5 ms·

I'm certainly misunderstanding something (considering they did it), but what I don't understand here is how the change of state of the crystal could have spread

by guizzy 13y ago

I'm certainly misunderstanding something (considering they did it), but what I don't understand here is how the change of state of the crystal could have spread faster than light could escape the crystal. Is the information spreading faster than the speed of light in that case?

kbenson 13y ago
Maybe they had multiple lasers arrayed around the outside to cause the condition of the crystal, and stopped them all at the same time while the light was in or approaching the center of the crystal (allowing for time for change to begin). Wouldn't the state change start at the outsides and move in? I really have no idea whether you can actually reason about this stuff like that...
john_b 13y ago
I'm not a physicist and the paper is paywalled so I'm speculating, but the speed of light in this crystal is probably much lower than the speed of light in a vacuum, and it's the latter that puts an uppper limit on the rate at which information can propagate (excluding quantum entanglement).
- TeMPOraL 13y ago
  > excluding quantum entanglement IANAP either, but AFAIK (ah, acronyms :)) quantum entanglement can not transfer information FTL.
  - alcari 13y ago
    I'm also not a physicist, but as I understand it entangled particles can affect each other instantaneously regardless of distance, but cannot transfer information due to random instabilities.
    - nbouscal 13y ago
      IIRC it's not due to random instabilities, but rather due to the no cloning theorem: http://en.wikipedia.org/wiki/No-cloning_theorem http://en.wikipedia.org/wiki/No-cloning_theorem
TeMPOraL 13y ago
Maybe because speed of light in the crystal is slower than speed of light in the vacuum (the latter being the theoretical limit for speed of information transfer)? AFAIR light traveling through material is not just flying through; it's constantly absorbed and reemited - thus "slowing down".
possibilistic 13y ago
I'm a biochemist, not a physicist, but I have had some quantum chemistry. Here's my (probably incorrect) thinking: Light passing through the "open state" crystal may travel significantly slower due to interaction/absorbance with the crystal atoms along the beam path. Energy injection from the lasers is probably necessary for maintenance of the "open state", and as soon as the laser is shut off there may remain photons that are being absorbed/emitted by the atoms in the crystal lattice. When the crystal is in the "closed state", the photons will be "trapped" (continuous absorption or non-emission or something?). It's all about quantized energy levels. At certain energies, the atoms will interact differently. Someone please correct my thinking here.
- rolleiflex 13y ago
  A question for you since you seem to know about light in media: my understanding is that the speed of light is also the speed events propagate through spacetime. So, considering a galaxy made entirely out of pure crystalline diamond, would events propagate slower in that galaxy? In other words, does time itself slow down under those circumstances, does it not change? It could also be that the speed of light is constrained by the speed events propagate through spacetime and not the other way around, but I am most probably thoroughly confused.
  - eru 13y ago
    > So, considering a galaxy made entirely out of pure crystalline diamond, would events propagate slower in that galaxy? In other words, does time itself slow down under those circumstances, does it not change? It doesn't change. See e.g. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation where electrons travel faster than the speed of light in a specific medium.

by guizzy 13y ago

kbenson 13y ago

Maybe they had multiple lasers arrayed around the outside to cause the condition of the crystal, and stopped them all at the same time while the light was in or approaching the center of the crystal (allowing for time for change to begin). Wouldn't the state change start at the outsides and move in? I really have no idea whether you can actually reason about this stuff like that...

john_b 13y ago

I'm not a physicist and the paper is paywalled so I'm speculating, but the speed of light in this crystal is probably much lower than the speed of light in a vacuum, and it's the latter that puts an uppper limit on the rate at which information can propagate (excluding quantum entanglement).

TeMPOraL 13y ago
> excluding quantum entanglement IANAP either, but AFAIK (ah, acronyms :)) quantum entanglement can not transfer information FTL.
- alcari 13y ago
  I'm also not a physicist, but as I understand it entangled particles can affect each other instantaneously regardless of distance, but cannot transfer information due to random instabilities.
  - nbouscal 13y ago
    IIRC it's not due to random instabilities, but rather due to the no cloning theorem: http://en.wikipedia.org/wiki/No-cloning_theorem http://en.wikipedia.org/wiki/No-cloning_theorem

TeMPOraL 13y ago

Maybe because speed of light in the crystal is slower than speed of light in the vacuum (the latter being the theoretical limit for speed of information transfer)? AFAIR light traveling through material is not just flying through; it's constantly absorbed and reemited - thus "slowing down".

possibilistic 13y ago

I'm a biochemist, not a physicist, but I have had some quantum chemistry. Here's my (probably incorrect) thinking: Light passing through the "open state" crystal may travel significantly slower due to interaction/absorbance with the crystal atoms along the beam path. Energy injection from the lasers is probably necessary for maintenance of the "open state", and as soon as the laser is shut off there may remain photons that are being absorbed/emitted by the atoms in the crystal lattice. When the crystal is in the "closed state", the photons will be "trapped" (continuous absorption or non-emission or something?). It's all about quantized energy levels. At certain energies, the atoms will interact differently. Someone please correct my thinking here.

rolleiflex 13y ago
A question for you since you seem to know about light in media: my understanding is that the speed of light is also the speed events propagate through spacetime. So, considering a galaxy made entirely out of pure crystalline diamond, would events propagate slower in that galaxy? In other words, does time itself slow down under those circumstances, does it not change? It could also be that the speed of light is constrained by the speed events propagate through spacetime and not the other way around, but I am most probably thoroughly confused.
- eru 13y ago
  > So, considering a galaxy made entirely out of pure crystalline diamond, would events propagate slower in that galaxy? In other words, does time itself slow down under those circumstances, does it not change? It doesn't change. See e.g. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation where electrons travel faster than the speed of light in a specific medium.