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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.
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
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.
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.
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.
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.