg, Born, Jordan and Dirac found more holistic and clean ways to approach the problem space.
The number of question marks piling up in cosmology does feel similar. It will help to shape new theories that reconcile all this experimental evidence.
Sometimes the questions keep piling up until someone happens up on just the right question. That question itself wouldn't have been thought of except for the thinking of all of the previous unanswered questions. Then the big Eureka!! moment and someone gets a Nobel prize 20 years later.
People dunk on cosmology because cosmologists have consistently, over decades, insisted, in public, that they knew more than they did, and are continually obliged to abandon what they insisted they knew. If they were more forthright about how much they don't know, they would get less criticism. They have much to learn from the biologists, who know they know practically nothing (even though massively more than you), and are happy to say so.
The health of a branch of science may be read from how eager its researchers are for you to know about what they have no clue about.
>cosmologists have consistently, over decades, insisted, in public, that they knew more than they did
Exactly, and each time the theories are proven wrong, it's explained as a never-ending series of "oddities", yet the theories are never altered in any meaningful way other than ad-hoc additions to explain each "oddity".
At some point there needs to be a reckoning that, for instance, the current theories of star formation are essentially completely wrong.
This is exactly what pushed me away from pursuing cosmology. One of the most important 'discoveries' in cosmology was that of cosmic inflation [1]. The issue is that if you model the big bang, what it creates is nothing like what we see. Regions of space that wouldn't have had time to have become causally connected (nothing could have gotten between them even traveling at the speed of light since the time of the big bang) are causally connected.
So the solution? There was some very specific period of acceleration, faster than light acceleration to some very specific degree, at some specific point right after the big bang which then ended at some other very specific point, at which point everything returns back to normal. What's the logic for it? Well if we do this, then what we see matches what we expect to see. It's an absolute retrofitting of numbers to make a model fit reality. And not only does that constitute good science in cosmology, it was sufficient to win a Nobel Prize.
It is literally unexplained magic being taken as a fundamental concept of science. And the worst part of it all is that it's completely unfalsifiable. We only have one universe to observe. So if it turns out that the discrepancy is actually being caused by many smaller effects we stand near 0 chance of ever discovering because each one of those small effects will have a million flaws, while the perfectly retrofitted inflation theory has "none." At worst they'll even get absorbed into the inflation theory model magic. Just add more epicycles!
It is one thing to identify a mechanism and show how in operation it must produce the numbers seen. It is entirely different to invent a name for a presumed mechanism, with no hint of how it happened to come to the numbers seen.
I was just thinking about video games where vegetation, animals, and hills spring into existence when you get close enough. Far away, and they don't bother to render the little things.
Depending what generation tech we're running on in the parent reality, JWST may be causing a noticeable jump in system load.
I had the same idea about magic. Back in the day people could do things that we can’t because nobody looked into details and the universe had enough “possibility space” to allow it. Once you turn your gaze into atomic or galactic workings, this space shrinks tremendously and further research becomes much harder because you glued the puzzle from its sides in a particular way and there’s not much left to hope for, except for solving it to the center in a bizarrely complex way. We may have painted ourselves into a horrible corner.
This is an excellent sci-fi premise. Also an interesting thought experiment to think of what an optimal research approach would be if you knew a priori that you were living in a universe in which the implementation details don’t exist until observed. Come to think of it, quantum physics is actually like this in some respects.
It may be more a question of a new generation of physicists, willing to consider that particle dark matter is not the explanation for the acceleration discrepancy.
Sadly, I'm to the point that unless we call it the Kardashian Space Telescope, the draw to new generations will not be there. We're closer to Idiocracy future than Interstellar future.
I think you're overly generalizing, I don't believe today's generation is much different from previous generations when it comes to interest in STEM and the like. Sure, their attention spans are different - I mean "ours" are due to the advent of the internet etc - but I don't believe their ambitions are that much different. It's just that they want to become youtubers instead of movie stars / musicians.
There is the esoteric "Cosmological Natural Selection" theory that predicts the discrepancies. This guy at https://theeggandtherock.substack.com/archive explains his version of this theory (albeit in an emotional way) that I find a pleasant read.
Would you bet that we'll see a paradigm shift of a similar nature to the classical physics -> quantum mechanics / relativity paradigm change, but for Cosmology in our lifetimes?
Yes, we are in the middle of a huge shift in the definition of intelligence. AND that could have enormous impact on our perception and ability to see reality.
I always wondered if we could somehow get a James webb telescope revolving around all planets of our solar system in the next 1000 years. That should give us pretty awesome visuals.
I want to venture that 1000 years is pessimistic. I just hope governments or private entities open up their wallets to build and launch more and better telescopes.
I'm reading the whole JWST project is estimated to cost $10 billion. That's about 4.4 overpriced Twitters, 77 US Department of Defense budgets (just for 2023), and 11.7 Facebook annual revenues.
We have the technology and the means, what's lacking now is the will.
There's definitely a benefit to placing a decent telescope outside the asteroid belt. From Earth, we get a lot of light reflected from the Sun from dust orbiting somewhere between Earth and 2 AU from the Sun, which pollutes our space images - it's called the Zodiacal Light [0]. A telescope outside this light pollution would be able to see faint objects much more clearly and easily than Webb.
not surprising imo, because of how limited our observational capabilities are. we'd probably progress quicker if we could look at far away stuff up close instead of from billions of light years away.
> It the pattern of previous science revolutions repeats, there could come a point where reinterpreting the large existing body of knowledge using a different paradigm would explain an number of "oddities" in a more economical way.
Could we train a GPT3 like model with the entire corpus of astronomical research and try to answer some questions that way?
GPT3 cant even play tic tac toe properly (at least in my attempts). What makes you believe it can build and manipulate a model of the universe, and then answer questions about that model in a way that goes beyond what humans can do?
I think it's a bit more subtle than whether it can synthesize, because clearly it can produce seemingly new work.
But what it definitely cannot do is seek new abstractions. It can't be curious about an inconsistency and probe its own knowledge for possible resolutions, or design an experiment that might shed further light in an unknown area. It can't even play a board game after ingesting the rules to it, much less identify contradictions or problems in such a ruleset. And a board game is a tiny microcosm compared with the laws of physics.
It's conceivable that one or more scientists could work in conjunction with an AI to help augment their own abilities, co-pilot style, but I don't think we have a picture yet of what exactly that kind of thing would look like.
I kind of feel like _all it can do_ is seek new abstractions. It’s clustering the data into what you might think of as “concepts,” even though we haven’t made all that much progress on interrogating those concepts directly. I just think clustering concepts by their latent relationships is sort of what abstraction is.
Hmm, interesting. I feel like that clustering/grouping part is like... the first stage on the way to finding an abstraction, but if all you've done is that part of it, then you haven't reasoned about what the abstraction is, or extrapolated out to a new hypothesis, or grappled with the other consequences of the grouping.
Thinking of mathematics, an abstraction is only as valuable as what it can tell us about the underlying system— a laplace transformation into the frequency domain isn't particularly interesting unless we either a) happen to care about some frequency domain property of the function, or b) we can manipulate the transformed function and then un-transform it afterward, yielding a novel insight in the original time domain.
My layman's assessment is that the current state of the art for machine cognition is about on the level of identifying that such a transformation might be possible, but not actually applying it or doing anything about it, much less unapplying it afterward.
I think I get the gist of your point which I would handwavily summarize as “there is no there there,” which I agree with. But I’m thinking that in terms of functionality, there is no real distinction here. Like If I train a model to do video game physics, and reward it for getting the tank shell missile to land on arbitrary targets, then in some sense the system must have an abstraction of gravity or at least parabolic movement or at least a functional equivalent of that, and it must be able to “hypothesize” about the consequences of its model because that’s what it needs to do in order to hit the target, ie, “everything I’ve seen before leads me to believe tank missiles move like so, therefore if I apply the following forces, it should hit the goal”—the degree to which it wins at this task is exactly the degree to which it can form working models of its environment and reason about the cause and effect of the actions it can take. But of course all those words in the previous sentence are wrong because it’s not exactly doing any of that, just something functionally equivalent and automatic.
Maybe we disagree about whether that last point means it can meaningfully “do abstraction” or not.
well, you could. And it might not be a complete waste of time. I would not expect any directly useful answers(...). But producing a semi-random collation of sentences that spans the corpus of cosmological facts and models and asking scientists to review / draw "inspiration" from it might remove some of the biases of the average cosmologist (like having to follow the latest publish-or-perish fad). This would only be useful if the answer is sort of hidding in plain sight (within the published stuff) and you tweak the algorithm not to ignore weird observations or theories that are not cited a lot.
But the beauty of science (and the human mind driving it) that important progress happens with creative jumps that invent completely new things (e.g., new mathematics) and frequently bear little resemblance to the past
If you give GPT3 code with a bug in it, and ask it to find the bug, it can't really do that. I'm pretty sure giving it all the data and asking it why things aren't working the way it should, it wouldn't have actual knowledge.
There's a depth to explaining things that GPT still can't do. It's still astonishing, and has completely changed my idea on what AI can do, like write plays with very incredible context (better than most humans!) but there are still major limits.
I think it's more likely a problem that the GP poorly worded their initial statement, rather than actually moving the goalposts. They were probably having trouble with a few thorny bugs, tried ChatGPT, got nowhere, and forgot to qualify their initial statement with "for the few non-trivial bugs I tried".
From the external point of view, the goalposts moved, but from within the GP's poorly expressed mental model, they haven't moved. But, that's just a guess.
FWIW, I've tried asking ChatGPT to walk through some thought experiments.
Things like, what happens if I shoot two bullet at c/2 in opposite directions on a train going at c/2? Now suppose, I'm an outside observer. And then trying to introduce quantum gravity.
My thought was that perhaps it could 'reason through'. Unfortunately, it was unable to. Eventually, it said that this is an unsolved problem. In other words, it 'recognized' the thought experiments. Perhaps if you use a phrasing that's not in the literature.
EDIT: Actually, just checked again, and chatgpt can't reason through relativity anymore:
Me: Imagine I'm on a train traveling at half the speed of light. I'm in the middle of a car and I fire bullets going at half the speed of light towards the front and back of the car. Do the bullets arrive at the front and back of the car at the same time?
ChatGPT: No, the bullet fired towards the front of the car will arrive at the front of the car first, while the bullet fired towards the back of the car will arrive at the back of the car later. This is because the front bullet is moving in the same direction as the train and the back bullet is moving in the opposite direction of the train. The relative velocity of the bullet and train will determine the time it takes for the bullet to reach the front or back of the car.
It is going to be like a drunk Michael Ross (the fictional character). I.e. great memory but too drunk to think beyond what can be recalled. If it’s corpus has the answer it will shit it out.
I think chatbots can probably answer known things, but we'll still need smart humans for original ideas.
That said, I can imagine a chatbot can help as a rubber duck, bring up things that weren't considered yet, or be so wrong as to kickstart the human into a breakthrough.
The article mentions that they're training neural networks to classify these objects. Give it a decade and this kind of high level number crunching will be as common as calculators are today. Transformers will find their place in all of this, and I am confident we will have a breakthrough in a few years regarding novel synthesis.
My favorite theory is that the universe is finite, some sort of (hyper)sphere or -torus. If we could just look far enough out there we would see our own galaxy
What would be even cooler is if it was warped like a moebius strip in a higher dimension, so that when we look out there, everything is mirrored from "our" reality :-D
That first theory would be interesting, but wouldn't it be basically impossible to prove unless the finite repeating universe were also pretty small? We see distant objects as they were in the past, and I'm not sure we'd recognize our own galaxy a billion years ago and a billion light years away.
It's actually an interesting thought experiment. If that theory were true, and assuming we could see ourselves face-on (rather than edge-on), then I wonder how far away and far back could we recognize ourselves.
Yeah, I realize we're looking in the past and can't "see" ourselves (probably not even our own galaxy, depending how far out we have to look). But I guess the theory in itself is not any more "weird" or "outlandish" as the idea of an infinite universe.
And maybe if we actually look both ways, we could find another galaxy that could be proven to be the same (because of some particularly remarkable stars/quasars/supernovae etc. in them). Who knows, maybe the universe is smaller than we think and we just don't recognize the "same" galaxies on different images because they are billions of years apart?
For all we know it might be - or it might actually be infinite - but the trouble is that we're limited by what we can see / detect, which is in turn limited by the speed of light.
Another commenter asked something like, what if the universe is much bigger than the observable universe, because everything beyond that 'border' has redshifted out of reach - or hasn't reached us yet / never will, because it's moving away faster than the speed of light.
That assumes that we can somehow see through time, which leads to a whole bunch of inconsistencies (aka time travel paradoxes). There's no way to look through large distances without looking back in time, unfortunately.
I don't see how seeing one's past may lead to paradoxes. Meddling withthe past would still be impossible, due to the,distance and the speed of light limit.
What am I missing?
The funny thing is that since we've been observing the universe for so little time, and we're so small, most of the evidence for the big bang and expansion is not direct, but a chain of deductions.
I mean that we can't observe the expansion because we can't really triangulate at galactic scale. If there is another reason the light from distant galaxies turn to red, kind of a long-distance light fatigue, we couldn't really know.
The reason I always heard that would be a confirmation, because it comes from a different causal path, was precisely the different composition of old galaxies. And now it seems they're not so sure.
> If there is another reason the light from distant galaxies turn to red, kind of a long-distance light fatigue, we couldn't really know.
It's not just red shift that demands an explanation, but also that the sky (space) is dark. If space wasn't expanding then the skies would be bright white.
Another thing is the second law of thermodynamics, which very strongly implies a lot of standard cosmology.
Of course, standard cosmology could be all wrong, but these deductions are quite solid as far as the physics that we know today.
It's not just red shift that demands an explanation, but also that the sky (space) is dark. If space wasn't expanding then the skies would be bright white.
Another thing is the second law of thermodynamics, which very strongly implies a lot of standard cosmology.
Don't you feel that these evidences just make a case from models checked in small scales and tell the whole universe what it should do?
I don't mean the reasoning is incorrect or unwarranted, just that there could be alternative explanations that involve unknowns.
Of course, standard cosmology could be all wrong, but these deductions are quite solid as far as the physics that we know today.
When applying Occam's razor, you try to minimize entities and simplify. But what appears simpler for a physicist is sometimes surprising for the rest of us. The equations don't work as expected? No problem, let's say that the entire universe is expanding or, even better, that space is expanding. Or that all the universe was at some moment in the space of a tennis ball. Or that big bang happened everywhere at the same time...
While some explanation fits the maths, it doesn't matter if it's totally alien to common sense. Actually I find all those weird explanations strangely appealing, they give me a sense of wonder and empowerment. Cosmology feels like a superpower :)
> Don't you feel that these evidences just make a case from models checked in small scales and tell the whole universe what it should do?
Yes, we like to think that the laws of physics we can deduce locally are global. That could be wrong, for sure. But consider that we understand the physics of our solar system (which has a star), and we see other stars in the skies which... implies that at least as much of our local physics that makes stars possible also applies where we see those stars.
Which is insanely far away and all light coming from there will have diminished in energy enough to be barely visible?
Inadequate explanation. Even if the universe was a closed box with perfectly reflecting borders, what you would actually see in the sky is something like an average brightness of the entire universe with some fluctuations.
It's not inadequate. Brightness diminishes for two reasons. One is absorption from cosmic dust (not that big of a factor), the other is that the object appears smaller, but the brightness per unit solid angle from the object does not diminish. If there were just more stars behind that you could see, the sky would have to be much brighter.
Photons do not "diminish" in energy except via red shifting (where does the energy go? into the expansion of the universe!).
Light scatters, gets absorbed and re-emitted, it's true, but if distances don't change then the universe would still be much brighter than it is today.
Any straight line you draw from earth to any direction in the sky will then reach a star.
Only if you think that there is infinite matter, all of it forming the same kind of stars, uniformly spread over the infinite space and there is no unknown form of atenuation for waves traveling millions or billions of years light.
> The reason I always heard that would be a confirmation, because it comes from a different causal path, was precisely the different composition of old galaxies
And you never heard of the CMB? That's generally considered the "smoking gun" evidence for the big bang.
Since everyone is mentioning their favorite whacky theories, mine is the one that says within every particle is a whole universe, made up of particles with their own universes and so on, and what we call our universe is really just a particle in an even bigger universe. And what if all of those universes were actually the same universe, like some infinite recursion?
[…] But to show him another prodigy equally astonishing, let him examine the most delicate things he knows. Let a mite be given him, with its minute body and parts incomparably more minute, limbs with their joints, veins in the limbs, blood in the veins, humours in the blood, drops in the humours, vapours in the drops. Dividing these last things again, let him exhaust his powers of conception, and let the last object at which he can arrive be now that of our discourse. Perhaps he will think that here is the smallest point in nature. I will let him see therein a new abyss. I will paint for him not only the visible universe, but all that he can conceive of nature's immensity in the womb of this abridged atom. Let him see therein an infinity of universes, each of which has its firmament, its planets, its earth, in the same proportion as in the visible world; in each earth animals, and in the last mites, in which he will find again all that the first had, finding still in these others the same thing without end and without cessation. Let him lose himself in wonders as amazing in their littleness as the others in their vastness. For who will not be astounded at the fact that our body, which a little while ago was imperceptible in the universe, itself imperceptible in the bosom of the whole, is now a colossus, a world, or rather a whole, in respect of the nothingness which we cannot reach? He who regards himself in this light will be afraid of himself, and observing himself sustained in the body given him by nature between those two abysses of the Infinite and Nothing, will tremble at the sight of these marvels; and I think that, as his curiosity changes into admiration, he will be more disposed to contemplate them in silence than to examine them with presumption.
For in fact what is man in nature? A Nothing in comparison with the Infinite, an All in comparison with the Nothing, a mean between nothing and everything. Since he is infinitely removed from comprehending the extremes, the end of things and their beginning are hopelessly hidden from him in an impenetrable secret, he is equally incapable of seeing the Nothing from which he was made, and the Infinite in which he is swallowed up.
If steady state gained favor that would be super fun, but this quote from the article seems to throw a little cold water on that.
> At the same time, she notes that yesterday’s disks are different than modern ones. “They’re not today's Milky Way,” she notes. “They're turbulent, they're messy, and we need to study them more.”
Experiment results that disagree with theory is EXCITING. I hope this contributes to progress and I'm giddy just imagining the model of the universe we have 50 or 100 or 500 years from now.
Great news. Finding stuff that doesn't fit into the current model and we need smart people to get to work understanding may be the surest sign that the JWST is invaluable.
Not only because it means we're about to learn some big stuff, but also because it would be completely *preposterous* if humans at our puny stage of development had already correctly figured out every last detail about insanely complex things like the exact size, age, and origin and age of galaxy-sized things that developed tens of billions of years ago, billions of light-years away from the tiny rock we stand on. Getting things wrong shows that people are actually doing science honestly!
We have known that the current model of physics is wrong for a long time. But the main focus has been on math. "If only we could figure out this formula, then we would understand everything"
It seems much more likely that we are not missing a formula but a basic understanding of reality. Much like the early astronomers trying to find a formula for the movement of the sun and planets that put Earth at the center of the universe
I really like this comparison. But isn’t the case with modern physics that we are getting something like 8 of 10 things right? So that’s a lot of correct triangulation - and throwing the current understanding out would throw all of that away - and potentially rearrange things.
Cosmology is one of those fields where I suspect we'll always be finding things that don't match with theory because we can never know nor replicate the initial state of the Universe.
