I understand that in semi-classical gravity the curvature of spacetime is based on the expectation value of the stress energy tensor, and so a massive object in a superposition of two possible location would curve spacetime as if the object was in the middle-point of the two locations, but when the state vector is reduced it would suddenly shift to one of those two points. While this does seem weird, no one has ever physically demonstrated that measuring this is actually possible, so until there is a demonstration that it is actually physically possible to measure this, there isn’t actually a contradiction between theory and experimental practice. All we can say is “that seems weird” but that’s not a scientific argument against it.

You say it diverges from reality but… how do you know that? No experiment has ever demonstrated this. It could be that this is just how reality works, or it could also be that it’s just not physically possible to probe this in the first place, and so it’s just a nonphysical quirk of the theory of computing something nonphysical in the first place. We can’t say for certain it is wrong until someone actually conducts an experiment to probe it, and if we find it is wrong, then not only would we rule out semi-classical gravity, but we would have the data needed to actually replace it with something.

This is my issue with “fundamental physics” these days in general: they do not actually demonstrate any contradiction between theory and experimental practice. The desire to unify quantum mechanics and general relativity is just based on some preconceptions that information shouldn’t be destroyed and gravity should be quantizable like every other force, but how do you know that with certainty? You did not derive this from experimental observation, because semi-classical gravity is currently compatible with all experimental observations. It is more that one begins with a preconception of how they think reality should work and says the theory is wrong because it does not fit those preconceptions. Yes, certain aspects of semi-classical gravity are “weird,” but that’s not a scientific argument against it.

Because of the influence of Karl Popper, people think science = falsifiability, so new theories are then constructed not based on experimental evidence but by trying to better fit into our preconceptions, but are also made to falsifiable because that is “science.” When they are falsified by an experiment that just reconfirms the predictions of semi-classical gravity, they just tweak it a bit so the theory is not falsified by that experiment any longer but still technically falsifiable, and they do this ad infinitum. You end up with decades doing this and what do you have, String Theory that is only applicable to an anti-de Sitter space, a universe we don’t actually live in? Or Loop Quantum Gravity which can’t even reproduce Einstein’s field equations?

Popper has been a detrimental influence onto the sciences. Science is not falsifiability. Science is about continually updating our models to resolve contradictions between the theory and experimental practice. If there is no contradiction between the theory and experimental practice then there is no justification to update the model. I have seen a mentality growing more popular these days which is that “fundamental physics hasn’t made progress in nearly a century.” But my response to this is why should it make progress? Why have not encountered a contradiction between experimental practice and theory, so all this “research” into things like String Theory is just guesswork, there is no reason to expect it to actually go anywhere.

The same is also true of the so-called “measurement problem” which as physicists like Carlo Rovelli and Francois-Igor Pris have pointed out only arise because we have certain metaphysical preconceptions about how reality should work which when applied to quantum theory lead to absurdities and so people often conclude the theory must be wrong somehow, that it’s “incomplete,” that it needs to be replaced by something like an objective collapse theory or a multiverse theory or something similar. Yet, this is not a scientific criticism, the theory is in no contradiction with the experimental evidence. We should just get rid of our preconceptions about how reality should work and accept how reality does. As Bohr said: stop telling God what to do.

There is no reason to assume the universe acts the way we’d like it to. Maybe the laws of physics really are just convoluted and break down at black holes. While yes, maybe one day we will discover a theory where it does not break down, it is anti-scientific to begin with an a priori assumption that this must necessarily be the case. It could be that the next breakthrough in fundamental physics even makes the mathematics more convoluted! You cannot just begin with a starting point prior to investigation that this is how nature works, you have to derive that a posteriori through investigation, and currently this is what our best theory derived from investigation states. It may be wrong, but there is no justification in claiming it is wrong without showing a contradiction between theory and experimental practice.

This is my issue here. The desire to replace semi-classical gravity with something else, the measurement problem, the desire to unify all forces of nature into a “theory of everything,” trying to solve the “fine-tuning problem,” these are all ultimately pseudoproblems because they do no derive from any contradiction between experimental practice and theory. They are not genuine scientific problems. I am not even against people looking into these, because who knows, maybe they will stumble across something interesting, but the issue with treating these all as genuine “problems” is that when they go “unsolved” for a century, it makes it look like there is a “crisis in fundamental physics.” There just isn’t. In fact, it’s quite the opposite: every experimental test reconfirms our current best theories, this is the exact opposite of a “crisis.” People pretend like we have a “crisis” because our current theories are too good!

If I am not mistaken, information loss inside of a black hole comes out of semi-classical gravity. If these symmetries are tied to the assumption that the laws of physics don’t change and the symmetries break down in semi-classical gravity, then does that mean in semi-classical gravity the laws of physics change? Is there a particular example of that in the theory you could provide so I can understand?

I don’t disagree that information is conserved in general relativity and quantum mechanics taken separately, but when you put them together it is not conserved, and my concern is that I don’t understand why we must therefore conclude that this necessarily wrong and it can’t just be that information conservation only holds true for limiting cases when you aren’t considering how gravitational effects and interference effects operate together simultaneously. I mean, energy conservation breaks down when we consider galactic scales as well in the case of cosmic redshift.

