So I was wondering if it could be that at the point of measurement it was moving very fast towards us. Napkin math says for photons to have 200 times more energy than expected it would need to be moving at 0.99995c. Huh.
Technically no, photons don't always have a speed of 1C, as C is the speed of light _in a vacuum_. In more dense matter the speed of light will slow down.
Blueshift == relative speed difference, which manifests for a photon in the form of more energy in the form of a shorter wavelength no? Gamma rays being an extreme example.
That much blueshift means that much more relative speed towards us.
Redshift being the corresponding speed difference ‘away’.
>These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tons, or about 900 times the mass of the Great Pyramid of Giza
Five billion tons packed within a teaspoon volume!? Incredible.
When it comes to cosmic scales, it is literally unimaginable by the puny human mind. I don't know about others but I frankly can't really comprehend what does the mass of an entire mountain condensed into a single pebble mean.
And there are stars full of this stuff. And there are stars spinning so fast its magnetic waves would rip the iron out of my blood and destroy the physics that hold my atoms together just because I am standing a few billions miles away from it.
It is absolutely humbling and make it ridiculous to think that there were men ages ago who thought the universe was created solely for human and somehow we, the sacks of meat so fragile it bursts at every miniscule amount of agitation, were "made" as some special, supreme beings in the universe and all of creations. Hilarious and sad.
That's us! We're not bathed in pulsar brilliance, we're picking up the sparse but energetic photons it emits from far far away. We cannot see the "highest energy pulsar" with our naked eyes.
> When it comes to cosmic scales, it is literally unimaginable by the puny human mind.
One of my favorite mind-benders is that on some level, we embody cosmic scales of our own. The "biggest length" is our observable universe is 10^26 m. The "smallest length" is the Plank length at 10^-35 m. That puts the "middle length" at about a millimeter, or (very roughly) human scale.
I find all this really incredible as well. But at the same time I also find it really 'mindblowing' that I am able to think about why and how all of this stuff was made, and while thinking about it, there will always come a point where you have to at least 'think' about an creator. Not that I think it was made especially for us, but it's still very strange. Somewhere I read when you think about the universe it is like "The Universe thinking about itself.".
I agree. I actually think that is a very common thought, at least from what I have seen with my colleagues who are mostly scientists in engineering and biotech. It could be because of our background but the kind of complexity and seemingly genius engineering solutions in some biological systems just boggle the mind and make us question how it happened. We often handwave them with evolution and sure we can come up with some ideas of how it actually evolved but at some point I personally felt some explanations we got became too contrived and overly convenient and nearly unfalsifiable...
To be honest though, I still don't think a creator is absolutely necessary. But I also think there is nothing wrong with the idea that there is one. I just personally don't think this creator, if exist, would belong to any of the major religion out there.
Most people won't like this answer, because it's too impersonal. Thus the search for a more inspiring origin story continues. There is no drama in thermodynamics, no love, no revenge, although there are explosions.
That is a great paper! Yes, from my engineering school I know if we dig deep enough, it would all be thermodynamics. But I was not sure if anyone dig that deep yet. This paper seems to be deeper than what I thought was done. Strange how I didn't see it, seems very relevant especially with all the LLM rage these days.
> Somewhere I read when you think about the universe it is like "The Universe thinking about itself.".
This reminds me of this quote from Jill Tarter of SETI, particularly the last sentence:
“Might it be the discovery of a distant civilization and our common cosmic origins that finally drives home the message of the bond among all humans? Whether we’re born in San Francisco or Sudan or close to the heart of the Milky Way Galaxy, we are the products of a billion-year lineage of wandering stardust. We, all of us, are what happens when a primordial mixture of hydrogen and helium evolves for so long that it begins to ask where it came from.”
I suspect it's been used in many places - we need to summon that quote investigator! - but I did make a note of this when I read Surface Detail by Iain M. Banks:
"All you ever were was a little piece of the universe, thinking to itself."
Paraphrasing: There are 100 billion galaxies in the observable universe, each galaxy contains approximately 100 billion of stars. It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other. It takes 100s of millions to billions of years to get from one galaxy to another. And all those galaxies are moving away from each other at mind boggling speeds 73 kilometres per second.
It’s humbling. And we kill each other for silly reasons. We are so significant, yet so insignificant.
>It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other.
The crazy thing is that at a constant 1g acceleration you could get to the Andromeda galaxy in your lifetime. Andromeda might be 4 million light years away, but relativistic effects mean that only about 30 years would pass for you.
Of course, constant 1g acceleration would require an unimaginable amount of energy (and something to thrust with).
> what does the mass of an entire mountain condensed into a single pebble mean
I find it easier to comprehend in the subatomic context, picturing the space between particles like the space between stars and planets on the cosmic scale. Mash all the stars and planets together in, say, our solar system, and the entire solar system would only be about the size of the sun. Then repeat that for all the solar systems in the Milky Way, and the entire Milky Way would only be about the size of the black hole at the center. Relatively, of course!
It is now that I recommend you read Dragons Egg, a hard sci-fi book about a species that evolved on the surface of a neutron star. I am contractually obligated to mention this any time I hear neutron stars mentioned.
Matter is mostly empty space. Atomic nuclei are small, the electron clouds around them are pretty far away. From this point if view, ordinary matter is more like foam, or aerogel, with very little matter spread over a large volume.
Neutron stars are made if matter with very little empty space embedded into it. This is why they are so small.
"It has the third-brightest optical component of all known pulsars (V = 23.6 mag) which pulses twice for every single radio pulse. The Vela pulsar is the brightest persistent object in the high-energy gamma-ray sky...
"Glitches are sudden spin-ups in the rotation of pulsars. Vela is the best known of all the glitching pulsars, with glitches occurring on average every three years.
I have a question - what would happen if you were to drop one of these spoons of matter that weigh 5 billion tonnes onto the floor right now, where would it stop?
Matter in neutron stars is compressed together by the enormous gravity. Once set free on your floor, this material would no longer be held together and will start expanding at close to the speed of light. The resulting explosion will probably obliterate the entire continent. A crude way to estimate it is to take into account the fact that the gravitational binding energy of matter at the surface of a neutron star is about 10% of the rest mass energy of the material, so once that material is removed it will liberate as much energy (If I got the numbers right, you get an explosion energy of 0.1 m c^2 ~ 10^13 megatons).
It would sink into the center of the earth and then oscillate around the center until friction stops it dead center. Materials in the earth's crust and mantle are not strong enough to stop that mass from sinking ever deeper.
But that assumes that this spoon of matter were stable in that state, which it isn't. That kind of density can only be held up with some force like gravity keeping up the pressure. The gravity of that spoonful is insufficient, so the internal pressure will drive apart the neutrons. The effects would probably look like a very very large nuke or large asteroid impact.
What motivates your first factor? 0.782343 MeV is the free neutron beta decay; where in the solar system are the free neutrons minutes after they are magically teleported to terrestrial ground zero as a something like a (degenerate, possibly ultra-relativistic) Fermi gas?
I think most attempts to arrive at an answer will end up somewhere between half and virtually all of them being "not very close" (~ light-minutes) away, and that's assuming one corrects for the differences in escape velocities. (The equatorial escape velocity of a spinning neutron star is in tenths of the speed of light, thus the sobriquet "relativistic star"). Without this correction, it is likely the bulk of the expanding drop of Fermi gas just exits the atmosphere in milliseconds (timed by terrestrial stopwatches), with time dilation extending the mean lifetime of the free neutrons in the drop comparably to the extended lifetime of atmospheric muons from cosmic rays. The bulk of the beta decays happen at a distance from terrestrial ground zero best measured in astronomical units.
