Index of refraction of space

[Mr Skeptic]

Everyone knows that the index of refraction of empty space is 1. But, as I understand it, space is never truly empty. Even if there weren't photons, neutrons, dark matter, regular matter, etc, there would still be virtual particles. Since virtual particles are created as matter/antimatter pairs, and some of them will be charged, a photon moving through that space would move any charged virtual particles due to its electric field, so that some of the photon's energy will be temporarily transferred to the virtual particles. That should slow down the photon. I suspect that such an effect would affect different wavelengths to a different extent.

 

A side effect of the above would be that photons would never travel at exactly c, so perhaps they do have a reference frame after all.

 

So, what do people think? Am I crazy, or what?

[Klaynos]

Photons ALWAYS move at c, even threw materials where there is a high refractive index...

 

I suspect that vacuum fluctuations do have some effect but it'll be tiny tiny tiny.

 

Most (read all) refractive indices have some wavelength dependence and we do see some lag from different wavelengths that we don't expect and I believe I've seen this put forward as a suggest for that... But that would have been in newscientist so as they may have gotten the essence of it it might have been just speculation...

 

I shall see if I can find out anything about this...

[npts2020]

I thought recent experiments had slowed the speed of light down as slow as around 35 mph? Does that mean "c" changes? Does that mean the light that was slowed is/was no longer photons (changed somehow) until exiting to be detected? It just seems less likely to me that every photon in the universe travels at exactly the same speed than to believe that mechanisms like gravity or virtual particles might have some effect on that speed.

[Mr Skeptic]

Photons ALWAYS move at c, even threw materials where there is a high refractive index...

 

I suppose that depends on whether you look at the classical EM waves or the quantum ones. Well, by saying "photons" you are using quantum, but you know what I mean.

 

I suspect that vacuum fluctuations do have some effect but it'll be tiny tiny tiny.

 

Most (read all) refractive indices have some wavelength dependence and we do see some lag from different wavelengths that we don't expect and I believe I've seen this put forward as a suggest for that... But that would have been in newscientist so as they may have gotten the essence of it it might have been just speculation...

 

I shall see if I can find out anything about this...

 

That's interesting, please do.

 

I thought recent experiments had slowed the speed of light down as slow as around 35 mph? Does that mean "c" changes? Does that mean the light that was slowed is/was no longer photons (changed somehow) until exiting to be detected? It just seems less likely to me that every photon in the universe travels at exactly the same speed than to believe that mechanisms like gravity or virtual particles might have some effect on that speed.

 

No, that just means that they found a material with an incredibly small index of refraction.

[big314mp]

Perhaps the Casimir effect could be exploited to show this difference if it does exist?

 

Based on my understanding, the Casimir effect creates a truly empty space, which you could then measure c in.

 

This is way out of my area though, so I am probably pretty far off base

[Klaynos]

Perhaps the Casimir effect could be exploited to show this difference if it does exist?

 

Based on my understanding, the Casimir effect creates a truly empty space, which you could then measure c in.

 

This is way out of my area though, so I am probably pretty far off base

 

No, the casimir effect does limit the wavelength of virtual particles (and tehrefore their energy) between teh plates, but it's still not a complete vacuum.

 

I thought recent experiments had slowed the speed of light down as slow as around 35 mph? Does that mean "c" changes? Does that mean the light that was slowed is/was no longer photons (changed somehow) until exiting to be detected? It just seems less likely to me that every photon in the universe travels at exactly the same speed than to believe that mechanisms like gravity or virtual particles might have some effect on that speed.

 

What happens is each photon moves at c (3x10^8 ms^-1), but when travelling in materals they spend some time being absorbed and reemitted, this is what creates the refractive index, if the index is high enough you can create a lag so that it seems the photons are travelling slower than c, but they are not.

[npts2020]

Maybe I am misunderstanding the concept of refraction as relates to quantum theory but in the dictionary (wikipedia and websters) it is defined as the bending of a wave through a medium by changing the speed of the wave while traversing the medium. Are those definitions wrong? Refraction if related to speed would only need to change speed of light an infitessimal amount to cause visible effect. If it is because the photons are absorbed then re-emitted how do we know that?

[Klaynos]

Maybe I am misunderstanding the concept of refraction as relates to quantum theory but in the dictionary (wikipedia and websters) it is defined as the bending of a wave through a medium by changing the speed of the wave while traversing the medium. Are those definitions wrong? Refraction if related to speed would only need to change speed of light an infitessimal amount to cause visible effect. If it is because the photons are absorbed then re-emitted how do we know that?

 

That's the classical view, which works but you can't apply if you consider individual photons.

[Mr Skeptic]

That's the classical view, which works but you can't apply if you consider individual photons.

 

If you simultaneously send two photons perpendicularly through a flat plane of glass, will one come out before the other?

[swansont]

I thought recent experiments had slowed the speed of light down as slow as around 35 mph? Does that mean "c" changes? Does that mean the light that was slowed is/was no longer photons (changed somehow) until exiting to be detected? It just seems less likely to me that every photon in the universe travels at exactly the same speed than to believe that mechanisms like gravity or virtual particles might have some effect on that speed.

 

They slowed the speed of light propagation, not the individual photons

 

If you simultaneously send two photons perpendicularly through a flat plane of glass, will one come out before the other?

 

If they the same color, no.

 

Perhaps the Casimir effect could be exploited to show this difference if it does exist?

 

Based on my understanding, the Casimir effect creates a truly empty space, which you could then measure c in.

 

This is way out of my area though, so I am probably pretty far off base

 

The Casimir effect is hypothesized to allow you to exceed c

 

http://en.wikipedia.org/wiki/Scharnhorst_effect

[Mr Skeptic]

If they the same color, no.

 

Not even by a little? If they get temporarily absorbed and re-emitted, that seems like it would be a rather random effect, and maybe one might get absorbed longer or more times than the other?

 

The Casimir effect is hypothesized to allow you to exceed c

 

http://en.wikipedia.org/wiki/Scharnhorst_effect

 

Now that is cool! Too bad it won't be measurable in the foreseeable future.

[Klaynos]

Not even by a little? If they get temporarily absorbed and re-emitted, that seems like it would be a rather random effect, and maybe one might get absorbed longer or more times than the other?

 

It is a bit random, but two photons of the same colour are identical, the material can be considered to be identical and there are so many interactions passing threw the material and so many possible interactions that they average out, any difference would be immeasurable.

 

Have a look into a Rayleigh reflectometer... I demonstrate an experiment for it.... it's rather and odd bit of kit...

[npts2020]

Thanks swansont and Klaynos, hopefully, I am beginning to understand the difference between propagation and photon speeds. Propogation and refraction has to do with absorption and re-emittance of photons, the delay causing the seeming change of the speed of light, got it. I still have a problem with every photon in the universe traveling at the same speed, though......