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Researchers warn FTL is somewhat an illusion in the experiment

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 researcher 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.



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Not to nitpick...
By lightfoot on 1/27/2010 5:30:28 PM , Rating: 5
But technically a Photon is light. And by definition however fast the Photon travels would necessarily be the speed of light.

Even if the photon was traveling nowhere near 186,000 miles per second, it is still light, and thus is travelling at exactly the speed of its self.




RE: Not to nitpick...
By General Disturbance on 1/27/2010 6:24:45 PM , Rating: 2
How does a single photon travel at the speed of light, at the same time, to two different observers who are moving at different speeds?
Are photons somehow duplicitous like this? Seems strange.


RE: Not to nitpick...
By Solandri on 1/28/2010 4:12:25 AM , Rating: 3
That's basic Relativity. The answer is that the two different observers' different speeds means their perception of the passage of time is different. This makes them both see the same photon traveling at the same speed - the speed of light.


RE: Not to nitpick...
By SiN on 1/28/2010 6:37:17 AM , Rating: 2
Simple!


RE: Not to nitpick...
By General Disturbance on 1/28/2010 7:53:12 AM , Rating: 2
But that is only at high velocity. At low speed, time dilation effects are negligible compared to the simple linear Galilean transformation, and same for length contraction as well.


RE: Not to nitpick...
By porkpie on 1/27/2010 6:28:15 PM , Rating: 4
No, because the 'speed of light' (technically: the speed of light in a vacuum) is a fixed constant.

Light travels in mediums such as water or glass at a speed much slower than "the speed of light".


RE: Not to nitpick...
By Oregonian2 on 1/27/2010 8:16:07 PM , Rating: 3
The speed of light in water is indeed slower than the speed of light in vaccuum, but it's still going the speed of light. That people often used bad English saying the "speed of light" and then assuming the maximum speed is meant doesn't invalidate the proper and literal English statements.

IMO anyway.


RE: Not to nitpick...
By grath on 1/27/2010 10:26:54 PM , Rating: 3
People who are aware of the distinction between c and c/n can easily determine the meaning of the terminology from the context in which it is used, and will be specific when using a term themselves.

The other 90% of Earths literate population understands "speed of light" = c, and would probably lose interest if you tried explaining propagation and refraction indices to them.

Anyway, proper literal English meaning is about as relevant to scientific terminology as lexicography is to your hair stylist.


RE: Not to nitpick...
By lightfoot on 1/28/2010 1:26:11 AM , Rating: 4
quote:
The other 90% of Earths literate population understands "speed of light" = c, and would probably lose interest if you tried explaining propagation and refraction indices to them.

However in an article describing light propagating through a medium it is misleading to imply that it travelled faster than the constant c, as implied by stating that it travelled faster than the "speed of light." In actuality it travelled faster than expected through the medium without actually exceeding the speed c.


RE: Not to nitpick...
By Byte on 1/28/2010 8:14:55 AM , Rating: 5
Traveling faster than photon propagation in a medium is done all the time ie nuclear reactors. Check out Cherenkov radiation.

This experiments calculations seem to show the photon traveling faster the c. However receiving information (which is more important) probably isn't possible.

Also remember that Quantum and General Relativity has not been unified yet, rules from one will not necessarily apply to another. Just look at dark energy or matter. It could be we simply we don't have enough instruments to calculate everything, or calculations of gravity change in the galactic scale.

Just as Einsteins calculations may seem to supplant Newtons, does not make the former irrelevant. Who knows, in a few years we might find both are just broken fragments of a bigger picture.


RE: Not to nitpick...
By lightfoot on 1/28/2010 12:22:00 PM , Rating: 1
quote:
Just look at dark energy or matter.

I tried, but couldn't find any. However there are people much smarter than me still trying to find it.


RE: Not to nitpick...
By Zavijava on 1/28/2010 7:43:38 PM , Rating: 2
Quantum field theorists would beg to differ.

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

4 fields of mechanics
Classical mechanics: low speed, large scale
Relativistic mechanics: hi speed, large scale
Quantum mechanics: low speed, small scale
Quantum field theory: hi speed, small scale


RE: Not to nitpick...
By djkrypplephite on 1/27/2010 10:42:30 PM , Rating: 3
This is how Einstein said that the speed of light is actually relative. Even if you were traveling at the speed of light, light would still be going faster than you.


