Maybe gravity will turn out to be just a computational artefact. The more energy and states in a volume, the "slower" progression of the [local] system. An effect like this could appear as curved space at energy concentrations. Perhaps GR could be derived from something like this?
Ideas like that are often mentioned here when related topics come up but they are almost surly totally wrong. Computing means doing something in several steps and that is - as far as we can tell - absolutely not what the universe is doing. Even if the universe did something like that it would just mean that there is another layer below evolving in a more fundamental way.
Many people seem pretty confused when physicist talk about things like the black hole information paradox. We think that all physical processes are reversible which means that distinct physical states will always remain distinct. If state A and state B could or would evolve into the same state C this assumption would no longer hold because you could no longer tell whether you arrived at state C from state A or B. The laws of physics would not be time reversible.
And this is the sense in which physicist talk about information, the description of the state space. If you throw something into a black hole the only things that remain visible are things like the mass, the charge or the (angular) momentum but you just lost all the details about the thing you threw into the black hole which is a problem for our understanding of physics.
> And this is the sense in which physicist talk about information, the description of the state space. If you throw something into a black hole the only things that remain visible are things like the mass, the charge or the (angular) momentum but you just lost all the details about the thing you threw into the black hole which is a problem for our understanding of physics.
Why is that a problem? The information could still exist, it'd just be inaccessible...
This seems no different to me than a spaceship going beyond the Hubble horizon.
It is a problem in either case - if it really disappears then time reversibility, a real corner stone of physics, is violated, if it does not disappear the problem is that we don't understand (well) where it goes. As far as I know the favourite theory is that the information is contained in the Hawking radiation and I believe to remember that there was a paper not too long ago that showed how to recover one (or a few) (qu)bit(s) from Hawking radiation in a special case. Because time reversibility is such a deep concept it seems likely that we just don't understand well where the information goes, I doubt that many physicists believe the information really disappears.
We believe that certain symmetries apply to the laws of physics. For example, we believe that the laws of physics are independent of the observer's position. I mean, look (visualize me stepping sideways here). So we can demonstrate that one pretty easily. And they're independent of rotation. Again, look (visualize me turning 90 degrees here). And exchanging left and right. I mean, look... (visualize me pausing with a confused look on my face as I try to figure out how to exchange left and right).
I can't actually do that experiment. And it turns out, when we got deep enough, we found out that things actually behaved differently (parity non-conservation).
When it comes to time reversal, we can't actually do the experiment, either, so we don't really know whether physics behaves the same when time is reversed. We expect, philosophically, that it will, but we don't know. But it seems to me, given how relativity mixes time and space, if physics is not the same with left and right reversed, then it can't be the same with time reversed either.
Saying we consider time reversibility true for more or less philosophical reasons seems a bit of an understatement to me. Conserved quantities prevent states differing in at least one conserved quantity from ever evolving into the same state, i.e. conserved quantities partition the phase space and states cannot cross those partition boundaries. This also has to hold for all isolated subsystems. And conserved quantities arise from symmetries like homogeneity and isotropy of space which are pretty solid empirical and experimental facts. It's all interlinked and I imagine it would not be to easy to eliminate time reversibility from the laws of physics without causing some odd consequences.
The entire point is that it shouldn't become inaccessible, because that is WHY time symmetry appears to break. Because it means that if you flipped the direction of time, something with a causal effect appears seemingly randomly out of nowhere.
What would cause losing time reversibility? I don't see any irreversible aspects. I don't doubt you know what you're talking about, I ask because I'd like to understand more.
I think in the idea I mentioned up time would stop in black holes. All of the information would be preserved.
If we understand correctly, the universe is about 13.7 billion years old. I recall reading once that there is enough mass (matter plus dark matter) that the Swarzchild Radius of that much mass is approximately 13.7 billion light-years.
What if we're inside a black hole? How would that affect how we interpret what we see at large distances? (For example, does that explain the Hubble redshift? Does it explain dark energy?)
And, if it's true, then what is a black hole? Can you have a black hole inside the Swarzchild radius of another black hole?
Honest question. If the concept of dark matter flows from our current understanding of gravity, and gravity is so admittedly poorly understood, how confident are we that dark matter is "a thing"? I know an intuitive sensibility is not the best foundation for an understanding of The Universe, but every time I read about dark matter, I get a very "Aether"-ish vibe. I just imagine comments section in the 2070 version of HN getting a good natured laugh about dark matter.
Gravity as a force/phenomena in space on its own is actually very well understood. In fact it's possibly one of the most well understood theories we have in physics because of general relativity. However, at a particle scale we lack the understanding of how gravity would work.
Dark matter is the collective name for whatever "stuff" exists in the universe that we predict it should have, however because it is noninteractive in any way other than exerting a gravitational pull (it accounts for a lot of astrophysical observations that otherwise are bewildering given what we see in the universe). We know it should exist, we don't know what it is and can barely understand its current properties. So indeed, it is quite possible that it might be Aether-ish if we end up finding something else that explains our current observations or a drastic overhaul of how gravity works at large scales (the latter being very unlikely because of how well GR has stood up to experimentation so far).
Systems like the bullet cluster (https://en.wikipedia.org/wiki/Bullet_Cluster) are taken as evidence that most of the matter in large-scale, gravitationally bound astrophysical systems does not behave like luminous matter.
It's a perfectly fine limiting case of G + Λg = 8πT.
A minor point: it's "the Newton equation" or "Newton's equation", but not "the Newton's equation" (in the same way that one could write "the Eisenhower presidency" or "Eisenhower's presidency", but not "the Eisenhower's presidency").
Maybe gravity will turn out to be just a computational artefact. The more energy and states in a volume, the "slower" progression of the [local] system. An effect like this could appear as curved space at energy concentrations. Perhaps GR could be derived from something like this?