Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Hawking radiation

  1. Aug 29, 2016 #1
    I'm reading this article...

    "Hawking proposed that the Universe is filled with 'virtual particles' that, according to what we know about how quantum mechanics works, blink in and out of existence and annihilate each other as soon as they come in contact - except if they happen to appear on either side of a black hole's event horizon. Basically, one particle gets swallowed up by the black hole, and the other radiates away into space." Science Alert

    Even if that is true wouldn't that mean that there is one of the two particles trapped by the horizon? One particle being trapped and one escaping doesn't mean that the black hole is evaporating does it? It seems that there is a net gain of one particle adding to the mass of the black hole.

    Can someone explain the evaporation effect please as it relates to the virtual particle theory please?

  2. jcsd
  3. Aug 29, 2016 #2


    User Avatar

    Staff: Mentor

    That's right.

    Indeed it does.

    The issue is that the mass of both particles comes from the mass of the black hole. So if one particle gets sucked up and one escapes then the black hole loses mass equal to the mass of the particle that escaped.
  4. Aug 30, 2016 #3


    User Avatar
    Science Advisor
    Gold Member

    Agreed, but, the notion of negative mass being inhaled by a black hole has always struck me as one of those spooky entanglement things.
  5. Aug 30, 2016 #4

    Ken G

    User Avatar
    Gold Member

    Many say that the picture of Hawking radiation that it involves virtual particle pairs is not necessarily a useful way to think of Hawking radiation. Hawking only suggested it as a way of picturing what is happening, not to be taken too seriously. Of course, you will never find any subject about which experts disagree more vehemently than what goes on in the vicinity of an event horizon! And the number two area of disagreement is the status of virtual particles, so this one's a double whammy. In fact, given the incredibly tenuous nature of the observational status of Hawking radiation, I think that topic must be after some kind of record for greatest amount of expert disagreement for something that is both most widely heard about by the general public and least likely to ever actually be observed coming from a black hole!
  6. Aug 30, 2016 #5
    Is the event horizon so precise of a sphere that it can split a virtual particle into two one which goes inward and the other which escapes?

    Or is that a mid assumption on my part. If the sphere is fuzzy at its surface then it doesn't make sense to me.

  7. Aug 30, 2016 #6

    Ken G

    User Avatar
    Gold Member

    It sounds like the sphere can't be fuzzier than the distance scale over which the uncertainty principle allows the virtual particles to virtually exist. Basically, if E is the energy of the particles, then the reckoning comes in a time roughly h/E, and the distance travelled in that time is ch/E if the particles are relativistic (they're usually photons). T is often very low, so E is very low, so the distance could be rather long. But I don't know if there's any theory about the fuzziness of an event horizon.
  8. Aug 30, 2016 #7


    User Avatar
    Gold Member

    Hawking has said that this whole thing about "virtual particles" to explain what is now called Hawking Radiation is just the only way he could think of to explain in English something that really only makes sense in the math. That is, it's an analogy, not an actual description of what happens.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted