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Pushing Microwaves Faster Than Light
ContinuousPark writes: "According to this NY Times piece, Lijun Wang of the NEC Research Institute in Princeton has reported an experiment where "a pulse of light that enters a transparent chamber filled with specially prepared cesium gas is pushed to speeds of 300 times the normal speed of light". A second experiment by three scientists for the Italian National Research Council is reporting also superluminal speeds. And yet, this seems to be consistent with Einstein's theories. "
Hehehe
-legolas
i've looked at love from both sides now. from win and lose, and still somehow...
As usual, you replace the "www" with "partners" to get the no login required version of the article, found h ere.
S tory here.
Pretty mindbending stuff, indeed. Once upon a time I could follow that sort of discussion, but I've been out of academia too long.
Constitutionally Correct
Hmm here is one you can use if you need one.
slashdotviewers/allowed
You could always use login, password: cypherpunk / cypherpunk.
__________________________________________
God did not appoint us to suffer wrath but to receive salvation through our Lord Jesus Christ --1Thes5:9
Can be found here at Nature.
Whilst the difficulty in this experiment is in interpreting the results, one thing to remember is that the speed limit c for any information is a postulate of relativity, not something that has been proved. It appears to be true so far, but there is nothing to say that it always applies.
The text states that this couldn't be adapted to signal information back in time due to the small timescales involved, well, what about a simple signal? like 'Don't switch the signal generator (laser or whatever?) on?. Would the ensuing paradox wipe-out the universe?
Can someone with a degree in physics answer these questions:
"...under these peculiar circumstances, the main part of the pulse exits the far side of the chamber even before it enters at the near side."
At first I was going to flame NYT for such a stupid claim, but upon reading the rest of the article that appears to be what the scientists themselves are claiming. So my first question is: What is speed if not distance travelled divided by time elapsed? If the time elapsed is negative, how is the speed "300 times c"?
The second question is about the obvious "time travel" aspects. They say several times "you can't send info faster than c", but they don't indicate a reason. The closest they come to justifying this statement is (paraphrase) "there is a leading edge to the main pulse that arrives sooner".
So which is it? Did the pulse exit before it entered OR was there a "leading edge". You can't have it both ways. Either the signal travelled faster than light (in which case signaling superluminally is possible, by definite) OR it did NOT.
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What sort of bandwidth can you get by transmitting down cesium-based fibre at 300 times the speed of light? ;)
According to what information my poor, physics dull brain could cull from the article:
You have to charge the particles with a certain kind of light?
You have to transmit annother certain kind of light? (or was it the same kind?!?)
So, there isn't too much information you could pass quickly through this chamber. The only thing that gets passed quickly through the chamber is the time that you shined the light on the "near" end of it?
Thank you for not thinking.
Do these experiments redefine physics as we know it? That is quite easy to find out: just wait one or two years. If Dr. Wang hasn't received the physics Nobel Prize by then, there was probably a fatal flaw in his equations.
Does anyone still remember the hype about cold fusion, the guys claiming to have sent information at v > c (that was the guys who bodulated a laser wave with music, but failed to notice the difference between group speed and phase speed of the light - or at least didn't bother to do so in their works...)
BTW, IAAP ( I am a physicist) and I have become more and more sceptical towards articles like this one during my studies - in almost all cases, "great discoveries" can be easily explained by physical properties not taken into consideration or just some stupid error. If it is published in a non-scientific journal before the scientific community notices it, a "discovery" usually isn't worth the paper it's printed on.
Cthulhu fhtagn!
I hear this supposed time travel 'paradox' cited all the time as a reason that FTL travel isn't possible. We can't send information faster than light because then we can 'see' events before an observer only a short distance away, and this is supposed to be a paradox.
What the heck am I missing? Are all these people stupid, or is it me? Why is it a paradox if information gets to someone at a distance before it gets to someone nearby? You're never going to get the information before the event occurs, so there's never any threat of paradox.
The Nature article was less confusing than the NYT article and it DID have a little more info. Except it didn't answer the questions I want answered. Namely, WTF are "evanescent waves" and why can't they carry information?
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Energy has no mass? Think again. That famous equation (verified countless times in the Nevada desert, in the Russian wastelands, and over two certain cities in Japan) works both ways, you know.
Mod down posts with a "Free Mac Mini/iPod" sig, they're spam!
The article states that the backward wave propogated at approximately 300 time c , which is the speed of light in a vacuum.
