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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?

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  • $\begingroup$ There is no event horizon. HR works around EHs. Getting 2 photons from nothing could hold impulse conservation, but it couldn't energy conservation. Thus, there is no such process. Virtual photons can exist, but only for a short time and you can't get energy from them. $\endgroup$ – peterh says reinstate Monica Jun 1 '17 at 20:16
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    $\begingroup$ Look up Olber's paradox $\endgroup$ – Ismasou Jun 1 '17 at 23:31
  • $\begingroup$ @Ismasou The Hawking radiation coming from the empty vacuum is zero, because there is no event horizon in it. Thus, there is no Olbers paradox in the picture. If you could decode any more meaning from the question as I could, just write an answer. $\endgroup$ – peterh says reinstate Monica Jun 1 '17 at 23:36
  • $\begingroup$ @peterh I saw that you made a good answer, I just added my comment as a side note. Maybe it's totally irrelevant, but I got a feeling that he might be interested. $\endgroup$ – Ismasou Jun 1 '17 at 23:41
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The main thing to say is that 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. So this answers most of your question.

Some further points are worth adding.

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.

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).

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Light is electromagnetic radiation and has different frequencies. "Glow" that humans could see would need to be in the visible spectrum and not infrared for example. It is true that particle-antiparticle pair combination produces photons but their energy might not be high enough to be visible to us. That is an example of mass converting to energy. The opposite can also be true and photons can break down into particle-antiparticle pairs which could theoretically be separated at the black hole horizon. When you say "normal universe away from black hole" I assume you mean in the vacuum of space. The fact is that even though these interactions are happening they aren't in a high enough concentration for us to notice. Bear in mind these we are talking about particles on an incredible tiny scale. If I gave you a tiny portion of one grain of sugar you might not even be able to detect it on your tongue and that would still be much much larger than single photons.

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