There's also a lot of fundamental questions we don't have answers on. For example:
- What does space expanding actually mean? Is space stretching or is new space being created? If so, what is the mechanism for that?
- Is time a fumdanental property of the Universe or is it an emergent property?
- What are the fundamental intereptations of quantum mechanics [1]?
And so on.
The cosmic microwave background is our earliest yet observation from the Universe. Before this the Universe was really too dense and hot for radiation signatures to survive. Interestingly, we may be able to peak even earlier than that with the cosmic neutrino background [2].
But there are a ton of things about the early Universe's formation and expansion we will probably never know and will only be able to guess at with models that will always break at a certain point.
Not so sure. If we're not early ourselves, the likelihood that the universe is swimming in intelligence -- if not already part of an enormous computational fabric -- is higher. That naively seems like it would place an upper limit on Earth-originated intelligences.
> Is it possible that the 'edge' of universe reflects light? Have scientists been able to conclusively rule that out somehow?
It's not an edge the way you think. It's the edge of what we can see based on the known age of the universe and how much light has reached us. I.e no real boundaries as best as we can tell.
The best way you can look at this is that early galaxies are being found earlier than expected based on our model of how the universe formed. The further you look, functionally the further back in time you look (not just further away)
This is an oversimplification and an astrophysics expert can give you something better.
Without getting into lots of detail, this is basically correct. It's why we talk about the observable universe. There's lots of stuff we can't see because the light from it won't reach us.
This is one of the most interesting aspects to the universe. It's not, "because the light from it hasn't reached us yet but is on the way and will get here eventually."
Rather it's that the rate of expansion of the universe is accelerating, so that we're moving away from parts of it faster than its light can cover the distance to us. It will never reach us.
> Rather it's that the rate of expansion of the universe is accelerating, so that we're moving away from parts of it faster than its light can cover the distance to us. It will never reach us.
It's actually even worse than that. Because of the accelerating expansion of the universe, over time the part of the universe that we can observe will get smaller, allowing us to see less and less of it. Eventually, all that we'll be able to see is our own local group of galaxies, where gravitational attraction will win out over the universe's expansion. However, this won't really be a problem for a few billion years.
I know it is considered increasingly unlikely, but: What a parallel to flat Earth ideas people had (...) hundreds of years ago, until they realized we are on a sphere. Maybe in a few hundred years people will laugh about our limited ideas of the universe as well.
This is wrong by an order of magnitude. It was already known thousands of years ago that the Earth is more-or-less spherical. The idea that people in recent history believed in a flat Earth is a myth.[0]
>The idea that people in recent history believed in a flat Earth is a myth.
The way you've worded this, you're incorrect. There are people today who believe in a flat Earth, crazily enough.
Of course, the idea that most of society (namely educated people) believed in a flat Earth is a myth. From your link:
"The myth of the flat Earth, or the flat earth error, is a modern historical misconception that European scholars and educated people during the Middle Ages believed the Earth to be flat."
What the typical serf working in the fields thought about the shape of the Earth is probably unknown.
If we had to guess (of course not good research to be guessing): The typical person working on a field probably believed what the church told them the world looks like. If they ever heard about being on a sphere, they would probably laugh and point to the horizon, saying: "How can Earth be a sphere? Don't you have eyes to see? Look into the distance, all is flat!" and any kind of argumentation, that it is simply so huge, that one cannot see it, would seem to them like a made up story, a lie to further some hidden agenda the explaining person has.
That does not really detract from my comment though. Thousands of years are also hundreds of years. Just more hundreds. So if we are getting technical about that, I don't think it is wrong what I wrote. Still, thanks for putting the time frame a bit clearer.
> Rather it's that the rate of expansion of the universe is accelerating, so that we're moving away from parts of it faster than its light can cover the distance to us.
From my understanding, it's not that we're moving away from parts of the universe, but that the distance between us is growing so fast that light sent from one part will find that after traveling toward us for some amount of time, the remaining distance to travel is actually more than than when it started.
One way for the distance between two objects to increase is indeed for those objects to literally be moving in opposite directions through space. But the expansion of the universe itself causes the distance between two otherwise-stationary points to nonetheless increase. Put differently, it's the cosmic yardstick that's shrinking, not the entities that must necessarily be moving.
(This is also why two points can be "moving apart" faster than light speed, the cosmic speed limit.)
So such an expansion phenomenon should affect everything uniformly right? Are we (people /animals) then getting "bigger"? Over time innthe extreme will it cause problems in signal transmission in our own nervous systems (since apparently we have a problem seeing light beyond the observable limit)
The strong nuclear force, electromagnetic force, and even gravity are strong enough to overwhelm the expansion within individual galaxies and even local groups of galaxies.
In other words the expansion of spacetime very very very slightly tries to shift the atoms of your body apart but we can't even detect it because ordinary forces like chemical (electromagnetic) bonds are exponentially stronger - enough to pull things back where they should be. Actually in the current epoch I'm not sure if the expansion is strong enough to shift an electron by 0.01% of its own width let alone move an atom.
Space is really really big so that tiny amount of expansion adds up over long distances.
I don't think that's true. Expansion is not very weak around matter, it just doesn't exist. It sounds a little counter intuitive to think that expansion "shutdowns" as we get closer to galaxy. But that's because expansion and gravity are a little more complicated that just a force.
We over simplify what expansion really is, which leads to this type of thinking.
Expansion and gravity are results of the same equations.
Einstein equations are difficult to use, so we usually split the results in two models, FLRW (empty space) and Schwarzschild metrics (around matter). Computing the equations leads, respectively, to expansion and gravity. And it's not like there's one and the other, with gravity fighting expansion. It's "one or the other".
Around matter (in Schwarzschild metric), solving Einstein questions, we see zero expansion drifting. If there is matter, there is gravity, and no expansion.
Quoting Wikipedia [1]:
> Once objects are formed and bound by gravity, they "drop out" of the expansion and do not subsequently expand under the influence of the cosmological metric, there being no force compelling them to do so
> Einstein equations are difficult to use, so we usually split the results in two models, FLRW (empty space) and Schwarzschild metrics (around matter). Computing the equations leads, respectively, to expansion and gravity. And it's not like there's one and the other, with gravity fighting expansion. It's "one or the other".
Arguably splitting a complex model of reality in two for convenience and saying that it’s “one or the other” is also an over simplification.
By the way, the same wikipedia entry also says things like “gravity binds matter together strongly enough that metric expansion cannot be observed on a smaller scale at this time.”
Gravitational attraction still dominates on even fairly large scales, and chemical bonds absolutely dominate over anything expansion could possibly do -- it would contribute an incredibly light force opposing any bonds. So no, we (and our galaxy) are in no danger of being inflated from the inside by space itself.
> So such an expansion phenomenon should affect everything uniformly right?
Apparently not. As far as I can tell (IANAC) cosmic expansion affects the empty space between galaxies, but not concentrations of mass. Galaxies (and everything in them) are immune to cosmic expansion.
I understood that cosmic expansion is a consequence of General Relativity; DE is supposed to explain accelerating expansion. Is that right? But wouldn't expansion result in there being more empty space and less nearby stuff; and therefore in accelerating expansion?
> Want to understand what we know about Dark Energy: the hypothetical form of energy that exerts a negative, repulsive pressure on the universe that effects the energy on the largest scales? Then enjoy this Dark Energy playlist!
And the question is "is the rate of acceleration accelerating?" If so, then make sure you watch "Could the Universe End by Tearing Apart Every Atom?"
If that question is of interest to you, PBS Space Time - Could the Universe End by Tearing Apart Every Atom? https://youtu.be/gEyXTQ9do-c gets into the "what if" of dark energy and its influence on matter.
You'll note that it isn't until the very end of the instant before the Big Rip that that make it so that the expansion of the universe that it overcomes the strength of chemical bonds.
With the current rate of expansion, no. We're still bound together more tightly than the rate. This extends all the way out to a fair distance (galactic distance).
If the rate does get to the point where it is noticeable the "galaxies can't hold together" you get into the Big Rip end of the universe situation.
You don’t get larger - just like you don’t dissolve in water and wind doesn’t spread parts of you all over the land. There are interactions of matter keeping you together.
> but that the distance between us is growing so fast that light sent from one part will find that after traveling toward us for some amount of time, the remaining distance to travel is actually more than than when it started.
Good clarification, that's what I meant, I guess I didn't say it accurately. I don't actually think of us as moving, but more like the scale of the entire universe is increasing while the ability to traverse it - light speed - remains a constant.
You have it right. My cosmology teacher at UVA a couple decades ago used the analogy of points marked on the surface of a balloon that's being inflated. (maybe more intuitive than other shortcuts to understanding?)
The universe is 13.7b yo, but due to acceleration of expansion, if you could "teleport", it's actually currently 93b ly across. So we're already in a bubble within a greater universe that we'll never be able to escape even if you could instantly reach lightspeed right now, and due to the expansion continuing to increase, the fractional size of this bubble relative to the rest is shrinking. Faraway galaxies that are "currently" on the edge of the bubble but expanding away are becoming forever unreachable as you read this.
> The universe is 13.7b yo, but due to acceleration of expansion, if you could "teleport", it's actually currently 93b ly across. So we're already in a bubble within a greater universe that we'll never be able to escape
This number, the age of the universe, has changed a few times since I learned to read 45 some years ago. What are the chances that this isn't really "the" universe, but what we know as the observable universe is really a mind-bogglingly massive black hole that was sucked out of the actual universe, and the actual age of "the" universe is incalculably old, trillions of quadrillions of years old, and it's only our baby universe is what is roughly 13.7Byo? Maybe the Great Attractor hides the mother of all singularities. I'm sure there could be a way to explain the CBR and what seems like the Big Bang and Inflation. Maybe this baby universe only appears to be expanding, when it's just a growing black hole.
