PeterDonis's latest activity
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PeterDonis replied to the thread I Euclidean geometry and gravity.But those hypersurfaces are not geodesic hypersurfaces, so it's not clear that an "intrinsically flat" object can be embedded in them... -
PeterDonis replied to the thread I Euclidean geometry and gravity.Yes, agreed. But how far it is deformed, under a given stress, depends on how strong the material is. A stronger material will deform...
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Claim: There is no difficulty defining a congruence of world lines representing a piece of paper far from a BH, that then has each...
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PeterDonis reacted to Ibix's post in the thread I Please explain how length contraction and time dilation result in a constant c with
Like.
You have forgotten the relativity of simultaneity, which is less popularised than length contraction and time dilation, but probably... -
PeterDonis replied to the thread I Euclidean geometry and gravity.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...
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PeterDonis replied to the thread I Euclidean geometry and gravity.First, you should say flat spacetime and curved spacetime. Those are the invariants. Second, while paper made out of the ordinary...
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Some additional cautions may be stated: A paper so oriented is not inertial, so you have to imagine some force holding it in place...
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PeterDonis replied to the thread I Euclidean geometry and gravity.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...
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PeterDonis replied to the thread I Formal derivation of statement from Peano Arithmetic system.Thread reopened after a post with an unacceptable reference (ChatGPT) has been deleted.
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PeterDonis replied to the thread I Euclidean geometry and gravity.Not if the conditions are the same. But what someone very distant observes won't be easily interpreted as "I'm seeing non-Euclidean...
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PeterDonis replied to the thread I Euclidean geometry and gravity.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...
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PeterDonis replied to the thread I Euclidean geometry and gravity.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...
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PeterDonis replied to the thread B What happens to information inside a blackhole.Yes. The coordinates don't matter; the model is the same regardless of what chart you use. The Kruskal chart is useful because it...
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PeterDonis replied to the thread B What happens to information inside a blackhole.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...
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PeterDonis replied to the thread B The Effect of Linear and Rotational Motion on Measured Weight.Why would it? Tangential motion doesn't affect the normal force. The direction of the acceleration vector does, yes. But the magnitude...