This is Smolin, making his usual, and valid, criticisms of modern physics. Smolin's basic complaint is that there is no experimental evidence for string theory. The math is pretty, and a whole generation of physicists have worked on it, but nothing is experimentally testable. Everything is too small or at too high an energy level. A practical implication is that it doesn't lead to any technology.
Smolin also doesn't like many-worlds, because it talks about unreachable regions. This he considers too speculative. There's a basic problem in quantum mechanics, which leads to Schroedinger's Cat, the Copenhagen Interpretation, and, in the end, many-worlds.[1]
Physics has been stuck on this problem for almost a century now. Philosophy won't help.
There's a lot of really strange stuff going on with QM and ST, even tho Brian Greene works primarily on ST he did somewhat coined the concept of the "giant leap" that to some extent theoretical physics has run off way too far from anything that can be proven using experimentation.
>Physics has been stuck on this problem for almost a century now. Philosophy won't help.
Philosophy does help, infact it might be the only thing that would help in it's essence philosophy is about how you approach and solve problems, and more importantly how you think about them.
It might need be that we do need a major philosophical change in the world of theoretical physics and start thinking about QM and the universe in general in completely different matter.
There is a lot of natural bias that pushes your thinking into a very predictable path and this plagues theoretical physics just like any other field if not more.
The bleeding edge of theoretical physics, especially in the past 60-70 years has really shifted towards almost the metaphysical regardless of how much elegant math there is behind it.
What is this idea that making the math prettier or more elegant is not important? That's like saying a new algorithm isn't important; new math or models make problems potentially tractable that aren't now.
All of our math is an attempt to represent things or ideas. The most important thing I learned in my physics education was how to read math as a metaphor for putting together things I understand into a picture of a thing I don't understand. But I don't think anyone serious thinks that their math is "true", such an assertion just makes no sense. The point of it is to find new ways to approach the evidence to see if it gives some different metaphor that wasn't obvious before.
I don't know enough modern physics to have an opinion on whether this is the case for cosmology or string theory, but I do know that in recent history just formulating a problem slightly differently can suddenly make the solution fit in the same framework as a known simpler problem. Not unlike things I read all the time about algorithm research at all, right?
Teaching and understanding models is predicated highly on metaphor, it's much easier to explain for instance that MRI works via a quantum effect that has the same math as a harmonic oscillator than it is to just... dive in. The model isn't the universe, but humans live by metaphor and so the model is important.
Which is perhaps not the point you were trying to make; I don't know enough modern physics to know whether a critique of these new areas as purely fantastical is justified, but it's also pretty fantastical to think of a particle in a box as if it were like a weight on a spring. Who am I to say that something about this approach can't make a currently intractable, approximate, or computational impossible problem solvable with time?
The danger with math is that it can prove its own truths based on its own internal rules, so there's a temptation to believe that whatever you can describe mathematically describes something that actually exists in the real world. But until you've tested it experimentally, you don't know whether you're describing a total fantasy world, like The Lord of the Rings, or something actually real, but boring, like an apple. Just because you've proven with mathematical certainly the existence of hobbits doesn't mean you'll actually find any.
> The danger with math is that it can prove its own truths based on its own internal rules...
Actually, there's a theorem about that ;) Godel's Incompleteness theorem.
I would describe the problem more like: The new model matches the old model in almost everything (because we've observed a lot). But the math works out quite nicely if itty bitty particles behave this way when exploded at super high temperatures. We have a hard time watching those particles explode, so it's not really tested. Either way it works out, it's not really going to matter for anyone who doesn't explode tiny particles.
Given that GP was discussing publicly, on a technical internet forum, the relationship between mathematical provability and truth/existence, don't you think it likely that GP was aware of Gödel's Incompleteness theorem? My concern is that the "actually", and the smiley face, seems, to me, very patronizing. I really don't mean to be attacking you for a small point of etiquette, and I also acknowledge that the main purpose of this thread (the nature of reality) is a bit more important, but I do make this point sincerely. This is something I find a real problem when discussing things with software engineers. I personally hate the feeling of being patronized in public, or of someone replying in public with the implication that I was not aware of something which I am perfectly well aware of. I'm not claiming that the GP is an expert on the Incompleteness Theorem, and I'm certainly not, but that "actually", and the smiley, sound and look awful. We should assume that others are competent and knowledgable on the subjects they talk about until given evidence to the contrary.
I believe you've misconstrued d13's intended meaning. In short, what they said is something can be mathematically consistent without being physically realistic. GIT is not really pertinent here.
I'm skeptical that theoretical physicists disagree. If anyone would be aware of these dangers, I would imagine it to be them; these are incredibly smart people! I only even got an undergraduate physics degree and this stuff was all quite obvious. Which isn't to say that arguing about which metaphors are likely to bear conceptual fruit isn't worthwhile, but even with much more physics education than most I would never deign to enter such a debate myself. The people doing the work definitely know what they're doing and I definitely don't, so to presume otherwise is weird to me.
I worry that it is the pop sci presentation of physics that non-physicists look at and think wrongly that the actual people carrying out the work are blinded by training bias (which is true for anyone, but I think far less true for experts in the field than otherwise) when in fact it's just the authors of pop sci articles and books who are ignorant of the difference between metaphor and reality. These are people who are paid to figure out how to think differently about their questions, they're not just following conventions and calculating pi to more decimal points.
Is an encryption algorithm "real"? Is the process used in proving a theorem "real"? Is the way that we model an atom "real"? No, of course not; they're all ways to represent an idea/observation through metaphor by breaking down a problem to make it look more like problems we already know how to solve. And if you just decide to approach the metaphor for understanding that idea differently, you can get massively more tractable problems.
As an example, a friend of mine in undergrad was studying crystalline domains in metals and wanted to find a way to understand better the relative misorientations of neighboring crystals in three dimensions. The metaphor as written strongly suggests that the right approach is some manner of statistical approach with a random variable representing orientation that can then be statistically analyzed to provide a misorientation distribution, but the problem is generally intractable in 3 dimensions whereas in 2 dimensions it's fairly straightforward math that way.
He instead decided to represent the crystallites in four or maybe five dimensions, which by so doing he was able to show that the math looks the same as that used for adding angular momentum using Clebsch-Gordon coefficients derived from quantum mechanical spin coupling. And found that by so doing he could turn a statistical problem into one with a closed-form solution that was quicker and easier to calculate in more sophisticated cases. With apologies if I'm explaining it wrong, this one never was quite comprehensible for me, he was far better at math.
Does he then think that crystallite orientation is literally quantum mechanical spin? Of course not. Does the math produce a testably distinguishable result? No, of course not; it should be the same result. But is it likely some future scientist with greater understanding of quantum spin coupling might be able to conceptualize the system more deeply? Definitely! This example is hardly unique.
So my point is that representation and metaphor matters, even if it's not a testably different result. To say that it doesn't matter to me seems to be saying that the current model itself is real, when it's not either! There's no fundamental reason to favor one over the other if the results predicted are the same, other than personal preference, ease of manipulation, or ease of conveying the model/metaphor to future students.
By encouraging different metaphors for the same system, you enable future scientists to be taught those alternative approaches so that they have a bigger toolbox to approaching some yet unknown future problem. We're just humans, and everyone looks at things a bit differently; none of us with a clear picture of what's really "real". Much like how there are a half dozen different approaches for quickly sorting a list, some are more intuitive or powerful or quick to execute than others.
Incredible smart people have a tendency to fall in love with there ideas and the beauty of the created concepts. Im pretty sure that physics as a field has the same problem with architectural astronauts as software engineering has.
Im not criticizing hard working mathematicians and physicists like your friend- the solution he found sounds rather elegant, and the results are testable.
And you are right about having no dogmas when it comes to approaching the riddles of tomorrow- and yet, if all work you do is untestable- you are not a scientist.
There are people whose job it is to make pretty math, they are called "mathematicians" ;-) So much of early physics, be it thermodynamics, electromagnetics, classical mechanics, is genuinely beautiful and elegant. I can see why quantum physicists would strive for that ideal as well. But at the end of the day I agree that physics should favor creating testable predictive models over developing untestable, elegant ones.
I'm sure most theoretical physicists would call themselves mathematicians. I don't agree physics should favour creating testable predictive models, because who are we to say what's testable in the future? Take the theory of relativity, for example. Would you have stopped Einstein et al from researching it, just because it wasn't testable at the time?
In my opinion, physics is and has always been about answering the big questions, the how's, the why's of our existence. That new technology sometimes comes out of it is a bonus, not the ultimate goal.
If that is so then why don't we just accept the religious answers to these big questions? Some supernatural entity is in the control of everything that's the answer and we are done. The goal of any science should be to answer questions such that those answers can help us solve the problem humanity faces and not just make us feel proud sitting in our chairs that we know answers.
I think you are generalising my comment quite a bit, it was just a reaction to the poster above.
We are never "done", that's kind of the point I was trying to convey. I completely agree that we should use science to help us deal with our current problems. Once we understand more about our world and ourselves, we will automatically get better at solving them. I'm just against the whole short-term, instant results way of thinking.
I didn't say that math is not important, but you can also dig yourself into a hole with it, there are quite a few competing theories all of which have a strong mathematical basis because you develop the math to explain your model of reality especially when you cannot gain sufficient evidence from experimentation.
The overall point was which I might not have expressed fully is that there is in my opinion too much bias in the field of theoretical physics, and to paraphrase Brian Greene again we took a giant leap and probably skipped a few steps and no one seems to want to look back and see if we missed something.
I think one of my favorite quotes that somewhat describes this view is by Rudolf Peierls:
“In recent years the debate on these ideas has reopened, and there are some who question what they call ‘the Copenhagen interpretation’ of quantum mechanics’ - as if there existed more than one possible interpretation of quantum mechanics.”
And I think that this view is antithetical to the advancement of current physics, and sadly this bias is instituted even unintentionally in most new physics students especially those who take physics as part of their degree in CompSci/Engineering.
I totally get your point, that getting stuck in a framework can make it harder to get out of said framework, but I also have every reason to think that the experts in the field (which may well include you) are aware of this trap and spend a huge amount of time trying to get out of it.
But I'd also expect that people making new theories be intimately familiar with the current ones, right? It would be silly to expect someone to come up with hamiltonian mechanics for the first time without having ever been exposed to newtonian mechanics, even though both give the same answers to every problem. Yeah, thinking outside the box is always super hard, but you have to at least deeply understand the box before you can know enough to replace it. I definitely don't understand this particular box, but I feel it's reasonable to assume that those that do are trying their darndest to escape it -- if for no other reason than fame if successful.
It might but we've been generating many imaginary solutions without a lot of take-home benefit for a while now. ST has had an extraordinary run given how useless it's been, especially since it's sucked up money and time that might have been better spent on real science.
Actually, many people believe that math is "true", and in many cases they believe that math is more real than the physical universe. The position is called Platonism, in its older form, though Kant has his own spin on the idea.
As I understand ST, by choosing particular parameters you can make it predict (more or less) anything. If so, what does it mean for it to have made a prediction?
I personally think pilot-wave theory is about to make a serious comeback in this coming decade. It certainly explains the exact same phenomena but it doesn't resort to any spooky stuff except action-at-a-distance. I'd rather embrace nonlocality than the crazy many-worlds stuff. We are just used to locality, why does it have to be an axiom? Seems like it could just as well be a result of the law of large numbers, same as any other macro effects in QM. That is, there is just a very high correlation that results in locality. Same as not being able to pass through a wall, or schrodinger's cat not appearing in the macro world.
I do too, i just find the concept considerably more elegant, and to my own feeble mind considerably more intuitive.
The Pilot Wave theory has also been getting some experimental support recently [0], and while it's still fairly early, it still beats string theory.
All the work in nonlocality also helps in my opinion the Pilot Wave theory to become relevant again, we have too many experimental data for use to disregard it and none of the other solutions that incorporate nonlocality seem as elegant to me.
I too think that the universe is most likely deterministic, and has strong realism which saves us from having to deal with the observer concept in QM especially some of the weirder interpretations of it[1].
P.S.
If anyone is interested in PWT one of the best materials I've seen is a series of lectures by Mike Towler of Cambridge University[2].
