4 ms·

"From the photon perspective there is no passage of time" What exactly happens when light travels through denser medium? Speed is less than c, so does that mean

"From the photon perspective there is no passage of time" What exactly happens when light travels through denser medium? Speed is less than c, so does that mean it experiences time?

aaaaaaaaaaab 5y ago
https://en.wikipedia.org/wiki/Ewald–Oseen_extinction_theorem https://en.wikipedia.org/wiki/Ewald–Oseen_extinction_theorem
eptcyka 5y ago
It bounces around, thus not travelling in a straight line, thus covering more distance whilst still moving at c.
- jcims 5y ago
  My understanding, which could be wrong, is that it doesn't 'bounce around' as much as it is absorbed and re-emitted. This process isn't instantaneous and accounts for the net propagation delay through the medium.
  - monocasa 5y ago
    Sort of. Refraction it better looked at from a wave perspective than a particle one, IMO. The wavefront expands at the speed of light, but the wave bounces off of the medium it's traveling through and self interacts in a way that means that the highest probability area moves slower than C despite the edge of the wavefront still moving at C. That smearing is also why the wavelength changes upon refraction. (And obviously leaving concepts like time dilation off the table for simplicity's sake).
  - wruza 5y ago
    Both ideas are incorrect. Bouncing around would be random and the outgoing light would be scattered (as in matte reflections) in all directions. Absorbtion simply destroys the original light. If photons are mostly absorbed, we call that “a wall” or ”a fog”, not “a transparent medium”, which to be transparent shouldn’t have electrons whose energy level differences correspond to a photon’s wave length. The transparency and slowdown effect is a complex interaction between fields in the medium, which I honestly don’t have enough courage to retell. https://youtube.com/watch?v=CiHN0ZWE5bk https://youtube.com/watch?v=CiHN0ZWE5bk
- cygx 5y ago
  That would imply light getting scattered willy-nilly as it crosses any medium, which it isn't in case of transparent media...
  - monocasa 5y ago
    There's no perfectly transparent media other than pure vacuum.
gumby 5y ago
> Speed is less than c, so does that mean it experiences time? There is no absolute clock in the world; we can only know about what happened where and when by looking. A way to understand this (and special relativity) is from an information-theoretic perspective, and to think of c as the “Mach number” of free space, nothing more and nothing less. So imagine that you couldn’t see but could only know about what happened where and when by hearing. All those phenomena (foreshortening, frequency shift, apparent time dilation) would be exhibited though the speed of information travel would be much lower. You have probably experienced the equivalent of blue shift/red shift yourself by listening to a high speed vehicle. Change the medium from ordinary air to something with a different density and all these phenomena will be detectable, even though the speed of sound will be different.
whatshisface 5y ago
There are two pictures that you could take of the situation. Classically, where the medium is smooth continuous stuff with a permeability and a permittivity, there are no photons, only waves. Quantum mechanically, where the medium is made up of lots of little particles, there are photons indeed, but no smooth medium, and no region where the speed is less than C (because there is no "region," only lots of separate particles). So there's one picture missing "photons," and the other missing "speed less than c," so you can't capture "photons in a region where the speed is less than c," in a single image. I guess if you wanted to pose that question in a framework where a medium where the speed was less than c, and photons, could exist simultaneously, you would want an effective field theory (maybe). But you will have to get someone else who knows more than me to explain that. :-)

"From the photon perspective there is no passage of time" What exactly happens when light travels through denser medium? Speed is less than c, so does that mean it experiences time?

aaaaaaaaaaab 5y ago

https://en.wikipedia.org/wiki/Ewald–Oseen_extinction_theorem https://en.wikipedia.org/wiki/Ewald–Oseen_extinction_theorem

eptcyka 5y ago

It bounces around, thus not travelling in a straight line, thus covering more distance whilst still moving at c.

jcims 5y ago
My understanding, which could be wrong, is that it doesn't 'bounce around' as much as it is absorbed and re-emitted. This process isn't instantaneous and accounts for the net propagation delay through the medium.
- monocasa 5y ago
  Sort of. Refraction it better looked at from a wave perspective than a particle one, IMO. The wavefront expands at the speed of light, but the wave bounces off of the medium it's traveling through and self interacts in a way that means that the highest probability area moves slower than C despite the edge of the wavefront still moving at C. That smearing is also why the wavelength changes upon refraction. (And obviously leaving concepts like time dilation off the table for simplicity's sake).
- wruza 5y ago
  Both ideas are incorrect. Bouncing around would be random and the outgoing light would be scattered (as in matte reflections) in all directions. Absorbtion simply destroys the original light. If photons are mostly absorbed, we call that “a wall” or ”a fog”, not “a transparent medium”, which to be transparent shouldn’t have electrons whose energy level differences correspond to a photon’s wave length. The transparency and slowdown effect is a complex interaction between fields in the medium, which I honestly don’t have enough courage to retell. https://youtube.com/watch?v=CiHN0ZWE5bk https://youtube.com/watch?v=CiHN0ZWE5bk
cygx 5y ago
That would imply light getting scattered willy-nilly as it crosses any medium, which it isn't in case of transparent media...
- monocasa 5y ago
  There's no perfectly transparent media other than pure vacuum.

gumby 5y ago

> Speed is less than c, so does that mean it experiences time? There is no absolute clock in the world; we can only know about what happened where and when by looking. A way to understand this (and special relativity) is from an information-theoretic perspective, and to think of c as the “Mach number” of free space, nothing more and nothing less. So imagine that you couldn’t see but could only know about what happened where and when by hearing. All those phenomena (foreshortening, frequency shift, apparent time dilation) would be exhibited though the speed of information travel would be much lower. You have probably experienced the equivalent of blue shift/red shift yourself by listening to a high speed vehicle. Change the medium from ordinary air to something with a different density and all these phenomena will be detectable, even though the speed of sound will be different.

whatshisface 5y ago

There are two pictures that you could take of the situation. Classically, where the medium is smooth continuous stuff with a permeability and a permittivity, there are no photons, only waves. Quantum mechanically, where the medium is made up of lots of little particles, there are photons indeed, but no smooth medium, and no region where the speed is less than C (because there is no "region," only lots of separate particles). So there's one picture missing "photons," and the other missing "speed less than c," so you can't capture "photons in a region where the speed is less than c," in a single image. I guess if you wanted to pose that question in a framework where a medium where the speed was less than c, and photons, could exist simultaneously, you would want an effective field theory (maybe). But you will have to get someone else who knows more than me to explain that. :-)