It's worth pointing out that there is a minority of physicists who don't accept the Big Bang as proven beyond doubt. An alternative theory would be a 'steady-state' universe which, as you suggest, would be much older than the ~14 BYO age. If the medium of space itself dispersed light for instance, red shifts might be observed that explain the astronomical data.
Just for any future historians: all us normal people are aware that the idea of the Big Bang seems a little fantastical, but relativity or whatever is, like, way complicated. Most of us just have to trust the physicists. Of course now that you have the Theory of Everything, notation and thought-experiments developed to make it obvious, and relativity is just a special case, we look pretty dumb. But if you look at the operators that your undergrads pull out to solve Theory of Everything equations and try to somehow derive them with ancient 21’st century math, they are actually really complicated!
Actually, having a bit of sympathy now for the folks who believed in the Luminiferous aether.
Eric Lerner is one of them and he's advocating for the idea that the BB never happened and that we'd see plenty of old galaxies with JWST. He's since updated his thoughts and there was a bunch of controversy:
The number hasn't really changed, it's just been measured with increasing precision. It is rather unlikely to be wrong given measurements via various methods are all in agreement. Summaries about these various experiments are available: https://imagine.gsfc.nasa.gov/science/featured_science/tenye...
It's black holes all the way down. Fun to note that, from the reference of someone outside a black hole, the singularity contained within hasn't happened yet, and never will.
So mindboggling that frankly I refuse to accept it.
The likelyhood that we'll figure this out in my lifetime is zero, but I simply can't comprehend a universe that accelerates without cause (dark energy) infinitely.
Just as we don't understand the root causes of dark energy, I believe it's just as logical to believe that something will eventually slow it down.
I have to believe that because only a cyclical theory of the universe makes sense to me. It's my faith, I suppose.
The more depressing part to me isn't that I'll never know, but rather it's entirely possible HUMANITY can never know, any more than an ant can know about General Relativity.
I think it’s actually quite a simple model to think of the universe as a network of discrete nodes, rather than a spatial thing that’s expanding and within which various things are accelerating. It makes the Big Bang simpler - we start from a small number of nodes and they grow in number, so we don’t need to think about what the universe is expanding ‘into’. And it explains expansion - nodes can divide like mitosis, so we don’t need to explain some force pushing things apart.
Something that’s even more mind boggling than that, at least to me is that the universe is still within the first few seconds (or minutes) of its life in terms of relative time we can comprehend. As stars collapse and black holes consume everything, the universe will spend 99% of its life in complete desolate darkness. An endless sea of black holes for billions and billions of years. The fact that we exist, in the split second that life can exist is unimaginable.
I'm still not convinced that the expansion of the universe is accelerating based on current evidence.
That argument largely comes from supernovae appearing dimmer than we think they should, and more distant things appear more red and it looks that way in any direction we look. But the thing is, we sometimes calculate how distant things are based on redness, so it's kind of circular reasoning.
Sure we have other things which help gauge distance, like brightness and periods of Cepheids, but if you look into history on Cepheids, the association that brightness is directly related to periods was built upon an assumption that the Cepheids in a galaxy were roughly all the same distance away. That may seem probable, but it isn't a given, as galaxies can be at various angles to our perspective, as well as being different size in various dimensions. It also assumes that it is impossible for fake Cepheids to exist, which might even confer a reverse association. How could we know if we're looking at false Cepheids vs real Cepheids, and that there's not multiple types of Cepheids with different causes for pulsations at various brightnesses?
Next you have to consider movement is relative. It's entirely possible a brighter galaxy is moving 2x faster away from us, than a dimmer galaxy that is actually closer to us. Yet this is hardly considered from distance calculations.
Lastly, people also say the Big Bang is not an explosion of matter moving outward to fill an empty universe, but rather an expansion of space between things. IMO, this is mostly just a model, a way of viewing things. The thing is, you can still look at things from normal intuition (of say an explosion), and it still conforms that definition (ie it's objects moving in space over time, vs it's space filling in between objects over time). And so, if looking further into the galaxy, means looking further in time, the dynamics of an explosion suggests that those galaxies will be moving faster away from us. As the outmost debris of an explosion, is the fastest moving debris of an explosion, and speed between two pieces of debris, is highly associated to their relative positions and tends to increase as distance between them increases, even regardless of where they are in an explosion. So even if further galaxies are indeed moving faster away from us, and it is faster the further we look, and looks that way every which way, I don't see why this would necessarily mean the expansion of the universe is accelerating. As it appears to me, it can be predicted by conventional (non-accelerating) explosion dynamics.
Considering the two methods for measuring the rate of the universe’s expansion differ by about 10%, the question seems unsettled at best. You’re not wrong to question it.
We don't (can't?) even know if there weren't multiple Big Bangs, right?
I.e we're just in a specific "universe" we can observe, but maybe several of these are just side by side, not necessarily parallel as in parallel realities.
assuming light from a big bang travels in all directions, then another big bang's light could be heading in our direction and potentially observable — the reason we can't observe the entirety of our universe is that spacetime is expanding in a way where light at the beginning isn't traveling fast enough to outpace expansion
Unless we figure out a way to take measurements of areas outside of space-time to compare against (which seems quite impossible), it’s probably a question humanity will never answer.
It might be a question with no meaning: The universe interacts with nothing else. It spawned out of nothing, and its expansion is only meaningful if you’re inside the universe to see it happening.
It could be a question with a lot of meaning: perhaps the universe exists on top of some higher dimensional substrate that is conducive to big-bang style expanding universes. Maybe the reason the universe expands is only possible to answer by having access to the information of what it is expanding into.
It could be question impossible to wrap our heads around: Maybe the area outside the universe runs on metaphor, and our universe expands in a sense that would make more sense to a writer than a physicist.
Basically, endless sci-fi can be written about that question. But given we are (probably) restricted to staying within our universe’s laws of physics, it’s quite likely we’ll never really know.
Correct, as I understand it. No matter can travel at the speed of light, and no light can travel faster than the speed of light. But the rule doesn't extend to the rate of expansion of the "field" on which those things exist.
I vote we bring back “aether” as a valid term. The aether is stretching everywhere, and in so doing it spreads distant things away faster than light can overcome.
Yeah, ideas like this are usually called "tired light" models, they have been extensively explored for the last hundred years or so. A lot of these models have been shown to be false by experiments, but I guess if you try you can probably cook up models which haven't been falsified by anything yet.
Think of the universe as some sort of information system. The speed of light caps the rate at which information propagates, which is a desirable or at least necessary property at scale. But there’s some discrete substrate underlying that propagation of information. That substrate can multiply, like inserting nodes in a graph or empty spaces in a linked list. That makes it longer to traverse from one end to the other. The rate of propagation stays the same but the map keeps changing.
If we had some absolute zero reference outside the universe - let's call it a great alien petri dish - we probably could find something moving faster than the speed of light, in reference to that absolute, out-of-universe observation point? But measuring that might be hard.
And on the other hand, we might be able to find two objects which are static with reference to the universe, but actually increasing the distance from each other at a speed beyond c or rather 2c, which should be impossible, because the universe between them expands?
This is very weird to think about, but accepting your reference framework - the universe - changes makes it easier.
> is it that space expands faster than light moves?
Yes. Picture an ant walking on the surface of a balloon. You could conceivably blow up the balloon faster than the ant could walk across it. If you were blowing up an infinitely stretchy balloon with an ant at the far end, you could conceivably blow it up fast enough that the ant could never reach you.
We have a concept of the Particle Horizon, the max distance light could have traveled in the universe, and that is our boundary, our effective edge of the universe.
There's the concept of the light cone, which is the total volume of observable light which can ever reach an observer, or inversely, the total volume ever traveled by a given point source. The expansion of the universe means that there is a certain boundary, a horizon where the universe expands too much for light to ever travel the required distance.
I guess it's reasonable to assume that there are parts of the universe that are far older and much further away (ie, their light hasn't reached us yet). Which would mean we can never really guess the age of the universe. We can only guess the age of our local area?
Which kind of sounds a bit like the whole "everything revoles around earth" transitioning to "everything revolves around the sun". The universe is what light has reached us transitioning to the area of light that has reached us is just a small spec of the actual universe?
> I guess it's reasonable to assume that there are parts of the universe that are far older and much further away (ie, their light hasn't reached us yet). Which would mean we can never really guess the age of the universe. We can only guess the age of our local area?
But older parts of the universe would emit light that would have more time to travel. So unless space is not continuous, we can confidently say that no older light exists. The main counterfactual is that there is an older universe that is discontinuous with the observable universe (but in what sense is that older universe part of "ours" then?).
But they can still be far away that the light hasn't arrived at us yet (or maybe never will?). It's entirely reasonable that space may not be continuous. There may be groups of galaxies far enough away from each other that they burn out before receiving the other's light.
How can we confidently assume this isn't the case?
No, there was a time that all space was hot, and we know from microwave background radiation that it is homogenous. So it’s not just “galaxies are far from each other”, it would take “space time is discontinuous somewhere and this discontinuity is just on the edge of our observable universe”. There is also no older light that can ever reach us, as the amount of universe that is observable is actually decreasing (beyond that, CMB will always be the oldest light as it predates any astronomical object formation). Anyways, CMB really constraints the age/homogeneity of the early universe.
I wouldn't be surprised if there's a hawking radiation equivalent for that edge, but the wavelength is on the order of the size of the universe, so basically impossible to measure
An analogy might be the horizon. There is no fixed horizon, it is just the boundary of how far your can view, given both the curvature of the earth and the quality of your eyes. It is relative to where you are on the earth, and by your altitude. So while it is calculable, it isn't a fixed boundary like a river, or a wall.
No, we have no evidence that the universe has any kind of "edge" that is topologically different from its interior.
