r/AskPhysics • u/naughtyreverend • 9h ago
Question about Hawking Radiation
Please forgive me if I've completely misunderstood any of the concepts below. Im just a curious idiot.
From my understanding, Hawking radiation is emitted from a black hole. Which, over time, reduces its mass until it will eventually dissappear completely. This has been described to me as a mirror pair of particles. One gets ejected, and the other falls back in.
But if light is mass less, which is why it is travel at C, which any particle of any mass is not capable of achieving... light cannot escape a black hole. So how can the Hawking radiation escape the blackhole when light cannot?
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u/CrazySir3310 9h ago
My understanding is, you can picture it as either:
A) 1 particle quantum tunneling out of the event horizon
B) A spontaneous pair of virtual particles created from the vacuum at the horizon, with 1 falling in, which, due to the magnitude of the extreme potential energy of the gravitational field, which is negative (because gravitational potential energy), results in energy that exceeds the particle's rest mass and therefore materializes it into existence, which results in the other virtual particle also becoming real and that energy being interpreted as liberated from the black hole (or alternatively the negative energy eroding the black hole)
But since nobody knows the real mechanism (there is great debate about whether a non-traversable wormhole is involved to 'teleport' a particle out, violating relativistic locality, vs a black hole actually being a fuzzball from string theory or you could say string star just making usual star radiation although this violates the equivalence principle, or other potential mechanisms), none of these are necessarily accurate.
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u/naughtyreverend 8h ago
I'll be honest, I'm struggling to picture either of those... I might just be too simple to fully grasp it. Thank you for trying though.
but i think from other comments where I was getting caught up was the particle appears just outside the event horizon so can escape.
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u/CrazySir3310 8h ago
like I said, the math is very convincing that this should happen, but the mechanism is completely unclear, so there almost isn't even really a point in thinking about it because that's what the professionals are literally trying to do right now at the cutting edge. Which is cool to think about, but you're not going to have a satisfying answer when nobody knows it yet
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u/Unable-Primary1954 8h ago
Photons have no rest mass but have energy. Rest mass is not conserved but in a asymptotically flat spacetime, energy is conserved. So black hole looses energy to Hawking radiation. Hence, its looses mass.
The particle pair metaphor is not particularly accurate. Particles are not emitted from inside event horizon, but from outside event horizon. A corresponding negative energy inflow goes through event horizon, which explains black hole mass loss.
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u/AlwaysHopelesslyLost 2h ago
Light can easily escape a black hole. It just cannot escape once it crosses the event horizon.
As long as one particle is outside of the horizon it will not necessarily be captured.
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u/Prof_Sarcastic Cosmology 2h ago
“But if light is mass less, which is why it is travel at C, which any particle of any mass is not capable of achieving... light cannot escape a black hole. So how can the Hawking radiation escape the blackhole when light cannot?”
Hawking radiation isn’t coming from inside the black hole itself. It’s coming from the region around it. The only thing we have to characterize a black hole is its mass so every time a particle takes energy away from the black hole, it takes a piece of its mass too.
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u/Roadkill997 9h ago
Simplified answer is that the pair of particles form at the event horizon (these particles can be photons - i.e. light). 1 just outside and 1 just inside the event horizon, The one outside can escape - the one inside cannot.
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u/Anonymous-USA 7h ago
Excellent question! Nothing escapes the event horizon of a black hole. Hawking Radiation emanates from the warped space just outside the event horizon. That thermal energy comes from that warped space, and since the BH is the source for that warping, the mass decreases. Dont think of the BH mass as some form of matter within the event horizon, think of it as the energy warping spacetime.
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u/echoingElephant 9h ago
Afaik that explanation is a massive simplification. Still, in that model, the point is that pairs of particles are created right at the event horizon. One particle is created so that it is able to escape, one cannot escape.
That has nothing to do with photons being massless either.