Yes, we can experimentally verify these laws of conservation, because in practice we can only ever observe gravitational effects and interference effects separately, as a limiting case, and thus far there hasn’t been an experiment demonstrating the plausibility of viewing them simultaneously and how they act upon each other. In semi-classical gravity these “weird” aspects like information loss in a black hole only arise when we actually consider them together, which is not something we have observed yet in a lab, so I don’t see the basis of thinking it is wrong.

You seem to suggest that thinking it is wrong implies the laws of physics change, but I’m not really sure what is meant by this. Is semi-classical gravity not a self-consistent mathematical framework?

It goes back to the French revolution where the people who sat on the left of the parliament opposed the ruling class, in that case the feudal aristocracy, while the people who supported the ruling class sat on the right of the parliament. Even after the aristocracy was gone, people started to use the term left to refer to people who oppose the ruling class of capitalist society (wealthy capital oligarchs) where as the right is those who support them.

“this isn’t right vs left, this is right vs left”

uh… okay?

I still don’t really understand why the information just can’t be destroyed. It seems like we’re starting from an assumption that it shouldn’t be destroyed despite it being so in semi-classical gravity, and then trying to think of alternative theories which could preserve it such as on the boundary or in its charge/mass/spin. Maybe that’s correct but it seems like speculation, and it’s not speculation based on any actual contradiction between theory and practice, i.e. not because semi-classical gravity has actually made an incorrect prediction in an experiment we can go out and verify, but only because we have certain preconceptions as to how nature should work which aren’t compatible with it. So it doesn’t really come across to me as a scientific “problem” but more of a metaphysical one.

There’s still a pattern in the results, so by one means or another we want to explain the results. Just calling it nondeterministic, if I understand right, would be just saying you can’t predict it from prior observations. So, whatever language you use to describe this puzzling situation, the puzzling situation thus far remains.

I mean nondeterministic in a more fundamental sense, that it is just genuinely random and there is no possibility of predicting the outcome because nothing in nature actually pre-determines the outcome.

A priori?

Through rigorous experimental observation, it’s probably the most well-tested finding in all of science of all time.

Or because it best fits with Relativity? It sounds about as strong as saying, “we know time is universal.” It’s obvious, has to be true, but apparently not how the universe functions.

So we can never believe anything? We might as well deny the earth is round because people once thought time is absolute now we know it’s relative, so we might as well not believe in anything at all! Completely and utterly absurd. You sound just like the creationists who try to undermine belief in scientific findings because “science is always changing,” as if that’s a bad thing or a reason to doubt it.

We should believe what the evidence shows us. We changed our mind about the nature of time because we discovered new evidence showing the previous intuition was wrong, not because some random dude on lemmy dot com decided their personal guesses are better than what the scientific evidence overwhelmingly demonstrates.

If you think it’s wrong show evidence that it is wrong. Don’t hit me with this sophistry BS and insult my intelligence. I do not appreciate it.

Maybe you are right that special relativity is wrong, but show me an experiment where Lorentz invariance is violated. Then I will take you seriously. Otherwise, I will not.

It could do that but what’s the evidence that it does? Or has someone proved this is already a feature of semi-classical gravity that just wasn’t noticed before? Or is it only a feature of a brand new hypothetical theory?

why’s it a problem? why can’t information just be lost at a black hole?

trvth nvke

Even though China gave up on most communist ambitions post-Dheng

No they haven’t.

Quantum nonlocality really is a misnomer. Nothing is nonlocal about it. We know from the No-communication Theorem that there is no physical interaction you could carry out with one particle in an entangled pair that would affect the state of the other particle, and we know it is compatible with special relativity, which is a fundamentally local theory, as such a unification of the two is how we get quantum field theory.

“Local realism” is also a nonsensical term. There is no agreed upon rigorous definition of “realism” and its introduction to the scientific literature has only served to confuse the discussion and promote quantum mysticism because people think because Bell’s theorem supposedly shows that “local realism” is false that you there have to choose between locality or realism, but not both, and since we know the universe is local, we have to conclude there is no objective reality, devolving into mysticism and idealism.

This isn’t just a problem in popsci articles but even in published scientific literature. This “local realism” hogwash has caused even otherwise respectable physics to publish nonsense about how reality doesn’t exist. The term “realism” is never used in Bell’s theorem and has tn relevance to it. Bell’s theorem is about local hidden variable theories, and it is complete nonsense to conflate hidden variables with “realism” as if your only choices are to believe the reality is deterministic or to deny reality even exists! What kind of options are those? What about a third option that reality exists and it is just nondeterministic?

What Bell’s theorem shows is that quantum mechanics cannot be replaced with a local hidden variable theory, and since we know the universe is local, that means it cannot be replaced with a hidden variable theory. It forces us to accept nondeterminism, it doesn’t force us to deny reality, nor does it prove there is nonlocality.

It can, under certain conditions, contain information about things at a distance, but a function is not a physical entity and its reduction is not a physical process, so none of this reflects anything superluminal actually going on in physical reality.