RE: Not to nitpick...
By delphinus100 on 1/29/2010 1:29:13 PM , Rating: 2
But as it would require your length in direction of travel to be zero (Lorentz-Fitzgerald contraction), time slowed to zero, and, most importantly, your relativistic mass to be infinite , your being at the speed of light is an unattainable condition, anyway...

But yes, this is how nature 'contrives' (for lack of a better word) to make the measured speed of light the same for all observers. You'll never observe it at any other speed (much less observe it 'standing still') in a vacuum.


RE: Not to nitpick...
By AnnihilatorX on 1/29/2010 3:22:14 AM , Rating: 2
No, photon is an incomplete description of light, due to wave-particle duality, it's both a wave and a photon.

With refractive indices and interferences of multiple electromagnetic waves (light) in the equation, you can do seemingly impossible stuff with group velocity.


RE: Not to nitpick...
By delphinus100 on 1/29/2010 1:19:15 PM , Rating: 2
Okay, now you need to explain that to all the other photons...

Still, I'm reminded of a woman who commented on another woman's hairstyle, noting that it looked almost like a Dorthy Hamill cut (back when that skater's hair style was popular).

"But it is a Dorthy Hamill." she insisted.

"No." the first woman said "Almost, but not quite."

She didn't realize that she was addressing Dorthy Hamill, and by definition...


somehow
By cludinsk on 1/27/2010 4:21:41 PM , Rating: 5
I don't think this is going to get us to Alpha Centauri




RE: somehow
By Screwballl on 1/27/2010 4:31:33 PM , Rating: 3
screw AC.... we need to be on our way to Nemesis


RE: somehow
By johnsonx on 1/27/2010 4:56:00 PM , Rating: 5
Then how are we going to get to the planning office to protest the new hyperspace bypass?


RE: somehow
By BruceLeet on 1/27/2010 5:42:07 PM , Rating: 2
You guys are something else.


RE: somehow
By XINFU4 on 1/27/10, Rating: -1
RE: somehow
By grath on 1/27/2010 9:46:06 PM , Rating: 2
BEWARE OF THE LEOPARD


RE: somehow
By PrezWeezy on 1/28/2010 1:10:38 PM , Rating: 2
Make sure you bring a towel.


RE: somehow
By Seemonkeyscanfly on 1/27/2010 5:55:40 PM , Rating: 4
If you pee'd while travel faster then the speed of light, would you be pissing on your future?


RE: somehow
By chagrinnin on 1/27/2010 6:50:52 PM , Rating: 5
R. Kelly?


RE: somehow
By grath on 1/27/2010 9:53:56 PM , Rating: 4
Didn't your mother always tell you to pee BEFORE violating special relativity?!


RE: somehow
By onwisconsin on 1/27/2010 10:59:53 PM , Rating: 5
And it would appear on earth you would be pissing for a year!


RE: somehow
By scrapsma54 on 1/28/2010 8:27:18 PM , Rating: 2
Don't let the thresher maw bite you in the ass on the way out.


Nonsense
By memocollector on 1/27/2010 9:28:47 PM , Rating: 2
Am I understanding this right? The time it takes light to travel distance of 80 nm in vacuum is o.267 femto seconds. The fact that it takes longer than this time to go through the material is due to the time delay between absorption and remission of photon by electron, and the lower bound on this time delay is given by the time-energy uncertainty relation.

So, unless the research is saying that light traversed 30 layers of material, each 80 nm thick, in 5.34 femto seconds, or that the time-energy uncertainty relationship has been violated (impossible to prove in this case), I don't see what the big deal is.




RE: Nonsense
By LongTimePCUser on 1/28/2010 12:09:35 AM , Rating: 2
Nonsense,
Thanks for doing the arithmetic.
These photons got through the target faster than the speed of light in the media. Not faster than the speed of light in vacuum.

No big deal.


RE: Nonsense
By JediJeb on 1/28/2010 11:00:13 AM , Rating: 2
Along these lines is a hypothetical question I have always wondered about.

If you had a rod that was one light year long, and you push one end one inch, how long would it take the opposite end to move one inch? Would it move instantly, providing faster than light communication at the opposite end, or would the movement be limited by the speed of light and take one year to propogate through the rod?