There is a boundary to what we can see. As the early universe cooled, it changed from an opaque plasma to transparent gas. So as we look farther away, and also backward in time, we see the last point at which it was opaque; this is the cosmic microwave background. But this isn't a "real" boundary that something could hit. And it long predates the formation of galaxies, so it couldn't have reflected images of galaxies.
also (citation needed, this is from memory from university cosmology classes over 20y ago, maybe misremembering or info out of date) the shape of the universe may be less like a sphere and more like a toroid, or a multidimensional moebius strip.
so (hand-wavy, impossible IRL but maybe illustrative / fun to think about) if you could freeze time and look far enough in one direction, you'd see the back of your own head.
There are some reasons why cosmologists don't like the idea of a universe that loops back on itself, one is that such a universe can't be both isotropic (the same in every direction) and homogeneous (the same at every point) [edit: while also being flat, as observations seem to indicate it is].
To get a rough idea of why, imagine taking a 1km by 1km square and identifying the opposite sides, you now have a homogeneous space (every point is equivalent to every other point), but it isn't isotropic because some directions are special. If you put a rock on the ground and walk due east, you'll have to walk 1km to reach the rock again (assuming you start in what used to be the center of the square it takes 500m to where the edge used to be, and another 500m from the edge back to your starting point). On the other hand if you walk south east you have to walk sqrt(2) km to get back to your rock (sqrt(2)/2 km to get to what used to be the south east corner, and another sqrt(2)/2 km to get back to where you started).
So although the torus space is homogeneous there are traces of the fact that it used to be a square, embedded in the fact that some directions are special (the 4 cardinal directions have the shortest distance to get back to where you started and the 4 intercardinal directions have the longest). Cosmologists think this lack of isotropy is essentially ugly, and don't like the idea of living in a universe where some directions are special.
Aside from just not liking the idea (which isn't very scientific) its also relevant that the universe looks pretty isotropic when do observations, we emphatically don't see traces of the sort of anisotropy you'd see in a toroidal universe anywhere.
Theres nothing massively wrong with it, it's a perfectly plausible model.
The one thing that isn't particularly nice is that spheres have intrinsic curvature, essentially if you draw two parallel lines on a sphere they will eventually touch. We can go and look at astronomical data and see if the universe has any intrinsic curvature that we can see.
People did this and it turns out that from all the astronomical data we have the universe looks incredibly, spectacularly flat. No curvature at all that we can detect. This doesn't mean it isn't a sphere, but it means that if it is a sphere it's a really big one. Much much bigger than the observable universe.
Ahhh, yes parts of that sound familiar. So, the reason we can (at least pretty much) ~~rule out~~ a 3-sphere [EDIT: I didn’t read carefully, and missed the “it could be a really really big 3-sphere so that the curvature is close enough to zero” part], is because you can’t have a flat sphere,
But you can have a flat torus (or some other shapes that “wrap around”), but we have different reasons to disbelieve those shapes (the “looks the same in any direction” and “looks the same in every position” expectations).
The far limit of the visible universe is the cosmic microwave background, which is the heavily red-shifted view of when all of space was filled with an opaque plasma of similar temperature to the surface of a star[0].
The process that caused the light we see as the CMB happened everywhere in the universe roughly all at once. At the time, from any given point, you'd just have seen blinding light but as things cooled, you'd see a sphere expanding around you where this light was dimming, as less and less, and finally none was being emitted around you, but due to the finite speed of light, light from outside that sphere would still continue arriving in your eyeballs. That's the situation we're in today; that sphere's just really big now.
During recombination epoch ~400,000 years after the Big Bang, this light would have been visible. Due to expansion, over time that light has stretched to longer and longer wavelengths, and we currently see it as microwaves.
Note: It's been ~30 years since I was actually studying physics & astronomy; others may be able to offer better explanations or correct me.
The CMB happened everywhere in the universe at the same time[0], so what we're seeing is the light which took 13-point-whatever billion years to get here[1] from some part of the universe in that direction at that younger age.
> My understanding is that the early galaxies still produced light after recombination.
I'm not sure what you're imagining about recombination, because I've not heard any suggestion of any galaxies existing before it, so they only produced light after recombination.
[0] for some definition of the concept, even though relativity is formulated with the assumption that there isn't any good concept of simultaneousness.
[1] from our point of view. From light's point of view, time isn't defined.
The edge of visible universe is Big Bang. Or more concretely, the time couple hundred thousand years after Big Bang when the universe became translucent to light.
Things cannot "reflect off of the edge of visible universe" because that would require that the light travel back in time which is nonsense.
As of this moment we cannot exclude possibility of discontinuities in the universe which would be cause for example by inflation. But we also have not observed any.
if time is a dimension, and we can only see the past and the present, could it not be that, if one's gaze were shifted, one could see the future? effectively looking at the "other side" of the dimension of time? looking straight at one "side" of time, you can only see the past and present. but if you had a galactic set of mirrors set up around "time", couldn't you "see" the other side where the future lies? effectively you'd be looking at a reflection of the future.
or, time being malleable (relative to things like mass and movement), wouldn't it be possible to refract or bend time the way light is, such that you could see things (that already happened in the past) sooner, even if they are really far away? maybe like how bending a race track can allow a vehicle to exert more force or go faster, but with light?
Time doesn't exist as a thing in the way you're thinking about it. It's why in physics we talk about spacetime. (The following is not entirely accurate and an oversimplification.)
Space and time are one thing, which have to be thought about together. Your current thinking imagines that you're in a box, with x, y and z coordinates, and that time is a thing passing inside it. Instead, it'd be more accurate to talk about that you're in a frame of reference with x, y, z and a, and all are tied together. There's no sense in which you can talk about space and not also be talking about time, and vice versa. For a similar idea, a 3d volume is not a plane plus a z axis, where you can talk about moving through just the x and y axis without the z axis mattering. You can talk about a view of that, but it doesn't mean the z axis isn't relevant. Ask two planes not colliding whilst viewed from above how important a z axis is. (Maths jokes are the worst.)
The actual physics involved for discussing this gets absurdly complex very quickly, but this is about as simple as I can think how to explain it whilst still being in the bounds of accurate.
What is the edge of the universe? How would you define that? In most models, the universe doesn't have anything that could be called an edge. Unless you are referring to the boundary of the local universe, which is defined as the sphere around us at which objects are too far away for their light to ever reach us. It's not a physical structure that could reflect light, it's more like the opposite of that.
Talking about the edge of the universe implies space is a thing. Physics works just fine if you imagine the x, y and z of particles describes an arbitrary set of coupled attributes on the particle itself. It is more likely that space is an emergent property of the entanglement between information, and in that case the idea of a boundary is nonsensical. Under that model, "spacetime" would behave like a foam - if one bit of it pulled far enough away from the rest it'd shoot off as a bubble.
Space and time are intertwined interstingly that way. If time somehow loops back or reverses (circular time) the it is not unreasonable to suggest space also loops back. Is it possible that at a certain boundary of space and point in time you loop back and start over at 0:0:0/0:0:0 space/time coordinates. At least in this current realm of reality, is it like one big space-time movie on a loop?
I have a memory from when I was a kid and learning about the universe. In my head it definitely had an edge, and it resembled a really really big hockey rink with boards. But it was also only 2d at that time, which I think I remember knowing that wasn't right but not being able to conceptualize a 3d universe. So yes, in the universe of my 8yo mind the "edge" might reflect light
Can someone explain to me what would be behind the galaxies if we could see it, to the point of 0 seconds after the big bang? Black, white, is it even possible?
We can't see down to 0 seconds, because very soon after the big bang, the universe was filled with dense, extremely hot, opaque plasma. The closest we can get is the "recombination epoch" [0], which is roughly 370 000 years after the big bang, when, because of universal expansion, the plasma got cold enough for neutral hydrogen to start forming, at which point the universe became transparent.
As protons gain electrons in high temperatures, they don't form in the ground state. Instead, the newly minted hydrogen atoms are in a highly exited state. As they fall back to their ground states, they emit infrared photons at ~3000K color temperature. These photons, redshifted by the expansion of the universe to ~2.7K, are the Cosmic Microwave Background, the uniform ultimate backdrop we have when looking in any direction.
[0]: Which has it's slightly incorrect name (should not have re-) because it was named before the big bang became a widely accepted or known theory.
What I'm going to ask you is completely dumb, but keep in mind I don't know much of physics.
If my understanding is correct, when mass gets dense enough inside, a star you have a black hole, that would be like a hole in the fabric of space time. Ok, we have black holes in the contemporary universe. So how was the primordial universe a ball of dense, extremely hot, opaque plasma without becoming a huge black hole?
Not a physicist at all either; but on a per particle basis, I know gravity is by far the weakest of the fundamental forces. However, unlike the others, it doesn't have spin/charge/polarity that results in their vectors repelling each other. As such, black holes form when the large scale weak gravitational forces combine into a greater force than the strong short scale repelling forces exerted by the others (and especially so when nuclear fusion is involved). In a hot primordial plasma, the particles are by definition extremely energetic; pushing each other in all directions with far more vigor than the extent to which gravity attracts them. Hence being a big bang rather than a big crunch, I suppose.
Because the primordial universe was in a state of extremely fast expansion, while black holes today exist in space-time that is almost exactly flat. In fact, if the universe really started from a singularity, the expansion was infinitely fast for an instant.
To hedge the next question then: Why was the universe expanding so quickly?
It seems that the expansion must have been so fast that it was going faster than light speed, right? Otherwise the very dense universe must have gone black-hole.
The expansion of space itself is not comparable to the speed of light, but yes, I would say it's probable that it would have caused particles (or whatever there was at that time) to spread out faster than light, thus disconnecting them causally and preventing gravitational interaction. As for the why, answering that would involve answering why the Big Bang happened, which given our current understanding would veer into metaphysics. As far as we can tell, it's just what the universe does.
I have no idea about cosmology, but I think maybe that if this dense matter where everywhere, then forces would cancel out and that's why you don't get a black hole.
