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Assume a photon enters the event horizon of a black hole. The gravity of the black hole will draw the photon into the singularity eventually. Doesn't the photon come to rest and therefore lose it's mass?

Qmechanic
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Kent Byerley
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  • I will let someone with a better knowledge of GR provide a full answer, but I will point out that a photon does not have mass in the first place so cannot lose it. – AdamRedwine Jan 20 '12 at 17:44
  • From reading on this site about photons: they have zero mass at rest, but they acquire mass (therefore effected by gravity) when in motion. – Kent Byerley Jan 20 '12 at 17:47
  • Okay, I can see that. My recollection is that photon mass due to motion is simply refered to in terms of the associated momentum since this is what is actually measured. – AdamRedwine Jan 20 '12 at 18:16
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    Photons have zero mass, period. They do have a nonzero amount of energy, because of their momentum. Also, photons never come to rest; they always move at speed $c$. – David Z Jan 20 '12 at 18:45
  • @DavidZaslavsky: light travels at speed $c$ in a vacuum, but not in a medium (hence the refractive index). Photons are halted in optical computing. I guess a black hole is not a vacuum? – Ramashalanka Jan 20 '12 at 19:12
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    @Ramashalanka: the reason light appears not to move at speed $c$ in materials is the time-averaged effect of interactions with the electron states of the material, not some fundamental change in the physics of EM waves. The important fact is that the medium doesn't create a rest frame for a photon. Also, a theoretical black hole is a (quantum) vacuum, except at the singularity. – David Z Jan 20 '12 at 19:16
  • The singularity is not a point in spacetime, the photon's path will just end on the singularity, and something else might come out. The question does require a full quantum gravity, but for gravitons scattering off model black holes, there are calculations in the literature. – Ron Maimon Jan 20 '12 at 23:44
  • Special Relativity tells us that 'true' mass is 'mass at rest' multiplied by lorentz factor (http://en.wikipedia.org/wiki/Lorentz_factor) - a result of this is that anything with a mass other than zero (at speed=0) will have infinite mass at speed c. So photons cant have any mass. –  Mar 20 '13 at 19:40
  • Why do you think the photon will come to rest when it reaches singularity? – shortstheory Oct 21 '13 at 10:24

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We don't know what will happen when a photon or any other particle hits a singularity of a black hole. The singularity is a phenomenon of classical general relativity and the singularity is really is an indication that classical general relativity breaks down there. To really understand what happens near a singularity we need a full quantum mechanical version of general relativity. String theory is the best quantum mechanical version of general relativity that we currently have but string theory is not developed enough to give a definitive answer to your question.

FrankH
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Meh, no string theory or singularity or unitology etc. Black Holes are accelerators. Every particle is broken down to the lowest level, accelerated to the highest speed and shot out. The path is non-vectorial, because the exitement of such magnitude makes the low-level particles act as "quantum binded particles". Which means, for every exited particle, there is another particle, it communicates. Through this binding efect, both particles and their respective "anti or dark matter" particles interact and lose energy. they slow down and under the rule of conservation of mass, stick together again. Far far away. the thing here is to think of binded particles as identical, reformable parts, rather than individual particles whizzing about.

Thats why general physics and traditional laws of nature break down in a black hole. Because the respective laws only go down as far as neutrons and protons.

Quarks, leptons, bosons, muons, tauonic particles etc.

Once we reach the bottom, we figure out the black holes. Until then, its all classical mechanics...on a cosmic scale :)

peter
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