111–120 of 120 posts
If I understand what I skimmed, the idea is that space-time itself rotates, not all the collective matter in it?
It's much like the expansion of the universe, which is separate from the ordinary momentum of the objects within the universe. But the objects within the universe do move apart along with it.
Earlier quoted context omitted.
That would imply a preferred direction in the universe (the axis of rotation) and thus anisotropy. There are stringent constraints on anisotropy from the cosmic microwave background. In particular, one can use the Doppler effect to check whether the CMB dipole is compatible with our velocity with respect to the CMB frame.
Well, the universe has an axis, found in the CMB: https://en.m.wikipedia.org/wiki/Axis_of_evil_(cosmology)
However, a 2016 study compared isotropic and anisotropic cosmological models against WMAP and Planck data and found no evidence for anisotropy.
Universe is called universe because it is the only one. Everything that exists should be part of the universe. When we say the universe rotates, what does it mean? Rotate relative to what? Does it mean that there's a larger "universe" that contains ours?
“Universe” is often used in the sense of “observable universe”.
If I understand what I skimmed, the idea is that space-time itself rotates, not all the collective matter in it?
Correct. Though the matter in it would also move, dragged along by the space-time. It's much like the expansion of the universe, which is separate from the ordinary momentum of the objects within the universe. But the objects within the universe do move apart along with it.
These things really challenge my physics intuition!
Earlier quoted context omitted.
If the universe is a black hole, would we be able to see anything falling into it after it crosses the event horizon?
You must be able to observe the edge to see that. And afaik the scientific community agrees no edge is observable in our cone of light.
"Obviously you are not convinced that this is the end of the universe. if you will place a quarter in the slot below, the peep-hole will open, and you can see for yourself."
And the captain was right. I paid my quarter and looked through the peep-hole. But it was nothing.
--From "Ado about Nothing, by Robert K. Ottum
“We show that a Gödel inspired slowly rotating dark-fluid variant of the concordance model resolves this tension…” Gödel wait what? I thought of him as “only” the logician who killed Hiblert’s dreams and caused people to question the very foundations of mathematics. Dude then took up physics as a hobby and trolled Einstein by discovering closed time-like curves?
Godel and Einstein were actually quite close.
Earlier quoted context omitted.
Rotation isn't relative. You can tell how quickly you're rotating without reference to any other objects.
But even then you can only tell that you are rotating relative to space itself. If I understand correctly here we are speaking about the space itself rotating, so that would not be possible unless something else contains our universe's space, right?
There is no "space itself" because then you're assuming it is relative, like the speed of light. Basically you're trying to rediscover the aether.
That was the question: light moves at speed C, but relative to what?
Earlier quoted context omitted.
Well, the universe has an axis, found in the CMB: https://en.m.wikipedia.org/wiki/Axis_of_evil_(cosmology)
The article says right up front that the universe does not have an axis: However, a 2016 study compared isotropic and anisotropic cosmological models against WMAP and Planck data and found no evidence for anisotropy.
Earlier quoted context omitted.
I would suspect since general relativity would break down that special relativity certainly would. The “relativity” aspect will almost certainly still apply in some way, and still form an emergent basis for the special relativity effects you point out. All of general relativity has to be emergent from the to-be-discovered laws of the underlying small scale structure of space. (I.e. general relativity isn’t wrong, it…
If special relativity breaks down, so does QFT - since QFT is based on special relativity just as much as on QM.
It doesn’t that any particular phenomena we understand today will break down. Just we will be able to see richer behavior, that has been there all along, than our models cover today. And so be able to understand more conditions than we do today. And perhaps new capabilities to engineer things than we have today.
Obviously quantum field theory, as it exists today, breaks down at the Planck distance too, since it can’t tell us what is happening at smaller distances either.
This isn’t the least bit controversial or surprising. It just means that even with both theories, we can’t explain everything yet.
When we do have an accurate theory of the fine structure of space and time, it will also be a theory of the fine structure of fields. Since space-time is integral to both theories.
It may even be the long sought after unification.
But for distances much larger than the Plank distance, the fine structure theory will still simplify into the GR and QFT we have today.
Just as GR under many conditions we encounter every day, further simplifies to Newton’s Law of Gravity.
Earlier quoted context omitted.
If special relativity breaks down, so does QFT - since QFT is based on special relativity just as much as on QM.
“Breaks down” just means our equations don’t know what to say about a situation. It doesn’t that any particular phenomena we understand today will break down. Just we will be able to see richer behavior, that has been there all along, than our models cover today. And so be able to understand more conditions than we do today. And perhaps new capabilities to engineer things than we have today. Obviously quantum field t…
For examples of the "good" kind, Newton's laws of motion are indeed just an approximation of special relativity. The Schrodinger equation is just an approximation of QFT.
In contrast, GR came in and showed that Newton's law of universal attraction is completely wrong, at the fundamental level. Sure, it predicts certain phenomena correctly, but so did the epicycles that it replaced. Similarly, QM/QFT showed that Newton's laws of motion are also completely wrong, that objects (or at least particles) don't even move according to some laws of motion, they are only described by a probability wave that moves according to some laws, and between two interactions they have no definite state and are not even localized.
And of course, GR and QFT disagree on these parts - GR generally agrees with Newton's laws of motion (with the SR corrections), and QFT generally agrees with Newtoninan gravity. But you can't use GR's gravity with QFT's laws of motion, so we know one or both are broken. A new theory is very likely to also "overrule" one or both of them and show that they are not just an approximation, but completely wrong, working only "by accident" on the scenarios where they have been tested. Especially if the new theory requires there to exist fixed space distances that all relativistic observers agree on.