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The Paradoxes That Threaten To Tear Modern Cosmology Apart
KentuckyFC writes Revolutions in science often come from the study of seemingly unresolvable paradoxes. So an interesting exercise is to list the paradoxes associated with current ideas in science. One cosmologist has done just that by exploring the paradoxes associated with well-established ideas and observations about the structure and origin of the universe. Perhaps the most dramatic of these paradoxes comes from the idea that the universe must be expanding. What's curious about this expansion is that space, and the vacuum associated with it, must somehow be created in this process. And yet nobody knows how this can occur. What's more, there is an energy associated with any given volume of the universe. If that volume increases, the inescapable conclusion is that the energy must increase as well. So much for conservation of energy. And even the amount of energy associated with the vacuum is a puzzle with different calculations contradicting each other by 120 orders of magnitude. Clearly, anybody who can resolve these problems has a bright future in science but may also end up tearing modern cosmology apart.
The only thing that's tearing cosmology apart is the gradual expansion of space.
If there are no particles moving at all, how does empty space have energy? It's the textbook definition of lack of energy. Empty space cannot impart energy on matter and it can't spontaneously create matter. There's some theory about virtual particles but their net energy is zero when they combine so that's not it. Can anyone explain why empty space has energy?
Perhaps the most dramatic of these paradoxes comes from the idea that the universe must be expanding. [...] yet nobody knows how this can occur.
Since when did "paradox" became a synonym for "unknown"?
Yeah, nobody knows how space expands, but how does that make it a "paradox"?
Oliver.
The vacuum seems to have energy, so if space itself expands, the vacuum left has to either not have any energy whatsoever or drain the energy from nearby space. And since the energy of the vacuum seems to be constant, the conclusion is that the expansion is creating vacuum with its own energy
I think it is because vacuum energy is calculated on the basis of the field theory, which in turn depends on constants like the charge of the electron. I am pretty certain that calculations of the vacuum energy do not depend on the size of the universe. Puzzles like these are really important so that people can think of new questions to ask based on problems they didn't previously realize existed. These puzzles challenge our notions of space and time, which to me, are pretty tenuous notions.
Join the IParty!
Yet you continue to visit, click, AND post.On almost every article!
How do you do it?
And you reply to your own post too...
I know the answer, you are a robot, I mean, I am a robot, oh god.... NO CARRIER...
I am not a physicist myself, but physics is a very interesting topic for me. A long time ago I theorized along these lines, and when I spoke about it with physicists, they told me that my hypothesis has already been considered, and it has a name, and that name is "tired light".
See "tired light" on Wikipedia: https://en.wikipedia.org/wiki/...
This guide is definitive. Reality is frequently inacurate. (from THHGTTG)
It has been known for quite some time that energy is difficult to define rigorously in General Relativity. A good explanation can be found in this post by CalTech physicist Sean Carroll. Key point:
As a simple example, imagine a photon traveling through an expanding universe in a region with no other matter or energy (dark or otherwise). The expansion of space stretches the wavelength of the photon (cosmological redshift, which is distinct from Doppler redshift), causing it to lose energy. The photon loses energy with nothing around it gaining. Energy is lost because spacetime itself is changing, so Noether's theorem doesn't apply.
void that killed the ether theory, explain why there is a limit to the speed of anything and would provide a medium of propagation for the forces without falling back to "magic" fields.
Any sufficiently advanced universe is indistinguishable from magic :-)
"Transparent" is a shit show that trades on every stereotype going. A man in drag is NOT a transsexual.
Even professional physicists like some good numerology sometimes.
Also, just so we're clear, you took a number e-26, multiplied it by a number e+23, and you ended up with a number e+0?
Don't blame me, I voted for Baltar.
> What's more, there is an energy associated with any given volume of the universe. If that volume increases, the inescapable conclusion is that the energy must increase as well. So much for conservation of energy.
??? Why cant the energy just be less dense?
The FLRW metric (which is what the equation that governs the cosmological expansion of spacetime) has a cosmological constant term in it, initially placed there by Einstein to maintain a steady state universe, but which we now know drives an accelerating expansion of the universe. This constant term is exactly that: a constant (negative) energy per volume of space. More space means more total energy.
However, TFS and TFA (I've only scanned the referenced paper, but that looks much more reasonable) are absolutely wrong about why this is a problem. It is a problem, but only in the sense of figuring out where it comes from (i.e. what exact mechanism drives the creation of this energy). The fact that energy is not conserved violates no law of physics: in fact, general relativity doesn't conserve energy anyways, and the expansion of the universe certainly does not (even without the non-conservative nature of gravity).
See, the conservation of energy is a result of Noether's theorem, which states that for any differentiable symmetry of the action of a physical system, there is a corresponding paired conservation law. For time symmetry, this is the conservation of energy. However, time on the scales of the universe is not symmetric. There was a beginning to the universe (which alone breaks the symmetry: you can't shift backwards in time more than ~13 billion years), and the universe as it is now looks nothing like it did 10 billion years ago. So we don't expect energy to be conserved in the universe as a whole (even if it is on local scales).
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
How can we definitively tell if the vacuum over there has the same energy density as the vacuum over here?
