# Would a black hole evaporate via Hawking radiation before you fall past the event horizon?

It takes an infinite amount of time for something to fall past the event horizon of a black hole from the perspective of someone outside the event horizon. Black holes also evaporate after a finite amount of time from an outsider's perspective due to Hawking radiation.

Does this mean that you would never actually reach the event horizon if you fell into a black hole because the black hole would evaporate?

• Just to be clear, if you fell into a black hole, you'd fall into and meet the singularity long before it evaporated, what happens to the person falling in and what the person outside watching sees are 2 very different perspectives of the same event. Aug 31 '16 at 11:48
• As userLTK indicates, the "infinite amount of time for something to fall past the event horizon" is only with respect to an observer watching an object fall in. The actual object doing the "falling" does not experience this so your question is moot. Besides, logic should indicate that if that were true, nothing could fall into a black hole and thus no black holes could every form or grow larger. Aug 31 '16 at 13:35
• @zephyr This is a point of large confusion and no one is quite sure how to resolve it. It doesn't have a complete answer yet. Aug 31 '16 at 17:10
• Possible duplicate of Infalling observer could never cross Black Hole event horizon? Jan 30 '19 at 10:46
• I've voted to leave this question open - it's the other question that should be closed as a duplicate, given parts of it were directly copied from this one. Jan 31 '19 at 5:43

I've asked this question to a couple of physicists a few days ago. Great minds think alike, huh?

First, bear in mind that Hawking radiation is only hypothetical. It is not theory. If we trust that hypothesis, this is what we can get.

In general relativity, black holes can be described through a number of approximations. For example, the Schwarzschild solution for a black hole describes it as an eternal object — not something that exists for some times, and doesn't exist for others. According to this solution, the event horizon must have always existed, and must remain existing eternally.

Schwarzschild black holes approximate black holes very accurately, but as you can tell, they fail to explain how a black hole can form, and (assuming Hawking radiation is real) they don't explain how one could eventually evaporate.

Of course, that solution won't help us. I've kept looking for one that accurately describes an evaporating, creatable black hole, but I've found nothing. The conclusion I've come to, along with those I've asked, is that our question has a major problem: Hawking radiation is explained via quantum field theory.

Thus, you can't simply use a GR solution for a black hole; you'd need some unholy mixture of quantum field theory and general relativity (keep in mind that both GR and QFT are incompatible in many situations).

In the end, it all comes down to how little we really know about black holes. It's not really possible to determine which solution is the best, and our inability to reconcile QFT with GR poses a big problem. The best answer I could give is "nobody really knows what would happen if you kept approaching a black hole".

We don't know if we would reach the event horizon, we don't know if the black hole will evaporate. We simply don't understand them well enough to know what solution would work, or how we would put QFT into it. If we somehow managed to find an approximation that properly combines GR and QFT, I assume (but don't quote me on this) the situation you described would be possible.

If it is possible, by the way, then we could confidently say that a black hole of any size could rip you apart through tidal forces. Tidal forces become weaker as the black hole's size increases, so one would assume a large enough black hole wouldn't rip you apart.

However, if we take Hawking radiation into account, and if your proposed scenario were indeed correct, the black hole would shrink as it evaporates. Since it would get smaller at a faster rate as we approach the event horizon, it would soon be small enough to rip us apart.

• So assuming (BIG assumption) that all this works out this way and we can somehow survive tidal forces, would we then witness the event horizon constantly shrinking away from us as we approached until it vanished altogether? And then at that point, we would notice that in the few moments it took (from our perspective) for the black hole to vanish, the rest of the Universe aged billions of years? Aug 31 '16 at 17:28
• @called2voyage I suppose? God knows what would really happen, but my assumption is yes. But even if you somehow survived the ever-increasing strength of tidal forces, you'd have to deal with the extreme heat from the accretion disc and the incredibly strong magnetic fields. Aug 31 '16 at 17:30
• I ask because that solution sounds an awful lot like a one-way wormhole to the future. Aug 31 '16 at 17:32
• @called2voyage That's just how time dilation acts. It would be the same if you kept approaching the speed of light — your time would progress slower relative to the rest of the Universe, and the Universe's time would progress faster relative to you. A black hole doesn't have magic time-travel abilities, it just uses gravitational time dilation. All objects with gravity apply gravitational time dilation, but black holes will continue to dilate your time to infinity as you approach their event horizons. Aug 31 '16 at 17:42
• Right, but in this case you never cross the horizon, you just end up in the future. Aug 31 '16 at 17:43

There's an existing FAQ for these sorts of questions:

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

For this particular question, the answer is no.

As it has been mentioned in a comment by @zephyr, the infinite time issue is actually a non-issue.

As you move closer to a black hole, the relative time to your point of view doesn't change in the same way that it does from a different reference frame.

Looking at your own situation, everything would happen in "real time" however, everything observed about you and your situation would take "and infinite amount of seconds for one second to pass."

This is also a contested issue because there have been measurements and possibly observations (I'd have to fact check this) of stars "falling" into black holes. So the infinite time from the outside observers perspective is also not possible.

In short, the best way to answer your question without going to much into theory, hypotheticals, or mad science, is simply to state: No, it does not mean that.

• If we've observed a star falling into a black hole (I'd have to check that myself), that doesn't mean we've observed the star reaching the event horizon. We might just see the star being torn apart. It would appear to approach arbitrarily closely to the event horizon, to the point that it would seem to vanish, without ever actually reaching the event horizon from an outside frame of reference. All the mass/energy of anything falling into the black hole could seem to be "suspended" just above the event horizon, with its apparent speed asymptotically approaching zero. (Or I'm wrong.) Sep 1 '16 at 16:32