RE: Nonsense
By TheEinstein on 1/28/2010 11:43:24 AM , Rating: 2
The physicists Günter Nimtz and Alfons Stahlhofen, of the University of Koblenz, claim to have violated relativity experimentally by transmitting photons faster than the speed of light.[12] They say they have conducted an experiment in which microwave photons—relatively low energy packets of light—travelled "instantaneously" between a pair of prisms that had been moved up to 3 ft (1 m) apart, using a phenomenon known as quantum tunnelling. Nimtz told New Scientist magazine: "For the time being, this is the only violation of special relativity that I know of."

As for the question of the rod, I hope you havce sufficient 'strength' to move a rod that long, and I hope it does not distort somewhere and invalidate the experiment. But I applaud the idea!!!!

As for relativity, I am NOT a proponent of it.

Time dilation has been conclusively observed. Both with atomic clocks aboard planes and with satellites in orbit used for GPS. If time dilation wasn't taken into account, GPS wouldn't be able to position you on earth.

Then there is the issue of lensing via gravity, which has shown some interesting aspects of space, and might just be showing us ftl light for sure...


RE: Nonsense
By Paperdoc on 1/28/2010 4:28:29 PM , Rating: 2
This was discussed (including my comments) some time ago in the forum, see this thread:

http://forums.anandtech.com/showthread.php?t=32643...

Bottom line is no, it will NOT move "instantly" because there is a finite speed of propagation of the mechanical force applied to the end of the rod, and in fact it is MUCH slower than the speed of light in a vacuum.


RE: Nonsense
By delphinus100 on 1/29/2010 1:35:45 PM , Rating: 2
Because nothing is 'perfectly' rigid and incompressible (which is one reason black holes are possible), it'll take something less that a year for anything you do to be detected at the far end.

Otherwise, you'd have the interesting situation of the speed of sound (in that medium) being faster than the speed of light...


RE: Nonsense
By eachus on 1/28/2010 12:35:26 PM , Rating: 3
The solution for games of telephone on the net is to go back to the original article. In this case: http://jqi.umd.edu/news/206-stacking-the-deck-for-... ..."the JQI researchers created stacks of approximately 30 dielectric layers, each about 80 nanometers thick"..

So the stack is 2400 nm thick and Google gives 8.00553828 × 10^-15 for 2400 nm/c or roughly 8 femtoseconds. So an effective transit time of 5.34 femtoseconds is a big deal.


RE: Nonsense
By TheEinstein on 1/28/2010 9:24:50 PM , Rating: 2
I disagree on that. I think that if it could be moved, then it moved. The structure would be unbendable, therefore with applied physics all atoms would apply pressure to all atoms simultaneously. Of course finding an unbendable material... beyond me, lol

But imagine if it were that we could make a graphene pole... how much bending would it do? Would it be able to 'violate' the rule sufficiently?

In a frame reference the movement is instant for sender, and instant for receiver...

Of course I hate the whole fallacy of frames, since I think this is the bad mojo science which is limiting us right now.


That's fantastic...
By JackBurton on 1/27/2010 5:07:55 PM , Rating: 3
That's fantastic. Now when am I going to get my flying car?




RE: That's fantastic...
By chagrinnin on 1/27/10, Rating: 0
RE: That's fantastic...
By grath on 1/27/2010 10:47:52 PM , Rating: 5
So 3.17x10^445 years eh? I bet iPhone still wont have Flash by then...


Inconsequential for communications
By jimhsu on 1/27/2010 7:22:25 PM , Rating: 2
Apparent FTL scenarios such as these are theoretically interesting, but are unusable for communication. Tunneling, entanglement, evanescent wave coupling, etc are all ways to "get" speeds above c, but sending a message (or any bit of information) using the above techniques has been proven to be impossible. So nothing new here really...




By jimhsu on 1/27/2010 7:25:55 PM , Rating: 1
Somewhat OT: Eve-online gives perhaps the most "plausible" means to achieve FTL, but even it is filled with pseudo-science gibberish ("conservation of noise structure? wtf?"): http://www.eveonline.com/background/communication/...


RE: Inconsequential for communications
By porkpie on 1/27/2010 11:30:52 PM , Rating: 3
You're absolutely right that there's nothing new here. After all, Feynman was saying in the '50s that photons could move faster than c, but that these amplitude fluctuations average out, and thus can't transmit information.

