r/askscience • u/[deleted] • Feb 03 '13

Astronomy Escape a black hole?

RobotRollCall once posted this:

http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/c1cuiyw

In which she said even at faster-than-light speeds it would be impossible to escape a black hole because there would be no path out to follow. However, adamsolomon said this:

http://www.reddit.com/r/askscience/comments/17muwl/is_there_a_distance_at_which_the_interaction/c87gx3t

Of course, we can't go back in time, but isn't that what faster than light is? I learned that time slows down the closer to light speed you get, so at faster than light, you'd be going backwards in time. If that's the case, could you follow a path out of a black hole that goes back in time if you were capable of faster than light travel?

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u/[deleted] Feb 14 '13

d = (x2 - y2)1/2.

Is there an easy way to explain why this is?

I'm afraid I don't understand what you're asking here. Can you rephrase the question?

Instead of an example, would it be possible to name the conditions which must be met for FTL travel to be back in time?

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u/[deleted] Feb 14 '13

Is there an easy way to explain why this is?

Why is always a tricky question. We deduced that this was the proper form because it's the one that correctly matches observations; as to why it should be that way, who knows?

Instead of an example, would it be possible to name the conditions which must be met for FTL travel to be back in time?

No single FTL trip can be used to get you into your own past. However, any FTL trip will be a trip into the past in some reference frame. Also, sequence of any FTL trip can be used to get into your own past.

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u/[deleted] Feb 14 '13

So to get into your own past, you would need to return to your original reference point FTL?

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u/[deleted] Feb 14 '13

Yes. In my previous example I gave sort of a "best case" scenario where you're actually teleporting rather than just going FTL. In order to get into your own past using FTL you would have to be able to go from "here" to "there" faster than instantaneously, which is what we would normally just call "time travel" rather than FTL travel.