Recent content by PeterDonis

That's correct. Note, though, that when you have a star in the center instead of a black hole, the spacetime geometry inside the star is different from the geometry outside, and that has to be taken into account. It's undefined. The black hole has no center in the usual geometric sense. The...

First, you should say flat spacetime and curved spacetime. Those are the invariants. Second, while paper made out of the ordinary materials we usually make paper out of probably would be torn apart, yes, we could imagine making paper out of thin sheets of Kevlar, or carbon nanotubes, or...

That's not what I said. What I said is that, if you're observing from a distance objects that are at rest fairly close to a black hole's horizon, there won't be a simple way to interpret your observations as showing you the non-Euclidean geometry of space in the region you're observing. That's a...

Thread reopened after a post with an unacceptable reference (ChatGPT) has been deleted.

Not if the conditions are the same. But what someone very distant observes won't be easily interpreted as "I'm seeing non-Euclidean geometry".

If the paper were oriented radially, then yes, you would be able to draw a triangle on it whose angles would not add up to 180 degrees. In effect, it would be as if you were drawing the triangle on a Flamm paraboloid: https://en.wikipedia.org/wiki/Schwarzschild_metric#Flamm's_paraboloid Please...

It depends on how the paper is oriented and what its state of motion is. But for a piece of paper of ordinary size and a black hole of stellar mass or larger, any effects of non-Euclidean geometry will be too small to observe. A better way of probing the spatial geometry around a black hole is...

Yes. The coordinates don't matter; the model is the same regardless of what chart you use. The Kruskal chart is useful because it covers the entire maximally extended spacetime with a single patch. But that doesn't mean the coordinates define the spacetime. They don't. No. We don't have one...

There is a mathematical model in which that's true, but it's not one that is physically realized in our universe. No, because in the mathematical model I referred to above, the white hole is to the past of the black hole, not its future. So there's no way for something that falls into a black...

Why would it? Tangential motion doesn't affect the normal force. The direction of the acceleration vector does, yes. But the magnitude of that vector also increases, in such a way that the vertical component, which is what affects the reading on the scale, remains the same. No. Again, why...

We won't know that for sure until we have a confirmed theory of quantum gravity. :wink:

I don't think the research program referred to is to use quantum gravity to explain the brain specifically. I think it is to use quantum gravity to explain why measurements have single outcomes, or more generally why decoherence leads to single outcomes. That requires some kind of nonlinearity.

It should be noted that there are plenty of others who disagree with this point of view. One of the most notable arguments against it was due to Daniel Dennett, the philosopher, who constructed a thought experiment scenario in which a Turing machine can actually prove its own Godel sentence! He...

As far as his claimed effect of microtubule-binding drugs on anesthesia, I have no idea. That sort of discussion belongs in the appropriate biology forum, as the experiment itself has nothing to do with quantum physics. It would be evaluated using the same kind of standards as any other...

@Anzerskiy you marked this thread as "B" level, but this is definitely not a "B" level topic. It's an "A" level topic (i.e., graduate level); it's not even clear to me that a useful discussion at the "I" level (undergraduate) is possible. (Note that that's going to be true of pretty much any...