The Naked Scientists

The Naked Scientists Forum

Author Topic: Bose-Einstein condensates and lightspeed  (Read 4736 times)

Offline stevewillie

  • Sr. Member
  • ****
  • Posts: 120
    • View Profile
Bose-Einstein condensates and lightspeed
« on: 01/01/2009 21:42:28 »
Light has been shown to be slowed dramatically in Bose-Einstein condensates (BEC-a quantum state existing very close to absolute zero.) What does this say about lightspeed as a constant? How does this affect the interpretation of the Lorentz factor? Does time "stop" for a light beam moving at only a few cm/sec?


 

Offline Mr. Scientist

  • Neilep Level Member
  • ******
  • Posts: 1451
  • Thanked: 2 times
  • http://www.facebook.com/#/profile.php?ref=profile&
    • View Profile
    • Time Theory
Bose-Einstein condensates and lightspeed
« Reply #1 on: 02/01/2009 07:23:03 »
Lots of problems with your understanding of time and photons in general. Photons never slow down from their frame of references; this is because their frame of reference is frozen, as relative to all other frames of existence which can be experienced. A photon does not experiencea time, so time never stops for a photon, because it never began.

The speed of light is always constant, but because it can indeed move through as medium that can slow it down, so that is why we say a photon can be slowed down when passing through a material. It does not change however, the constant speed of the photon, because it will be found to leave a material at the same speed it entered i, which is around 186,350 miles per second.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Bose-Einstein condensates and lightspeed
« Reply #2 on: 02/01/2009 10:31:34 »
When light is "slowed down" it is essentially the same process that causes materials to have refractive indicies which imply a slower speed for light.  The photons are always travelling at light speed but are continually being absorbed and re-emitted unchanged with a Hisenberg related delay between absosbtion and re-emmission. so in effect they are "new" photons.
 

Offline stevewillie

  • Sr. Member
  • ****
  • Posts: 120
    • View Profile
Bose-Einstein condensates and lightspeed
« Reply #3 on: 02/01/2009 20:42:31 »
When light is "slowed down" it is essentially the same process that causes materials to have refractive indicies which imply a slower speed for light.  The photons are always travelling at light speed but are continually being absorbed and re-emitted unchanged with a Hisenberg related delay between absosbtion and re-emmission. so in effect they are "new" photons.

I agree with you in the case of ordinary matter, but what about Bose-Einstein condensates (BEC)? Here you have the merging of distinct quantum  probability waves into a condensate that can be described by a single elementary wave function. This is no ordinary state of matter. In recent experiments, you can actually see a light beam slowly moving through a patch of BEC. My question is, does your explanation apply here where the condensate may in some sense be considered a single "particle"?
« Last Edit: 02/01/2009 20:56:13 by stevewillie »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11987
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Bose-Einstein condensates and lightspeed
« Reply #4 on: 03/01/2009 11:39:24 »
I found a very nice description here, even if somewhat old.
http://www.physicstoday.org/pt/vol-49/iss-8/vol49no8p11-13.pdf
And here you have a more concise one.
http://guava.physics.uiuc.edu/~nigel/courses/563/Essays_2008/PDF/bian.pdf

But you are correct Steve, the BEC will behave as if all atoms were in the same quantum state.
It's very strange ( and cool :)

« Last Edit: 03/01/2009 11:48:21 by yor_on »
 

Offline stevewillie

  • Sr. Member
  • ****
  • Posts: 120
    • View Profile
Bose-Einstein condensates and lightspeed
« Reply #5 on: 03/01/2009 23:16:40 »
I found a very nice description here, even if somewhat old.
http://www.physicstoday.org/pt/vol-49/iss-8/vol49no8p11-13.pdf
And here you have a more concise one.
http://guava.physics.uiuc.edu/~nigel/courses/563/Essays_2008/PDF/bian.pdf

But you are correct Steve, the BEC will behave as if all atoms were in the same quantum state.
It's very strange ( and cool :)

Thanks for the references yor on. When you say BCEs are cool, you're not kidding, like a few pico-degrees Kelvin above absolute zero!

Stevewillie
« Last Edit: 05/01/2009 07:04:46 by stevewillie »
 

The Naked Scientists Forum

Bose-Einstein condensates and lightspeed
« Reply #5 on: 03/01/2009 23:16:40 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums