Timeline for Is there a medium less dense than vacuum, in which light can travel faster than $c$?
Current License: CC BY-SA 4.0
8 events
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| Nov 7, 2018 at 22:15 | comment | added | AmbretteOrrisey | Still, though it might not be an absolute truth that group velocity <c, I did find it instructive to observe how, in a scenario of waves propagating linearly with a 'spread' of freqencies, the phase veloctity ̸ω/k was greater than c because of sub-unitic refractive index, whereas the pulse travelling with the group velicity dω/dk was travelling at speed <c. In this scenario, the speed of the pulse was the speed of information-travel, and the principle of absolute maximum speed was epitomised, in that the phase velocity was the speed of wave absolutely steady therefore sansform. | |
| Nov 7, 2018 at 21:49 | comment | added | Peter Diehr | but in my answer I chose to stay away from the concepts of phase and group velocity, because they are not required to answer the original question as asked. As an experimental laser physicist, I prefer to give answers that can be explained with simple experiments. | |
| Nov 7, 2018 at 21:47 | comment | added | Peter Diehr | Group velocity greater than c occurs under some conditions; see en.wikipedia.org/wiki/…. | |
| Nov 7, 2018 at 13:13 | comment | added | AmbretteOrrisey | Yep that's effectively what I'm getting at there, arguing that information cinveyance is essentially bound-up with a change of the signal: and that howsoever slight the change might be, it always incurs a group velocity of less than $c$. | |
| Nov 7, 2018 at 12:09 | comment | added | Peter Diehr | the phase velocity can be greater than c, but information never travels faster than c. | |
| Nov 5, 2018 at 1:06 | history | edited | AmbretteOrrisey | CC BY-SA 4.0 |
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| Nov 5, 2018 at 0:53 | history | edited | AmbretteOrrisey | CC BY-SA 4.0 |
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| Nov 5, 2018 at 0:46 | history | answered | AmbretteOrrisey | CC BY-SA 4.0 |