However, its incorrect to say superluminal information transfer has "been proven impossible". There's certainly a huge amount of evidence against it being possible. But nothing in science is ever proven beyond a shadow of a doubt.


By jimhsu on 1/28/2010 4:02:01 AM , Rating: 2
Note I said "using those techniques" (i.e. entanglement). There have been mathematical proofs (too lazy to dig them up) that show that resolution of entanglement by observation is not distinguishable from random noise (google EPR paradox, Bell inequality, etc). There has been no conclusive evidence for or against FTL communication, though all attempts so far have failed.


Sounds like...
By porkpie on 1/27/2010 4:43:22 PM , Rating: 4
...the old "phase velocity vs. group velocity" error some researcher seems to make every couple of years or so.




RE: Sounds like...
By GourdFreeMan on 1/28/2010 1:11:43 AM , Rating: 3
Not just phase velocity vs. group velocity, but phase velocity vs. group velocity vs. front velocity... the third of which I am not even certain can be meaningfully discussed considering the assumptions that go into quantum mechanics and the wave-based series expansions that are at the heart of the theory.

I am sure we are in for even more confusion before we get clarity.


Hmm
By Spivonious on 1/27/2010 4:40:36 PM , Rating: 3
Have they tried sending the photons through a dilithium crystal?




RE: Hmm
By Spookster on 1/27/2010 5:32:47 PM , Rating: 3
I'm givin 'er all she's got Captain!!


Photon FTL?
By icanhascpu on 1/28/2010 1:56:04 AM , Rating: 2
quote:
With the photon passing through the stack in 5.34 femtoseconds the photon appears to travel at faster than light speeds.


So let me get this straight... a photon is a particle of light. They are saying a photon is exceeding light speed, now tell me how light can travel faster than light.




RE: Photon FTL?
By eachus on 1/28/2010 1:07:40 PM , Rating: 2
quote:
So let me get this straight... a photon is a particle of light. They are saying a photon is exceeding light speed, now tell me how light can travel faster than light.

Technically it doesn't. If you want to say that the photon travels through some other dimension, fine. But my preference is to stay with the QM view. A photon (particle) hits the stacked dielectric layers, and as a result of the interference between the waves reflected back and forth in the dialectric layers, in some cases a photon is emitted with reversed momentum (reflection) and in a few cases a photon is emitted from the far side of the stack (transmission).

If you get reflection does the photon bounce off the stack, or is a new photon created with reversed momentum? In the transmission cases, talking about the photon traveling at faster than the speed of light is simply wrong. If you try to detect the photon inside the stack, that is a different experiment, and you will get different results.

Look at the reported results. They did three experiments. A: 40 layers stacked LHLHLH... where L stands for low density, H for high, B: 41 layers LHLHL...HLHLHL, and C: 41 layers HLHLH...LHLHLH. The transit times measured were 12.8, 16.4, and 5.3 fs. There is a nice graphic in the original article at the JQI: http://jqi.umd.edu/news/206-stacking-the-deck-for-...

My point is that the three closely related experiments lead to wildly different transmission times for the transmitted photons if you insist on imputing a velocity to what you hope is the same photon. QM says they are identical, but are they identical twins? No way to tell. But notice that if you assume that experiment A was experiment C with one layer removed, then the time to transit the added layer is -7.5 fs. I can live with the overall QM view, but measuring a photon that has traveled backwards in time? I'd like to assume that even if it is possible, it is not happening here.


NOT nonsense, but missense
By manofhorn on 1/28/2010 2:57:45 AM , Rating: 2
while i might be getting dangerously close to bastardizing the energy-time uncertainty relationship, as so many love to do, the scientist's comment that if enough photons were recorded the average time through the barrier would average out to the expected "normal speed of light" is the salient point here.

as there are probabilities to record certain positions of quantum particles, there can also probabilities to record certain times. this extrapolation from the position-momentum uncertainty relationship is a bit odd because of the fact that it sets the time and position variables on equal ground, but, alas, it makes just as much sense as all the rest of quantum mechanics (i.e. none at all).

therefore, there are specific probabilities to record the photon's travel time through the barrier to be too small and too large and just right. if enough recordings are made they would average out to the value we all expect.




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