I propose an experiment to test a faster than light hypothesis I have. The hypothesis is more of a hunch somewhat based on science I have read.The idea is that quantum fluctuations affect the speed of light. Everywhere in our universe there are quantum fluctuations, supposedly these fluctuations are fairly uniform in vacuum. Like i said, I think that in the absence of these fluctuations light may travel faster than light.. The casimir effect is due to the reduction of fluctuations in between two plates. If I understand the basics, it is caused because wavelengths of light/particles cannot fit in the small distance between the plates. So, to test this one would place two plates close together and shine a light between them. This may be difficult to test since casimir forces arise at very small distances and so the wavelength of light would have to be correspondingly small (20 nm) and very difficult to obtain as well as dangerous. So, an easier method may be to use some kind of a colloidal mixture. The particles in the colloid, if close enough to one another, should also block quantum fluctuations. To obtain maximum reduction of quantum fluctuations one would find a solvent with a very distinct wavelength cut-off and then a solute with a distinct wavelength cut off going in the other direction but as close to that Please Register or Log in to view the hidden image! So, if most of the fluctuations are accounted for by photons, this should cancel those which are in the absorption spectrum. If quantum fluctuations effect the speed of light then photons should pass more quickly through this medium (however the refractive index would still slow these photons down, which is why two plates would be the most effective...) Now that I think of it the fluctuations are not necessarily all photons, so this may or may not be an issue. I will have to do some more reading on the casimir force to decide. Furthermore, only a very small percentage of quantum fluctuations may be blocked this way (but still enough to result in a sizable casimir force) and the success of the experiment may be hard to discern from a failure. I suppose in the total absence of all fluctuations light should travel at no time at all from point a to point b.. I don't this has been tested, at the very least.. please feel free to criticize my hypothesis and/or discuss casimir forces and vacuum fluctuations.
Hmm well the Casmir force isn't exactly caused by photons not "fitting" in the space between the plates, it is caused by a reduction in the number of allowed virtual photon states between the plates. I guess this is like the virtual photons don't fit, but they don't fit in the sense that their wavelengths are not appropriate integer multiples of the distance between the plates. When there are no plates any wavelength virtual photon is possible, but the plates suppress some of these. It's not like anything above or below a certain wavelength is cut out though, it is more like you cut out every second wavelength (in a really vague sense). As far as actually getting a laser or something and zapping it between the plates goes, I guess the plates would just act as a waveguide (assuming they are reflective, I actually can't remember what sort of properties the casimir plates are supposed to have, dielectric I think...). The propagation modes of the waveguide should be related to the allowed casimir virtual particle modes... I guess you'll just find there are certain frequencies of light that won't propagate through the plates, although the modes are only restricted in the direction joining the plate faces, perpendicular to that the modes are unrestricted, so actually this probably doesn't restrict the propagation modes... my waveguide theory is a bit rusty. Anyway I think you'll find that the light goes slower between the plates than in free space, not faster, this is what usually happens in waveguides I believe. It's not really like the speed of light changes though, it's just that you changed the environment the light is propagating in. In vague terms the light just bounces around a bit in there and takes a bit longer to get to the other side than if it went straight. I'm not sure that can be said to have anything to do with the casimir effect, but it is probably the dominant effect you'll see.
I have read a bit into waveguide theory and a general rule is that wavelengths greater than two times the width of the waveguide cannot propagate through the waveguide. This is a general rule and I suppose there are exceptions to it. The reason I think this may be worth testing is that it is not something that would be observed in nature - the fluctuation density is fairly constant everywhere and rarely do we test the speed of light going through very specific substances - as far as I know we do not actually test this with every material but rather use an equation Please Register or Log in to view the hidden image! Where one part is the permittivity and the other permeability. As you say, it is the environment that is changed and not light itself - an environment that has not been explored, at least to my knowledge. The light will indeed bounce around but this could be accounted for and should be minimized. To say that fluctuation densities don't change anywhere in nature may be going too far - after all the atmosphere is composed of molecules which may possibly affect these densities. What do you think, do atoms of a gas have any effect on zero point energy? Another straightforward way to test this might be using fiber optics. One would first measure the amount of time that light takes to travel through a fiber cable and then do the same with a different cable.. both cables would be composed of the same materials but they would not be of the same structure, so that the zero point energy may be altered within the cable. . .
