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Hawking Radiation


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In every reader friendly explanation of how black holes can effectively give off radiation by pulling in spontaneously appearing negative particles, thereby freeing the equal but opposite positive particle, I get stuck on...

...why the black hole doesn't pull in an equal number of positive particles thereby cancelling the whole thing out. Clearly I'm missing something. Please help :)

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When in the vicinity of a black hole, the vacuum creates a pair of virtual particles (like an electron and a positron), it does so on borrowed energy. The energy is returned when the particles annihilate each other.

The situation changes when a black hole captures one of the two particles.  By doing so, it makes the pair a real particle pair, rather than a virtual pair. That costs energy. The black hole loses an amount of mass equal to the energy that it takes for the particle pair to be formed. One of the particles it gets to keep, the other one escapes. The black hole effectively loses a bit of mass in the form of the escaping particle. From a distance, the black hole seems to have spewed out a particle.

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Is the point in question though that this happens at the event horizon which is the point beyond which nothing can escape.

The virtual pair are created on the event horizon, one particle gets pulled into the black hole and the other is just able to escape.

Sent from my iPhone using Tapatalk

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I get that there is no net gain for the Universe. My problem is with the fact that in every explanation I read, the black hole ends up only taking the anti particles. These cross the event horizon and destroy a particle already in the black hole, balancing the equation. The newly minted particle outside the event horizon steams away as Hawking radiation.

So my question is this: why only take anti particles? If it's random equal numbers of positive and negatives will fall in as be freed. The net result is no change and no radiation.

I'm not questioning the clever science, just the incomplete explanations btw.

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You changed the terms of reference !

You started by asking

"spontaneously appearing negative particles, thereby freeing the equal but opposite positive particle,"

It does not, it randomly takes one or other of the spontaneous particles. It does not mind which it takes, just the one that happens to be created heading towards the bh.

Then you said

"ends up only taking the anti particles"

Yes, a pair of particles is created, each is the anti-  of the other, one is taken the other escapes.

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Oh, come on. Arnie is just confused by what he reads and he wants to understand better.

Arnie, 

I see what you mean, the black hole can eat either particle of any virtual pair. Statistically it will eat as many positively charged particles as negatively charged ones. It's almost completely random.

Almost completely random, because if the black hole becomes charged, say negatively, the positively charged halves of virtual particles will have a slighter bigger chance of being captured, which brings the black hole closer to being neutral again.

You know, what you read are actually metaphors that try to describe a model in understandable terms. The reason of the metaphor here is explaining how the black hole gets lighter by eating half a particle pair. Lot's of writers struggle with this one.

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Okay, sorry. I thought you were complaining about the OP not understanding. That seemed harsh to me. Of course I misunderstood you.

I see what you mean :) sorry, didnt mean to be harsh.

No, I was just trying to say it was not to do with positive or negative

and _then_ not to do with anti- anything  ,  either,  just chance.

It is a poor thing this text stuff and language and all :)  **

Anyway, Arnie : how are we doing so far ? Have we confused you :) helped you any more,

ask away if not :) :)

** I was about to go to Qualia's thread on "Questions of origin"

which hinges on language "A universe" or "the Universe"

Perhaps I'll leave that till tomorrow :) :) !!

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Seems to me that those 2nd hand writers may not be helpful to understand whenyou can take it from the master himself :-)

Seems to me that  :)

someone comes askin a question, twould be rude to send him away to RTFM !  **

Anyway, who was it once said " if you cant explain it then you probably dont unnerstand it "

So are you saying that us 2nd chickens dont understand it well enough ?

Heee :) :) :) :) you could be right there  ( caveat : I cant speak for BigMak and Ruud ;) )

It would be a very quiet forum if all the answers were " GoTo . . . press handset 1) Newton 2) Einstein

On the other hand one might wonder why one bothers if it results in all this noise ?

Personally, I find it educational to say my piece, then someone says " Ah but no cos you forgot the such&such" and I can then say "ah yes, I had not thought of that " etc  [not often though :) heeeee ]

** seems to me ! that he might already have tried that and hence why he is here asking these , , , ?!

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Dont worry :) no prob :) I was taking a liberty ;)

That was why I included a liberal sprinkling of "Heeee" and " :) :) :) "

and also the "chicken" appended to the 2nd ;)

All good fun,

mind-u I did read a fair bit of Hawking, but I stll could not explain his "imaginary time" axis !!

so if someone could do that bit for me ? , , , ,

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