The speed reported is for the backward wave, apparently. This is similar to how a traffic clot might propogate backwards through traffic even though the traffic itself is moving forwards, as the article points out.
Take a look sometimes how traffic responds to a sudden discontinuity in flow, such as a slow-poke or an accident. If it's near "saturation", the backward wave of clogged traffic moves very quickly, which is VERY similar to the phenomenon being reported. Notably, the more "saturated" the traffic, the quicker this "wave" moves. As the article indicates, the experiment was performed in a chamber that's designed to amplify light waves by saturating the cesium with energy from one source and then triggering the release of that energy with a different source at a particular frequency. In this case, the microwave involved is not releasing the saturated energy.
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Pick any reason, or several :^)
No longer sell "Speed-O-Lite" Wheel Bearings at local Pep Boys.
Tensile strength of tube insufficient, centripetal force would disintegrate tube at suprisingly low speed.
Cost of tube of sufficient tensile strength to approach c: "Astronomical".
Electrical flux of moving tube sufficient to cause interruption of Art Bell show; mass hysteria about "Gosh darn space invaders" and "Damn gov't conspiracy" causes WWIII.
Trivially solving for E=Mc^2, Motor would have to impart near infinit amount of energy to accelerate tube of any mass to c.
Cost of near infinite amount of energy: "Pretty way up there", according to General Electric spokesperson.
Inability to anchor motor to counter torque of rotating wheel/tube.
Whistling of tube at near-c velocity could cause graviton wave, angering greys on nearby Alpha Centauri.
Imbalance of rotating assembly at any speed causes catastrophic failure.
Cost of near-c tube assembly hurtling through Earth's atmosphere, piercing the core like a toothpick through an olive, instantly vaporizing the surface and ending all life on the planet: "Priceless"
Don't try this at home.
As I write this there are 3 responses to my questions, 2 of which agree on a (purported) answer to the second question. The question they answer is "what does 'leading edge of the pulse' mean", the queston I'm asking is "why does this keep you from sending a signal superluminally"?
Let's say the answer they give is correct, as far as it goes. The cesium atoms "reconstruct" the light wave from the leading edge. But what if the information is in the main pulse? If the atoms can reconstruct the main pulse, why not the information contained therein?
For instance, the leading edge is presumably much weaker than the main pulse. So let's say you had some "work" (in the mathematical sense) to do on the far side. The main pulse (containing all the energy) gets reconstructed and does the work before a "traditional" signal would have gotten there.
I was going to come up with a more detail example, but then I realized I had another question: What does "leading endge" mean? The pulse is travelling backwards in time. Anything travelling forwards in time must get there later, meaning it can't be "leading".
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First you have to realize that the pulse of light looks kind of like a gaussian. It has a tail on both ends. In this case, the leading tail contains enought information to reconstruct the entire pulse. So .... theoretically, once the tail get all the way through the chamber, all the information in the pulse has already arrived. The only thing that the chamber does is make it so that the center of the pulse arrives at the end of the chamber at the same time the leading edge of the pulse gets there. "Information" didn't get there any faster, but _part_ of the pulse did! The way I understand it the chamber creates a replica of the pulse based on the information in the leading tail of the pulse and places that replica at the end of the chamber. Then, when the actual pulse arrives it is absorbed by the chamber, returning everything to its ground state. This is neat, but not earth-shattering. Then again ... I havn't read the Nature article yet (and news media never gets it right), so maybe I am missunderstanding...
The item is actually old news. For those of you who missed it originally, I will re-post here the text oif a previous, and more exciting. development:
Overclocker Creates Rift in Space-Time Continuum
Alter your definitions of what it means to detect a light transmission, or even to *begin* a light transmission, and it would seem like results like this would be possible.
;-)
That there's a tail to the light posits that there's a time delay in which some small information-bearing light reaches the far end. This tail is not a staccato burst--there's a beam of light behind it. Perhaps whatever happens at the far end causes a cascade reaction(to keep the rush hour analogy, traffic gets backed up *real fast) to amplify backwards in a manner that is *detected* superluminally but is not superluminal itself(such detections are common--shine a laser on a far away mountain--your beam moves superluminally, even though your light doesn't. Persistence of vision is a human trait, not an optical property of nature.)
That these atoms seem primed for amplification of light makes me particularly curious if their amplification traits are triggering false speed measurements. Even if the wavelength is theoretically set for crystal clear propogation, something as major as 300*c transmission would call for further study on exactly what's being detected. My personal guess is that either the time of the initial transmission is being misjudged(imagine a buffering operation taking place within each atom, now imagine those atoms releasing their buffers in the manner they might if they were backpropogating a wave, all in sync to 300C).
That's my guess. But who knows--least of all me
Yours Truly,
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DoxPara Research
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Therefore, the conclusion is that EMR is being transmitted faster than EMR.
Therefore C > C.
There's something seriously skewed with that result.
IMHO, unless I'm seriously out in left field, what they're more likely to have shown is that C has been badly calculated, and nothing has gone back in time or violated C.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Uhm 2 things:
1. Sound would actually travel FASTER through water (or rock or anything dense) than it does through air.
2. Converting light to elctrons would be easy...converting them back to light at the other end would be difficult.
None of your conjecture explians the faster than normal speeds for the light.
Never by hatred has hatred been appeased, only by kindness - the Buddha
The light does not really travel through the chamber at all,
so therefore it does not travel faster than the speed of light. What occurs is that the highly
excited cesium atoms act in a manner similar to einstein-boseium condesate for purposes of light
absorbtion. The atoms exist in such an exited state that they can neither absorb nor reflect the light
pulse. The atoms at the end of the tube emit the light at the same time as the atoms at the
begining absorb the light, because the atoms are so highly excited they must emit light before
than can absorb any. The leading edge spoken of is a gedanken construct to explaing the reverse
wave of negative light that propogates from the end of the chamber to the begining. When
the negative light wave hits the original light wave they cancel each other out. The emited energy
of the mirror of the negative wave(which is the wave of light that is emitted from the end of the tube)
is identical to the original pulse and is emitted from the end of the tube at the same instant
the original pulse enters.
hope this helps explain things.
weird one
"Secrecy is the keystone of all tyranny. Not force, but secrecy
Using this, there's finally a chance to beat the bandwith of a truckload of backup tapes :-)
Disclaimer: IANAP (I Am Not A Physisist), not even qualified to understand the Relativity Theory. But when I attended the classes in highschool and college I got a little grains of understanding of this difficult-to-envision topic. Not from the teacher though, he only sited examples from the books without being able to explain much that made any sense). Here goes nothing.
In science you need a way to define time meaningfully. What does it mean that two events _are happening at the same time_? How do you define that?
Of course in science you need to test, observe, measure and calculate every hypothesis you come up with before you can write down established theories (which may later be called 'bogus' anyways, that's how rude and arrogant some people are..).
Since you must observe everything to prove anything, and light is the fastest known way of communication we know of (except gravity), you need to define two events happening at the same time to an _observer_ as when their emitted lights arrive so that you can observe. If you never receieve anything, the events never happened.
Of course, this is not how reality really works. It is how we choose to _perceieve_ reality scientifically. Now, when you define time like this, the light from the stars (supernovas etc) are telling us what is happening up there _right now_ _scientifically_ (the light from a nearby tree and the light from a distant star is perceived at the same time). This is just because someone was smart enough to redefine time, that is why this is all so confusing!
Note that we're really talking about theoretical light in theoretical arguments about RT, since real light can be altered by gravitation and mirrors (without altering our whole map of space-time that much). Theoretical light moves with a speed in all direction with the speed of c.
So in this case the signal must be received before it was transmitted in order for it to be faster than light. That doesn't mean it went backwards in time according to a more "universal time".
- Steeltoe
http://www.debunkingskeptics.com/
People,
The speed if light in a vaccum is the absolute speed limit, 3.00x10^8 m/s approximately. Nothing faster then go at speed of light in a vaccum.
When light enters a medium [glass, air, water] it slows by n, the index of refraction. for clear class, n is 1.50 so the speed of light in water is (3.00x10^8)/1.33 m/s or approximately 2.00x10^8 m/s.
However, the law states that the speed of light in a vaccum is the fundamental speed limit. So, in glass, things can travel faster then speed of light in glass (2.00x10^8) but obey the law at slower then speed of light in vaccum.
Hence, in that experiment they were saying 300c with c being speed of light in that medium.
Singer
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For those of you who's relativity is a bit rusty, when talking about distance and time in relativity you must talk about interval, since time and space are related.