What about the phase delay of a dichromatic filter or some other alternating thin optical layers? Wouldn't that be a test of your casimir = FTL idea? But it was my understanding that these are well-modeled by QED, in which case the quantum information propagates at speed c. http://en.wikipedia.org/wiki/Dichroism http://en.wikipedia.org/wiki/Optical_coating
I think you might be referring to this. I read it and it brought back this idea i've had for a while.. it doesn't seem like this is the same thing - or at least not the same explanation. It seems that this is indeed ftl information transfer. Still, if there is a causal relationship between 'injecting' photons into the stack and the photons coming out the injection event will travel ftl. I don't see what they mean by 'seem'.. if there is a causal relationship then you can transfer a signal ftl this way. It comes out to something like 486,000,000 m/s. On top of this it is not travelling through vacuum. As for my hypothesis regarding this experiment, the layers are certainly thin enough (80 nm) and both certainly aren't completely transparent - some fluctuation density lessening may be taking place. But the fact that alternating the layers makes for such a large time difference cannot be explained by my hypothesis .
It sounds like a quantum tunnelling effect, which occurs randomly. Since it is random whether or not a photon tunnels through the barrier then I imagine you can't transfer information this way.
I read the paper and from the little I understood it was mistakenly identified as tunneling, but the authors also declare information is transferred slower than c. If you fire a single photon at one side and it comes out the other side faster than a photon could travel in vacuum, it seems like its superluminal, as the paper also states. :shrug:
Hmm, interesting. I only read the introduction and conclusion but yeah it seems like either they don't think it is analogous with tunnelling at all, or else it is some kind of complicated process which doesn't match simple tunnelling models, I wasn't quite clear which. The difficulty seems to be that there aren't simple tunnelling experiments for photons like there are for electrons, because they are neutral I suppose and you can't use something simple like an electrostatic field as a barrier. Tricky. I think they were hoping these dielectric stacks would work in a simple way like this, but it looks like they don't.
Shouldn't the zero point energy be .. lower inside of humans? If two dielectric plates block fluctuations in between them, the trillions of atoms and molecules that compose people should also block out some fluctuations. (Opaque) Matter in general should block out fluctuations, no?
Well it is a trick of the geometry, it is in fact possible (in theory, I'm not sure if it has actually been done...) to make two objects repel using the casimir effect, I think you need one of them to be a conductor and maybe a strange shape, I don't really remember. So it is pretty hard to say what any given arrangement of matter is going to do to the vacuum around it. Most of the time nothing noticeable I guess.
I've heard of one effect where the photons are delayed a bit and then propagate faster than light. Information travels slower than \(c\) in this case because of the delay time required before the effect can be achieved. I think there's also an analogous classical effect where changes in the electromagnetic field propagate at the speed of light, but there's some kind of interference pulse you can add which delays the effect, so when the interference stops, it appears as if an electromagnetic ripple is travelling through space faster than light. In relativistic quantum mechanics there's no speed limit on particles, they can instantly vanish from somewhere and pop up on the other side of the galaxy (and even travel backwards in time while doing so). But there's a cancellation that occurs between matter travelling forward in time from A to B and antimatter travelling backwards in time from B to A, so information still propagates slower than \(c\). But this does have me thinking, and I actually have a question to pose to those in the know. I've seen QFT (quantum field theory) calculations showing that information travels slower than \(c\), but these calculations depend on the propagating particle not interacting with anything, including itself. Once you start adding particle interactions and vacuum perturbations, my understanding is that such calculations are no longer valid. Is there some kind of mathematical proof in QFT that relativistic causality is always preserved? Or perhaps, does the requirement that causality be preserved pose any restrictions on QFT? I don't know much about CPT symmetry so I don't know if there's any sort of connection here.
Hmm, I believe causality is respected so long as the commutators of the field operators vanish for spacelike separation, i.e. both fields must be independent of each other at those points. I don't know if there is a proof telling you what properties your theory must have to get this result, I guess it's quite possible that not all QFT's respect this.
An issue in such a field would be relativistic energy - if inside of this lowered field the speed of light goes from c to some higher value, and a particle enters that field at a speed close to c then it seems like it should lose quite a bit of relativistic energy in that field And if it does not? Maybe time goes by faster where zero point energy is lower- and so an outside observer would see light travelling faster than c, but in this frame it would still only be c. If this is true then particles entering the field would seem to speed up but would still have the same energy and velocity. :shrug: Hmm, of course its not as simple as I thought. Please Register or Log in to view the hidden image! Well thats interesting - if fluctuations are blocked inside of certain media this is exactly what I would expect. If 'fluctuation-blocking' is as simple as disallowing certain photonic wavelengths (..?) then most glass should have a lowered refractive index. But because there are other effects in glass the overall speed is still lower than c. Do you remember the name of this effect? From the wiki on cerenkov radiation: I suspect a higher velocity while moving but still a lower average velocity due to the interactions.
Now that I think about it the part on cerenkov radiation kind of defeats my hypothesis - the refractive index does not alter the speed of light, it only adds lots of 'stops'. So the refractive index does not really alter the speed of light, it only alters the rate at which it moves through a medium? I suppose stops could also appear in vacuum, but I think that this would also lead to scattering - which does not occur in vacuum. There are materials which, when pure, do not scatter light but only slow it down due to these stops, so maybe the vacuum would be like this material. How does that work anyhow, that vacuum fluctuations do not cause scattering of light? Atoms don't appear in vacuum do they? Molecules of gas cause scattering, so fluctuations can't be as big as that.
I was mostly thinking about perturbational effects. As I understand it, the nice clean quantizations which lead to vanishing commutators don't work in the interacting picture. I'm definitely curious about whether this property can be generalized, or if it's still up in the air as a mathematical question.
You've gotta be careful throwing around terms like "vacuum" etc. I'm learning a lot of the more nitty-gritty details of quantum field theory right now and it's some pretty incredibly heavy stuff. A lot of the results you get only come out after some extremely laborious and tricky calculations, it's not something you can just deduce from speculation. I really have no idea what you mean by "vacuum fluctuations" leading to scattering light, but it's known that beams of light can scatter each other by temporarily forming virtual positron-electron pairs. As far as refraction goes, what's happening is photons are constantly being absorbed by the electrons orbiting the atoms of the material, and these electrons get excited into higher orbits. In these higher orbits the electrons are unstable, and they tend to go back to their original orbits and spit the photons back out within a very short time. On a large scale, the effect is the same as if the atoms were producing their own EM waves in order to partially cancel the ones passing through them (a natural tendency for materials such as dielectrics), and the net sum of the incoming wave and the wave produced inside the material as a response will together look like a slower beam of light with a lower wavelength.
Well, via logic I can conclude that these positron-electron pairs can't form in vacuum or otherwise the light from stars would get scattered before it reached earth. :shrug: Or maybe this scattering happens so rarely that it doesn't have considerable effect on imaging - after all there is some gas in interstellar space that scatters light but not enough to make interstellar space opaque. The way I understand QFT is that there is a quantized field everywhere with a minimum but non-zero energy, resulting in particles appearing sometimes. Please Register or Log in to view the hidden image! This is my understanding as well - photons get momentarily absorbed and then spontaneously re-emitted with the same amount of energy. In non-linear media two photons are absorbed by the same electron and then the re-emitted photon is of higher energy.
I sure hope you're right. No one would be more delighted than myself to find out faster than light travel is possible. However, caution needs to be exercised- Quantum Gravity remains a poorly understood subject, and the only evidence we have for negative gravity comes from cosmological observations. It could still turn out that these phenomena have natural explanations which forbid warp bubbles like the ones Dr. Albucierre proposed. My term paper in General Relativity was on the very tentative hypothetical possibility of faster than light travel, in this case through the use of a higher dimension such as those proposed in String Theory. My focus was on the Horizon Problem, which involves evidence that some sort of faster than light signalling was possible in the very, very early universe. The problem is you still have the potential for time paradoxes and such, which would require yet more work to address and explain. It could be possible for us to communicate with distant galaxies even far in the "past", as long as whatever return signals could be sent the other way are guaranteed to arrive after our own signal- that would protect causality, but it would also introduce certain notions of preferred reference frames that I can't see being justified by any scientific knowledge at present.
Yeah I'm with CPTBork, the whole concept of what the energy of the vacuum really means is pretty poorly understood. QFT sort of says it is infinite energy, but since that kind of makes no sense we just reset that infinite vacuum energy as the new zero. In that sense the casimir vacuum does kind of look like it should be a negative energy region, but since it was us who decided what the measure of zero energy was it isn't really like it has negative energy in a gravitational sense. Which is the whole problem of course; energy in QFT and energy in GR are different beasts. This is just wild speculation on my part, but it sort of seems to me like if light can go faster through a "less dense" vacuum, then it is more like we just got the original "vacuum speed of light" definition a tiny bit wrong. I.e. the most "empty" vacuum possible would define the "real" speed of light, i.e. the speed limit of the universe. The changes would be so tiny I can't imagine it contradicting any relativity experiments that have been done. Thus no causality violating effects would exist.