It's probably one of the better constructed lectures I've seen of QM in general, it hits the very rare sweet spot of being actually informative without falling into the realm of popular science while not requiring PHD level physics to follow (infact depending on the country you went to high school if you did cover QM in year 10-12 it's almost everything you need).
You should be careful with the language. Pilot Wave Theory gives rise to the quantum formalism. Anything predicted by standard quantum mechanics is a prediction of PWT.
Of course, the PWT viewpoint may suggest new ideas and understandings; it is, after all, what led Bell to his inequality and thus spawned all of the entanglement uses including quantum cryptography. But it gets reincorporated into standard quantum mechanics.
None of that really matters. People reject PWT because they want to reject it. There have never been any good reasons. It is an extremely simple theory that answers the questions.
If it gets accepted in the future, it will only be because of a new generation being more willing to embrace it.
At first the physicists said it was impossible and then when it was obvious that it was possible, they said it was too trivial. This is a hallmark of reason being used to justify an already decided on outcome.
It is also not in conflict with string theory. One could imagine string theory actually having strings that evolve. This would be the spirit of PWT applied to that realm.
I'm curious what language would that be? I didn't thought i made any strong statements.
Yes in it's essence PWT doesn't conflict with the concept of strings (nothing really does), I'm not so sure that I doesn't conflict with the leading "complete" string theories out there today.
Can there ever be an experiment which proves which interpretation of QM is correct? I have heard that there isn't but I find that so weird. Don't they have any difference in their predictions at all?
GRW (spontaneous collapse of the wavefunction) is a different theory and theoretically experiments could get good enough to prove it wrong.
But most interpretations have the same statistical predictions as standard QM. The standard Copenhagen setup can be argued to not actually be a theory (the split between quantum and classical in a fundamental theory is an absurdity since the classical is made up of quantum ), but assuming that an interpretation is clear enough to be called a theory and has the same statistical framework as standard quantum mechanics, then experiments will not distinguish them.
The different interpretations, however, may lead to different insights for extending the theory. And in that game, one may pull ahead of the other. For example PWT inspired Bell's results. PWT can also explain the impact of the topology of configuration space convincingly since the configuration is a fundamental part of the theory. It leads to many insights that the others just have to assume.
GRW with a flash ontology has a relativistic version with no foliations. So that's cool.
IMHO, PWT can be proved with two slits experiment and FTL electrons: they will behave like particles, because their wave will be unable to interfere with itself.
PS.
To clarify, if double slit will be put in a medium where speed of light is much slower, then there will be a speed, when electron with that speed will stop behaving like wave. This point will be depended on speed of electron, speed of light in medium, and distance between slits.
Is that even possible to construct? won't any dielectric media interfere with the wave/particle duality regardless if the speed of light is slower or faster than the speed of the electron in it?
IMHO, it still possible to adjust slit experiment in such way, that slight increase in speed will break interference, i.e. at speed X electron will behave like wave, but at speed X+1 electron will behave like normal particle.
What does it mean if particular probability for x vs y is an irrational number? Can you really have a number of universe forks counted in something that isn't integers?
If you don't really have independent universe forks but something physically continous, what mechanism makes us seem to only observe a single independent branch at all times?
Given the assumption of quantum foam (from the uncertainty principle) at the Planck length + relativity (the Planck length isn't constant like the speed of light, every observer measures it differently relative to others), how many universe branches are really created every picosecond in every Planck length (volume) across the visible universe?
IANA physicist, but my layman's understanding was that under many-worlds the universe doesn't actually fork. Rather, the superposition of states observed in things like the double-slit experiment applies to all particles all the time, including the ones in our brains. When we observe a system undergo an apparent collapse of the wave-function, what's actually happening is that we/our brains have become entangled with that system, so each of our brains' states becomes correlated to one of the system's states. To a consciousness generated by one of those brain states, it appears that the system under observation has undergone a collapse; however, the result of that collapse appears different to each such brain state.
Nonlocality means there may be interactions between particles across space. That seems reasonable because what we intuitively think of as space and time may just be strong correlations. Causality etc.
But if at every moment you literally have an infinite amount of worlds branching off, then that's vastly bigger than one world in which interactions can be nonlocal. It violates everything from Occam's Razor to practicality.
The question of why time is non reversible can be answered by saying that entropy of a system grows with time, which is a consequence of simple statistics. But with many-worlds you have branching in the forward time direction? Can you explain anything about it?
> if at every moment you literally have an infinite amount of worlds branching off
As I said in my reply to Natanael_L, I was given to understood that the idea of worlds branching off was a misapprehension of the many-worlds interpretation. But I'm prepared to be corrected.
> I personally think pilot-wave theory is about to make a serious comeback in this coming decade.
Which is a shame, because John Bell of Bell's theorem was already a fan back in the 60s. He correctly labelled non-locality as the fundamental problem of QM, where other interpretations just let them gloss over this difficulty by labeling such questions "non-physical".
But realistically, I think information-theoretic formalizations of QM will simply gain more popularity in rather than something like de Broglie-Bohm. There's simply too much anti-realism sentiment in the physics community for it to gain much traction.
Yeah that and pilot wave has some elegancy to it that finds simmetry at so many other scales. So in other words as long as them will all be interchangeable and unverified, I'll fanboi for pilot wave.
> Philosophy does help, infact it might be the only thing that would help in it's essence philosophy is about how you approach and solve problems, and more importantly how you think about them.
I'm genuinely curious to know how you think any post Frege philosophy helps. At best philosophy can help prevent research/effort being expended in plausible non-sense; but certainly not in the sense of providing a positive result or foundation for one (which is to my understanding what those doing ST are ultimately seeking).
I'll also take the time here to gripe about post-wittgenstein philosophy which went willy-nilly with formal constructions and basically managed to ignore PI entirely (or otherwise remain mum about it) as well as the his remarks on the foundations of mathematics which set up a lot of problematic for the later.
> but certainly not in the sense of providing a positive result or foundation for one
I don't think philosophy strives to provide positive results. That is left to science. But philosophical ideas can help direct science, and that is a great contribution.
> post Frege philosophy
Post Frege? Even if you only value analytic philosophers, and mostly for their contributions to mathematical logic, I think you should at least acknowledge Russel, Kripke, Putnam and possibly others, if only for their immense contributions to computer science.
> in it's essence philosophy is about how you approach and solve problems, and more importantly how you think about them
This. This is what helps.
> how you think any post Frege philosophy helps
If it doesn't then that explains precisely why we need more new philosophy to make the breakthrough.
Physics can never be about a specific philosophy until it works. Without a working philosophy, we're stuck, which is pretty much where we are right now. We need to keep thinking, and we are, so it's really only a matter of time.
If you really dig into what they're talking about, it presents potential avenues for "solutions" to issues from why physical laws are what they are to how consciousness and free will would be possible. It's a lot more than just angels-on-head-of-pin stuff, and goes far beyond Smolin's previous critiques of string theory.
If a philosophy is making positive statements it's an obvious sham - the best you can do with a meta logic is define the limits of what can be expressed within a logic (postive and negative as related to this world) it cannot have anything to do with producing results.
But it can. Philosophy can clear the brush between two competing paths. If we take path A, that leads to X, Y, Z, whereas if we take path B, that leads to J, K, L. Philosophy has done nothing to say whether reality is more A-like, or more B-like, but in delineating and making clear the consequences of an A-like world vs a B-like world, it has done a significant service in producing physical results. When experimentalists show an inkling of a tiny sliver of 'K', we know can collapse with logical certainty around the B-like world.
Trudging down those paths prior to experimental evidence is of very real value and is not disconnected from the physics itself.
Philosophy is not correctly defined as the generation of logic. If the philosophy you learned is defined in connection with logic then it can be term deteriorated philosophy. The proof is that if we had learned philosophy correctly we also form our own eye of wisdom to see what is in the truth but no one can verify what is true through logic alone as you cannot verify your axioms without external referents. The reason is that truths can only be verified through problems. This all means we can't see the world through thinking, but through the problems.
Why does a precise definition of the discipline matter? AFAIK, there is no such definition of what constitutes physics or even mathematics. Those disciplines are usually "defined" by whatever it is that the people associated with them choose to study. Physics is as physicist does; philosophy is as philosoper does.
Good question. It shows that this is the snit we've gotten ourselves into: philosophy=formal systems. Physics must be based on a formal system, therefore we must have an advancement in formal systems to help physics. There is no advancement, yadda yadda.
The "good" parts of philosophy are the mushy parts. And when you've created a formal system that's self-consistent yet offers no value, you're going to have to step outside formal systems for a while.
That's gotta be a painful leap for a lot of folks who believe that math is the ultimate reality.
I wouldn't equate philosophy with formal systems, philosophy is more about what a formal system is, what formalisms actually mean, and deciding when they are important tools for knowledge, and when they are not.
>The bleeding edge of theoretical physics, especially in the past 60-70 years has really shifted towards almost the metaphysical regardless of how much elegant math there is behind it.
Which is a major problem, given the truism that theory is under-determined by experimental evidence! If given any simple theory of physics I can construct a more complicated theory that makes the same predictions, then we desperately need to confine ourselves to theories that do make unique predictions, lest we be generating ever-more-complicated versions of theories we already had.
That's like saying "we need to confine ourselves to business plans that make money." Everyone understands and agrees on the importance of this as an ultimate goal but nobody knows the path to get there -- the hard work is in trying and rejecting promising paths until you find one that works.
Right. So there's room for developing hypotheses that we don't yet know how to test. Because some branch might be testable, or some new technology might become available. Just as with business plans and profit. But at some point, someone should maybe call bullshit. Kuhn etc have explored criteria. One of them, as I recall, is asymptotically increasing complexity.
The focus hasn't been on developing more complicated theories, but instead on developing less complicated theories. This provides additional explanatory power, and provides a mental model in which we can ponder thought experiments that may yield further insights.
For instance, many-worlds is actually conceptually and formally simpler than Copenhagen.
I'm curious to know your opinion. Suppose an individual appeared who said they knew the reality of gravity and how to design an apparatus to verify it. How would s/he be treated?
The quantum gravity community alone has a whole plethora of competing, mutually contradicting theories even within subgroups like string theory. Well-known and respected physicists make their careers off of proposals like:
- Two time dimensions [1]
- Reality is actually a discrete, combinatorial graph [2]
- We live in a Euclidean space virtual machine on a
general relativistic virtual machine on a Euclidean actual machine [3]
- Reality is a souped up version of liquid helium,
and of course dark energy is just surface tension [4]
I took a bit of license with these descriptions, but when this stuff doesn't get you written off as a crackpot (as long as you've got an actually theory going on and can explain it to others), what will?
Outlandish but testable claims are treated well by the Physics community. Take the recent example of the EmDrive[1], which has gotten a few replication studies. Nothing conclusive yet, but it hasn't been dismissed out of hand by everyone.
Are you from the physics community? The EmDrive wasn't viewed well at all, it's viewed as completely baloney. None of the early experiments afaik was none with sufficient experimental rigor to reveal anything surprising. All this while making an absolutely huge claim. The average physicist (I'm not one) wouldn't want to waste any more time with it than with the 2nd-law-violating "free energy" claim of the week.
Getting replication experiments is "well" for a crackpot claim. Having the average physicist accept it would be a bit too much -- the point was that the claim was testable and thus not universally rejected.
You say they're treated well, but the EmDrive was specifically sponsored by NASA, which means you're not answering the same question as what I asked, but changing it by presupposing that I asked how such a person would be treated if they were already institutionally sponsored.
First, I can't possibly answer the question you asked, because you asked for the opinion of someone else. Second, if you had read into the second paragraph of the link, you would see that the EmDrive is not institutionally sponsored nor developed by NASA. Third, offering analogous evidence is not the same thing as changing the question.
Actually, it was institutionally sponsored, because the very work to peer review it was done by labs directly sponsored by NASA.
If the initial work were not peer reviewed, you would not be holding it up as an example of something successful.
Therefore, it's NASA's sponsorship of the peer review which is a necessary and direct cause of you calling it successful here.
So my initial assessment of what you said stands. You're saying the physics community is receptive because NASA sponsored an attempts to verify it. That proves nothing about the receptivity of the physics community nor of even NASA. But I don't expect this to be something you can easily agree with. After all, you're proving my point.
It isn't very clear what you think should happen here.
A fairly outlandish invention was developed outside the mainstream physics community. The community saw it and made the effort to test it. This is good, right?
Of course I can. I have been. Now if you want to know something more specific, you need a more specific question which you can make by using things I've said.
EmDrive has not been "sponsored" by NASA. The researches at their Eagleworks labs built a prototype and tested it, but that's not quite the same thing.
Would we be here talking about the EmDrive as anything like a possible breakthrough which was well received if it were not for that NASA-sponsored work?
I think so. NASA has done relatively little with it so far.
It's not like they've given it their stamp of approval. Eagleworks is NASA, but as I understand it, they are on a pretty loose leash, and it's their business to investigate somewhat-crackpot ideas.
Why do you say that? There are adaptations that have creation and annihilation of particles in Bohmian mechanics: http://arxiv.org/abs/quant-ph/0303156
The main issue is that QFT does not generate a mathematically well-defined evolution of the wave function, but there are promising directions on that front as well: http://arxiv.org/abs/1506.00497
Basically, they treat the Hamiltonian as a whole instead of a perturbation and use a domain for it that has the probabilities flowing from one area to another appropriately to the different particle sectors.
There is also work on dealing with relativity which is a separate issue. While there are solutions, mainly centering on finding a natural foliation, the tension with relativity has not really been resolved, a tension which exists regardless of interpretation.
> While there are solutions, mainly centering on finding a natural foliation, the tension with relativity has not really been resolved, a tension which exists regardless of interpretation.
Exactly, John Bell had it right 50 years ago: non-locality is the problem of QM that needs to be solved, and other interpretations let you simply gloss over the problem without really addressing it. The recent work for finding a natural foliation present in any formalism with a wave function, including Bohmian mechanics, proves every QM shares this problem (or if you think one doesn't, then none of them do for the exact same reasons).
> This is Smolin, making his usual, and valid, criticisms of modern
physics. Smolin's basic complaint is that there is no experimental
evidence for string theory.
Uhmm, he’s working on quantum gravity too. Just a different approach.
The same applies to loop quantum gravity.
> A practical implication is that it doesn't lead to any technology.
Who cares? It’s science not engineering.
> Smolin also doesn't like many-worlds, because it talks about
unreachable regions. This he considers too speculative. There's a
basic problem in quantum mechanics, which leads to Schroedinger's Cat,
the Copenhagen Interpretation, and, in the end, many-worlds.
The string landscape [1] and the many-worlds interpretation [2] are two
completely different things. The string landscape indicates that string
theory may never be able to make any predictions. Some physicist try to
use many universe in combination with the antropic principle to “solve”
this problem. But I’m pretty sure this is a very small minority.
The many-worlds interpretation of quantum mechanics is just that, an
interpretation. It doesn’t make any measurable difference from any
other interpretation. And the Copenhagen interpretation doesn’t lead to
many-worlds, they are just two different interpretations of the same
theory.
> Physics has been stuck on this problem for almost a century now.
At this time I wouldn’t call it a “problem” of physics. If all
predictions are the same it’s just a matter of taste which
interpretation you prefer. To bring it into the realm of physics you
would need to come up with some kind of theory of the measurement
process that actually makes testable predictions.
It's not a matter of taste. Philosophy is about which questions you ask.
More specifically, it's about what kind of questions are considered worth asking. You can track the changes through history, and philosophy often leads politics and art as much as it does science.
Philosophy looks like the most abstract and possibly trivial pastime, but in fact it's incredibly powerful and influential, because it literally makes some world views thinkable and others unthinkable.
The different interpretations of QM are trying to ask different questions about reality. The fact that they're empirically indistinguishable suggests that either they're literally irrelevant - because they all give the same answer - or that no one knows how to ask a more insightful question yet.
If a more insightful question exists, it may come from some completely unexpected direction.
Physics has had a century to think about the problem, and hasn't gotten any closer to a definitive solution.
That suggests either more time is needed and we just haven't got there yet. Or perhaps the real explanation is literally unthinkable within the world view we have today.
> Uhmm, he’s working on quantum gravity too. Just a different approach. The same applies to loop quantum gravity.
String theory isn't a quantum theory of gravity in the same way that loop quantum gravity (LQG) is, LQG is background independent. String theory assumes there is a flat background spacetime already present and perturbatively builds off of that. LQG doesn't make this assumption and tries to create spacetime from scratch.
LQG did make some testable predictions, as has string theory in recent years. One was regarding the smallest units of area and volume that might have been seen in light scattering in cosmic ray or gamma-ray burst experiments[1]. Another suggesting evaporating black holes could be used to probe LQG [2]. String theory proposed supersymmetry, where each fundamental particle had a supersymmetric partner. Electron => selectron, quark => squark, etc. But none of these proposals have panned out as yet. Thus far supersymmetry has not been found and LQG has not been able to recover general relativity in a classical limit.
> The many-worlds interpretation of quantum mechanics is just that, an interpretation. It doesn’t make any measurable difference from any other interpretation.
In the last couple years, many-worlds researchers have come up with some potentially measurable consequences [3].
Just reading the abstract to [3], I do not see any claims that they have tested any unique predictions of many worlds. Rather they have used this model to recover some known results.
Yeah, many of the 'popular' discussions of Quantum Mechanics that show up here on HN do often diverge well into philosophical directions and away from hard science.
It's true that science and philosophy did come from a common discipline (my undergrad uni originally had a Natural Philosophy dept that only became a physics department somewhere between 100-150 yrs ago).
Though I thought one of the physics professors when I was in grad school said it best : "Physics is philosophy with integrals".
I agree but I think there are important philosophic[1] questions raised by quantum mechanics and, to a lesser extent, special relativity. One hundred years ago the founders of the new physics had the same questions but could not resolve them to everyone's satisfaction. One of the founders of modern physics (I forget who) said (I am paraphrasing) that all the different views on the "meaning" of the new physics amounted to where you want to hide the contradictions. The Copenhagen "interpretation" was not a definitive win but a truce.
These brilliant men argued for a decade and could not resolve it so they decided to bury the questions. It was not unreasonable in that context to accept that they did not know the answers but the theories work so let's use it and see where it leads. I am sure the hope was that the answers to the philosophic questions would become clear as our understanding of the new physics grew. There was a lot of work to do aside from the philosophic questions. Fast forward 100 years and here we are, the philosophic questions are still unanswered, and the Copenhagen interpretation has hardened into dogma banning any discussion of fundamental questions in physics. I have respect for Smolin for at least trying to re-raise these important questions.
[1] I am of the view that philosophy is distinct from physics in that it studies the nature of reality and knowledge, thus it applies to ALL fields not just physics. WHAT do we know and HOW we know is the more (or the most) fundamental science. The physicists are throwing out the baby with the bath water when they reject philosophy en masse instead of rejecting bad philosophy.
The quote was by Zlatko Tesanovic, a brilliant and witty theorist who sadly passed away a few years ago. Here's a link to a page of some of his other quotes, as recorded by his students. IIRC he said the integrals quote when I was the TA for his statistical mechanics and thermodynamics class.
"Physics is philosophy with integrals." -- Well, too bad for physics... But where to look for guidance? Philosophy tries to answer questions that do not have answers; theology studies that which does not exist. What a waste of time. Even Einstein, how many years did he spend trying to understand the meaning of these philosophical "integrals", to no avail? Even his mind was powerless trying to come up with an interpretation of the quantum mechanical theory that would make sense. Should we accept this as an indication that there are limits to our ability to understand, just as there are limits to what we can achieve physically?
"Should we accept this as an indication that there are limits to our ability to understand, just as there are limits to what we can achieve physically?"
World-over, the degree conferred for significant contribution through original work in Science (and Engineering) has principally been Doctor of Philosophy. I doubt if it will ever change.
> It sure seems to be an epistemology problem which puts it
> squarely in the realm of philosophy, not physics.
It's absolutely a physical issue, not a purely philosophical one. Under the Copenhagen interpretation, the probability densities which drop out of Quantum Mechanics reflect some sort of objective physical reality, as in Schroedinger's Cat. The alternative to this is the so-called "hidden variables" theories [1], which posit that those densities reflect variability in some kind of hidden extra state in quantum-mechanical systems of which we are currently ignorant. The very real Bell's inequality experiments [2] are an example of the physical quality of this dichotomy.
It may be that my memory does not serve me well, but I think I got an impression from the history of the philosophy that once there is a field of philosophy that actually starts solving problems, it very fast changes its name to something else than philosophy. For example[1], Newton's 1687 Mathematical Principles of Natural Philosophy later became classified as a book of physics.
That's my thinking too. When trying to define what philosophy is, I have settled on this: Philosophy is the reasoning about poorly defined things, using similarly fuzzy steps. This is not a value judgement.
Once we get a better grip on an area, then, finding more proper definitions for its concepts, we branch it off as a subject of its own.
It seems more like the usage of the word 'philosophy' has gradually shifted to mean something very narrow, when at times it could have been used as a synonym for 'science'.
Philosophers disagree a lot in their specific definitions, but most definitions assume it is the study of the broadest and most general questions, like what is truth, what is reality, what is the good, and so on.
Also, any particular field you study has philosophical assumptions, like about the reliability of sense data. The reason modern science is so fabulously successful is the philosophers who established it got rid of the supernaturalist assumptions of previous science, and added the assumption that reality is mathematically describable.
What Smolin and Unger are saying is that the particular philosophical assumptions behind string theory and a lot of related physics are mistaken. This would seem to be at least possible.
> Philosophy is the practice of looking into questions without clear-cut answers.
Indeed, or the practice of asking questions about the nature of questions, ie. what questions are meaningful, well-formed, yield knowledge, etc. in any given subject.
When you understand the nature of the questions in a particular subject, then you're no longer practicing philosophy, you're gathering knowledge of that subject, ie. math, physics, chemistry, etc.
Yeah, I like it too :-) Philosophy has surely delivered unicorns: Mathematics, Physics, Biology, Chemistry, Computer Science! The question is, can Philosophy deliver another one?
That happened just once, though (as far as I know). "Natural philosophy" was a catch-all term for anything that involved the study of nature, before everything was formalized into categories such as physics and biology, and we decided "science" was a better, snappier term for it.
The word "scientist" was only invented in 1834. The scientist who coined it, William Whewell, also thought up "phycisist" and a whole bunch of other modern terms. [1] Interestingly enough, "naturalist" still survives as a legit term, as does "natural history".
There's an interesting back and forth with Boltzmann and Mach that touches on this:
> Boltzmann's kinetic theory of gases seemed to presuppose the reality of atoms and molecules, but almost all German philosophers and many scientists like Ernst Mach and the physical chemist Wilhelm Ostwald disbelieved their existence. During the 1890s Boltzmann attempted to formulate a compromise position which would allow both atomists and anti-atomists to do physics without arguing over atoms. His solution was to use Hertz's theory that atoms were Bilder, that is, models or pictures. Atomists could think the pictures were the real atoms while the anti-atomists could think of the pictures as representing a useful but unreal model, but this did not fully satisfy either group. Furthermore, Ostwald and many defenders of "pure thermodynamics" were trying hard to refute the kinetic theory of gases and statistical mechanics because of Boltzmann's assumptions about atoms and molecules and especially statistical interpretation of the second law of thermodynamics.
> Around the turn of the century, Boltzmann's science was being threatened by another philosophical objection. Some physicists, including Mach's student, Gustav Jaumann, interpreted Hertz to mean that all electromagnetic behavior is continuous, as if there were no atoms and molecules, and likewise as if all physical behavior were ultimately electromagnetic. This movement around 1900 deeply depressed Boltzmann since it could mean the end of his kinetic theory and statistical interpretation of the second law of thermodynamics.