> the uniform ultimate backdrop we have when looking in any direction
Is the CMB exactly uniform in every direction? Or is this early light slightly more redshifted when we look up versus when we look down or left or right? Does the oldest light we see in any given direction vary slightly in color?
I'm imagining the universe expanding as a sphere from a central point, but we're located off-center. Wouldn't the early infrared photons emitted from the other side of the central point of expansion from us be observed by us now as a slightly different color than the early infrared photons emitted closer to the edge of the early expanding universe?
A rabbit hole of questions:
- When did space start expanding?
- Did it have to rapidly expand for 400k years as extreme forces propelled matter apart?
- Was that expansion faster or slower than the current expansion of space between galaxy groups?
- Is expansion uniform across the universe?
- Or is expansion slower closest to the original center of the universe?
- Maybe there's a central point in the universe that's not moving relative to a reference frame outside our universe?
- Is space discrete or continuous?
- As space expands do new "units" of space appear between units of space that have grown farther apart?
- If not, wouldn't physics work differently for areas of space where the units of space have grown farther apart than areas of space where the units of space aren't as far apart?
There is a very obvious dipole in the CMB due to our peculiar velocity. This has been removed in almost all images you saw because it's just an artifact of our particular movement and not physical. It's just the Doppler effect.
So if we can see CMB in all directions, why do we really even say "the observable universe" as though there could be more matter and more galaxies beyond what we can see? If the maximum of what we can see is implied to be before all galaxies, then shouldn't it be implied that all galaxies that exist can be seen?
Here’s the important point I think you are missing. You are looking in TIME, not in space. When you look very far away, you are looking back to the beginning of time, back to a singularity where all matter and energy existed at a single point. In every “direction” you end up looking back to the same time and the same place, the beginning of everything. There’s nothing “beyond” that, it is the beginning.
If you ask, what exists today, beyond 13.7 billion light years from earth, the plausible answer is “mature galaxies like ours” but there is no possibility of collecting data or evidence of what is there, since the evidence would take more than 13.7 billion years to reach us, and in fact would never reach us because the expansion of the universe means that distances are getting larger between 2 points all the time.
But if we're looking in the direction of a galaxy far far away (i.e. 14bn ly away) (which we don't know it's there, but let's assume it is, because likely some galaxies must be there), how come we see the CMB, which is 13.7bn years old, and not the galaxy itself, which is (by definition) less than 13.7bn years old?
Because what we see from that direction are the things that were there in the last 13.7bn years. But the farther we look we see older images. So while we can see image from 10bn years ago of something that's 10bn light years away, when we try to see something 13.7bn light years away we just see microwave soup because that's what was there 13.7bn years ago. And if we try to see something 14bn light years away we see nothing from there because 14bn years ago there was nothing there.
Is it true that space had no volume at the Big Bang? I understand that density rises without (known?) bound as we approach the Big Bang, but even if you compress infinite space by an infinite factor you might still have infinite space -- infinity divided by infinity is undefined.
If you run the density backwards far enough, eventually everything in the visible universe is effectively at a single point, in some theories this was modeled as an actual infinite singularity, but it’s quite possibly unknowable since our first evidence is the CMB 380k years into the whole thing. As we rewind time from there things being to get highly speculative.
To "what exists today, beyond 13.7 billion light years", I'd rather say that "it doesn't exist yet". Because, otherwise, it assumes there's some "global universe time" like UTC or something. But all there is is our light cone.
That is fair. We are veering into metaphysics or religion if we talk about what exists there today, or even if there could be any relationship between our “today” and their “today”. By definition there is no causal connection. I’ll get back to you on that once I finish inventing my Time Machine.
The "observable" universe is about what we will ever see in the future, rather than about the past. If you waited around for billions of years, you could watch those early galaxies evolve.
There might be galaxies even further away, but you can't ever see them, not even in theory. The light from them will never reach us because they flying away from us further than the speed of light.
The CMB isn't really about galaxies. We know there won't be any galaxies past the CMB because galaxies couldn't have formed before the CMB was emitted.
In theory we can "see" past the CMB using gravitational waves. (There was a thought, in fact, that we'd already done that, but that appears to have been faulty.) The CMB is just kind of a practical limitation rather than a fundamental matter of spacetime: you can't see because it's too cloudy.
The question of whether galaxies beyond the observable universe "exist" is kind of a matter of metaphysics rather than astrophysics. As an astrophysicist, you basically just say they don't exist and you're done with it. But if you want to know where the universe "came from" (whatever that turns out to mean), you try playing around with notions like "our universe is an observable sub-part of a wider ensemble, which we'll never detect, but here's a pretty set of equations which explain our universe in terms of it".
Due to accelerating cosmic inflation, some galaxies are receding from us at faster than the speed of light, so their light will never reach us. The majority of galaxies (everything outside of our local cluster, IIRC) will eventually be receding faster than the speed of light and be beyond our vision forever.
Yes, this means most galaxies will appear to actually pass through/into the cosmic background, from our point of view.
I don't think we understand enough about the dark energy driving inflation to say that. If the force is constant for a given pair of particles at a constant distance, and the atoms are currently stable, that would seem to imply that the force from dark energy pushing the atoms apart will be the same as they are now.
However, as I said, I don't think we know enough about dark energy to say anything about its effects on the atomic scale either now or eons hence.
You're describing the Big Rip. It's now thought that the acceleration of expansion is not high enough for that to happen. Gravity is strong enough that the particles inside galaxy groups will stay causally connected indefinitely. Long enough into the future, whole groups will become disconnected from the rest of the universe, though.
No, because galaxies almost certainly exist which are further than the CMB. It's just that the light travelling from them has not been able to reach us in the time since it was emitted.
Well most physicists assume it is massively bigger than we can see. It is in principle possible that we see nearly all of it, but that would be very coincidental. The only thing we know is that it is at least as big as we can observe, but it could be hundreds of times bigger, 10^100, or even infinite.
There are speculations one could make that imply a minimum size, I recall a reading a prediction of 10^50 times bigger or so.
Fascinating... so we see the CMB, got it. I wonder if someone could take what seems like the random pattern of the CMB and reverse it into some vision of the BB..
As everyone has already pointed out, the Cosmic Microwave Background Radiation is as close as you can get to the Big Bang.
But to the larger point, these galaxies were suspected before, based on Hubble work. You see, the COBE satellite from 1989 to 1993 mapped the microwave background radiation very precisely (two of the Principal Investigators on COBE won the 2006 Nobel Prize in Physics for this work). And they found that while there are minute fluctuations in the radiation, those fluctuations are measured at the parts-per-million level of difference. But the Hubble has found that the farthest back galaxies it could see were some of the largest and most massive things ever witnessed. So we had this gap between 'everything everywhere is the same to parts per million' and 'there are some supermassive galaxies' and so the Webb telescope was specifically designed to find the things that were redshifted so far they were out of the visible spectrum (so Hubble couldn't see them) but not so far that COBE could see them in microwave: in the infrared spectrum that lies between those two, that's where Webb is supposed to focus and help us understand how these galaxies form.
Because this question of what happened between the CMBR and the visible light range is the biggest question left over from Hubble, so it is what drove the design of the Webb. This is how astronomy has worked for centuries: you build a new telescope to answer some questions, but that leaves you with more questions, so you need to build new telescopes to answer those questions, GOTO 1. That's what's been happening ever since Galileo looked through that telescope at Jupiter all the way back in 1610.
We can actually already see that time period, in its present form. It's called the Cosmic Microwave Background. It is the (now extremely cold) energy which permeated the entire universe in that very early time period. The entire universe was opaque and extremely hot... then as it expanded, it began to cool enough for particles and then atoms to form. Only then were stars possible, and later galaxies.
How/why can we see the CMB? Well, it was everywhere. Literally every point in the universe was a nearly uniform sea of blazing energy. So if you look far enough in any direction, you will see the cold echoes of that time period.
edit: Beat to the punch! I hope among our many answers you've found something enlightening
edit 2: Important to note that the CMB is not synonymous with the beginning of spacetime. It is more like a wall, beyond which we can't see anything, and it came down very early in time.
No, models predict that an extremely short amount of time elapsed before this. Like orders of magnitude less than 1 second. However, we know our models are not perfectly accurate, so it is possible there is something else very weird going on.
Cosmic microwave background is behind the galaxies, and we can see it. The universe is mostly transparent these days, so light can travel across the universe from a distant galaxy to our eyes or telescopes. Long ago, the universe was full of ions-free electrons and protons-and these are very effective at scattering light, so the universe was effectively opaque at that point. The universe became more transparent as the universe shifted towards hydrogen atoms instead of free electrons and protons.
Whatever the universe happened to look like during that transition period, from opaque to transparent, is still what we see. It's the cosmic microwave background. Anything from before that time got absorbed.
It's conceivable that we could observe gravitational waves during that period before the CMB, because they're not blocked by the un-recombined electrons and protons. If we ever get there, it could help explain the small variations in CMB from place to place. But that's a long way off.
Not an expert here but it sounds like you might be describing the Cosmic Microwave Background. This is basically the remnant of the early opaque plasma cloud that filled the entire universe. As we look far away/back in time, the photons reaching us have redshifted due to the expansion of the universe. That's why these originally extremely high-energy photons are now just low-energy microwaves. The "background", 0 seconds after the Big Bang, is in all directions, and presents as the Cosmic Microwave Background. Or so I understand.
There is a wonderful sequence in the (2nd?) Book of Enoch (~150AD?), where the viewer is transported up through the heavens, past the planets, and finally beyond the stars, and eventually sees the incomprehensible face of God lying behind it all, visible all across the far end of space.
The very early universe can't be observed with visible light. It was filled with ionized hydrogen and thus opaque over long distances. The oldest light is from the era of "recombination", when things had cooled enough (c. 370k years after the big bang by consensus models) to permit light to travel. This is just the thermal glow of the universe, redshifted (way, way) down into the radio spectrum. And we can see it just fine; it's the cosmic background radiation and has been very well studied.
