# Hawking Radiation **URL:** \ **Category:** Factual Questions\ **Created:** [June 17, 2009, 2:16pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066 "2009-06-17T14:16:00Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Sizzles](https://avatars.discourse-cdn.com/v4/letter/s/e480ec/32.png) [@Sizzles](https://boards.straightdope.com/u/Sizzles)\ **Post date:** [June 17, 2009, 2:16pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/1 "2009-06-17T14:16:00Z")
How does Hawking radiation work ? My understanding is that particles and anti-particles form near the event horizon of a black hole, the anti-particle falls into the black hole, the particle doesn’t and eventually the black hole evapourates. Why does are anti-particles more likely to fall into the BH, surely it would be 50-50 ? ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [June 17, 2009, 2:23pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/2 "2009-06-17T14:23:55Z")
It is 50-50. The black hole emits both sorts. ---
**Author:** ![Sizzles](https://avatars.discourse-cdn.com/v4/letter/s/e480ec/32.png) [@Sizzles](https://boards.straightdope.com/u/Sizzles)\ **Post date:** [June 17, 2009, 2:32pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/3 "2009-06-17T14:32:49Z")
Then what causes the BH evapourate ? Thanks. ---
**Author:** ![unclelem](https://avatars.discourse-cdn.com/v4/letter/u/ac91a4/32.png) [@unclelem](https://boards.straightdope.com/u/unclelem)\ **Post date:** [June 17, 2009, 3:01pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/4 "2009-06-17T15:01:35Z")
> [@Sizzles](#): > > Then what causes the BH evapourate ? > > Thanks. The particles form in pairs to conserve energy, charge, and most importantly momentum. To conserve momentum, they must be moving in opposite directions from one another. The case of interest is when they form on the horizon with one moving inward and the other outward. (which particle is in- or out-ward bound is random for any given pair). The one aimed outward escapes, the partner unfortunately does not. The hole has lost one particle (of random type). In aggregate it loses a bunch of particles (roughly of 50-50 composition) ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [June 17, 2009, 3:31pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/5 "2009-06-17T15:31:39Z")
The black hole evaporates because it lost a net particle/antiparticle. A particle goes out into the universe, and since its partner virtual particle is now inside a singularity it can’t recombine back into nothing. Since nothing can come from nothing, the black hole has to pay for the free lunch the universe just got. ---
**Author:** ![Sizzles](https://avatars.discourse-cdn.com/v4/letter/s/e480ec/32.png) [@Sizzles](https://boards.straightdope.com/u/Sizzles)\ **Post date:** [June 17, 2009, 3:57pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/6 "2009-06-17T15:57:29Z")
I’m still missing something. Doesn’t the BH only loose a particle if the anti-particle falls in ? So sometimes it looses a particle and sometimes it gains one, on average its mass is unchanged. ---
**Author:** ![Happy\_Fun\_Ball](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/happy_fun_ball/32/17664_2.png) [@Happy\_Fun\_Ball](https://boards.straightdope.com/u/Happy_Fun_Ball)\ **Post date:** [June 17, 2009, 4:10pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/7 "2009-06-17T16:10:37Z")
I think you are under the mistaken impression that anti-particles have negative mass/energy. Both particles and anti-particles have mass, thus if the black hole loses an anti-particle it loses some mass. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [June 17, 2009, 4:23pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/8 "2009-06-17T16:23:47Z")
I am confused too about this explanation but I think I can clearly describe my confusion. When the particle/anti-particle pair was created, where did it come from? If it was created from energy/mass from the black hole, then it would be understandable that the loss of one particle would be “evaporation.” But without knowing how it was created, one might confuse this phenomenon with spontaneous creation of particles in a vacuum. ---
**Author:** ![Hal\_Briston](https://avatars.discourse-cdn.com/v4/letter/h/a9a28c/32.png) [@Hal\_Briston](https://boards.straightdope.com/u/Hal_Briston)\ **Post date:** [June 17, 2009, 4:33pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/9 "2009-06-17T16:33:13Z")
_“Raaaaadiation! Get’cher radiation here! Fresh, hot radiation!”_ I’m sorry…I’ll stop now. ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [June 17, 2009, 4:34pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/10 "2009-06-17T16:34:03Z")
You read my mind **Hal** , right down to the exact wording. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [June 17, 2009, 4:53pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/11 "2009-06-17T16:53:42Z")
