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

Practical possibility of Hawking radiation?

  1. Jan 29, 2010 #1
    i have long been a skeptic of hawking radiation. i would like to explore my concerns, and see what your reaction is.

    the concept hinges around the idea of a spontaneous particle pair being created somewhere near the EH of a BH. radiation would occur if one of the particles manages to escape falling into the BH, while the other does not escape. further, the particle which does not escape, MUST be a negative energy particle. (i will not attempt to deal with the "negative energy" aspect of the problem here, since i do not understand what negative energy, being measured at infinity, can mean... it seems like the question would be, does it have negative energy in relation to the BH, which i do no see how it can - but, again, i will avoid that confusion here.)

    when a spontaneous particle pair is created, the two particles (particle and anti-particle) must essentially share the same momentum and velocity, traveling basically side-by side for a period of time less than allowed by the HUP, and then combine and annihilate. is that correct?

    for all practical purposes, then, you have essentially two particles with essetially the same characteristics as far as the BH is concerned - two particles which have identical mass/energy (though one is anti), same velocity/momentum, same position in spacetime in realtion to the BH, and both near the EH of a BH.

    anywhere near the EH of a BH, a particle would need to have a near-C speed to allow it ANY possibility of escaping the gravity fo the BH. if, indeed, spontaneous particle pairs can possibly be created with near-C speeds, by what mechanism could one escape while the other does not? if particle pairs are not created with near-C speed, by what mechanism could one possibly escape while the other does not?

    it seems to me that, given the near-identical characteristics of particle pairs mentioned above, if one escapes so will the other, and if one is close enough to the EH to be affected, so would the other - because the differences in their location, speed, momentum, etc are insignificant in relation to the gravitational field of the BH.

    yes, i understand that my argument here is somewhat specious and based on a lack of knowledge about many things. please explain to me where i am misunderstanding this. thanks.
  2. jcsd
  3. Jan 29, 2010 #2


    User Avatar
    Science Advisor
    Gold Member

    I think the typical process is that the created particle become physical long enough to radiate a photon or two before being pulled back into the BH. So the original positive energy half of the virtual pair needn't get all the way out to infinity, it need only manifest outside the BH long enough to radiate a photon (losing some energy) so that when it plus its negative virtual partner recombine inside they have less than zero total energy (the energy which escaped via the photon). That gets subtracted from the BH's mass.

    It may also help to keep in mind that these fluctuations do not transmit signals from inside to outside. The causal one-way street is still uncompromised.
  4. Jan 30, 2010 #3


    User Avatar
    Science Advisor

    I should mention that Hawking Radiation can be derived in a large variety of different ways, and so seems quite robust as a result.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook