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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 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
how does empty space have energy?
That was my question as well until I read Brian Greene's explanation in his book, The Fabric of the Cosmos.
In short, the Higgs Field. Long answer, think of what we call space as a fabric (hence the title of his book). The Higgs Field is the fabric upon which everything else "sits". Even if there are no particles in a given unit of space, it is not empty because the Higgs Field is still there.
Start on page 254 of his book and work your way through as he describes the field and how it (supposedly) permeates everything.
We will bankrupt ourselves in the vain search for absolute security. -- Dwight D. Eisenhower
Paradox - "a statement or proposition that, despite sound (or apparently sound) reasoning from acceptable premises, leads to a conclusion that seems senseless, logically unacceptable, or self-contradictory."
The paradox is that energy is supposed to be conserved, but space has energy and is increasing. So, we have a logically unacceptable a conclusion.
Just because it is a current paradox doesn't mean it can never be resolved. We find an energy source, or figure out the laws of physics which in this case allow for the creation of energy and is stops being a paradox.
Quantum physics calculations say the vacuum energy is one value while measurements of the curvature of the universe say it is a different value. That is a paradox especially when both Quantum physics and the physics involved in measuring the curvature of the universe seem to both be right in other respects such that making changes to resolve this paradox causes them to stop describing other things accurately. So, we have logically unacceptable conclusion.
The red shift thing doesn't look like a paradox, but a really cool test of our understanding of cosmological red shift.
And, the homogeneity problem could be a paradox linearity of expansion says the universe is homogenous, observations say it is not. But, they don't mention whether observations have done a reasonable job of determining the dark matter distribution of the universe.
There are paradoxes in the article, but it does drift into one topic that is not a paradox and another that is borderline.
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)
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.