Measurements of expansion rate from distances and from the CMB closely match models that have a constant energy density per unit volume. That is about as simple as it gets for the moment. Until there is good justification for why we would expect the energy to be different at different places, whether from large scale measurements, or theories about small scale things like QFT, there is no basis to assume things are different. But there is always the possibility things are more complicated than they seem.
in fact, general relativity doesn't conserve energy anyways,
GR does conserve energy, but in a very messy way with a lot of subtleties that means it gets skipped over in the grad level intro courses. Especially when dealing with an expanding metric, it is possible to formulate a contrived analogy to potential energy.
There was a beginning to the universe (which alone breaks the symmetry: you can't shift backwards in time more than ~13 billion years), and the universe as it is now looks nothing like it did 10 billion years ago.
The beginning of the universe does not need to conserve energy, but things as far as we can tell are conserved after that. The fact that things look different doesn't contradict the type of symmetry needed by Noether's theorem, just as Noether's theorem applies just fine in classical mechanics despite the second law of thermodynamics.
I remember something like this vaguely coming up in a comment before on Slashdot, and I hope it was not you making the same mistake, as comments spelled out in those cases clearly that it was a case of density * avogadro's constant / number of atoms gives you the average atomic mass, which is pretty close to 1 for deep space.
so... i went... density = 7 * 10e-26, avogadro's const = 6.023 * 10e23, multiply the two together you get 4.2154. just for fun take the cube-root and oo! you get 1.6153982
No, you multiply those two numbers together, and you get 0.042, which is also a meaningless value because you now have kg/m^3/mol... and it is not like deep space is anywhere near a constant density, as there is a large variation in density and temperature (read about warm intergalactic medium vs. hot intergalactic medium).
I don't know how this got modded up. Not saying it should have been modded down, but you just took two random numbers, one of which doesn't even have that deep of a connection to space as you imply, and multiplied them together incorrectly, and tried to draw vague conclusions from that.
There's also no evidence that energy is being created.
This!
Given how quantum non-locality appears to work, we can in some cases be forced to consider that the energy in question is distributed until it becomes "not distributed" by some process that collapse it's superposition. Examination by most physical measurement processes does this.
Even though Einstein abhorred the implications of quantum theory, his own general approach to working out relativistic theory stands, which is to base our examinations of the universe on 2 things:
1- That which we observe and can confirm by experiment and
2- The implications of what we observe and can confirm by experiment which then must be observed and confirmed by experiment.
I do agree that there is a point where each explanation ceases to function to explain the whole, newtonian physics functions to explain how macroscopic objects behave to a certain precision and it breaks down when the curvature of spacetime is altered by extreme amounts of mass in a small place or limited masses being accelerated to such speeds that they require descriptions of how they alter spacetime by effect to be described properly. This description breaks down when we attempt to explain objects existing at the sub atomic level and a whole other set of rules come into play that exist in between the frames of the macroscopic and relativistic linear framework we are used to using to describe things. Beyond this we are at the point where we do not have the tools yet to perform experiments we need to test the implications of the things which we have observed at that level.
Sometimes analogies can be helpful, sometimes they can just confuse the issue. In the case of expanding space, I prefer to think of it as something analogous to plate tectonics, We know the Earth is not expanding, but we know that the floor of the Atlantic ocean is getting wider and wider across geologic time scales, matter is not being created, but the distance between the coastlines of the eastern United States and Western Europe gets a little larger each century. When considering vacuum energy I think of the plate tectonics analogy and remember that even though it seems like the vacuum energy should be becoming more vacant, the implications of what we observe in the Hadron collider confirms that when taken altogether, the total amount of energy in the universe balances out to zero and comparing different sized slices of this pie to one another confuse the issue.
You can't assume that everything everywhere behaves the same. You can't assume that energy drawn from one location will show up as a deficit in another (you find running water in the street's gutter... you learn Joe's pool is draining. Assuming Mark's pool is also draining doesn't follow.) You can't measure anywhere but (very) locally, which also means you can only measure data very near temporally -- and so you really have no bloody idea what is going on without resting your conclusion on assumptions made entirely free of supporting data.
What you're claiming is equivalent to saying you know exactly what's going on on a planet orbiting some star in Andromeda because you've done some observations as to what is going on here. Evidence is utterly insufficient to your claim.
I've fallen off your lawn, and I can't get up.
IANAP, but my admittedly also very shallow understanding, is that when we're talking about the energy of the "vaccuum", we mean "energy associated with space itself".
A vaccuum is typically defined by the absence of matter in a volume of space (but not necessarily light or other energy). But let's exclude those too - there is no matter or electromagnetic radiation at all.
Even with those exclusions, at a fundamental level space appears to be a seething maelstrom of quantum particles popping in and out of existence. There seems to be some energy associated with "empty" space.
Some people posit that the vaccuum (i.e. space as we know it) may be "unstable" - that the particular energy it possesses could be lower than it is - and that we're just caught on a local bump in the energy landscape. If the vaccuum ever "fell off" that bump to a lower level, it would apparently spread at the speed of light across the entire universe from wherever it started, destroying everything that currently exists, and leaving behind... I don't know what. More vaccuum, but with a much lower energy associated with it, and with lots of new matter and energy created by the release of the vaccuum energy. Probably.
Anway, happy for a real physicist to correct me on some or all of the above - that's just my very lay understanding of what is meant by vaccuum energy.