A staple of science fiction for decades has been the ability to travel at faster than light speeds. Researchers studying photons and have observed the particles of light seemingly traveling at faster than light speeds in experiments.
Researchers from the Joint Quantum Institute (JQI) have conducted an experiment that has been able to speed single photons to what appear to be faster than light speeds. The experiment was conducted to confirm predictions in quantum-physics that the transfer time of light though complex multilayer materials doesn't depend on the thickness of the material. The study is the first to be published observing a single photon.
The researchers created 80nm thick stacks of 30 dielectric layers. The layers were equivalent to about a quarter of the wavelength of light traveling through them. The individual layers in the stack alternated between high and low refractive index materials that cause light waves to bend by varying amounts. Single photons hitting the boundary of the high and low layers have a chance of passing through or being reflected.
The researchers observed that single photons that completely penetrated the stack passed through in about 12.84 femtoseconds. If the team added an additional single layer of low refractive index material to the stack at the end the photon took an additional 3.52 femtoseconds to pass through the stack.
However, if the team added a single high refractive index layer to the end of the stack the single photons were able to pass through the entire stack in 5.34 femtoseconds. With the photon passing through the stack in 5.34 femtoseconds the photon appears to travel at faster than light speeds.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
Does that mean the speed of light is some kind of an average?
_________________ The kingdom of heaven is like a merchant seeking fine pearls who, when he found an especially costly one, sold everything he had to buy it.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
Does that mean the speed of light is some kind of an average?
Yeah, this is where they lose me a little - I wish I had the time to bone up on this stuff. But it's because I still think in terms of particles and (I think) should be thinking more in terms of potential or probablilities when it comes to sub atomic 'particles'. My brain says 'But if the distribution is equal to the speed of light, surely some particles do exceed the speed of light, and therefore it is not an illusion.' And I don't know why my brain is wrong.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
Does that mean the speed of light is some kind of an average?
Yeah, this is where they lose me a little - I wish I had the time to bone up on this stuff. But it's because I still think in terms of particles and (I think) should be thinking more in terms of potential or probablilities when it comes to sub atomic 'particles'. My brain says 'But if the distribution is equal to the speed of light, surely some particles do exceed the speed of light, and therefore it is not an illusion.' And I don't know why my brain is wrong.
Well, it has to do with the "relative" in "relativity." The "speed of light" which can't be exceeded is from any reference point, any observation. Nothing can be observed to exceed it. Like two ships traveling 0.9 the speed of light (with respect to some fixed external point) should be going 1.8 the speed of light when compared to each other. But if they look at each other, it's no more than the speed of light.
So all sorts of examples where you go, "surely X would be going faster than light," turn out not to be so. The rule enforces itself. But apparently they think they have an exception here.
If some of of those photons in the distribution are tachyonic, then theoretically causation is broken and they arrived before they left.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
Does that mean the speed of light is some kind of an average?
Yeah, this is where they lose me a little - I wish I had the time to bone up on this stuff. But it's because I still think in terms of particles and (I think) should be thinking more in terms of potential or probablilities when it comes to sub atomic 'particles'. My brain says 'But if the distribution is equal to the speed of light, surely some particles do exceed the speed of light, and therefore it is not an illusion.' And I don't know why my brain is wrong.
Well, it has to do with the "relative" in "relativity." The "speed of light" which can't be exceeded is from any reference point, any observation. Nothing can be observed to exceed it. Like two ships traveling 0.9 the speed of light (with respect to some fixed external point) should be going 1.8 the speed of light when compared to each other. But if they look at each other, it's no more than the speed of light.
So all sorts of examples where you go, "surely X would be going faster than light," turn out not to be so. The rule enforces itself. But apparently they think they have an exception here.
Yes - but they are saying that it is an illusion. That's the bit I don't get. I know the rest - that's why I'm a bit baffled by these claims.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
Does that mean the speed of light is some kind of an average?
Yeah, this is where they lose me a little - I wish I had the time to bone up on this stuff. But it's because I still think in terms of particles and (I think) should be thinking more in terms of potential or probablilities when it comes to sub atomic 'particles'. My brain says 'But if the distribution is equal to the speed of light, surely some particles do exceed the speed of light, and therefore it is not an illusion.' And I don't know why my brain is wrong.
Well, it has to do with the "relative" in "relativity." The "speed of light" which can't be exceeded is from any reference point, any observation. Nothing can be observed to exceed it. Like two ships traveling 0.9 the speed of light (with respect to some fixed external point) should be going 1.8 the speed of light when compared to each other. But if they look at each other, it's no more than the speed of light.
So all sorts of examples where you go, "surely X would be going faster than light," turn out not to be so. The rule enforces itself. But apparently they think they have an exception here.
Yes - but they are saying that it is an illusion. That's the bit I don't get. I know the rest - that's why I'm a bit baffled by these claims.