It's the region between recombination and the currently-visible-to-telescopes galaxies that Webb is particularly well-suited to study.
We can see it and it’s called the Cosmic Microwave Background https://en.m.wikipedia.org/wiki/Cosmic_microwave_background. It’s not t=0.0000001 though as the time before the cosmic microwave background the universe was opaque to photons, you wouldn’t be able to see anything.
What's even crazier is that those civilizations could have built and advanced for a 100 million years and we would never know about it because they are so far away. The light from Canis Major, our closest galactic neighbor, is older than our civilization (25,000 years). The average distance between galaxies is 1 million light years. For all we know, there have been billions of civilizations that have lasted longer than the lifetime of our solar system and we haven't even seen the light from them yet.
I don't know. Life needed almost 5bn years to get to this point on Earth. Let's say we lucked out and it almost always takes 3 times as long. Then we look like early birds in the Universe.
What's more, earlier solar systems had a bit boring chemistry. We need a lot of supernova made stuff to really function so this narrows the time window.
You might think that near galactic core there's a lot of really cool stuff made but I think interstellar environment might be less stable because of that and maybe life doesn't even have a 5bn years of quiet time to develop there.
You don't know that. Life might be possible with simpler chemistry too.
Chemistry was sufficient 100 million years ago for intelligent life to evolve, so some other solar system could've easily have had intelligent life for that long or even longer if they were lucky.
Our lives have changed beyond recognition in the last 500 years. Imagine a civilization that's thousands, tens of thousands or even hundreds of thousands of years ahead of us.
> Life might be possible with simpler chemistry too.
Yeah, but we since we know of only one instance of life developing we don't really know what's actually possible and what only might be possible.
> Chemistry was sufficient 100 million years ago for intelligent life to evolve, so some other solar system could've easily have had intelligent life for that long or even longer if they were lucky.
What I'm saying is that time it took life to develop on our planet is so close to the age of the universe (not even one order of magnitude of difference) that it's entirely possible that we were the lucky ones and the next intelligent life (or even eukaryotic life) in the universe won't show up for another few billions of years. Although it will inevitably show up.
> Our lives have changed beyond recognition in the last 500 years. Imagine a civilization that's thousands, tens of thousands or even hundreds of thousands of years ahead of us.
However technological capabilities of life didn't change at all in last 4 bn years despite it being in control of the whole planet for that long. Technology seems to need a really long runway to fly off.
Another thing is that once technology kicks in as you noticed it develops incredibly fast and it influences the environment at the same speed. And life doesn't really like fast changes to environment so the technology in hundred thousand years might make this world completely unlivable.
Didn't that happen within like the first 2B years? First Sol-like systems were I think at 5B years, which would still make Earth ~3B years late to the party.
The tl;dr is that we're finding quite a few red galaxies and red can mean distant (and therefore old) but you need to follow-up and do further direct measurements of each galaxy to be really certain that it's old and not red looking for some other reason.
Some of these unexpectedly red galaxies have been followed up on, and some are indeed old, but it's not enough data points yet to be certain of anything.
The fun part of science is that either way it's pretty exciting!
"These candidates await spectroscopic confirmation: Their redshifts are only estimates for now. But so far, spectroscopic confirmations of other galaxies have confirmed the vast majority of preliminary distances. Even if only half of Yan’s selection turn out to be nearby galaxies masquerading as distant ones, the latter number would still be unexpectedly large."
Something is wrong with the cosmic distance ladder. Space is anisotropic, or gravity interacts with itself somehow. The distances are not what they seem to be. I think this will eventually be the solution to the galaxy rotation / dark matter problem.
Personally, I think this is strong evidence that primordial anyons were inflated — and we’ve failed to account for the energy these stored from inflation.
MOND is not compatible with all observations but neither is dark matter. A lot of scientists think MOND is a better explanation than a new particle that we've not yet observed. Have a look at Sabine Hossenfelder's work for some of those arguments.
Which researchers (as opposed to pop-sci pundits) think MOND is a better explanation than Dark matter?
That is a very, very fringe alt-science view that so far exists in various pop-sci blogs and informal youtube discussions, rather than in mainstream conferences, journals, and research centers.
I'm not saying it's bad to speculate or write whimsical blog articles about these topics, there's lots of room for creative speculation, but MOND does not respect Lorentz invariance which is basically a deal breaker for virtually all serious researchers. Fewer things have more robust empirical support than Lorentz invariance, so discarding it forces you to say that your violation is always just over the horizon of what is testable (and this horizon keeps getting pushed back). That's generally a discrediting feature of any theory and a huge red flag. Much better to say "you don't know" than to postulate something which requires such massive fine tuning to always be just beyond the horizon of what is testable, but close enough to that horizon to have explanatory power for observed phenomena.
But again, the 2017 experimental data [cited previously] in support of Lorentz invariance and the 2016 bullet cluster data in support of dark matter basically killed MOND in the eyes of most researchers.
As I said before, nothing wrong with writing papers exploring the consequences of MOND or trying to come up with alternatives, science does not work by consensus, but the bar for dropping Lorentz invariance is really high given the experimental support for it.
I don't know where you're getting this idea that MOND breaks Lorentz invariance. I've never heard of anyone claiming that that is evidence against mond. Hell, a search of mond and Lorentz invariance turns up your comment as one of the top results.
First, it might be 'a lot of scientists' in absolute terms because this is such a fertile field, but it is a tiny minority of cosmologists who believe MOND is the best explanation for these effects.
Secondly, even the proponents of MOND concede that you need to introduce some amount of dark matter in order to explain e.g. observations of the Bullet Cluster. So the competition isn't between new particle vs MOND, it is between MOND + new particle vs new particle.
This is not unusual. There's many predictions made by MOND ahead of the fact that are borne out by reality. But don't worry - dark matter will be "retrofitted" so that it fits the facts and everybody will suffer collective memory loss again.
Edit: see for example table 1 on page 12 here: https://arxiv.org/pdf/2110.06936.pdf from a review of prior expectations by both MOND and dark matter vs how they turned out against reality for a large variety of astrophysical scenarios.
MOND is not compatible with some observations. It and dark will probably be tweaked until both agree with observations. At that point they will be the same.
That's a false equivalence. MOND has made several predictions before they were observed (external field effect, linear Tully fisher relationship, early galaxies). I think LCDM's made fewer if any predictions.
Dark matter is the umbrella term for the observed discrepancies. MOND is one possible possible explanation for DM. The paper you linked doesn't compare MOND to DM, because that doesn't make any sense. It compares MOND to ΛCDM which is a competing explanation.
Am I understanding that paper correctly that their suggested solution to explain the Bullet Cluster using MOND is too introduce an additional kind of matter which can not be detected on earth and doesn't interact with light (namely sterile neutrinos)?
"dark matter but not as much" is still an improvement if you replace it with something better. If MOND predicted these observations and LCDM didn't it's reasonable to say that it is better.
Yeah that's fair. I guess it could also explain why DM has been so hard to pin down, if both MOND and DM are true then there might be DM candidates that have been unfairly ruled out.
I do think it significantly hurts the (more philosophical) argument that MOND is simpler or has fewer parameters than DM though.
So the ongoing problem with LCDM is that the parameter space for allowable particles keeps getting pushed back. We keep falsifying classes of potential particles that could be WIMPs. MOND+ some standard model-adjacent particle (like say right handed neutrinos), if we can have a phenomenological estimate of how much of them should exist, would at least be credible on account of having a constrainable set of parameters, whereas the density of WIMPs in normal LCDM has no constraint besides the same measure that we have to infer its existence (gravitation)
I always wonder if light traveled billions of years to get here wouldn’t it be possible that it got distorted along the way? What if all these galaxies are just a sort of a typical pattern of what light looks like after an unfathomably long journey through space/gravity/time/etc? It could be likely that what we’re seeing is no indication of what was ever actually out there.
This can further reinforce the idea that the unobservable universe was always there and that the big bang is only a pattern of movement of the cluster of galaxies and it is only the information that has managed to arrive from our position.I want to see how big bang theory falls into an optical illusion.
Ok, I'm curious. How does the explanation for everything's existence being "God did it" not simply push the question up a level to wondering how to explain God's existence?
I just noticed that if you replace "God" with "Big Bang", it's pretty much the same question.
The answer to Big Bang is that before it, there was no time itself, so there's no notion of "before" (or if you wish, it's an error in the question itself that assumes there was "before").
I may be stupid, but considering that the models of galaxy stability are based on a universe where we are made from star stuff and not energy stuff, is it not possible that they formed way quicker with less complication because it was basically only hydrogen and empty space?
Does this mean that big bang either didn't happen or happened in a different way that we think of it? Or happened far earlier than we think it did? Complete layman here.
I'm not an expert but from what I understand, scientists observed the very distant galaxies which shouldn't be visible according to most popular model of the universe evolution. And if these observations will be confirmed then we might get more accurate model which totally differs of the most popular one the scientists agrees upon.
Far distant young galaxies should be seen as "red", but these aren't and that's the issue here - JWST captured these very bright. It's possible that the universe evolves in a different way and Hubble's law doesn't applies
Incomplete/unconfirmed data is showing some discrepancies for what our tentative models of the early universe predict. The data could be wrong or misinterpreted, the models could be wrong, incomplete or misinterpreted, or the could be fundamental problems with the very foundations of cosmology. The models we have of early galaxy formation are very incomplete and based on very little data. It's exciting to get data that will discover new things about the early universe and help refine those models.
We have lots of theories, but we'll never be certain as we will never see back to the BB. Everything was hot plasma for 370k years after the BB. We can get maybe that close, but no further. We are still exploding anyways.
Sorry for an likely ignorant question, but can someone ELI5 why we are confident that evereything in universe is less than 13 billion years old or whatnot, and not just redshifted beyond recognition?
