0

Some of my questions haven't been well received, because I seem like I'm challenging well respected theories without having done the proper university training and study.

I have been studying this online as a hobby for over five years though. I have a problem with the idea of Hawking radiation.

If you have a black hole such as the one in the center of our galaxy, with the gravity of tens of thousands of suns, how can a photon or anything possibly escape that gravity?

I've heard that Hawking radiation supposedly happens through quantum tunneling, because we can see sub-atomic particles popping up here and there in labs, but if a photon managed to "tunnel" it's way out of the event horizon of a black hole with such amazingly huge gravity, through some other dimension where gravity doesn't have any effect, then wouldn't it appear just outside the event horizon, and be sucked straight back in anyway?

If it didn't go straight back in, it would be caught in some sort of orbit of the black hole, or bump into the material that was surrounding it, wouldn't it?

I don't understand how it could be possible for anything to ever escape a black hole of that magnitude. How far have they observed quantum particles tunneling in the lab? The event horizon would be many kilometers, and anything that popped up in that space would go straight back in.

rowanman28
  • 231

1 Answers1

7

I discuss this in my answer to Black holes and positive/negative-energy particles.

The idea of Hawking radiation being caused by virtual particles is just a metaphor. The radiation is actually due to the fact that in curved spacetime there is no unambiguous choice of the vacuum state. What appears to be the vacuum state for an observer close to the event horizon will appear to be a state populated by particles to a distant observer. These particles constitute the Hawking radiation.

Community
  • 1
John Rennie
  • 355,118
  • The way I see things, there are only a few things which stand in the way of the big crunch theory being the likely end of the universe. One would be dark energy and how it behaves over time, and the other would be Hawking radiation. Two unproven theories based on science which you admit that you don't fully understand yourself. – rowanman28 Jul 01 '14 at 07:58
  • 1
    @rowanman28: that isn't true. Even without dark energy the universe will not recollapse. The evolution is described by the FLRW metric and the average density of matter/energy. Unless we are wildly wrong in our estimate of the average density of matter/energy the universe will not recollapse. – John Rennie Jul 01 '14 at 08:11
  • I looked up unambiguous, not open to more than one interpretation. I looked up vacuum state, but the part about the observer looking at subatomic particles near a black hole and further from a black hole doesn't make much sense. Every part of the answer assumes that the theory is right when trying to explain why it's right. I think that gravity would be too strong for anything to escape, no matter what type of energy it is. – rowanman28 Jul 01 '14 at 08:12
  • What if dark energy is actually very similar to normal energy in that it's just little strings of energy that formed into different subatomic particles? They would be sucked into black holes, and over time there would be more and more gravity in the black holes, and whatever the reason for the pushing of dark energy, it would have it's own gravity. – rowanman28 Jul 01 '14 at 08:14
  • If you calculate that every type of energy in the universe has it's own gravity, and there is no pushing effect left at some point, any point in the time period, no matter how far or fast the universe is expanding, it will slow and collapse. – rowanman28 Jul 01 '14 at 08:27
  • 1
    It may sound like I'm being very pedantic, but if it's a choice between dark energy being a completely different substance to all the other types of energy we can see and it being the same as a photon or a gluon or any of those things, it seems likely given we don't know to assume it is the same energy. It also seems logical to say that if all energy has gravity, nothing could escape a black hole with the mass of 100,000 stars. No reason to assume that the crazy ideas are true, and they are crazy unproven theories based on math and nothing else. – rowanman28 Jul 01 '14 at 08:52
  • then wouldn't it appear just outside the event horizon, and be sucked straight back in anyway? Outside the event horizon, escape velocity is less than the speed of light. A photon outside the event horizon and not in a path that passes through it will not be "sucked" by the black hole. – Thermo's Second Law Jul 03 '14 at 20:50
  • rowanman28, I think your comments are getting a bit far from the original question. You appear to be challenging several different theories by loosely-connected reasoning. +1 for @JohnRennie's answer and the link to another question. – HDE 226868 Aug 04 '14 at 18:24
  • Also, Hawking's book, A Brief History of Time, discusses Hawking radiation pretty well. – HDE 226868 Aug 04 '14 at 18:26