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The event horizon of a black-hole is defined as the point at which light itself cannot escape, supposedly due to a black-hole's immense gravity and effect on spacetime. However, would this not require the acceleration caused by gravity to result in a velocity higher than the speed of light? And since photons are not classed as 'empty-matter' this would contradict the principal of invariant light speed.

P.S, I'm only at GCSE level so I'm not familiar with any hyper-complex terminology or anything like that :)

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  • $\begingroup$ The speed of light is a local quantity. I don't know what you mean by "classed as empty-matter" means to you. Such an expression is not being used in physics. Photons are the quanta of the electromagnetic field. How an electromagnetic field at the quantum level behaves near or at an event horizon is not known. We can speculate to some extent and have, but the exact dynamic equations of motion of this system are unknown. "We don't know" is a fair and exact statement at this moment, however, nobody expects there to be a superluminal effect in there. $\endgroup$ – CuriousOne Feb 24 '16 at 23:30
  • $\begingroup$ I've never liked the term empty-matter, however it's the only explanation I've been given to explain how the universe could expand at a speed faster than light during inflation. I suppose it's matter without content, although that alone seems like an impossibility considering that something cannot be composed from nothing, but I guess that's moving towards the realms of dark energy and such. Either way, thanks for the comment! $\endgroup$ – fonix Feb 24 '16 at 23:40
  • $\begingroup$ The local speed of light is not violated in inflation models, either, and inflation is not being assumed as happening in a matter free universe. Quite the contrary. A mental model for inflation that may work for you is that of a phase transition, which can also happen faster than the speed of sound in the medium. $\endgroup$ – CuriousOne Feb 24 '16 at 23:44
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    $\begingroup$ For an interesting application of the warping of spacetime in order to travel faster than light, search for "Alcubierre warp drive". Alcubierre found solutions to the Einstein field equations which support FTL, but nobody has found a way to physically obtain those solutions. $\endgroup$ – Peter Diehr Feb 24 '16 at 23:50
  • $\begingroup$ So by manipulating spacetime in such a way, negative mass can be created? So I guess the final solution would be down to the theoretical velocity of spacetime itself opposed to the travelling body. That is assuming that spacetime can be altered in such a way... $\endgroup$ – fonix Feb 24 '16 at 23:56
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According to General Relativity, no.

The reason is rather simple:

By definition, General Relativity says that one can always go to a local rest frame to get Minkowski metric.

The above in layman's terms: If you are the observer, nothing very close to you can move faster than speed of light.

On the other hand, if we are dealing with 'extreme warping of spacetime' such as singularities, General Relativity is expected to break down and who knows what happens then.

Edit: The space can expand "faster than the speed of light". So technically, it may look like something is "moving faster than speed of light" far away.

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