> After Mach's resignation in Vienna in 1901, Boltzmann returned there and decided to become a philosopher himself to refute philosophical objections to his physics, but he soon became discouraged again. In 1904 at a physics conference in St. Louis most physicists seemed to reject atoms and he was not even invited to the physics section. Rather, he was stuck in a section called "applied mathematics", he violently attacked philosophy, especially on allegedly Darwinian grounds but actually in terms of Lamarck's theory of the inheritance of acquired characteristics that people inherited bad philosophy from the past and that it was hard for scientists to overcome such inheritance.
> In 1905 Boltzmann corresponded extensively with the Austro-German philosopher Franz Brentano with the hope of gaining a better mastery of philosophy, apparently, so that he could better refute its relevancy in science, but he became discouraged about this approach as well.
> The reason Aristotle didn't get anywhere in the Metaphysics was partly that he set off with contradictory aims: to explore the most abstract ideas, guided by the assumption that they were useless. He was like an explorer looking for a territory to the north of him, starting with the assumption that it was located to the south.
> And since his work became the map used by generations of future explorers, he sent them off in the wrong direction as well.
I have a lot of respect for PG, but boy, is he off track on that.
Aristotle was highly specific and highly empirical. His ethics, for instance, is an elaborate study of the various ways individual go right or wrong in their decisions. His politics was based on extensive studies of the constitutions and political histories of nearly a hundred Greek states. And of course there was his biology, based on empirical studies of over a hundred different animal species.
And as for his physics, according to this astounding article by Carlo Rovelli (yes, that Carlo Rovelli), his physics is accurate for the phenomena he was studying. Rovelli even converts his ideas into equations.
> For example[1], Newton's 1687 Mathematical Principles of Natural Philosophy later became classified as a book of physics.
That is a good example. I was trying to think of others since then. That was 500 years ago or so. What are some more recent ones for physics?
I imagine if logic is considered part of philosophy, perhaps boolean and propositional logic had a hand in helping computing...
Then if ecology or sociology is considered I can see how philosophical ideas about class, society, environment would be incorporated into practical fields or be used to start societal transformations (Marxism perhaps?).
But I can't think much for physics recently? I have read and seen known physicists dable in and use philosphy to explain what they accomplished or observed. Bohr, for example, was fond of Kierkegaard. It would be good to have examples of philosophers who changed the course of physics.
Except for being the origin of physics, astronomy, medicine and other fields? "Philosophy" is a wide spectrum of which only a very small part is concerned with problems so abstract that we cannot expect a solution to them.
Exactly, when philosophy actually started solving a problem it became another discipline.
So what's left in philosophy is the stuff that no one has gotten very far in solving in 3K years. Why is life worth living? What is a good life? What is the best beer?
Only in the same way that a patent troll invented using cookies to keep a shopping cart. Philosophy expounded enough ideas both good and terrible that they where the first ones to say X. However, plenty of scociety's who never heard of X did the same thing. If anything science is the antithesis of philosophy as it does not care about abstractions only observations.
Philosophy is the epitome of scientific navel-gazing. Don't get me wrong, gazing at one's navel is an important thing to do – sometimes – but this continual attempt to backwards-justify all sciences as flowing out of philosophy are overblown.
Astronomy and medicine are two very obvious examples. Primitive cultures didn't need philosophical underpinnings to notice and record the patterns in the sky or to figure out which plants helped with fevers or how to set broken bones. Philosophy might have helped science in places with structural issues, but it's reaching too far to say that nothing would be around without philosophy.
And calling philosophy navel-gazing is navel-gazing.
The philosophy of information is a great example of where it's incredibly important [1]. I seriously, seriously doubt that information theory would have come about without many of the philosophical underpinnings that came before it. It's not just about structure.
I would suggest you study more non western history. People did a lot of what we think of as science and math with very different underpinnings. Without a basis for comparison you can't separate what is actually important from an accident of history.
PS: The two most widely used and useful parts of math where completely unknown to the anchent Greeks. Aribic numerals are the first example of useful information theory after writing.
I understand what you mean, but calling it an accident of history is a pretty strong minimization of what amounts to applied philosophy towards genuine innovation.
When I talk about information theory, I'm talking more about the more generalized forms of it (Shannon, etc), not necessarily something that could generally be described as 'information' in a more classical definition. Specifically, https://en.wikipedia.org/wiki/A_Mathematical_Theory_of_Commu....
(this is a subject I'm actively learning over time, so please correct me if I'm wrong!)
If you consider morse code was 100 years old at that point, there had already been a lot of very practical work under that heading. With earlier effort focused on designing and cracking encryption systems.
Shannon was more an outgrowth of having already abstracted information and looking for ways to encode that for transmission. I don't want to downplay the value, but in historical context it's very different from how you learn about such things after the fact.
Most of Computer Science isn't science in the sense meant by describing physics as a science. Most of what is science in computing is simply applied physics and applied mathematics.
That doesn't make it any less worthy of study of course.
This reminds me of the old adage about the drunk looking for his keys under the lamp post because "that's where the light is". If the solution in physics requires a revolution in philosophy then that is where we must look.
Maybe because much of what started as the goals and methods of "philosophy" were later appropriated and redefined as "science"?
They are both human endeavors to better get at and understand the truth about ourselves, the universe, reality, etc. Philosophy often extends further into realms such as art, morality & ethics, dignity, aesthetics, the role of society, and human nature. Philosophy even takes a meta-view of science, asking how we are justified to even claim to know something to be true at all (epistemology). And for the most part, these questions are answered in terms of and in concert with our scientific understanding.
Moreover, evidence-based science itself is to some degree an outgrowth of Descartes' "method of doubt" and rationalism, then the empiricist philosophical movement, and on and on. It's no wonder that throughout history often the leading scientists/mathematicians and the leading philosophers were the same people.
Concepts such as natural rights, liberty, free will, social justice, etc. all originated in philosophical works, and have indeed "solved problems" by influencing people who are say, in the process of forming secular governments after a political revolution. You can draw a fairly straight line from Plato to Descartes to Hobbes to Locke to the Constitution. When we talk about a "bill of rights" -- where is this concept of a natural human "right" even from? Philosophical theories such as utilitarianism, the meaning of good vs. evil, are used every day in our legal system, economics, politics, and foreign policy.
Moreover, often a breakthrough in science or development in society may have very practical consequences which FORCE people to face unavoidable philosophical questions. Should scientists be legally permitted to clone humans? Should a Tesla kill its own driver to avoid plowing through kids crossing the street? Should there be a minimum wage? Should pharmaceutical companies make life-saving drugs free? When should abortion or infanticide be permitted?
These questions must be answered reasonably-- I'd much rather have them discussed through the lens of rational philosophical discussion rather than religious or purely emotional "go with the gut".
So philosophy has served as an on-ramp to science. But among its benefits, it also helps us move from the descriptive study of the universe to the prescriptive-- to paraphrase the great philosopher Dr. Ian Malcolm-- there's a benefit to moving from the scientific question of if we could to consider the philosophical one of if we should.
Just like there's a "God of the gap"-- a notion that a need for God pushed back as our scientific knowledge expands, so it seems there is a "philosophy of the gap"-- some people seem to redefine "philosophy" to mean useless mental spaghetti that goes nowhere. Do you judge science by the same criteria? Does every "failed" experiment constitute a failure of science?
Given its usefulness, especially as an alternative to religious methods where "science" doesn't offer a clear answer about how people and societies "should" behave, I think damning philosophy too hard is kind of unfair.
Bullshit. How do you think your computer functions? You don't get high level programming languages without philosophy. Where do you think natural sciences came from?
Alchemy is a good example. Alchemists dabbled in chemisty but they also took for granted that chemistry has deep symbolic and semantic meaning. Figure it out and chemistry will crack.
It turned out to not be the case, time after time.
There's no inherent meaning in how substances interact. There are laws, they're consistent but devoid of any meaning, on human level.
That's why I'm deeply scetical towards any New Age-style ideas.
The body of results from alchemy resulted in the narrow, useful part of it becoming formalized as chemistry. The body of results from string theory (or many worlds interpretations) is non-existent.
What "philosophers" are we talking about here? Lakatos? Chomsky? Newton? Logicians? Or do we have some composite postmodern blowhard in mind? (Like any industry's products, philosophy's product quality varies with factors like producer. So specifics are important.)
There's a bias in physics culture against philosophy. (It's no doubt elsewhere too, but very apparent in physics.) But fortunately, there's many exceptions who like to take a step back and think about what they're doing.
Peeling back a level, science is a belief system based on observations. What is a valid observation - if I say I saw it once that is not valid, if I say look in this place or way and you can see it too, well, that is. But what if I say "look in this place and way and you will see this kind of thing once out of a billion trials, and all the other things that are seen are not real"? Science admits that view, and I would not disagree but I am aware that this is a choice - a philosophical view that I have adopted as part of the assumptions that I make to use the belief system that we currently call science. This system is different from the versions of science that were in use 100 years ago, and is changing now with the rejection of intervalism (p=0.05). So bring in 1000 scientists and let them do some philosophy, because to do anything that's what they have to do.
Is the practice of science fixed? Do scientists use, unwaveringly, the methods of their predecessors? Why do the methods and practices of science vary over time?
I fail to see the relevance of any of your questions to the topic at hand, so rather than playing the Socratic method, how about you just lay out your argument.
> It sure seems to be an epistemology problem which puts it squarely in the realm of philosophy, not physics.
Sounds like a good idea and would like to see, for example, a philosophy professor from some university one day publish a paper in arxiv and turn the world of physics upside down with it. It would be like "... because of these logical inconsistencies ... x, y, z quantum mechanics is actually governed by hidden variables, q.e.d"
I just don't see it in practice though. I think it only seems as if philosophy is deeply entwined with and ready to be exploited to help physics, but it is only because physicists were marginally interested in it and offered some philosophical explanations after the equations and experiments have been proven. I think most of those were mostly for curiosity's sake and were rather secondary to their main achievements.
> It would be like "... because of these logical inconsistencies ... x, y, z quantum mechanics is actually governed by hidden variables, q.e.d"
They already do this. Many philosophers of science pursue realist interpretations of QM though, like de Broglie-Bohm, and so they aren't published very widely. The measurement problem is the serious stumbling block for anti-realist interpretations, and why many such philosophers are realists. The measurement problem just doesn't trouble practicing physicists.
You have to be very careful about which multiverse theory you refer to. There is a Many-worlds interpretation of quantum mechanics which don't lead to any different physics. It's fundamentally untestable and doesn't matter. So far you can't derive new measurable consequences (to my knowledge) of this, and there's no physics that really hinges on it. If you don't like this interpretation, you can pick some other one until you're happy and shut up and calculate with the schroedinger or dirac equation which has been verified stupidly well with experiment.
Multiverse theories in general may say that the universes interact. They may have differing coupling constants. You know you might try to come up with some new physics but your new physics hinges on these things existing... and that's fine... that's how new things are discovered, but we're at a point where SUSY is taken as a given and multiverses are taken as a given and theorists have this really much more convenient model of the universe that they're starting from and making unmeasurable conclusions and it just seems so removed from reality! That's the issue.
Modern academic philosophy won't help because it's dominated by certain false ideas.
The problem with physics today is rationalism - constructing theories with only partial reference to experimental data. Some fields, like psychology, have the opposite problem - empiricism - where they accumulate countless statistical correlations but fail to integrate them into consistent theories.
I suggest anyone who's seriously interested in a solution to these issues to listen to the following, then look up Leonard Peikoff and David Harriman's other writings on the subject.
> The problem with physics today is rationalism - constructing theories with only partial reference to experimental data. Some fields, like psychology, have the opposite problem - empiricism - where they accumulate countless statistical correlations but fail to integrate them into consistent theories.
"Rationalism" is still serving us very well in pretty much every other field of physics except unification theories. We're still coming up with great new theoretical models based on working with the laws we have, sometimes driven by the need to explain existing experimental results and sometimes to look for new places to do fruitful experiments. There's a much better balance between the two for physics as a whole than you're making it out to be.
I'm not sure how wrapping in Ayn Rand's theories with all their politics is going to streamline physics.
I think then, that by IsaacL's definition, those other parts of physics where theory and experiment are well balanced don't suffer from (excess) "rationalism", which he seems to define as a reliance on theory without experiment.
I have no idea what this is supposed to mean or imply in this context, but it seems to be a classic HN response asking people to judge a book by it's cover instead of its contents/arguments, which is even less helpful.