If we play Star Trek transporter games such that the neutrons arrive at ground zero at rest in local East-North-Up coordinates, you'd want to know the internal kinetic energy (KE) density of the (pure-)neutron star, which will be in the range of 20-40 for x in 10^{x} J m^-3. The 10^25ish or even 10^30ish joules of KE will be released from our several cm^3 spoonful practically all at once and practically omnidirectionally from ground zero (so again, most free neutron decays happen at ~ AU distances from ground zero because they'll zip right through the atmosphere). The expansion of the suddenly unpressurized gas of neutrons will make a mess, particularly the fraction that slams into and through the ground. Part of the mess is neutron scattering physics, and I have no expertise there, but I would guess there wouldn't be any free neutrons near ground zero (and probably not within the solid Earth) in ~minutes.
Additionally, one might compare the R-process <https://en.wikipedia.org/wiki/R-process> for kilonovas
in which a binary neutron star collision ejects high-neutron-density matter which decompresses pretty spectacularly, forming lots of heavy elements.
To summarize, I think the free neutron decay timescale (mean lifetime ~ 15 minutes, multiply by ln 2 if you prefer half-life) is simply too long after the neutron star material is teleported to Earth: any free neutrons that haven't been absorbed into heavy nuclei likely will be millions of kilometres away from ground zero when they decay.
> I think most attempts to arrive at an answer will end up somewhere between half and virtually all of them being "not very close" (~ light-minutes) away
Mean free path of free neutrons moving past normal matter is only in the order of centimetres, exactly how many centimetres depends on the neutron energy and the specific nuclei it's interacting with, but still order of centimetres.
Given the relative masses, I can assume the air above will be exploded out of the way; but the half going down will have all of the earth as a moderator… and also serve as a neutron-absorbing backstop that will probably increase the actual yield.
I'm also ignoring any binding energy between the neutrons. I'm basically treating them as disconnected from the first moment, which may be a terrible idea, but AFAIK nobody actually knows how long a macroscopic combination of this scale would remain stable for.
I don't know enough about neutron physics to comment usefully on your mean free path logic, but I do know that solar eruptive activity can launch relativistic neutrons at Earth which can be detected even at sea level using scintillators, and that mountaintop detection has been around since the early 1980s. Shibata 1994, Propagation of Solar Neutrons <https://sci-hub.se/https://doi.org/10.1029/93JA03175>, §4.2.1 (Fig 3) higher energy neutrons get further into the atmosphere, so I don't think the atmosphere is much of a barrier for the comparable (MeV-GeV) teleported neutron-star neutrons.
We seem to agree that free neutrons don't stay free neutrons when they slam into the solid earth.
I too wanted to think about neutrons as a non-self-interacting gas, but that just doesn't work: Meyer 1994, https://ned.ipac.caltech.edu/level5/Sept01/Meyer/Meyer3.html (Paragraph beginning with, "Only the strong gravity of the neutron star keeps such matter from exploding apart." Cold in this context is partly explained in the preceding paragraph; in inner regions the matter is a degenerate gas meaning the particle kinetic energy becomes dependent on the density or equivalently pressure becomes independent of temperature; even at enormous pressures, degenerate gases don't hold much thermal energy -- that was practically all radiated away when the NS was young. Our teleporting (of inner region matter) therefore engages a very low-entropy r-process.
Outer regions are just too complicated and varied for a HN comment. The crust is thin -- a few to a few hundred metres or so compared to an NS radius of ~ 10km. It's also much less dense, so is a small fraction of the NS mass, and thus maybe not a target for our teleportation. Here's a 180-page open access review: https://link.springer.com/article/10.12942/lrr-2008-10 Pesky electrons and protons complicating things.
If I'm reading that figure right, at sea level the attenuation is at least a factor of 2000 for all energies they're graphing. That sounds about right to me.
I realise now that I may have been unclear in intent previously: if you look at figure 2, and then consider a typical solid or liquid's cross sectional mass density, hopefully that explains why I was speaking of neutron mean free path of centimetres — 100g/cm^2 is 1m of water.
However this is just the initial condition, and I don't think this scenario is one where the atmospheric density can be accurately approximated as constant over time.
I wouldn't sweat it, and I don't know enough about the nuclear physics to keep up (and we haven't even been talking about the neutrino energy in beta- decays, the gamma spectrum, or what becomes of the electrons; resonances go way over my head). This isn't really a gravitational problem (but...footnote [1]), so I'm not so useful here.