> [@Hal\_Briston](#): > > _“Raaaaadiation! Get’cher radiation here! Fresh, hot radiation!”_ > > I’m sorry…I’ll stop now. Is that a quote from something? 'Cause Google says it never heard of it. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 17, 2009, 5:07pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/12 "2009-06-17T17:07:29Z")
**Hal** is hawking radiation, much like one might hawk any other product. > [@](#): > > When the particle/anti-particle pair was created, where did it come from? The answer to that is “no”. Virtual particles pop up all over the place, but the net energy of the particle-antiparticle pair is zero, and they promptly recombine back into nothing, so nobody gets too bothered by them. When one falls into a black hole, though, they can’t recombine, so the one that’s left can’t be virtual any more, so it has to have positive energy. That’s the most common explanation, anyway. Personally, I much prefer the thermodynamic argument: The Second Law of Thermodynamics requires that black holes have entropy, since black holes are formed from other systems that have entropy. Everything that has an entropy has a temperature, so black holes have temperature. And everything that has a temperature radiates, so black holes radiate. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 17, 2009, 5:28pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/13 "2009-06-17T17:28:23Z")
I think of it this way: Virtual particles appear all the time. They’re always very close to each other, and always configured so that they can cancel each other other (no net spin, charge, etc.) In a pure, unadulterated vacuum, they form and disappear so quickly and with so little energy that we can’t prove they were ever there - and as long as we can’t prove it, the uncertainty principle lets them keep forming. But a black hole is not unadulterated vacuum. It’s vacuum under an intense gravitational gradient. This gravity is able to spend energy to make the particles heavy/energetic enough to be real (that is, measurable) under the uncertainty principle, and I think it’s this separation that is really the source of the energy cost. The black hole reclaims some of the energy by pulling in one particle, but the particle that escapes represents a net outflow of energy. (If it didn’t have more energy than the other particle, it wouldn’t have been the one to escape). I don’t know if that’s helping to make it more clear. Wikipedia’s phrasing for this is “This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being “boosted” by the black hole’s gravitation into becoming real particles.” ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [June 17, 2009, 6:25pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/14 "2009-06-17T18:25:09Z")
Didn’t Hawking come out and say the the black hole is not emitting radiation, and that it just sits above it? I am being very simple here, but if we are talking about Hawking Radiation, we can’t talk about a black hole emitting it. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 17, 2009, 6:35pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/15 "2009-06-17T18:35:12Z")
Well, it only occurs where there’s a black hole, and the net effect is that the black hole loses mass. Call it what you like, but that quacks like the hole itself emitting the radiation. ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [June 17, 2009, 8:19pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/16 "2009-06-17T20:19:07Z")
It seems to me that the black hole is inducing radiation by its influence rather than emitting it directly. Am I anywhere close to understanding it? ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [June 17, 2009, 9:46pm UTC](https://boards.straightdope.com/t/hawking-radiation/500066/17 "2009-06-17T21:46:29Z")
I would agree. “Emitting” is the problem word. Going forward, it might be best not to connotate it this way. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [June 18, 2009, 1:42am UTC](https://boards.straightdope.com/t/hawking-radiation/500066/18 "2009-06-18T01:42:09Z")
Old post of mine: > [@](#): > > Virtual particles are not real particles. They exist on borrowed energy and must quickly annihilate and repay this energy. However, the extreme tidal gravitation of a BH can pull them apart with enough force that they gain enough energy to become real long lived particles, and at the same time pay back the energy debt to the nearby negative energy regions of space. > > So when the hole captures one of these now real particles, it in effect radiates the other one. It has therefore supplied enough energy to create two particles, but only gets the energy of one back. Thus it loses mass. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [June 18, 2009, 2:26am UTC](https://boards.straightdope.com/t/hawking-radiation/500066/19 "2009-06-18T02:26:43Z")
I just realized about all my post did was say the same thing that dracoi said. As far as the emitting thing, you have to remember that the event horizon is basically a thermodynamic membrane, and therefore is most certainly radiating. Whether or not you call these radiated particles emitted or not seems to be a matter of semantics.