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It says hawking radiation appears due to a particle and anti-particle pair one of which gets sucked in and other one escapes , these particles are said to appear out of nowhere , appear everywhere in the universe and are opposite of each other.

As such in normal universe away from a black hole why doesn't their recombination and Annihilation lead to emission of energy as light or heat like combination of matter and antimatter should?

Why isn't the universe glowing and all of us dead because of the energy from recombination of these particles everywhere as hwaking suggests?

Qmechanic
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user1062760
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3 Answers3

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Hawking radiation comes from the region near a black hole, it is not produced 'throughout space' as you suggest. In this respect the situation is not very different from a star, where the emitted radiation comes from the outer layers. In the case of the black hole it is the region fairly near to but outside the event horizon that radiates.

Next, Hawking radiation itself is mostly electromagnetic. The numerous popular articles which say that Hawking radiation is particle/anti-particle pairs in which one of each pair gets swallowed by the black hole are misleading. Hawking radiation is almost entirely electromagnetic radiation---that is, photons. You can still use the language of particle/anti-particle, but it is a bit misleading.

Finally, Hawking radiation is extremely dim for black holes of ordinary size. For a black hole small enough to emit brightly, the emission process itself uses up the energy of the black hole and it evaporates. So overall one does not expect much Hawking radiation in total from all the black holes of the universe, compared to other sources of light such as stars (except there remains some room for uncertainty about this since it is not yet known very well what the distribution of small black holes may be).

Andrew Steane
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  • This answer is edited to take comments into account -

1) Hawking Radiation is a phenomenon limited to Black Holes, caused by the Event Horizon. Neutron Stars also evaporate (by comparison) but not via Hawking Radiation.

2) For Hawking's model of the thermal emission and area decrease (evaporation) of Black Holes the term particles can be used as an aid towards a superficial understanding only.

  • Therefore the phenomenon of particle-antiparticle pairs spontaneously appearing out of nowhere is a MYTH
Wookie
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Hawking radiation has nothing to do with matter-antimatter annihilation. Mass and anti-mass are both forms of positive energy, and therefore matter and antimatter particles emit energy when they annihilate in accordance with conservation of energy. The particle-model of the quantum foam involved in Hawking-radiation consists of "virtual particles" with positive and negative energy (which is a bit odd, because permanent negative energy particles are not known to exist, but virtual particles in well accepted quantum field theories already break all sorts of rules that normal particles follow). These negative particles could conceivably be negative matter, or negative antimatter, or negative bosons (if you don't think bosons should be called matter). When equivalent positive and negative energy particles annihilate each other, it releases no energy, which is in accordance with conservation of energy because the net energy is zero. The way these particles can (at least theoretically) exist in vacuum is that their net energy always adds up to 0 in such situations, (or, if it turns out that vacuum actually has some minimum energy, it adds up to that).

I will tell you now that I don't actually understand the physics, but the basic idea behind Hawking radiation, as well as Unruh radiation, is that something about gravity/acceleration can change the behavior of what would otherwise be vacuum (from a different observer's perspective) so that it emits black-body radiation. The theory behind Hawking radiation then says that something about the nature of black holes creates a net effect where positive energy moves up (away from the black hole, i.e. the Hawking radiation) and (in accordance with conservation of energy) negative energy moves down, reducing the mass of the the black hole. (Note that the energy density of space is believed to be what curves spacetime, creating gravity. I suspect this somehow ends up always being "mass" in some sense because of relativity or virtual particles or something, but I really don't know.)

Mr. Nichan
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