So, more for the original questioner than for us:
What's inside a neutron star stays inside a neutron star. Unless of course the NS is destroyed via e.g. collision, tidal disruption, or infall pushing it over a mass limit like Tolman-Oppenheimer-Volkoff.
Sci-Fi teleporters don't exist, and there's no basis to think they ever will.
The closest neutron stars are between hundreds and a thousand light-years away and IIRC all the close ones are isolated (in the sense of no stellar multiplicity; they have no binary partner(s)).
Consequently what ben_w and I have been yakking about is inaccessible to experiment (we can't generate the relevant pressures, and artificial neutron sources are not very bright yet (pardon the BrightnESS pun, <https://europeanspallationsource.se/about>)).
It's not accessible to astronomical observation either. The closest physical phenomenon I can think of is an NS mass ejection (for which there is an ample and active academic literature), and that's far from a close match. At least in some parts of the spectrum we can see a large NS mass ejection -- large meaning somewhere around 10% of the mass of the sun -- but there's practically no hope to see just a spoonful, and not hurled into a close-by planet's atmosphere or even that of a noncompact companion star.
So the answer to the question ultimately is -- if we imagined the magical arrival of a small ball of NS matter on Earth at rest on the Earth's surface -- "complex nuclear physics" is in the details of the practically-instantaneous kaboom, and a lot of that complexity is because the Earth is not the practical vacuum around a neutron-star/neutron-star collision that ejects a lot more than a spoonful of material.
- --
footnote [1]: I mean, one can think of it in terms of Raychaudhuri's equation (and that's where I started, in fact): the initial radial divergence of the acceleration vector from the sudden release of pressure dominates, causing the bits to tend to fly away beyond the hope of recollapse. But the solid earth (and as the thread involved, considerations of nuclear interactions even in the atmosphere) generates enormous shear via contact forces, so some of the energy-density of the NS matter will stick around, and in due course what wasn't ejected "to infinity" settles back to a basically round Earth (hydrostatic equilibirium returns). From this perspective comparing the NS matter with an asteroid impact makes sense to me, but probably undersells the nuclear fallout.
I've heard that black hole matter is stable at any size, so how much difference in density is there between neutron star matter and black hole matter where it crosses the threshold of stability from its own gravity?
Black hole's aren't matter, they're pure gravitational binding energy. A neutron star becomes a black hole when the neutrons pushing against each other can't push back at the gravitational forces (neutron degeneracy pressure) and the neutrons do something we're not sure of... but whatever happens, they're crushed down into something smaller than a neutron star; into a singuality and we see the result.. a black hole. Eternal darkness for the poor neutrons; this bit gives me chills.
Black holes are not made of matter… the matter has collapsed into pure energy. The form of energy is a mystery (it’s inside the event horizon) but since the gravitational field persists, it’s often referred to as pure gravitational binding energy. I graduated physics at Manchester Uni and I’ve still got a ‘preference’ to be as correct as possible when talking about BH’s and what they’re ‘made’ of. Kip Thorne also often refers to the stuff BHs are made of as ‘gravitational binding energy’ so I thinks it’s safe to do the same.
In GR, black holes have only three distinguishable properties: mass, charge, and angular momentum. If you have one made from matter, one from antimatter, and one from sufficiently concentrated light, all three are indistinguishable.
As I'm not a physicist, I wouldn't risk phrasing this as "pure gravitational binding energy" just in case this has a specific and different meaning.
I read the interior of an event horizon immediately causes problems with quantum mechanics' no-cloning rule, so I suspect the actual problem here is "QM and GR are fighting again" and we can't get any answer until we've resolved that.
Taken out of the gravity keeping it together it would instantly explode in a sort of small supernova. There would be no survivors. It is not immediately obvious if there would be a planet left afterwards.
If it somehow stayed bound together it would start a sort of elliptical orbit inside the planet slowly losing energy and punching a long spiraling hole towards the center of the planet.