Because you can literally see the remnants of the big bang. Basically, if you look out far enough, you see a wall of plasma from a time where the universe was so hot and dense that light couldn't travel freely. It's called the cosmic microwave background and is impossible to explain in a static state universe. Before you get to the wall, you first see younger and younger stars (which we can tell by their composition, which influences their spectra), then a region which is void of galaxies (because it is such a young region of the universe that galaxies hadn't yet formed), and then said wall.
Not only that, but the CMB's properties, like its frequency spectrum or its tiny anisotropies match what you would expect to an astonishing degree.
As I understand it, the most basic calculation came from modeling the Cosmic Microwave Background temperature changes in reverse time. If I recall correctly, that runs into a discrepancy that requires the addition of inflation to account for it.
I don't know why articles are titled like this. it's annoying, though, I'll tell you that
we are finding the exact correct number of galaxies of the exact correct ages; our expectations are wrong, or how we determine what we've found is wrong. generally, our understanding is wrong. not the rest of the entire universe.
>The classical big bang cosmological models describe gravitation by Einstein’s general theory of relativity. These models are able to treat the matter content of the universe quantum mechanically where appropriate, but they do not take into account the interplay of quantum theory and gravity.... The earliest universe was presumably quantum mechanical through and through, and we can no longer describe its initial conditions in a classical language. We must instead treat the whole early universe as a quantum system and formulate its initial conditions in the language of quantum mechanics.... Quantum gravity theorists have not shied away from the challenge. At present there are some half a dozen contenders...."
Depends what you mean by the big bang theory. The theory that the universe expanded almost from a point will probably survive forever, but ΛCDM might not survive the decade.
Articles like these make me want to stop doing everything and isolate in the basement for several months to study physics. Then I realize I have a family to feed and elderly parents to take care for.
Sigh, so many beautiful mysteries in the world, and only one life.
edit: A friend told me germans have the word "Sehnsucht" to describe such a feeling. So I guess it might be somewhat universal.
Same, but I imagine doing it in a country house with a table looking out into a lovely garden, and a mountain path nearby for long walks thinking about things.
I don't know if it's any consolation, but a few months are not nearly enough to understand this on a meaningful level. I spent almost a decade studying physics, still feel like I don't really understand it and could barely wait to get out at the end.
I have kind of done that for last few months. Chat GPT helped immensely with that. I recently even asked if it's worth it to go back to academia. Still exploring that.
A few things that I recently understood or read about.
- How age of solar system was calculated. I previously thought just like the universe is expanding, so is solar system. Turns out that is not the case. The distances have been more or less fixed. (i thought sun would be losing some mass, weakening gravitation for that to happen, nothing like that).
- Exo-planets.
- a lot of nuclear physics.
- Parallel universe theory according to quantum mechanics.
Interesting approach. Aren't you worried that chatgpt is feeding you bullshit without you noticing? I'd imagine chatgpt read as much science fiction content as science one, so there's no way to know if it tells the truth or hallucinations. How do you deal with that?
It's a good starting point. It may get some things wrong, but that's where my ability to research and truth seeking lies. I usually google more anyway because i want to go deeper than what chatgpt offers. I will eventually get to the truth. But the basic questions are well answered. I once asked it to explain the whole "Field has momentum" theory in a way a Feynman lecture would. It did it surprisingly well. I had some background so I kept asking more questions, and it was alright. Augments the curiosity, and make the topic seem simpler. Tools I use are: Google, science publications, and archive to see if there is text around it.
One small thing, the idea that chatgpt will feed bullshit is possible, so you have to be a bit skeptic and check the info, but it gets things right most of the times. Fun fact: I confused chatgpt about static electricity ie "Why does my hair get a static charge by rubbing a balloon?" It kept saying positive charge or negative charge, with transfer of electrons. Truth is, it's still poorly understood. [1] this paper highlights the conundrum.
For a beginner in college level physics, chatgpt is an excellent resource for understanding concepts.
Not all of it is from chatgpt. It's a good starting point, and essentially tells me what to google and how to read further. When I get something, I anyway want to read more so would google around the topic. The ability to ask a cross question is what makes learning easier. If the answer is not true, i will end up finding that out anyway from google or other science publications.
For me, it's been learning about the topic of last year's nobel prize in physics. Shedding light on Einstein's famous "God does not play dice" through, literally college algebra and a somewhat mundane experimental setup. The only thing stopping people from doing it sooner was obscurity and a comfortable attitude towards to status quo!
Now I'm convinced we can understand really fundamental things about our reality, and that is so so interesting.
I'm dreaming of going back, getting a math master's, then a physics PhD ... Maybe
Yikes, it's BlackLight! I had no idea this joker was still around. For reference: this was popular snakeoil on USENET back in the 90's when I was in college. This is some really crufty nonsense, and I'm kinda shocked it's still being recycled.
The theory has not changed much since the original work by Mills in the 1990s but the experiments and engineering have overcome a lot of hurdles and there are now many experiments that match the predictions of the underlying theory and prove the existence of hydrinos.
What you're saying doesn't make sense - not even according to the bizzaro theory you mentioned. Even if there was a previous cycle, there would be no galaxies left from it to witness.
I watched a few videos about variable speed of light. I know nothing about this but it is fun to ponder different explanations for Dark Matter, Dark Energy etc.
You may like my silly theory (made with zero evidence) to bring back the Big Crunch Theory. Imagine that spacetime is a sphere, and the Big Bang happened at the "north pole" so to speak. All matter will eventually meet back together and recombine at the "south pole" after which a new Big Bang will happen. Absolutely zero evidence for my idea and it's probably impossible to prove anyway but it's fun to theorize.
It's pretty clear that it's the same at the atomic level as well.
The spectra look exactly like they look here. They're red-shifted, but the gaps between the peaks are exactly the same. That comes from the atomic level, the way the electrons are arranged within the atom.
If something were different at the atomic level, it would surely change the characteristics of the light they give off. The only way to see what we see would be if there were two things different, that somehow counteracted each other in the things we can see but were nonetheless different in some other factor we can't observe.
That's not impossible, but it would be a bizarre coincidence.
Instead of one big bang, imagine an infinite number of big bangs, all colliding on a cosmic scale in time and space. That’s not necessarily a multiverse, but it is a megaverse with universe as the old paradigm.
Yes, just why assume a multiverse and not a megaverse? Of course, the superhero movies (which I enjoy) give an unrealistic view of what a multiverse would be.
You've just moved the "what caused the..." question up another level and then pleaded that your new level is somehow more special than the previous level without any actual justification. It's turtles all the way down and gods all the way up.
So what you do is you form a ordinal-indexed hierarchy of “why”s,
And then you go up a universe level so that the class of ordinals in the lower universe level becomes an actual set and not just a class,
and then you somehow (exactly how... remains to be seen) appeal to Zorn’s lemma , and construct a why-of-all-whys that explains everything in the lower universe level.
And you call that thing [ERROR: NOT REPRESENTABLE].
A lot of academic/scientific belief is based on ignorance. Hear me out.
The entire academic/medical establishment believed the appendix was "just a vestigial organ" which served no purpose. It was taught in every university, in every textbook. Every medical professional knew it was a fact. Why? Because they had not identified a purpose. In their ignorance, they adopted the position "I don't know what it does, therefore I can state as a fact that it does nothing." Except it turned out they were all wrong, for a very long time.
The appendix is not the only example of that mentality.
The same has occurred when it comes to estimates of the age of the universe.
When the most powerful telescope could see N lightyears, people believed the universe was N years old. Tiny gains or new images using that telescope adjusted the estimate to N.fraction years.
When the most powerful telescope could see 2N lightyears, people believed the universe was 2N years old. Tiny gains or new images using that telescope adjusted the estimate to 2N.fraction years.
When the most powerful telescope could see 3N lightyears, people believed the universe was 3N years old. Tiny gains or new images using that telescope adjusted the estimate to 3N.fraction years.
This happens every time. Yet astronomers and cosmologists refuse to learn the lesson, and keep repeating the same mistake.
Vestigiality is not about having no function, but about losing the original function. Vestigial organs are also often in an atrophied state when compared to analogs in other species. The appendix is indeed vestigial, and while not entirely without function, it is almost entirely without one, to the point that you can not have it and not even realize it.
>When the most powerful telescope could see N lightyears, people believed the universe was N years old. [...]
What are you talking about? Before the 20th century it was believed that the universe was eternal. After then, advances in determining the age came primarily from theoretical models, not improvements in equipment.
>Yet astronomers and cosmologists refuse to learn the lesson, and keep repeating the same mistake.
You seem to be under the misapprehension that the goal of science is to not make incorrect statements. It's not. It's to incrementally (by necessity) learn about reality. There's nothing with the statement "by our best current measurements, the universe is about 13 billions years old" even if tomorrow new findings point to it being twice as old. To demand otherwise would mean that no conclusions can ever be drawn, because necessarily all scientific conclusions are tentative. It is true at all times that tomorrow's evidence may overturn today's conclusions.
"Yan found 87 distant galaxies behind the galaxy cluster SMACS 0723" --> this is not true. They found 87 galaxy candidates. To be fair to the article, they do note that these await spectroscopic confirmation but experts only believe those with spectroscopic confirmation. Everything else is tentative and we don't yet have good numbers on confirmation rates. Finally, the Yan et al candidates are wildly inconsistent with almost every other estimate of high-redshift galaxy samples. You can see a comparison in Table 4 here: https://arxiv.org/pdf/2212.06683.pdf. They claim more than double the number of high-redshift sources compared to everyone else. JWST data is still very new and hard to both reduce and analyze. One particular problem is correlated hot pixels which can appear as very high-redshift sources. I don't know if this impacts the Yan et al paper but just an example of something that is not 100% straightforward to deal with. I highly recommend people take this with a healthy amount of skepticism until everything has a spectrum.