Objectivism is basically built on a bunch of strange axioms, and to a large part completely denies that they're arbitrarily chosen axioms instead of hard facts. They treat logic built on other axioms as inherently wrong.
It's hard to summarise. Read "Introduction to Objectivist Epistemology" which contains the fundamentals of a theory of knowledge, specifically a theory of the nature of concepts. That's the part which is relevant for this discussion and is also the foundation for everything else.
Ultimately you have to read Rand rather than read about her, as so many of her critics enjoy a somewhat loose relationship with reality. For example, the comment in this thread about "randian evangelism" on HN. I've encountered two other Objectivists on HN, whereas every week we have multiple hundred-comment threads on how fantastic an idea universal basic income is. That's pretty ineffective evangelism.
Would like to read the book to know more. While the criticisms of "we're wrong headed to try this" might be valid, I don't know if anyone really has a better idea of what would be the "right headed" direction to go in.
If string theory shows 10^500 possible universes, then what if tomorrow we come up with a way to identify which universe we're in? Would we still discard string theory just because it wasn't developed with an empirical footing and start over, or would we begin to examine its other consequences?
That string theory is pretty much just a theory at this point is, I think, not a strong enough argument to not pursue its mathematics. Especially since the theoretical effort has apparently yielded interesting mathematical tools for other areas. If that contribution is discounted, then it pretty much becomes an argument about funding.
Secondly, I'm not sure why time needs to be any less 'real' if it happens to be emergent. The expression "it all adds up to normality" has some power to it. If you think about our current notion of time which holds that a photon crosses all points along its path "at the same time", but that isn't true of the electron or proton, what could we even mean by "time is real"?
I think philosophy can definitely help here. One philosophical answer to this problem is that physics or the physical world are just an ideas / models in our minds (I think it's obviously true but most people disagree). As long as a model is consistent with our perceptions (experiments), it's correct (correct up to this moment).
That's basically the whole point of the scientific method and that's how it evolved during the Renaissance when we went from philosophers and logic to scientists and experimental data. Few scientists have the delusion that our theories are anything but crude aproximations of the real world, each requiring extensive caveats and each with its own domain, outside of which they're useless (i.e. Newtonian mechanics is useless for high velocities and relativity is useless at the quantum level).
The problem is that we need a convincing mechanism to explain how the irreversibility implied by the Copenhagen interpretation arises, which to my knowledge no one has come up with yet.
What we understand so far is:
* the measurement process can be described as an entanglement of a quantum system with a large external system, followed by a dephasing of the wave function that is caused by the huge number of degrees of freedom in the external system.
* this dephasing decouples the individual terms of the wave function of the system that is being measured, thereby effectively suppressing any further quantum effects in those measured states. This is what we call a transition from a quantum state to a "classical" state.
* the measurement process itself is not a discrete event: We can perform continuous weak measurements on a system's state, which will only partially collapse the wave function (there have been many experiments done on this e.g. by Serge Haroche's group and more recently with superconducting systems as well).
* this whole process is completely reversible and can be described by the Schrödinger equation.
Now, if we want to introduce irreversibility into this picture (which is required for the Copenhagen interpretation), we need a mechanism for it to arise. To my knowledge, no one has come up with a good theory for this, as it would require to modify the Schrödinger equation in a way that subtly depends on the characteristics of the system being measured and the measurement system. This mechanism would need to contain a variable A that would account for the size of the measurement system, as we need to preserve reversibility when the measurement system is small (i.e. has a small number of degrees of freedom), while destroying it when the measurement system is macroscopic.
I'm honestly a bit surprised that no one makes this argument in favor of the many-worlds interpretation of quantum mechanics, as it's the only theory which accounts for all experimental evidence while not forcing us to invent a mechanism that "eliminates" the many realities that we don't want to accept, while in fact they arise naturally out of the theory. I think that many people just don't want to accept that the universe could work this way, even if it's the simplest and most straightforward explanation.
> I'm honestly a bit surprised that no one makes this argument in favor of the many-worlds interpretation of quantum mechanics, as it's the only theory which accounts for all experimental evidence while not forcing us to invent a mechanism that "eliminates" the many realities that we don't want to accept, while in fact they arise naturally out of the theory.
I think you're projecting the existence of these worlds. Certainly you could view the equations that way, or you could view the particles as fundamentally real and obeying a non-classical law of motion, as in de Broglie-Bohm, which was actually the first the interpretation to correctly account for measurement.
Math is not reality, sometimes it happens to describe reality, sometimes it doesn't, that makes math useful in doing science, but math is not science unless experimentally verified.
You can't say that the Schrodinger equation hasn't been experimentally verified. The problem is that we can only practically test it on microscopic objects, which means that people can introduce ad hoc mechanisms like waveform collapse to say it doesn't apply for macroscopic objects.
That's a very odd way of going about things. We can't actually observe galaxies over long enough timescales to be sure that gravity applies to them but their appearance is consistent with the existence of gravity so we don't even both to consider the possibility that there might be some separate force causing them to look that way.
> You can't say that the Schrodinger equation hasn't been experimentally verified.
I didn't. I said math doesn't always predict reality, sometimes it's just interesting math. Some maths are also physics, some maths are just maths and have no bearing on physics.
> Math is not reality, sometimes it happens to describe reality, sometimes it doesn't
Conjecture. It seems self-evident that our reality reflects the structure of basic discrete mathematics, ie. if there are two apples, eating one leaves 1 apple. No amount of rationalization will refute this fact. The fact is, the basic structure of our world is mathematical in some way.
It's not conjecture, it's a fact; you're describing a case where it does match reality, that doesn't contradict what I said. There are plenty of maths that are self consistent but don't match anything in reality. Just because someone can come up with some self consistent math doesn't mean that math predicts anything in the real world. To further clarify
> The fact is, the basic structure of our world is mathematical in some way.
Yes, but that doesn't imply the inverse, that all maths are reflections of reality. Reality can be described by maths, but not all maths describe reality. Or to further simplify, physics is the subset of maths that describe reality, which necessarily implies that not all maths do.
It is conjecture, because the most parsimonious position is a form of Platonism, of which the mathematics describing our world is but one structure in the mathematical universe.
Even if you wanted to subscribe to some form of mathematical naturalism, that still doesn't support your point that math that doesn't appear to have a natural analogue, doesn't physically exist. We thought this of many prior mathematical abstractions, like complex numbers and non-euclidean geometry, and they are both now indispendensible tools for describing reality as we know it.
You didn't address a single point I made, repeating yourself is not a valid form of argument. You are effectively claiming that all maths are physics, if you don't see the absurdity of that claim, which you continue to ignore, I can't help you. Beyond that, you're arguing with a stawman
> hat still doesn't support your point that math that doesn't appear to have a natural analogue,
I never made that point, and if you think I have, you've failed to understand the point actually being made.
What is the physical analog of the square root of -1? If all math is physics, then what physics does that predict? Maths are a language invented by humans, some of those language describe physics, some don't, that's not a conjecture, that's a fact.
> You didn't address a single point I made, repeating yourself is not a valid form of argument.
You didn't make any points, you merely repeated the dogma that there exist maths that have no physical analogue, which I already addressed in my first post. I merely provided more context on the philosophy of mathematics so you can read up on why your position is problematic at best.
> You are effectively claiming that all maths are physics
No I didn't. I pointed out the least problematic and most accepted position on that question, which refutes your claim that your position on mathematics is obviously the only valid position.
Your question about the sqrt(-1) is perfectly exemplary of the elementary misunderstanding of what your position entails. Abstractions don't exist a vacuum. I can just as easily ask you of the physical analogue of the number 1.
It's a meaningless question. Mathematics is an abstraction describing structure, and many things share the structure of the number 1. The structure of the sqrt(-1) appears in many places, like in wave mechanics.
The fact that you conflate maths with the particular syntax we use is another elementary misunderstanding. A grammar also has a structure, and we use that to represent the structure of mathematical objects, but math is not about syntax.
Finally, on the matter of absurdity, I suggest you reread my previous post. While you amazingly seem to think it's devoid of content, I can assure you that I point to two primary philosophies of mathematics, one which disagrees and one which sort of agrees with you, but still doesn't support your claims. It's up to you if you actually want to learn what mathematical truth is really about.
> > You are effectively claiming that all maths are physics
> No I didn't.
Great, then you agree with me, all math isn't physics, and there's nothing more to talk about.
Here's what you don't seem to grok.. from your own original rebuttal...
> The fact is, the basic structure of our world is mathematical in some way.
I agree, I've never once disagreed with that position, you simply failed to understand the point being made and that you're continuing to try and argue it is just... boring now.
> Physics has been stuck on this problem for almost a century now. Philosophy won't help.
This "problem" is exactly a metaphysical one, so only philosophy can help. And there are plenty of interpretations that don't suffer from these problems too, like de Broglie-Bohm.
In a historical sense, things are only called philosophy until they become a science. Not so much in modern times, but certainly during the early years of philosophy.
Correct me if I'm wrong, but isn't the multiverse different than the many-worlds interpretation of QM? The multiverse talks about multiple big bangs and universes as bubbles.
The Planck scale, where quantum gravity should have directly observable consequences, is ~10^18 GeV. The world's most powerful collider to date, the LHC, reaches a collision energy of ~10^4 GeV, not far from the theoretical maximum attainable by a ring of its size [1].
If you wanted to scale up the LHC by an energy factor 10^14, you would have to deal with the energy loss caused by synchrotron radiation (charged particles going around a ring are constantly accelerating, so constantly emitting electromagnetic radiation) which is ~E^4/R per turn [2]. To keep the same energy loss as at the LHC and pay an electricity bill which is only 10^14 times larger, you would therefore need to grow the radius R by a factor ~ 10^14^4 = 10^56.
The LHC radius is 4.5 km, so let's go with R = 10^56 km. That's 10^43 light years. For comparison, the radius of the observable universe is ~10^10 light years.
A linear collider would not be long enough. A circular collider would need either unattainable magnetic fields to curve the trajectories of the particles or itself have curvature that is small enough (i.e. have a radius similar to that of Earth's orbit around the Sun).
So yes, it is really unattainable.
Cosmic rays bombarding the atmosphere do attain such energies, but they are not controllable in a fashion that would permit most collider experiments.
All our manipulation of particle trajectories use electromagnetic forces.
If we were to be able to come up with the technology to manipulate the strong force, would that open up possibilities for alternative colliders?
One problem that I can see is that the strong force might be stronger (strength of 1 vs 1/137 of the electromagnetic force) but the acting range of the force is much smaller (diameter of a medium sized nucleus). The electromagnetic force has a far superior range (technically infinite, but the power drops off depending on the distance)
Arm chair physicist here... I would love your knowledge on the general idea.
Theoretically, yes. If you set up billions (maybe even trillions) of powered electromagnets in a stable, very precise orbit around the sun and injected particles into the loop. However, this is hugely impractical and the sources of error would be huge. Electromagnet misalignments (with the error compounding over stellar distances), stray asteroids and comets, cosmic rays, etc would all effect the particle beam.
One way is to probe them indirectly. For example, string cosmology makes testable predictions (verifiable by observation, e.g. of the CMB). Conceivably, evidence could be found of something that happened in the early universe that is most easily explained within the string theory.
If memory serves, I believe a collider with a diameter the size of a galaxy would be needed to accurately test string theory. This isn't to say that we won't come up with some alternative method of producing high energies though.
I don't think the problem is string theory per se — I think the problem is that we're running up on the bounds of what we can test experimentally, and further progress is going to require some really cleverly designed experiments that can probe Planck scale events. Although the greatest physicists throughout history have for the most part been theoreticians, it may be the case that in the future, the greatest physicists will be experimentalists because of the extraordinary amount of creativity needed to design novel experiments that can probe the most obscure corners of reality.
String theory isn't pseudoscience, because it does make testable, falsifiable predictions. In fact, it makes the same predictions that quantum field theory does for the phenomena that we are currently capable of testing (and arguably using a more elegant framework than QFT provides). The problem is that the predictions that string theory makes beyond QFT are currently way outside the realm of experimental assessment. This doesn't make the predictions false — if that's the way the universe really is, we just may be incapable of knowing that for a long time. There are a few hints that at least some of the predictions of string theory may be incorrect — we have yet to find any evidence of supersymmetry, and many physicists thought the LHC would turn up at least some evidence of this if it existed.
Regardless, I think people get too hung up on buzz-phrases like "is time real?" or "are we in a multiverse?". A lot of these are what I consider irrelevant to science, as the goal of science is to make accurate predictions about the future. If there is another universe out there, it is by definition unreachable from our current universe, so it makes no difference to science whatsoever. Likewise, what is or isn't "real" has no bearing on how accurately one can compute the evolution of some system's state through time.
> Regardless, I think people get too hung up on buzz-phrases like "is time real?" or "are we in a multiverse?".
If by people you mean science vbloggers like VSauce or Veritasium or even NDT's new Cosmos, then I'd say their goals are not to do or teach science but to inspire the next generation. Pop-sci is not for today's scientists. It is for the next generation of scientists and I think these philosophical questions are a fantastic way to get people interested in pursuing a career that doesn't have much glamor but can be very promising and fulfilling.
> String theory isn't pseudoscience, because it does make testable, falsifiable predictions.
I feel like it's also worth pointing out that string theory is also a possible solution to an extremely difficult mathematical problem. You don't fully get an appreciation for this when reading popular accounts. You don't realize that string theory is not just mumbo-jumbo about strings that someone made up but rather that the extraordinarily sophisticated math behind it actually works out, something that can't be said for the vast, vast majority of attempts at resolving the issues that string theory does resolve.
The difficulty of this problem is such that even coming up with possible solutions is itself a Herculean feat (witness the fact that Edward Witten, who proposed M theory, was awarded a Fields medal). This is ultimately why string theory has ever been taken seriously. None of this means string theory is correct, of course.
"is time real?" -- I am somewhat puzzled by this question being so popular. (Perhaps, people are mystified by what appears to be a perpetual and unstoppable progression of things from the past to the future which is not under our control.) Of course time is real, just like, for example, distance (length) is real. You can measure time, just like you can measure distance - in some units that you can choose. So, if one has doubts as to reality of time, there is no reason why one should not also doubt reality of space with all its attributes, i.e. pretty much reality of anything at all.
Time is weird though. With e.g. mass, you can define the kilogram as the mass of a certain number of atoms, which makes sense. Time though is defined as some amount of caesium oscillations. Also, time (and therefore length, or vice versa if you prefer) changes in relativistic scenarios, only the speed of light is constant. Even as a physicist, I've often thought that time is more of a useful mental construct, but maybe it's time for something else.
And then there's the question of why time doesn't flow backwards (aka the arrow of time), which is genuinely interesting. Only a few fields have answers for this, e.g. thermodynamics with entropy. I hope answering this question will give us a much better framework to define time. I'd love it if it was shown in my lifetime that time is quantised.
You just said yourself that only speed of light is constant, mass is also relativistic like time.
And how do you know that time doesn't flow backwards? On quantum scale, how do you tell past from future?
Gravity is one directional too, but somehow everyone are mystified by time. I think it's because it's far too easy to let the imagination run wild on the possibilities of reversing time, but much less intuitive to imagine "reverse: gravitation or reverse entropy.
> And how do you know that time doesn't flow backwards? On quantum scale, how do you tell past from future?
E.g. you don't observe a glass un-smashing. But as you probably also know, the question if/how a quantum arrow of time relates thermodynamics is currently unsolved and probably Nobel Prize territory. Not sure how much progress we'll make on Hacker News.
> Gravity is one directional too
I assume you mean it's purely attractive? It isn't too difficult to imagine a sphere with negative mass repelling another (like magnets), even if you've never seen negative mass :)
How do you picture reversing time? If you imagine it like reversing a video, it's obvious how this breaks down, again from the glass un-smashing. Entropy can be very visceral.
Glass unsmashing is an emergent behaviour. Even if you were an operator of a simulation of that glass being smashed, you could never change the rules so that the glass would come back together like it was.
Time is not some parameter you can adjust. Time is just a word we have to express amount of quantum interactions that happen to an object.
That's why I don't imagine reversing time. It makes no sense. You can't reverse effects of interactions even if you reversed the laws of nature. And you can't record reality and play it backwards too.
> If there is another universe out there, it is by definition unreachable from our current universe
We can't know that yet, universes if parallel may interact at small scales in such a way that they can't be detected and reachable. To say they're unreachable by definition is hubris.
I think he means that universe = universal = everything so that if parallel universe-things did turn out to be observable then we would have to expand our concept of universe to include them, rather than call them separate universes.
Well then feel free to expand because frankly the sentence I quoted cannot possibly in any way be interpreted to mean what you said; you're having a reading comprehension issue if you think your interpretation in any way matches what I quoted. What you said is an entirely different thing than what he said, they aren't even close.
> If there is another universe out there, it is by definition unreachable from our current universe
As this quote by definition accepts the distinction of multiple universes as it makes zero sense otherwise. To take him at his word means he believes it's possible that there is another universe, but that it cannot be reachable from our own; no where does this statement imply he believes there's only one possible universe and it directly implies otherwise.
His correction merely makes it clear he can't express himself clearly because what I just quoted above does not and can not make sense from the position of there being only one universe.
I'll even say props to you for parsing that nonsense because what he said in no way matches what he claims to believe.
As a layman, one thing I don't understand is why we suppose there has to be dark matter and energy in the universe.
I understand that dark matter is used to explain gravitational irregularities when observing galaxies. However, saying 'there is x amount of unobservable stuff there' in order to make our calculations correct seems like lazy science.
Are there any theories that don't include dark matter or energy? Can gravity function differently depending on its location (space or time) in the universe?
> However, saying 'there is x amount of unobservable stuff there' in order to make our calculations correct seems like lazy science.
That's not how this works.
Dark matter and energy are placeholders for anything that can explain the discrepancy. The most likely explanation for dark matter is just undiscovered particles, but changing the physics of it to make the calculations come out right is also something that people do.
There's not really a difference between the two either. Post-QFT the concept of a particle is much blurrier than before, and "changing the physics" might just involve introducing a new background field that behaves differently in different places based on its concentration. In essence, you have introduced a new particle.
Please note that while it feels like lazy science, coming up with alternate theories that have the same success and rigor as QFT is very hard. Its not that they are hanging up their pencils and declaring premature victory. It is that literally the best description of physics out there to date doesn't explain this, and within that description yet-to-be-observed particles is its best bet. They are working on better explanations, but Rome wasn't built in a day.
The gravitational waves we're detecting come from black holes, but the readings we have from LIGO suggest that they most likely come from 'primordial' black holes formed at the birth of the universe.
If many of these black holes were formed they would be distributed much as MACHO theory predicts. 'Normal' black holes have very specific mass profiles so were generally ruled out as MACHOs, although obviously 'dark matter = black holes' has had a lot of consideration.
"The most likely explanation for dark matter is just undiscovered particles" <--- all valid points but I'd argue that dark matter may actually be strictly the result of yet-to-be-understood underlying fields. e.g. dark matter may not have any particles itself but could be the gravitational of spacetime in a sense
> why we suppose there has to be dark matter and energy in the universe.
PBS Space Time has a set of short videos[1] that do a very good job of explaining dark {matter,energy}. It starts with Einstein's field equations and GR, then walks through what the Friedmann equations say about the expansion of the universe.
For those who haven't seen yet any of the PBS Space Time videos and are interested in physics and cosmology, it is really well done. I recommend checking it out. Each episode is pretty short, entertaining, and jam packed with well explained information.
I'm now hooked on the series, and feel like I am more informed about our latest understanding of physics and the universe.
However, saying 'there is x amount of unobservable stuff there' in order to make our calculations correct seems like lazy science.
"Dark matter" and "dark energy" don't refer to unobservable things, just to things whose existence we suspect but which we have not yet been able to observe. The planet Neptune was once in that category, as was the neutrino, and both of them were predicted "backwards" from a discrepancy between theory and observation (the observed orbit of Uranus didn't match what theory predicted, and it turned out the gravity of as-yet-unobserved Neptune was the cause; beta decay appeared to violate conservation laws, and it turned out the as-yet-undetected neutrino accounted for the "missing" energy and angular momentum).
I don't know anything about dark energy, but I can talk about dark matter.
So, lets look at the galaxy rotational curve data[1]. (Go look at the picture in the top right.) Galaxies don't spin like a record, because they aren't stiff. Instead, the stuff spins at different speeds. Also, galaxies are not like the sun and planets, where almost all the mass is at the centre, but rather it's spread out over the disk.
Now, we can try and predict how the mass is spread out, based on the size and colour of the stars we can see, and use that to get one prediction of how the galaxy should rotate.
We can also measure red/blue shift from stars, and use that to try and actually measure how the galaxy is rotating.
The problem is that these two don't match up. Which is a problem. So, we're trying to find ways to explain why they don't match up.
Now, one way to do this would be to note that if there was X amount of matter that we didn't account for when we only looked at the stars, then the curve would in fact match up.
Since this matter isn't stars, and doesn't give off light, it was called dark matter. And it seems more likely that there's a bunch of mass we can't see than that gravity works weird.
It's worth point out that we have additional direct evidence of dark matter besides the rotation problem, like most thing's it's not perfectly cut an dry smoking gun evidence but:
Dark energy is experimentally confirmed to exist. It's existence isn't a problem for modern physics; the problem is that it's many orders of magnitude smaller than predicted.
Whoa whoa whoa. It's experimentally confirmed that the discrepancy between what GR predicts the cosmological structure of the universe should look like and what our measurements can glean fits a uniform energy field with a specific density that accelerates expansion. It's never been observed in any other capacity, and dark energy is generally just taken as a way of saying "whatever makes this particular term necessary in GR at certain scales".
There's not even a consensus on how to fit it into GR; the simplest and original solution is the cosmological constant, but there's also the approach of treating it as a field that is dynamic (can vary in space and time) in principle but just happens to be too uniform for us to tell. That doesn't even take into account the fact that this could be a sign that GR is simply missing something when it comes to the large scale structure of the cosmos. We've ruled out some proposed alternate theories experimentally but not all, and that's just the proposed ones.
The Casimir effect and Lamb shift are strong experimental evidence of vacuum energy, which is mathematically equivalent to Einstein's "cosmological constant".
How are they remotely mathematically equivalent? The Casimir effect/Lamb shift calculations do not need any input from the cosmological constant's magnitude or anything equivalent. You can calculate them with naught but the constants you need to fix the form of QED. If you try to go the reverse direction and claim that vacuum fluctuations are what the cosmological constant is really about, like you said you have to explain a massive (orders of magnitude!) discrepancy.
Considering that the cosmological constant is nothing more than a magnitude as far as we can tell, a theory about a link that gives the wrong magnitude is completely useless. You can draw a parallel between them conceptually, but that connection is about as solid as the connection between the cosmological constant and any other isotropic scalar field like the Higgs. This is another speculative explanation, but again there is no theory that actually manages to explain the value.
>like you said you have to explain a massive (orders of magnitude!) discrepancy.
Yes, I admitted that earlier. This is the tricky part, not that dark energy exists. There are a number of plausible theories as to why the magnitude of dark energy is much lower than expected, but nothing hard and fast yet.
No, the tricky part is where you conclusively link the cosmological constant to vacuum energy with no evidence for and a lot against. There are equally plausible theories that connect dark energy to completely different things like the Higgs field, or just leave them unrelated, so appealing to demonstrations of vacuum fluctuations as evidence of dark energy being "experimentally verified" makes about as much sense as calling string theory "experimentally verified" because it agrees with the QFT/GR in the proper domains.
What verified, novel predictions do any of the plausible theories make that makes them the defacto solution? I'd be really curious to know because it doesn't appear that many physicists are aware of this defacto solution.
So as per usual with headlines in the form of a question, the answer from the article appears to be no. It might be more accurate to title it "Physicist and Philosopher question the empirical underpinnings of physics". There's not really anything here to disprove anything from the current standard models.
