crazynutsx Posted June 9, 2011 Posted June 9, 2011 scientists have now slowed light down to a speed of 32 mph in the lab under controlled conditions using low temperatures in a vaccume They then went onto make it stop completely Does this prove realitiviy is not correct ?
ajb Posted June 9, 2011 Posted June 9, 2011 scientists have now slowed light down to a speed of 32 mph in the lab under controlled conditions using low temperatures in a vaccume In vacuum? This is a mistake, you mean in some medium? Can you provide a reference? Does this prove realitiviy is not correct ? This does not violate special relativity at all, but you need to point us towards the original work to make a proper statment. 1
crazynutsx Posted June 9, 2011 Author Posted June 9, 2011 take a look see at this article http://news.harvard.edu/gazette/1999/02.18/light.html
ajb Posted June 9, 2011 Posted June 9, 2011 Ok so not in vacuum (and this is not exactly new news). There is no violation of special relativity. 1
crazynutsx Posted June 9, 2011 Author Posted June 9, 2011 could you explain why you think it dosent violate realitivity please
ajb Posted June 9, 2011 Posted June 9, 2011 could you explain why you think it dosent violate realitivity please Because the light is not propagating in vacuum. There is nothing in special relativity that states that light cannot be slowed down when travelling in a medium.
mississippichem Posted June 9, 2011 Posted June 9, 2011 The speed of light in some medium is given by: [math] v= \frac{c}{n} [/math], where [math] c [/math] is the speed of light in a vacuum (the one that never changes) and [math] n [/math] is the refractive index of the medium. This is by no means new and is taught in freshman physics classes everywhere.
Janus Posted June 9, 2011 Posted June 9, 2011 could you explain why you think it dosent violate realitivity please You have to understand what happens when light passes through a medium. Imagine a single photon making its way through the medium. When it incounters a molecule it is absorbed an stored as energy by by the molecule (during which time the photon does not exist. After a brief delay, the molecule gets rid of the extra energy by emitting a new photon, which continues along its way until it encounters another molecule. While it travels from molecule to molecule, it travels at c. If you time how long it takes from the moment the first photon enters the material until one comes out the other side it will be longer than the time it would take a photon to cross the same distance at c. This is because all those little delays between the absorption and emission of photons by the molecules add up. This makes the the apparent speed of light through the medium to be less than c. What the experiment has done is use special mediums in which this delay has been extended by a large amount. In the "stopping light" example the delay is indefinite. The molecules holds one to their extra energy until the experimenters "give them a kick" causing them to release it as emitted photons. The photons (when they exist) still always travel at c.
mathematic Posted June 9, 2011 Posted June 9, 2011 An interesting aside is Cerenkov radiation, where particles going close to the speed of light enter a medium, where the speed of light is slower than the particle speed. The particle will give off radiation in a shape that resembles the shock waves off a supersonic aircraft.
ydoaPs Posted June 10, 2011 Posted June 10, 2011 They didn't actually slow down the light. The light travelled at c the entire time. It just got absorbed and re-emitted several times. Since there is a delay between the absorption and the re-emission, the net effect is that the light seems to have slowed down as the pulse took longer than c to reach the destination. Poor journalists mistake this for slowing light.
swansont Posted June 10, 2011 Posted June 10, 2011 They didn't actually slow down the light. The light travelled at c the entire time. It just got absorbed and re-emitted several times. Since there is a delay between the absorption and the re-emission, the net effect is that the light seems to have slowed down as the pulse took longer than c to reach the destination. Poor journalists mistake this for slowing light. Even worse is "stopped light," where the photons are absorbed in a real state for an arbitrary length of time. Instead of "they didn't slow the light" I prefer to say it didn't slow down the photons, since I think that's a more precise description. Regardless, it doesn't violate relativity, and trivially so. The speed of light in a vacuum was not changed as the interaction was with something that was decidedly not a vacuum.
Moontanman Posted June 10, 2011 Posted June 10, 2011 Reminds me of a book about something called slow glass, great stuff, lets you see back in time....
regan Posted June 24, 2011 Posted June 24, 2011 You have to understand what happens when light passes through a medium. Imagine a single photon making its way through the medium. When it incounters a molecule it is absorbed an stored as energy by by the molecule (during which time the photon does not exist. After a brief delay, the molecule gets rid of the extra energy by emitting a new photon, which continues along its way until it encounters another molecule. While it travels from molecule to molecule, it travels at c. If you time how long it takes from the moment the first photon enters the material until one comes out the other side it will be longer than the time it would take a photon to cross the same distance at c. This is because all those little delays between the absorption and emission of photons by the molecules add up. This makes the the apparent speed of light through the medium to be less than c. What the experiment has done is use special mediums in which this delay has been extended by a large amount. In the "stopping light" example the delay is indefinite. The molecules holds one to their extra energy until the experimenters "give them a kick" causing them to release it as emitted photons. The photons (when they exist) still always travel at c. So when light travels through a certain medium it is not the original light that passes out of the other side but the product of the absorbtion of light that passes?
swansont Posted June 24, 2011 Posted June 24, 2011 So when light travels through a certain medium it is not the original light that passes out of the other side but the product of the absorbtion of light that passes? That's the QM model, but the photons are identical; you can't tell if it's the same photon or not.
Hal. Posted June 24, 2011 Posted June 24, 2011 Does the presence of a photon in a vacuum itself invalidate the vacuum ? What is the speed of a photon in a photon ? Is that ridiculous ?
Janus Posted June 24, 2011 Posted June 24, 2011 (edited) Does the presence of a photon in a vacuum itself invalidate the vacuum ? What is the speed of a photon in a photon ? Is that ridiculous ? Photons do not interact with each other, so to a photon, space filled with other photons behaves just like space filled with nothing. Edited June 24, 2011 by Janus
Hal. Posted June 24, 2011 Posted June 24, 2011 Supposing , photons don't interact with each other and they behave as if the other photons are not there , then can more than one photon be in the same place ?
swansont Posted June 25, 2011 Posted June 25, 2011 Supposing , photons don't interact with each other and they behave as if the other photons are not there , then can more than one photon be in the same place ? Yes — they're Bosons, so there is no fundamental restriction on having an arbitrary number in the same place.
csmyth3025 Posted July 1, 2011 Posted July 1, 2011 (edited) Yes — they're Bosons, so there is no fundamental restriction on having an arbitrary number in the same place. This is an interesting idea. I believe there are six known and postulated bosons: in the Standard Model, there are six bosons which are elementary: the four gauge bosons (γ · g · W+/-· Z) the Higgs boson (Ho) the graviton (G) (ref. http://en.wikipedia.org/wiki/Bosons ) If I understand you correctly, all of the photons, gluons, W+/-, and Zo bosons, as well as the postulated but as yet undetected Higgs bosons and Gravitons in the early universe could all have quite comfortably occupied just about any arbitrarily small measurable space. The energy density would be immense, of course. Does our understanding of bosons still hold up at extremely high energy densities? This leaves the various fermions (quarks and leptons) remaining after the inflationary period and subsequent reheating to take up "space" so-to-speak - which was by this stage quite large as I understand it. Conversely, if quarks and leptons are thought to have already been present when the inflationary period began, this might set a lower limit on the "size" of the early universe that our known physics can accomodate. The mental picture I'm developing on this may be entirely off-base, so corrections are welcome. Chris Edited to correct errors in grammer Edited July 1, 2011 by csmyth3025
swansont Posted July 1, 2011 Posted July 1, 2011 Does our understanding of bosons still hold up at extremely high energy densities? As far as I know, yes.
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