## Can you see the future as you fall into a black hole? (Intermediate)

People keep saying that when you get sucked in a black hole, you can see the future or the past. Is that true or is it false. Why?

That depends what you mean by "see the future". It is true that if you watch the outside world as you are falling into a black hole then you will see time evolve faster there. Everyone's watches will appear to be running faster than yours, and they will appear to be moving as if someone had pressed the "fast-forward" button.

This is a consequence of general relativity, which explains that the gravity of a massive object causes time to slow down near that object. Since your time is slowing down as you fall into the black hole, everyone else who's far away will seem to be evolving faster from your point of view. This doesn't just apply to black holes, by the way - in fact, the effect occurs at least a tiny bit for any massive object - but it can become quite extreme (and very noticeable!) near a black hole because the gravity there is so strong.

As you approach the event horizon of the black hole (the point within which nothing can escape), truly bizarre things begin to happen. An outside observer who is very far away and watching you fall in will see your time slow down so much that it approaches a complete stop! To them, you will appear to slow down and freeze as you approach the event horizon, then fade away into darkness. It is as if their time were passing by infinitely faster than yours.

So when you look out at them, the rate at which you see their time passing will approach infinitely fast - however, this does not quite mean that you get to see the entire future of the universe evolve before your eyes. The problem is that there is no way for you to sit still at the event horizon. As soon as you get there, you are, by definition, pulled very quickly towards the center of the black hole. As this happens, you will be shredded to pieces and killed by the black hole's tidal forces (assuming this hasn't happened already), and furthermore, you will hit the singularity at the center of the black hole where nobody really knows what will happen to the material that used to be you! Whatever happens, you certainly won't get a chance to see or make sense of any of the light that is coming in from the outside. Your trip from the event horizon to the singularity is so short that most of the light from faraway distances doesn't have time to reach you so that you can see it.

Exactly how much of the future that you get to see depends on how slowly you are able to approach the event horizon. The more you are able to "hold yourself back" before you fall in, the more of the outside universe's future you will be able to witness.

For another physicist's take on this question, see this link.

#### Dave Rothstein

Dave is a former graduate student and postdoctoral researcher at Cornell who used infrared and X-ray observations and theoretical computer models to study accreting black holes in our Galaxy. He also did most of the development for the former version of the site.

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