The word "empirical" implies that there's some evidence to back up the claims in the work on string theory and the multiverse. A more apt summary may be "Physicist and Philosopher point out lack of empirical underpinnings for esoteric branches of physics"
Also most of the rest of physics has been chugging along pretty well. People that are working on this particular problem from any angle (string theory or any other attempts at unification) are a minority in the physics community. If the title was theoretical high energy physics was in a crisis, I'd be more inclined to agree.
Agreed. I'm really unclear on what is is supposed to be new about this post.
As far as I know, it's considered that multiverse is highly-theoretical (potentially non-falsifiable). String theory, a dozen dimensions, etc are still speculative and treated as unproven. Nobody said any of that was proven.
That we aren't capable of experiments that distinguish between various forms of string theories doesn't negate the fact that string theories are already compatible with all the experiments we've already done and are likely to be done in the near future. This is no small achievement. There is no other framework that is even in contention right now.
Perhaps when we have some alternative theory that survives that basic hurdle, we can discuss whether we're wasting time pursuing string theory rather than some other idea.
In my field we call this "overfitting." String theory and multiverse work are adherent to all experimental evidence by design and offer no predictive capabilities (correct me if I'm wrong, please).
You can design arbitrary systems to fit observations without identifying the underlying mechanisms, especially if said arbitrary systems are complex (which symmetry arguments are).
If these models are only predictive after the fact, then what good are they? The vindication for Einstein is that his various predictions are still being proven out a century later. Hawking found evidence that ran contrary to our theoretical understanding and has spent his life trying to explain the divergence.
String theories aren't in contention outside of the fringes, they're interesting mathematical models but they are on a par with our study of the ether in the late 19th century, something that will be looked back upon as a diversion away from the truth of our universe.
This may be true of string theory but not unitary quantum mechanics, which predicts a multiverse. It makes quite specific predictions which are tightly constrained by experiments, for example the Born rule.
I think you're making a leap when you say it "predicts a multiverse." (please correct me if you have field expertise)
To refresh my memory I ran through this paper [1] briefly. My understanding is that multiverse arguments based on the Born rule are circular. One possible interpretation of the Born rule is the existence of a multiverse but it is not the only interpretation and it requires one to make some pretty big assumptions that the existing Quantum mechanics models being perfect representations of reality (which we know it is not).
Over the past year I've developed a good grasp on the modern consensus, by reading everything I can find that might shed light on the subject and lurking on physicsforums.com. Despite the common physicist trait of shying away from philosophy, there is a general acceptance that decoherence can lead to an effective collapse, which reproduces our classical world (and many others).
Some arguments deriving the Born rule may be circular; I don't know - I don't see how that matters - because others are not.
There are some critics but they mostly start from philosophical considerations: that a multiverse is untestable outside the quantum scale, imposes a high cognitive burden or requires us to redefine probability. Those objections are only valid if you consider a multiverse a priori unlikely; the evidence and math is clearly in it's favour.
If you want better answers I would look through that forum, or consult a recent review of the literature around decoherence.
Reading up on decoherence, the phenomenon itself doesn't lead to a many worlds hypothesis but allows for the conjecture of many worlds. Information becoming immeasurable/irretrievable is not proof in and of itself of a multiverse.
I have some modest undergraduate work in modern Physics, I think you may be taking the dominant voice on the physicsforums.com at face value when there's a high potential for self-selection bias in online forums. Going back to the experiment evidence and underlying mathematics there just hasn't been a breakthrough of any sorts.
The point is more that there is no need for a breakthrough, because there is no need to postulate a mechanism for actual collapse, since decoherence is sufficient to explain the results of experiments.
I'm not sure what your argument is, but nobody is proving a multiverse, it's just an observation.
Supersymmetry is one (although it's not really a competitor to string theory, more an orthogonal theory).
One of the complaints on string theory, as I understand it, is that it ends up being too general: it sort of implies that just about any phenomenon could be plausible, which makes it really hard to falsify. It's not so much that it's made predictions that turned out to be true, but rather that it can be accommodated to fit prior experiments. From a Bayesian perspective, we haven't received any evidence of its truth, only evidence of nontruth of other theories.
I'm not a theoretical physicist, but my understanding is that supersymmetry is in fact a prediction of many versions of string theory. So it's definitely not orthogonal at all. It's a fundamental part of superstring theory.
This is a complaint rooted in sociology. People thought back in the 80s & 90s that string theory might be so constrained that can only describe one universe (presumably ours). They were wrong. String theory's more constrained than quantum field theory, but it's still capable of describing a lot of different universes. Most of the people who study it at the moment study it because it's been a fruitful source of ideas about quantum field theory. These people don't give press interviews very often, though.
If you disregard aesthetics, what are the questions we're trying to answer in physics, particularly those that involve observable phenomena? I get that string theory replicates the predictions of the theories that preceded it, the critique I'd infer is that it doesn't offer any practical advantages over the previous theories, it doesn't predict anything new that we can observe, and it does not make any problems more tractable (I think the opposite? Ie most problems are far more intractable using string theory)
It seems like there's some lack of imagination here, like physics is "done", there's nothing more to answer, it's all just up to other sciences to answer the rest of the (many) questions about why the world is what it is and how it works. A reset of approaches is interesting, but it still needs to be in service of something, doesn't it?
> what are the questions we're trying to answer in physics, particularly those that involve observable phenomena?
(disclaimer: I am not a physicist, etc.)
Between GR and QM, we can explain most observable phenomena, but it's intuitively obvious that both are emergent properties of some deeper law.
I don't suspect frontier physics is ever really studied with an eye to application. Those tend to follow, but the bleeding edge of physics is usually advanced just out of intellectual curiosity, to try to understand the universe.
In this sense, String Theory is just an attempt the unify General Relativity with Quantum Mechanics. The fact that it's not apparently testable is unfortunate,
We can have pedantic arguments about whether that's "Real Science", since science by definition requires testable hypotheses, but at the end of the day, I don't think it's crazy to pursue a model to encompass QM and GR, even if it can't be called "Science".
My problem with string theory is that so far string theory has gotten EVERYTHING wrong. Not a single of their predictions were true. Yes, they adjust the theory once their predictions are proved to be false, but it just turns the theory into constant best fit theory for current observations.
In my opinion string theory is a very complex case of interpolation. Yes, it "explains" our current knowledge, but it goes way off just after the last point to which it is interpolated. I like that it exists, as it will surely make history in science a grandiose attempt to unify GR with QM, and it is real science in a sense that the methods used in it might be transferred to other fields, but I don't expect for it to give any insight into our universe.
Treat it like a theoretical physicist toy, and when you look at it that way, it isn't that bad at all.
> I don't suspect frontier physics is ever really studied with an eye to application.
Previously they did have experimental results they were trying to understand. There might be follow up experiments to confirm, but there were already experimental tensions.
> I don't think it's crazy to pursue a model to encompass QM and GR, even if it can't be called "Science".
I'm not so concerned about whether something is science, it just seems like vanity to pursue unification that provides no insight into the complex world around us.
If calling it science bothers you, then call it mathematics instead.
It's obvious to everyone involved that GM and QM, both the best physically verified theories at their respective energies, are deeply incompatible with one another.
Unfortunately, physical situations where we can see them disagreeing are outside of our reach at the moment. You're suggesting the entire physics community just give up theorizing until we can plausibly reach unification energies, even if that's a thousand years from now?
> it just seems like vanity to pursue unification that provides no insight into the complex world around us
Pure theory has a funny habit of finding applications in the most unexpected places.
Anyway, if it's an interesting problem, and people want to spend their time thinking about it, who are we to tell them to stop?
> I think the opposite? Ie most problems are far more intractable using string theory
It's a better framework for some problems as a model of other (comparatively mundane) quantum phenomena. But yes, generally you're far better off sticking with QFT or GR separately for observable physics.
In theory, future technology will be able to observe some of the regimes string theory (and other attempts at unification) throw at us. But this of course requires experimenting in places where quantum and specifically general relativistic effects (QFT already incorporates special relativity) are both strong. We don't really have any places where we can observe distinctly GR effects that aren't on some sort of literally astronomical scale (the closest we can go is Earth's orbit with timing for satellites). Since QM likes to stick with the small, this puts us in a real bind until we can do something crazy energy-wise.
> It seems like there's some lack of imagination here, like physics is "done", there's nothing more to answer
Physics isn't more done than any of the other sciences: there's an incredible breadth of active research that makes up most of the fields of physics (condensed matter, quantum information, atomic/molecular/optic). We might have a formulation of most of the fundamental ground rules, but then so do biologists and chemists by the same token. I think the unofficial motto of condensed matter physics sums up the opportunity for exploration pretty clearly: "More is different".
Most biology problems are intractable using particle physics. You use the correct toolset at the correct scale. Unfortunately the scale where string theory is the best available toolset is unreachable to us right now.
They should take their own medicine. How would one test those three assumptions they make?
As for Mathematics being selectively real, I agree with that totally. Mathematics is just a language we use to describe models and their properties in a most rigorous way. That's all. Can we find a model of the universe from which we can derive all its properties? Unlikely (see Gödel), if so the model would have to be pretty "primitive" and thus too large for comprehension. But so what, we can find great models for certain aspects of reality, and I don't see a limit for how far this can be taken to get better and better models for more and more areas of reality.
Logical and structured thinking is good tool when doing physics, because a precise model can be used as a language and communicated and taught, since it's simple.
But those models are correct only in what they describe, they don't completely describe nature. They are just that, models. Every time science has progressed, it's either an "exception to the rule", or a re-understanding of an incomplete theory.
I'm not a scientist, but I vividly remember how a physics professor warned us about the laws he was teaching. Those laws work well, use them, but never pretend that they're universal and that they will be for the next 20 or 100 years.
You can see this problem in quantum mechanics. Quantum mechanics is being very hard on philosophy and certainty in general. Up to a point, using models might be a limit to physics.
I am a physicist and one thing that you realise, as you develop as a scientist, is the fact that the perception that "physics describes everything perfectly" is not true. When you start out, lets say as an undergraduate, you feel the pressure to be "correct". You struggle to find the correct answers or construct them. The breakthrough comes when you realise that we use mathematics as a tool to extract answers; we do our best to make the best educated guess we can and interpret the results.
A great example would be with something like density functional theory (DFT), where we make extremely crude approximations for exchange and correlation functionals. By understanding the limits of our model we can use this information to improve the results; as Feynman said: "The first job of a theoretical physicist is to prove yourself wrong as fast as possible".
I'm not sure I agree with your last statement:
>Up to a point, using models might be a limit to physics.
I argue that this is the most important thing to physics. The moment you start to leave a model, you allow for subjective speculation. I argue that this has no place in physics and is the prime reason that physics has broken away from philosophy.
Don't you need to speculate at one moment or another to improves physics?
Of course you can only do that once you studied physics a lot, but if you want to be creative in physics, don't you have to "speculate" that work with the data?
And yet, that's all the point of theoretical science. To think in ways even if they are not provable at this time. And then experimental scientists come along, look at the theories and then think about how to experiment on them. That's how it works. And I think if they want to disprove any of this they need to show that this system is broken. I need to google but I'm sure everybody can remember hearing a few times in their life that there were scientists like Einstein who had ideas that could not be proven in their life time but could be proven now with modern computers and now we know they were true. We admire that and we need that. And that's the thesis they need to fight if they want to convince me of theoretical science being wrong or bad.
Nope. The point of science is to follow scientific method, which is, contrary to the popular opinion, not about piling up meaningless abstractions cemented by dogmas and wishful thinking, but throwing every possible objection to the hypothesis, finding controversions and inconsistencies with other aspects of reality, and only when it stands nevertheless, that hypothesis could be accepted as a current approximation to the truth.
This "science" is as bad pile of nonsense as Hegelian "philosophy".
Shallow criticisms of string theory usually miss how difficult it is to come up with physical theories that don't lead to some kind of contradiction. For this reason, lots of new physics has been discovered by looking at mathematical constraints first and experiments second. The math of string theory is pretty, but more importantly it works out, and this alone makes string theory worthy of some attention. If it's getting too much attention, that's probably more a sign that there are very few interesting research directions left in physics than that all the physicists are deluding themselves.
Genuine confusion here -- how can you assert time is real?
