3 ms·

> it just takes time to ping-pong around a lattice/gas. Photons hit particles, get absorbed, and re-emitted Well, actually the speed of light, specifically th

by Bjartr 6y ago

> it just takes time to ping-pong around a lattice/gas. Photons hit particles, get absorbed, and re-emitted Well, actually the speed of light, specifically the rate of propagation or phase velocity, is not slower in mediums because of absorption and re-emittance. Instead, a photon is affected by feedback loops between its oscillating electric field and the charges of atoms it is passing near, without being actually absorbed by the atoms. Paraphrased as best I could from: https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation https://en.wikipedia.org/wiki/Refractive_index#Microscopic_e...

randallsquared 6y ago
Okay, but I would expect the main takeaway is that, for the purposes of things like tachyons and black holes and CTCs, the "speed of light" is still c, not whatever speed one measures in various non-vacuums. The only assertion of which I'm aware that the apparent speed of light in a medium is what really matters for relativity was Ron Mallet's work: https://www.phys.uconn.edu/~mallett/main/papers.htm https://www.phys.uconn.edu/~mallett/main/papers.htm . I don't believe there's been any experimental confirmation of it, though.
marcosdumay 6y ago
Whatever way you cut it, the photons themselves can not run in any speed that is not c. Besides, electromagnetic interaction is modeled as emission and absorption of photons on a small enough scale. You are just using a population simplification to dismiss the individual based analysis (what would be pretty reasonable because the later one is meaningless when you can't observe individuals, except that the entire point is pedantic, and pedantism can't be subject to dismissal by meaninglessness).
- cygx 6y ago
  It doesn't work the way you imagine. Cf. http://dx.doi.org/10.1103/PhysRevLett.68.2421 http://dx.doi.org/10.1103/PhysRevLett.68.2421

by Bjartr 6y ago

randallsquared 6y ago

Okay, but I would expect the main takeaway is that, for the purposes of things like tachyons and black holes and CTCs, the "speed of light" is still c, not whatever speed one measures in various non-vacuums. The only assertion of which I'm aware that the apparent speed of light in a medium is what really matters for relativity was Ron Mallet's work: https://www.phys.uconn.edu/~mallett/main/papers.htm https://www.phys.uconn.edu/~mallett/main/papers.htm . I don't believe there's been any experimental confirmation of it, though.

marcosdumay 6y ago

Whatever way you cut it, the photons themselves can not run in any speed that is not c. Besides, electromagnetic interaction is modeled as emission and absorption of photons on a small enough scale. You are just using a population simplification to dismiss the individual based analysis (what would be pretty reasonable because the later one is meaningless when you can't observe individuals, except that the entire point is pedantic, and pedantism can't be subject to dismissal by meaninglessness).

cygx 6y ago
It doesn't work the way you imagine. Cf. http://dx.doi.org/10.1103/PhysRevLett.68.2421 http://dx.doi.org/10.1103/PhysRevLett.68.2421