Photon in time versus photon not so much-ish in time

  • Thread starter Thread starter Sublite
  • Start date Start date
  • Tags Tags
    Photon Time
Sublite
Messages
2
Reaction score
0
Okay, second question I have to ask, again, hopefully not stupid. First, I've been perusing the forums and see the common question asked again and again, what's it like for a photon "experiencing" reality, and I totally agree or understand the standard answers: the math breaks down, we don't/can't know, the frame is invalid, but an electron moving at .99c would see such and such. The proper time for a photon is null and it travels through no space to arrive at its destination. So it has this null, or completely unextended, aspect. But within spacetime it's an energy/momentum transmitter, and acts as a carrier wave for information. Maybe this is a meaningless question, or perhaps my characterization is inaccurate, but does anybody have a good explanation for how this dual aspect works?

Again, thanks for any help.

C.
 
Physics news on Phys.org
It's a good questin. Part of the thinking about it should be "how long is a photon"? The answer is that it depends on the definiteness of it's energy. Most of us think a photon has a definite specific exact energy h*f. But this is only true for a photon that is extremely long in space. By the uncertainty relation it's possible to emit a photon over a very short period of time so that there is great uncertainty about it's energy. It's a "white photon". This white photon would have a very short spatial extent.

Back to your question, whether a photon has a very narrow energy or whether it is "white", it travels at c and doesn't experience time. To a photon there is no difference between traveling a millimeter or traveling 10 billion light years. You are right about null proper time but it has extent and that extent is embedded within a travel distance. Two circularly polarized photons of 300 MHz are sent into space. One hits the moon and twisted 402 million times. The other is still going and will twist uncounted times before it hits something distant but no proper time elapsed for either. It's difficult to imagine how this looks in the photons frame.
 
OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
ASSUMPTIONS 1. Two identical clocks A and B in the same inertial frame are stationary relative to each other a fixed distance L apart. Time passes at the same rate for both. 2. Both clocks are able to send/receive light signals and to write/read the send/receive times into signals. 3. The speed of light is anisotropic. METHOD 1. At time t[A1] and time t[B1], clock A sends a light signal to clock B. The clock B time is unknown to A. 2. Clock B receives the signal from A at time t[B2] and...
Back
Top