Agreed on how baffling it is. Just pointing out that there's not even supposed to be an "illusion" of faster than light travel. That's why they think they've done something, I guess. Relativity is supposed to mean that no matter how you set things up, no observation will ever seem to be of faster than light travel.
I suspect a dissenting science would say they have not set up a proper Einsteinian frame of reference or something.
I am still having trouble getting past the particles' behavior changing merely by being observed.
You have to realize that light particles are painfully self-conscious whenever they think somebody's looking at them....
_________________ The kingdom of heaven is like a merchant seeking fine pearls who, when he found an especially costly one, sold everything he had to buy it.
Last edited by That meddlin kid on Fri Jan 29, 2010 2:50 pm, edited 1 time in total.
A staple of science fiction for decades has been the ability to travel at faster than light speeds. Researchers studying photons and have observed the particles of light seemingly traveling at faster than light speeds in experiments.
Researchers from the Joint Quantum Institute (JQI) have conducted an experiment that has been able to speed single photons to what appear to be faster than light speeds. The experiment was conducted to confirm predictions in quantum-physics that the transfer time of light though complex multilayer materials doesn't depend on the thickness of the material. The study is the first to be published observing a single photon.
The researchers created 80nm thick stacks of 30 dielectric layers. The layers were equivalent to about a quarter of the wavelength of light traveling through them. The individual layers in the stack alternated between high and low refractive index materials that cause light waves to bend by varying amounts. Single photons hitting the boundary of the high and low layers have a chance of passing through or being reflected.
The researchers observed that single photons that completely penetrated the stack passed through in about 12.84 femtoseconds. If the team added an additional single layer of low refractive index material to the stack at the end the photon took an additional 3.52 femtoseconds to pass through the stack.
However, if the team added a single high refractive index layer to the end of the stack the single photons were able to pass through the entire stack in 5.34 femtoseconds. With the photon passing through the stack in 5.34 femtoseconds the photon appears to travel at faster than light speeds.
The researchers warn that the perceived faster than light speed of the single photon is "something of an illusion" because only a small portion of the photons actually make it through the stack and if all the photons that initially hit the stack were recorded the distribution of times would be normal.
The theory that explains how to calculate the interaction of photons with matter is called Quantum Electrodynamics (QED for short), and its predictions agree with experiment to within the limits of accuracies we are currently able to measure and calculate. In QED, when calculating the result of a photon moving through space, you have to include the contributions to the probability amplitude that ALL possible paths contribute to the result...INCLUDING the possibilities where photons are moving at any possible speed (including faster than the measured speed of light in a vacuum, and even photons moving backwards in time). It turns out that all of the contributions by the "unnaturally" acting possibilities cancel out on the whole, and you get the averaged result that agrees with the observed speed of light. But my point is that there is some small probability that an individual photon CAN move "faster than the speed of light" in our current understanding of things, so don't let that make your head explode.
But I'm not sure why these guys are going on about the photon's moving faster than light speed as being "an illusion" or only "perceived" in this case. Their cop out of "well, when you send in a whole lot of photons, only a very few get through this fast, and if you average them in with all the rest, they average of the distribution would be the normal speed of light" does not make sense to me...they still seem to be getting some photons coming through at faster than light speed, so why be wishy-washy? A different reporting of the article I found says that these apparently "faster-than-light-speed" photons can occur because theory allows for them in any case where the photon can't transmit actual information at faster than light speed...but I don't understand why they think these few photons that come out early are not transmitting information. So I'm not sure what to make of this article as yet.
_________________ Because life is a treasure. —Dave Powell
But I'm not sure why these guys are going on about the photon's moving faster than light speed as being "an illusion" or only "perceived" in this case. Their cop out of "well, when you send in a whole lot of photons, only a very few get through this fast, and if you average them in with all the rest, they average of the distribution would be the normal speed of light" does not make sense to me...they still seem to be getting some photons coming through at faster than light speed, so why be wishy-washy? A different reporting of the article I found says that these apparently "faster-than-light-speed" photons can occur because theory allows for them in any case where the photon can't transmit actual information at faster than light speed...but I don't understand why they think these few photons that come out early are not transmitting information. So I'm not sure what to make of this article as yet.
Now I don't feel so thick because that's exactly the thing I don't get (without the 'theory allows' bits that I didn't know).
Common sense doesn't work for quantum mechanics. The way we perceive the universe has developed so that we could hunt and survive on the African savannah. It doesn't help at all with understanding the way the universe behaves at the quantum level. Particles can pop in and out of existence from nothing and are doing so all the time. Empty space has energy - dark energy that is causing the expansion of the universe to accelerate. No one has any idea what it is, and neither od they have any real idea what dark matter is, despite the discovery of the Higgs boson. It is the most interesting branch of modern science I think.
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