# Tag Info

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Relativity just requires "constant speed of light in vacuum". It makes no claims about the speed of light in a medium. When you are moving relative to water, you will observe a different speed of light depending on your relative velocity. But you will still have all the other effects of relativity at work - such as time dilation.

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Actually, the assumption of a psuedo riemannian manifold doesn't require many tacit assumptions. Can you measure time and distances? Can you define a right angle? Ok, you now have a manifold equipped with a metric. Want to include time as a dimension? Now you have four dimensions. You can't turn around in time like you can in space, so you need the time ...

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You can't "scootch the material from the event horizon" because in the coordinates of anything approaching the hole, the matter does in fact fall in. However, you could study for example radiation from the matter. This is thought not to resolve the paradox for several reasons (note I gave a very similar answer to Can the event horizon save conservation laws ...

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My interpretation is that you are raising the following objection to the black hole information paradox: According to observers distant from the hole, causal lines take infinite coordinate time to cross the event horizon. To these observers, infalling information is thus never lost, but only very strongly redshifted; in essence it remains "painted" on the ...

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I wouldn't know that any of the answers above has shown that, from an outsider's perspective, anything can ever reach the horizon, which was essentially the question of the OP. From an in-falling observer's point of view, there is no problem because kinematic time dilation and gravitational time contraction of the rest of the universe ("looking" in the rear ...

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Your confusion might originate in what it means a simultaneous measurement. The fact that "Light from farther end leaves before it does from the closer end" is irrelevant. That would be true even if the object were at rest. One way to make a simultaneous measurement to determine the length is to have clocks along the path of the rod, at rest relative to ...

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The length of the rod will always appear smaller in your frame than in the proper frame, the mathematical relation between both lengths is given by: $$L=\gamma L_{o} \,\, ,$$ Where $$\gamma=\sqrt{1-\Big(\frac{v}{c}\Big)^{2}} \,\, .$$ I'm not sure if I've understood very well your question, but I think it can answer your question.

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The geometry for a spinning ball changes. If you consider the circumference as small line segments, the fact that they are spinning means that the line segments are moving in the direction of motion and exhibit Lorentz contraction while the radii are not foreshortened since they are moving perpendicular to the spin. You are now dealing with non Euclidean ...

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A reference frame is equivalent to a choice of coordinates. So, choosing an accelerated frame in Minkowski space is equivalent to choosing a specific coordinate system on Minkowski space. Most importantly, this means that there is not genuine curvature in an accelerated frame, i.e. it is fundamentally different than gravity. The equivalence principle ...

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as far as i could imagine the ball would be vibrating, it would have frequency, because it has a very large momentum or better to say that it has energy which is very huge with respect to its mass, you can't see that ball because it is too fast to be observed by our necked eyes, you can only see it with a super super slow camera. You see what the ...

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Sometimes people talk about "relativistic mass" which depends on your reference frame... this is perhaps what you're thinking of when you talk of your mass increasing as you approach the speed of light. However, more typically if a physicist says "mass" they mean the "invariant mass" or "rest mass" which is just your energy content (divided by the speed of ...

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The mass of your spaceship and your mass is not affected in your frame of reference. However from an outter stationnary observer measuring your mass in some kind of way would see it increase, they would see your spaceship contract along its direction of motion and they would even see, if they could look at a clock in your spaceship, that your clock tics ...

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Do you know Bernard Schutz's book: A First Course in General Relativity? Check out the first chapter of that book. There is a derivation of invariance of proper time using first principles in section 1.6. Basically, the idea is to start from expressing $\Delta \bar s ^2$ (interval in the barred frame) as a linear combination of $\Delta x_i$'s (vector ...

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