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

Confining a photon to form a black hole

  1. May 12, 2008 #1
    How small a box can you confine a photon to before its mass is large enough to form a black hole?

    I think you can make an estimate on the momentum (and therefore the energy) based on the size of the box using the Uncertainty Principle - knowing the energy gives you the mass via E=mc^2, but how do you figure out the mass and size needed to form the black hole?
  2. jcsd
  3. May 12, 2008 #2
    That would be the Schwartzchild Radius, given by:


    Use E=hf and E=mc^2 to figure out the Schwartzchild radius for a photon of a given frequency.
  4. May 12, 2008 #3
    Hi Bernarami,

    The minimum frequency that a photon must have so that energy of the photon confined within its own wavelength has sufficient energy density to form a black hole is 1/(2Tp) where Tp is the Planck time interval. The wavelength of such a photon would be 2Lp where Lp is the Planck length and the mass equivalent of the photon energy would be Mp/2 where Mp is the Planck mass. Using the equation for the Schwarzschild radius of a black hole (R=2GM/c&2) the radius of the black hole photon would be GMp/c^2 = Lp and diameter would be the wavelength of the photon which would satisfy the conditions required for a stable standing wave.

    Ref: http://en.wikipedia.org/wiki/Planck_units
    Last edited: May 12, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook