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Virtual pair production - black holes

  1. Jun 29, 2005 #1
    this is about particle antiparticle pairs being produced outside the event horizon of black hole. this is what i know about it:
    we know that a black hole has entropy. it therefore must have temperature and hence must radiate. however, a black hole is defined as a body which pulls in everything inside its event horizon. the explanation i know is -- virtual matter - antimatter pairs are produced for a short while, one of the particles with positive energy and the other with negative energy(Hiesenberg's uncertainty principle allows such pairs to be formed for a short time) the one with positive energy escape and the other enters the black hole and thus reduces its mass.

    however, this is what i read about it in a website:

    "Consider a virtual electron-positron pair produced just outside the event horizon. Once the pair is created, the intense curvature of spacetime of the black hole can put energy into the pair. Thus the pair can become non-virtual; the electron does not fall back into the hole. There are many possible fates for the pair. Consider one of them: the positron falls into the black hole and the electron escapes. According to Feynman's view we can describe this as follows:

    The electron crosses the event horizon travelling backwards in time, scatters, and then radiates away from the black hole travelling forwards in time."

    i cant understand it. what are they trying to say. its going over my head. pls tell me, which one is correct.

    Also, if my view is correct, then could this be the reason we have more matter than antimatter in the universe. i believe matter and antimatter were created in equal quantities at the big bang. it could be possible that 'matter' usually has a higher probability of obtaining positive energy.
  2. jcsd
  3. Jun 29, 2005 #2
    Just do a search for virtual particles, on this forum or check out my journal. This topic has been dicussed many times here.

  4. Jun 29, 2005 #3
    Antimatter particles (such as positrons) look just like their matter equivilents (such as electrons) moving backwards in time. Check out Feynman's book QED for a better explanation than I can attempt to recapitulate. I raised a question on Feynman's interpretation of pair creation/annihilation and got mixed responses, so don't take it as gospel.

    In this instance, what appears to use like an electron-positron pair being created on the event horizon, with the positron falling into the hole and the electron escaping, may actually be a single electron coming out of the black hole backwards in time (so it looks like a positron falling into the hole), scattering, then continuing out from the event horizon forwards in time (so now it looks to us like an electron).

    Another view might be that of a positron moving towards the hole backwards in time (so it looks like an electron coming away from it), scattering, then falling into the black hole forwards in time.

    In this approach, it is arbitrary which particle, the electron or the positron, is considered to be itself moving forwards in time.
  5. Jun 30, 2005 #4

    George Jones

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    I don't think this is the mechanism responsible for there being more matter than antimatter. When virtual matter-antimatter pairs are created, the probability that the antimatter particle has positive energy is equal to the probability that the matter particle has positive energy, i.e., both probalilities are 1/2.

    Hawking radiation does not come about because antimatter particles sometimes fall into black holes; it comes about because negative-energy particles (both matter and animatter) sometimes fall into black holes. Some popular-level treatments of black holes obscure this, and even sometime get this completely wrong.

    Sometimes it is difficult to give accurate non-mathematical descriptions of processes that involve advanced physics. This is particularly true for Hawking radiation - it is very hard to see the correspondence between the non-mathematical description involving virtual matter-animatter pairs and the actual mathematical description.

    Steve Carlip is a physicist who tries hard to make physical concepts clear, both for laypersons and for experts. You should read his non-mathematical description of Hawking radiation, which is more challenging than most non-mathematical descriptions, but which also is more accurate than most non-mathematical descriptions. If you have questions about his description, just post them.

    What happens, very roughly, is this. Energy is associated with time and spatial momentum is associated with space. When an matter-antimatter pair of virtual particles is created *outside* the event horizon, they can become a little bit separated in the time that the Heisenberg uncertainty principle allows them to live. Tidal forces caused by the curvature of spacetime help them to separate, and, sometimes, the negative-energy particle (which could be either matter or anitimatter) wanders over the event horizon and into the black hole. Inside the event horizon, the roles of time and space coordinates get interchanged. Thus, according to what I wrote above, the roles of energy and spatial momentum get interchanged. What was negative energy becomes a negative spatial component of a local (for an observer inside the horizon) momentum vector. Only a virtual particle can have negative energy, while any particle, real or virtual, can have a negative component of spatial momentum.

    Bottom line: the whole process can become a real process. In this real process, an observer outside a black hole "sees" the black hole hole swallow a negative-energy particle while emiitting a positve energy particle (the other member of the matter-antmatter pair). The balck hole radiates.

  6. Jun 30, 2005 #5
    thnks, George, ur site helped me understand a lot.
  7. Mar 8, 2008 #6
    thanks a lot for that ! but i hav heard that this matter antimatter pair is created because of fluctuations caused by the field of the blackhole. but which field gravitational or magnetic ? dats the question. how can matter be created. does this have a relation vit the space vortex theory ?
  8. Mar 8, 2008 #7
    tahnks ! i got it !
  9. May 22, 2009 #8
    But if the matter particle (of the matter-antimatter pair) is created close to the black holes event horizon, wouldn't it just fall in. Doesn't it has mass?
    Wouldn't it need to have a speed equal to the speed of light to escape the black hole?
    If it doesn't have mass, how can it have an anti-particle? And why would tidal forces effect it?
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