A timelike interval is one in which two seperate events can be seen, from at least one non-accelerated frame of reference, as happening in the same place but at different times. Think of a clock striking 1 and 2: if you are moving with the clock, it was in the same place, but at different times.
A spacelike interval is one in which two seperate events can be seen, from at least one non-accelerated frame of reference, as happening at the same time but in different places. Think of two bombs going off: at the right place they will seem to be going off at the same time, but never in the same place.
Light normal covers an interval that is neither spacelike nor timelike, but a 50/50 mix of both. However, in this case (if the experiment is to be beleived) the light going through the chamber covered a spacelike interval, but even if you sent the pulse through the chamber and back, it would still not have covered a negative timelike interval. So, you cannot report back the date of the Microsoft breakup and cash in on the stock market.
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for those not "up to speed' on this issue, here is a quick summarry:
as a final note, there were those who also argued that Mozart's 40th Symphony was not information in the first place, and so relativity was not violated.
This brings a certain smile to the face, depending on you musical tastes.
"It is a greater offense to steal men's labor, than their clothes"
Wish I had a whiteboard. Let's try doing this with ASCII art.
Just before the pulse hits the chamber, things look like this:
Pulse Cesium chamber
Note that the pulse has a 'leading edge' -- a rise time before its maximum intensity. Once that leading edge hits the cesium, the cesium recreates the entire pulse on the other side:
So the pulse appears to have gone faster than light through the cesium. Another way to look at it is that the cesium, using nothing more than the leading edge of the pulse, spontaneously created a new pulse. Actually, it created two new pulses, as you can see after a little more time:
|~/#####\->~~~~~~~<-/#####\~| /#####\->
The two pulses within the chamber are moving towards each other, and they'll deconstructively interfere, cancelling each other out. (Actually, they cancel out as soon as the original pulse is completely in the chamber, but it's easier to draw this way.) Meanwhile the pulse outside the chamber is moving away from it and towards your measuring equipment.
So the pulse is not travelling backwards in time. The pulse isn't travelling far at all; it's being annihilated, really, but a copy of it is generated . It just happens to be generated some distance away.
Note that my drawings are flawed; the light pulse was probably longer than the cesium chamber. So the original pulse was already half-destroyed by the time the new pulse emerged from the other end. That would have been difficult to draw.
Why can't we use this to send information faster than light? Read the article again -- they're not really sure that you can't. One person is arguing that the information is packed into the leading edge of the pulse (sort of an optical gzip) and so you're compressing information but not sending it superluminally. Other people (Dr. Nimtz, third paragraph from the bottom) say that they really are sending information faster than light.
Personal opinion: This looks like some kind of wave phase propagation trick to me. We've always known that you can cause a phase shift in a beam of light to propagate superluminally, but the problem is that you can't encapsulate information in phase shifts adequately, due to (IIRC) the uncertainty principle. Not to say that this isn't an exciting experiment, but it doesn't appear to have a practical use. Now, the microwave experiment that travelled at 1.05 c excites me...I'd like to see if they can extend it to interstellar distances and through vacuum. :)
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
If a processor worked faster than light it could generate output before the input was entered
This would be very embarasing when it spits out the answer let's say 42 and you forget what question you wanted to ask.
134340: I am not a number. I am a free planet!
Again, I'll freely admit that I don't understand the first thing about relativity.
So why even post this?
Special relativity works like this:
Normally, if you're on a train moving at velocity V, and you walk forward at velocity W, you would think that your velocity relative to the ground would by V+W. Well, you'd be wrong. It's very close to V+W, but is actually a bit less thanks to Special Relativity. This is no fiction; it's a measurable phenomenon (perhaps not with people walking on trains, but it's measurable in other situations).
This "little bit" grows as you move faster, to the point that if V and W are almost the speed of light you don't move anywhere close to V+W. Relativity always comspires to give you a combined velocity less than c.
one moment you're going 'c'-0.000001 and all is peachy; the next moment, you're going 'c' and the very fundamentals of perception change?
Not at all. Things would be very, very different at 'c'-0.000001. Relativity is not something that "kicks in" at the speed of light. You experience it even taking a leisurely stroll on a train.
--
Patrick Doyle
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Thiotimoline dissolves before you add the water - and the interval depends on the amount of uncertainty in the mind of the experimenter... This was published under Asimov's real name just before his (Biochem?) PhD thesis defense - its a delightful story, and its been used by authors like Silverberg as the basis for other time travel spoofs.
Reality is catching up with fiction, eh?
"I will take the Ring," he said, "though I do not know the way."
My professor (who has two phd's after his name) says (from about a minute glance) that:
The entire beam of light is not traveling faster than c. What is happening is that some of the peaks in the frequency are moving faster than c.
This is from reading a paragraph long synopsis, so here's your grain of salt. Also, I probably mangled what he said.
This contredicts every thing I've learnt (not that I am saying it is impossible, the theory of relativity contredicted everything classic physics said). According to what I know, when calculating speed relativly, it is impossible to go above the speed of light, here is the reason why I can't figure it out:
1/((1-(v^2/c^2)^0.5)
When you go above the speed of light, v^2 becomes larger than c^2, giving you a negative number within a squareroot, how would you get past this?
On the other hand, nothing ever moved faster than light. So far as I can tell, when sound moves at Mach 1 (or so), it's not because your mouth emits particles that are moving at mach 1 and they reach the other person still moving at mach 1. The wave moves faster than the particles involved at any given time.
Patterns aren't things.
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..and here it is. I don't think that we can think of the speed of light as a constant (do we?), but rather as a number related to its situation. If you don't think of it in this manner then you get into the sticky area of C > C, which gives me a headache when I think of it too much.
Therefore, if you were to say that an object with zero rest mass is able to travel at the speed of light, you must qualify that statement with a statement of the conditions under which it would be travelling the speed of light. This would become more important in situations where an object with a non-zero mass approaches the speed of light and the energy of said object is being calculated.
Then again, I almost failed grade 12 physics, but that was over a girl, not lack of understanding.
"Share your knowledge. It's a way to achieve immortality." -- Dalai Lama
OK, here's the reason why things can't go faster than the speed of light.
Relativity (Special Relativity at least) is based on 2 postulates:
For example: you're on a train, and your friend is next to the track as the train goes past. This is quite a fast train - it's going at half the speed of light. You shine a torch ahead of the train: The light coming out of the torch is going at the speed of light (from your point of view - your 'frame of reference') Your friend standing by the side of the track also sees the light coming out of the torch. From her point of view, it's also going at the speed of light. It looks like we have a problem here: She sees the train moving at half the speed of light, and the light moving at the speed of light - the light is going at half the speed of light relative to the train. You on the train however see the light moving away from you at the speed of light.
Paradox? No. Einstein showed that it is actually our concept of space and time that is wrong. From your perspective on the train, everything else (including your friend) is actually squashed up in the direction of the motion of the train - parallel to the tracks. So the light has gone 'further'. Your friend sees the train squashed up (parallel to the tracks) and that time has slowed down on the train.
All this is effectively saying is that where the light is at a particular motion is not disputed by either you or your friend, so there is paradox.
So that's relativity. All you need is a speed which is the same in all reference frames. It doesn't have to be anything to do with light at all. There isn't anything which forbids 'faster than light' travel.
There is a consequence though: If something is travelling faster than light in one frame of reference, there will we another frame of reference where it appears to be travelling backwards - it comes out of the end of the chamber before it's entered the other side.
This causes problems with causality. Things happen before they are caused to happen.
BB.
PS. I'm studying physics at Oxford, England.
-BB
More on the traffic flow idea here.
I am dyslexia of borg - your ass will be laminated.
As the beacon turns, the beam can have a linear velocity (wr, w=angular velocity, r=radius of measurement) perpindicular to itself in the plane of rotation greater than c. Does this transmit information? No.
With a large enough pair of scissors, closing them will cause that point where the blades cross to move away from the pivot at a speed faster than c. Note that nothing physically moves faster than c, but only the point of contact between the blades.
Furthermore, superluminal displays have been available for years. I have an English "How-it- works" encyclopedia at home that has a picture of a blue glow generated by particles exiting a nulcear reactor core submerged in water. These particles exiting the core are travelling faster than c in water (dielectric constant of water is 76.7 -- Pozar "Microwave Engineering") That means that the speed of light through water is c*sqrt(76.7) = 34.3e6 m/sec!
Every time I talk to a vendor of microwave substrate materials, they tell me about their high-Er products. They tell me how great they are for shrinking microwave circuits, where the size of circuit features are all scaled to be fractions of wavelengths. *I* always ask for lower and lower dielectric constant materials, as they don't know how much trouble they're causing me from a manufacturing standpoint. Sometimes I joke and ask for sub-unity dielectric constants. That way I could make a millimeter-wave board with geometries that aren't microscopic! :)
This reminds me of a similar result reported a few years back by Raymond Chiao on superluminal tunneling of light (Phys. Rev. Lett., v.71, p708, 1993). Although it is not exactly the same thing, I thought it might be relevant to the conversation here - especially since Ray was quoted in the NY Times article and cited as having laid some of the groundwork for the current experiment.
The question was: how long does it take a photon (or any other particle for that matter) to quantum mechanically "tunnel" through a classically forbidden region? Although superficially simple, this problem has a lot of depth because it strikes directly at the kinetic energy of a tunneling particle. In classical physics, a particle cannot enter a region in which its potential enegy would exceed its total energy (which is the sum of its kinetic and potential energies). However, in quantum mechanics, there is a non-zero probability for finding a particle in such a classically forbidden region. This implies a negative kinetic energy, since the potential energy exceeds the total energy, which in turn implies that the particle's momentum, which is proportional to the square root of the kinetic energy, is imaginary. Thus, the question becomes, how "fast" does a particle with imaginary momentum move? In all fairness, this is a very quasi-classical way of looking at the problem. A better way is to ask how long can the particle be in the forbidden region for a given energy uncertainty consistent with Heisenberg's uncertainty principle (HUP). But at the end of the day, they both reduce to the same problem.
Now, in practice, optics experiments of this type are performed with wave packets - typically gaussian envelopes of narrowband electromagnetic energy. The frequency spectrum of such a packet is also gaussian with a bandwidth proportional to 1/(pulse length). It is a well-known result of quantum mechanics that the phase velocity of the individual spectral components of the pulse can exceed the speed of light but that the aggregate "group velocity" of the center of the pulse cannot. This leads to dispersive effects such as pulse spreading as the packet propagates consistent with the HUP (which really has less to do with physics than with the relationship between temporal resolution and bandwidth of any signal). This turns out to be significant here.
If I recall correctly, the punchline in Chiao's superluminal tunneling experiments was that the _PEAK_ of the tunneling packet emerged from the forbidden region faster than the _PEAK_ of the original packet could have traversed the same distance at the speed of light. However, the _LEADING EDGE_ of the tunneling packet did NOT arrive any earlier than the _LEADING EDGE_ of the original pulse could have traversed the forbidden region at the speed of light. If you read the NY Times article of the Nature blurb you probably see where I am going with this. It was strongly implied in those articles that the peak of the superliminal pulse does not arrive any faster than the leading edge of the luminal pulse. Futhermore, it was pointed out that phase velocity of the light used in the experiment greatly exceeded the group velocity of the wave packet. This implies that when the leading edge of the luminal pulse enters the chamber, its spectral components can travel faster than the speed of light through the cesium and reconstruct an apparently superluminal pulse at the far end of the chamber (while simulataneously cancelling the input pulse). But, I suspect from Chiao's earlier work, that the the leading edges of the input and output pulses WILL maintain their luminal relationship and, thank heavens, causality is preserved.
So, the moral of the story is: a feature of a signal can arrive at its destination superluminally as long as the signal as a whole does not. In this case, I suspect that the leading edge, which represents the arrival of the signal, travels luminally or, more probably, sub-luminally. However, the peak, which is just a feature of the signal's envelope, appears to travel superluminally. This implies that the peak has moved closer to the leading edge of the pulse and all this is but a feature of the change in phase velocity for the spectral components in the electromagnetic pulse upon entering the cesium-filled chamber.
Please realize that this all conjecture since I have not actually seen the article being discussed (it is still in peer review). However, I believe this is a reasonable interpretation based on information available and is consistent with similar prior results. So, ultimately, I think that this is less an issue with relativity than an issue with quantum mechanics and that nobody need worry that their disgruntled grandchildren are about to travel backwards in time to kill them in a universe-shattering temporal paradox!
Hoorah! Now we can create microwave ovens which cook you're food before you even see it!
--------- Beware the dragon, for you are crunchy and good with ketchup.
...a Michael Crichton novel about this within the next four years.
And his SF novels are so utterly formulaic and predictable that I could almost write this one for him myself. Ya listenin', Mike?
"How many light bulbs does it take to change a person?" --BMcC-->
Just wondering, but if this were to really go faster than light, it still wouldn't violate causuality(sp?), only appear to do so. Let's say a laser is fired at Bill Gates. Due to his massive control on technology and US gun laws, he installed a FTL signal generator in said laser. Instantaneously he recives "duck you fool". If the laser is suffiecently far away, he will be able to duck before perceiving the laser(perceiving the laser also equaling being shot). The image of him ducking will reach you an equal amount of time as the laser takes to reach him. From your POV he ducked after you shot him, but somehow escaped unharmed. erm, maybe I've fallen out of my train of thought
This reminds me very much of those cloud chamber pictures that show virtual particles appearing before they are supposed to. The explanation is that these particles are "borrowing" energy from the vacuum and returning it later: the energies balance eventually. (This is related to the phase-transition problem and the electron tunneling phenomenon as well.) What's interesting here is that this "borrowing" effect appears to be happening at a macro (i.e. non-atomic-scale) level: that alone could win the authors of this experiment a Nobel Prize.
DNA is a Turing machine. You, however, being dynamic and emergent, are not.
Actually, this is mere conjecture. I don't believe we have ever tested the 'speed' of gravity, or detected the 'graviton', or anything else. Due to gravity being the weakest force we know, coupled with our inabiltiy to make large amounts of mass just appear and disappear....
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The flaw is this: if you have an evanescent wave affecting the outcome of the experiment, you switch the properties of the interface at which the wave is being generated.
A simple way of observing this is to do the following:
Set up a glass prism, with light totally-internally reflecting on the back face of the prism. (the evanescent wave comes out of that face of the prism, but is not yet "realized").
Get another prism, put its back face against the backface of the prism. Provided that the gap between faces is less than the decay-length of the prism (which is why you generally do this experiment with microwaves in a lab), then what happens is that the back face no longer totally-internally reflects, and instead becomes transmissive, because the evanescent wave can now be transmitted before it decays.
The gap size then can be modified to determine how much of the wave is transmitted straight through (based on how much the evanescent wave decays), and how much of the wave is reflected (namely, the amount the wave decays before resuming transmission in an appropriate medium, is the amount that's reflected).
This effect *is* seen all the time in quantum physics; it's the principle behind tunnelling (except of course, with QM, it's an all or nothing affair; either it tunnels or it doesn't, and so you have to start looking at it in terms of probabilities, rather than the amount of wave that's transmitted).
Feynman described *exactly* this effect in his lectures on physics; a particle comes in, hits a barrier, and then crosses the barrier as an *antiparticle* (that is, as a particle going backwards through time; ie. faster than light). Another particle is then generated on the other side of the barrier, where the antiparticle is reflected *back* in time to destroy the original particle.
The problem is, of course, getting the gap big enough and still having the signal not decay too early.
Now personally, I have my eye on another method of faster than light transmission involving particle/antiparticle creation events, but its been too long since my degree, and as such I don't have the grounding or the math to check up on it. Mind you, if I ever win the lottery, I'll fund the guys at CERN to see if I'm correct. The experiment is dead simple, and it'll either work or not.
Simon
Coming soon - pyrogyra
The only reason we ever thought of light as a hard speed limit is because some (Like Albert) thought this would violate cause and effect not any physical law
Even with special relativity you can show that if you can send a signal faster than c in one frame of reference, you can pick another frame of reference where the signal goes backward in time.
And since physics is invariant between reference frames you could use anoter moving-with-respect-to-the-first-frame apparatus to send another faster-than-light signal (as viewed in the second frame) to return the information to its starting point in the first reference frame's space (as viewed in BOTH frames), arriving before it left.
Now you've got a signal back in time to a point inside the "past" light-cone of the moment in spacetime where it originated (or at least before it entered the first FTL apparatus). Use it to disable the sending signal (as by realligning a mirror if turning off the laser is too slow, given the length of your apparati) and you've got a causality paradox.
THAT's why "some (Like Albert)" thought this would violate cause and effect.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
I'll bite..
The explanations of the experiment state that a pulse may travel faster than light (over a short distance) as an 'evanescent wave', but it can not carry information.
How then is it detectable? I mean, if you can tell it's arrived, didn't you just send information?
The fact that a Morse-code dot has arrived is information, isn't it? The sequence of transmissions carries data, not any single 'bit' pulse. What am I missing?
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This is an analogy that I have floating in my head...is it valid, does it even make sense?
Ok, imagine a long line of people standing side by side. Each person can hold a cube above their head and one below their head. Just think of people as units of space and the cube position as an excitation level or something.
Now populate this line of people with some random distribution of cubes either in the high position or the low position or both or neither.
Now I come along to the first person in the line and have a pattern of cubes I want them to transmit to the other side. In order to take my first cube in the correct position they need to ensure they have room for it. So if they already have a cube in that position, they must pass it on to the next person in the line. And that person must pass it on to the next, and so on, until it reaches the end. I continue handing cubes to the first person in the pattern I want, and that person, to make room, implicitly propagates my pattern to the other side. It looks as if my pattern of cubes is coming out the other side before I even finish giving it to the first person! (somebody mentioned that in fact the pattern comes out the other side a bit before I have finished giving my cubes to the first person...let's just say then, I tell them ahead of time the pattern I am giving them - this is where the "head" of the wave comes in I guess) Now, the second I have completed giving the pattern to the first guy in the chain), my actual physical set of cubes needs to be physically transmitted to the other side. So each cube is handed over to the next person in order. Now, the last guy can't simply drop his cubes on the floor when he recieves them from the next person. The cubes must be preserved. So he magically simultaneously hands BACK the cubes he has as he recieves the new ones. As you can imagine, when the cubes he hands back reaches the center of the list of people they will annihilate with the cubes being propagated.
Does this make any sense? I know it really doesn't because the analogy is flawed with the pattern of cubes. It seems to me, that the pattern you push in from one side, is causing an equal and opposite reverse echo from the far end which annihilates in the middle as your pattern is physically passed. Fortunately your pattern has already come out the other side because in order to recieve your pattern, the pattern holding material has had to give up the necessary slots, thereby implicitly passing on (or pushing out the other side) the pattern before it is actually physically recieved. Make any sense? Do I need medication?
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Seems to me we must determine whether the "leading edge" is a hypothetical made up to save causality or a real information carrier resulting from the bandwidth limitation of the pulse. To separate these cases we must answer this question:
Does the apparatus recreate the entire pulse, or just the main body?
Phrased another way: If the information is all contained in the hypothetical "leading edge", does the leading edge get reproduced with the same lead as the rest of the pulse?
The way to answer this is to send the allegedly sped-up pulse through one or several additional steps (or a much longer device) and see if it continues to be transmitted FTL and correctly recreated in each device. Keep increasing the hop count or the length of the hop until the total time the pulse arrived early (as compared with propagaion in vacuum) exceeds the time-length of the hypothetical leading edge, and the pulse is either distorted beyond readability or still intact.
If it arrives intact, then the WHOLE PULSE, including any information it carried, got moved forward, sending information FTL. If it doesn't, then the information went out in the leading edge, and the FTL transmission was only apparent.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Seems counter-intuitive. If gravity propagates at c, then a black hole would 'capture' it's own gravity inside it's own gravity well. Even taking into consideration that a gravity well may not collapse into a black hole in any finite amount of time, as the well collapses towards the event horizon, the propagation of the gravitational field would slow down as the time frame slows, which would cause an orbiting object to orbit, not where the proto-blackhole was a minute ago, but where it was a century or a millenium ago.
It's the delta-G that travels at C, not the G itself. Think of it as a rubber sheet. Sure, the black-hole stops null-line particles (eg. photons) from getting out, but they're travelling on *top* of space. The gravitational waves *are* the space itself. Gravity is also weird; gravitons would appear to affect other particles, but not each other.
Simon
Coming soon - pyrogyra
Well, in that case, light has mass, and therefore, *loses his train of thought* ... i dunno, a lotta physics assumptions are wrong I'm guessing.. i've never taken physics.
:)
:))
Of course light has mass - E=mc^2 and all that jazz.
However, light has zero rest mass; that is, if you ever had a photon of light that was stationary wrt. your reference frame, it'd have no mass.
Given that light is always travelling at C, regardless of the reference frame, this can't happen though. So yes, photons have mass.
(btw: photons still travel at C in non-vacuum media too, but there's a whole load of other effects at work that make the *observed* speed of light lower... it's not always the same photon the whole way through
Si
Coming soon - pyrogyra
NASA has a research group that focus on all aspects of physics that *could* lead to the developement of superluminal drive technology.
They recently accepted some proposals for experiments that will receive a grant from NASA. One of them, number 5, is essentially the same we are talking about in this discussion.
BTW, do take a look at the BPP site and "Warp drive When" page, if you didn't have already.
Ciao,
Rob!
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