From my limited understanding, time is merely the measurement of change. A comet goes from point A to B, and like a screen flickering, it is in a discrete point in space every step along the way. It is time that is introduced when asking ourselves, "how long did it take?" or "when was it at X?" but how can it be woven into the fabric of the universe? If we take reality to be right here, right now, it doesn't seem to exist but rather is a human invention to help us map change.
Thing to understand is that time is not a measurement, time is what we measure - as a phenomenon that has independent existence as part of the physical reality. More accurately (and perhaps more confusingly), time should be thought of as one of the aspects (components) of the 4-dimensional "spacetime", where spatial dimensions are, in fact, inseparable from the temporal dimension - so that the results of measurements of each component individually end up being dependent on the frame of reference.
This was a pretty useless article with no real information or details to counter existing theories. I know the layman usually isn't interested in the details, but you can't just write about nothing. Are there consistent theories with those three features? What are features of existing models of cosmology which will have to be changed if the three features are assumed? The reader will never know.
To me, it's all a matter of the empirical data and the math that attempts to model that data. Those two sides of science have continually bootstrapped each other to the point we've arrived at today.
Quoted from the book in the article:
"Our mathematical inventions offer us no shortcut to timeless truth... They never replace the work of scientific discovery and of imagination. The effectiveness of mathematics in natural science is reasonable because it is limited and relative."
I'm not sure what the authors mean by this. Are we to ultimately abandon our attempts at a consistent, logical explanation of what we see? If so, that's when we revert to un-scientific and, essentially, religious ways of thinking. I'd argue that the pursuit of a mathematical explanation of observations is the work of scientific imagination. Mathematics is merely the most reliable way we've devised of communicating what we imagine to other people. And sometimes the math, itself, sings to you and that drives advances in understanding that are totally valid.
While I agree with Smolin that much physics has moved away from experimental observation, especially string theory, I think the three numbered points in the article are wrong.
My take - the only way the universe could have got here from nothing as it were is if it's basically maths and seems real to us. I mean what does basic particle behavior look like - a bunch of maths and not much else, and what exist without needing creating - mathematical patterns and relations and nothing else. Hence from observation it's probably all maths.
Hence:
1) There is only one universe. - Nah probably all mathematically possible universes seem real to their occupants.
2) Time is real. - Sorta but more like how time exists in a DVD of a movie. Or as some guy wrote "...for us physicists believe the separation between past, present, and future is only an illusion, although a convincing one."
3) Mathematics is selectively real. - Nah it's real.
Problem with philosophy is that it views all anthropocentric. On the other hand, we are beyond anthropocentrism in modern physics in the sense that sensorial / bodily experience (our way to interact with the outer world) doesn't help any more and thinking / mind abstraction (our special way to represent the outer world) is unprovable because technologies and tools are not there yet. More than philosophy, it is literature to stand up when we need a change of paradigm, in particular science fiction: minds trying to carve skewed views of the universe starting from non-mainstream philosophy. Suffice to say, it will be many more misses than hits but gold is there.
I'm quite surprised that there's not a consensus about the philosophical framing of physics (metaphysics).
The way I see it:
- Consciousness (perceptions, feelings, thought) is the only thing that really exists.
- There are patterns in what we perceive, for example, when we drop a rock, we see it falls and hear the impact.
- So we develop models to describe patterns in our consciousness. Physics is just a description of those patterns. So the physical world doesn't really exist, it's just an idea in our minds.
The problem is this is self evident and doesn't explain anything. Saying that consciousness is the only thing that exists is like saying God created the universe. Well then who created God? We have to try to explain what all this is through our conscious experience, and if it happens to be that it's impossible for us to do so, we'll have to re-evaluate our options then. I personally don't believe this to be the case - I think everything exists and consciousness is only one way too perceive that everything, but that's another debate I guess
> The problem is this is self evident and doesn't explain anything.
Definitely not self evident, vast majority of people don't see things this way. It doesn't have to explain anything, it's something akin to observation. Just a description of how things are, not an explanation.
> Saying that consciousness is the only thing that exists is like saying God created the universe.
I don't get this, how is this remotely similar, what does God have to do with this? The way I see it, history is just mental concept / idea. We take our physical model and similate the current state of the universe backwards - and call this history.
> I personally don't believe this to be the case - I think everything exists and consciousness is only one way too perceive that everything, but that's another debate I guess
Well, you only have perceptions (what you see, hear, feel, ...). It's the only thing you can be sure of. The "real world" is in its essence a thought, idea, mental model. Think about what does the statement "Eiffel tower exists" mean. It's a probabilistic statement about future perceptions - if you go to Paris, you will probably see it.
> Just a description of how things are, not an explanation.
In my opinion it definitely is an explanation. There's a difference between a world where only consciousness exists, to one where the real world exists and consciousness is one aspect of it.
> I don't get this, how is this remotely similar, what does God have to do with this?
Saying only consciousness exists doesn't explain what consciousness is. Same as saying that God created the universe doesn't explain what created God. If it happens to be that the physical world exists and consciousness is a phenomena of the brain, as we see it today through our perceptions, then consciousness is NOT the only thing that exists, and we can start to probe what the role of it is in the bigger picture.
> It's the only thing you can be sure of. The "real world" is in its essence a thought, idea, mental model.
But what if it isn't? What if the real world is tightly coupled to the physics that we perceive, and that our concept of it in consciousness actually comes from physics and not from our mental model. There is definitely a chance that all our perceptions are false / an illusion of some kind, but since as you say, they are all we have, we have to presume some level of reality outside our mind and then go from there, and then if some day it's proven to be totally false we can evaluate our options then.
This is called Idealism. I wouldn't go so far as to say I "believe in it", but I often think its implications should be explored much more. Unfortunately, hardly anyone takes it "seriously" enough.
They don't seem to take anti-materialistic monism seriously either! :-)
It's hard to get tenure these days if you ever mention solipsism, the direct conclusion of Descartes' cogito (which he never seemed to quite get to himself) or solipsism seriously. Individually or in some creative combo move. I don't know if that's because people think that Kant has been beat up enough that they don't want to be seen standing near his stinking corpse, or thinking about it just makes some people feel 'icky' or what.
Which is too bad, because I find that Johnson's (to Berkeley) "I refute it thus!" to be more of a hissy fit than a satisfying response. IDK. Maybe I'd just like someone to use more words? :-)
I find my views are somewhat similar to idealism, solipsism and dualism. Interestingly, it seems those are minority views, but I believe that this clearly the correct worldview.
Well, they're wrong. What exactly do they mean when they say that the physical world exists? When you say that the moon exists, you basically mean that when you look up at night, you expect to see moon. It's a statement about your perceptions / consciousness.
What about the rules governing the position of the moon on the sky?
If we switch off all consciousness by giving strong sleeping pills to all humans (animals too? - or is it just you who matters (solipsism)?), will the moon change its position while we are sleeping?
So will your/the consciousness move the world while you/we are unconscious - using some simple and higly regular rules (called physics)?
But if you/we are unconscious, then why on earth should we call that unconscious mover of the world consciousness?
Basically yes (depending on the definition of solipsism). From your point of view, all that really exists is your current consciousness. Other people's minds are just a part of your mental model of the world.
In other news:
1. Time Gravitates!
Physicists discover stable wormhole configuration by accounting the effect of gravity on time!
and then
2. First wormhole to another universe successfully created!
The final experimental proof of multiverse theory, which grants us access to all 10^500 universes, and any place in our own corner of the world"
and then
3. Now in portable format, just for $299!
I read this book a couple of years ago. About 1/3 (Smolin's) of it is really interesting. The main point about the primacy of Time is that traditional models of physics have an implicit time dimension for the laws, in additional the the time dimension of spacetime. Smolin suggests that the the laws of Physics are dynamical, evolving as a function of the state of the system.
Hm i wonder why someone thought there is some invisible, unobservable dark matter instead connecting gravitational waves with super massive black holes in center of every galactic. It seems for me like a lot better answer to question what is keeping galaxies together if observable mass is not enough.
I found it a bit hard to understand before I actually took the course in university, but I'll try to explain simply:
You can infer the mass that is interior to an orbit by measuring the speed at which an object is orbiting. By measuring the redshift and blueshift, we can get speeds of different parts of the galaxy. It turns out that we can account for more-or-less all of the mass near the centre of galaxies, but as we get further out, orbital velocities seem to be higher than they should be implying more mass is there than we can actually see.
In other words, we can tell that the missing mass is not at the centre of the galaxy, but rather spread throughout it.
> ... reification of mathematics can lead physicists into dangerous territory where mathematical "beauty" and "elegance" get substituted for real information about the real world.
If it can happen in physics, it can happen anywhere -- maybe even your neighborhood.
I agree with much of the sentiment such as string theory and multi universes are nonsense.
Yes math is just an abstraction tool, with mutually understood/ agreed rules , the rules and representations are not exactly true in the real world, users just agree them to assist with communication between users and over time.
Time is Not Real, it's an abstraction / quantification of change, but yes change is I think real i.e. the universe is always changing.
However his statement- Our ability to map out the history of the universe back to a fraction of an instant after its inception is a triumph - ruined it for me - an absurd statement for a scientist - we have no idea how the universe started we are only guessing it's history, the big bang theory is just a theory, probably no more real than Lord of the Rings.
This took the predictions from the big bang theory about a small hot dense universe, and measured the cosmic background radiation, and it matched perfectly.
The idea is that when the universe was young, it was so hot that all the matter was in a plasma cloud, and that photons (and other EM radiation) couldn't travel very far at all before being absorbed and re-emitted in
a random direction. Then, the universe expanded and cooled enough that the cloud became transparent. But there were still those photons (etc) that now just kept going in all directions. Some of them happen to be arriving from all directions no matter where you are (unless you're on the rim of the universe or something). That's the cosmic background radiation.
And we measured it, and it matched so well with the predicted numbers it was astounding.
This is also the graph that shows up on the "Science, it works bitches!" xkcd shirt.
Some claims don't have to be falsifiable to be true. For example, some people say that solipsism is not falsifiable - I don't see what's wrong with that.
You know what's cool?
If they can reach better prediction, faster, with that approach, it will strengthen.
If they can't, they will be a footnote.
At least, if the scientific method is alive and well.
The scientific method has been "on hold" in theoretical physics for a while; because our experimental technology just can't cope up with it. This is one of the main criticisms of string theory, for example.
This is like Fermat's last theorem. A whole lot of smart mathematicians spent their time solving this theorem instead of finding better things to solve that can benefit humanity.
NPR is not immune to betteridge's. Physics isn't "wrong" about string theory. String theory is a currently untestable theory, a mathematical model, and that's fine but minimally useful.
That the block universe model is just that : a model which is useful for solving problems, not a description of reality. This is a big problem for physics; confusing the modelling for truthiness. If you go for it all the way eventually you end up in a room with very, very think wallpaper engaging Max Telmark in a shouted conversation. This is part of the maths as selectively reflective of reality conversation.
> This is a big problem for physics; confusing the modelling for truthiness
I'm pretty sure it isn't ; ever since quantum mechanics physicists have been very good at separating the two. Popsci, not so much, but the actual physics is very clear about it being a model.
Ok - all that is needed is for physicists to do interviews where they say "it's only an interpretation of part of a model for solving problems after all" repeatedly when asked about time in the universe, holographic principles or many universes.
But this is not what a lot of physicists seem to do.
Like I said, "popsci, not so much". It's pretty implicit when physicists talk about it with each other -- they understand how to keep it separate, but they won't caveat everything they say. This means that they may keep it implicit when talking in interviews, too. And popular science reporting just loves to say things like "the universe is a hologram!!!" so they are happy to spin it that way.
It's not like this lack of context-sensitive speech is specific to physicists either. Programmers do it all the time too.
Smolin also doesn't like many-worlds, because it talks about unreachable regions. This he considers too speculative. There's a basic problem in quantum mechanics, which leads to Schroedinger's Cat, the Copenhagen Interpretation, and, in the end, many-worlds.[1]
Physics has been stuck on this problem for almost a century now. Philosophy won't help.
[1] https://en.wikipedia.org/wiki/Copenhagen_interpretation