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. "

Comments

No login mirror

[Janthkin]

As usual, you replace the "www" with "partners" to get the no login required version of the article, found h ere.

real URL

[ChristTrekker]

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.

Re:NY Times Login

[Adversary]

You could always use login, password: cypherpunk / cypherpunk.

More information

[spiralx]

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.

Huh?

[FascDot Killed My Pr]

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.
--
Have Exchange users? Want to run Linux? Can't afford OpenMail?

Re:Huh?

[Sir Tristam]

So which is it? Did the pulse exit before it entered OR was there a "leading edge". You can't have it both ways.

Actually, you can have it both ways. When the pulse enters the chamber, the leading edge enters before the trailing edge. The time difference between when the leading edge exited and when it entered is the same as the time difference between when the trailing edge exited and when it entered. If you would have a fixed observer at the entrance, and another fixed observer at the exit, the fixed observer at the exit would see the pulse before the fixed observer at the entrance.

If you looked at the whole system, this is probably what the experiment would look like: A pulse is emitted from the exit of the chamber, and a mirror copy of that pulse appears to be emitted back up the chamber from the exit. While this pulse is travelling up the chamber, the microwave transmitter emits a pulse towards the entrance of the chamber. The transmitted pulse and the pulse travelling up the chamber meet at the entrance to the chamber, where they appear to destroy each other. Notice that the pulse travelling backwards up the chamber is a mirror image of the other two pulses (which are actually the same pulse.) If the leading edge of the pulse outside the chamber is to the left of the trailing edge, then the leading edge of the pulse is to the right of the trailing edge inside the chamber.

For those who are interested by this subject, Nick Herbert wrote Faster Than Light: Superluminal Loopholes in Physics in 1989; it still remains quite interesting and speculative.

Re:Huh?

[YoJ]

Superluminal speeds are pretty cool. There is a great descriptive article in Scientific American, August 1993 about superluminal tunnelling effects that I found very helpful in intuitively understanding these types of things.

In the SciAm article the experiment is set up so that two pulses get shot and detected by separate photodiodes. One pulse goes through vacuum the whole way, and the other one has to tunnel through a thin barrier. The one that tunnels through the barrier gets to the detector first! Does that mean the pulse went faster than light inside the barrier? Well, sort of.

What's really going on is a quantum mechanical effect. A pulse isn't really a sharp spike. It exists in the real world, so it has width and really looks like a hump. When it hits the barrier, most of the hump gets reflected back. Only part of the hump tunnels through. The part that tunnels through is the front edge of the hump. When the two pulses get detected, the center of the tunnelling hump is ahead of the center of the non-tunnelling hump.

This explanation is less crazy than the faster-than-light explanation, and it explains why this type of thing can't send information faster than light. If you think about it, the height of the small hump is the same as the height of the leading edge of the untunnelled hump. So for a given detector, you can sense the presence of a pulse at the same time whether it tunnelled or not.

I don't really know exactly what is going on in this case, but I imagine that looking at it in the right way makes it less sensationalistic and more intuitive.

-Nathan Whitehead

The real interest...

[Saraphale]

What sort of bandwidth can you get by transmitting down cesium-based fibre at 300 times the speed of light? ;)

Easy to show whether they are wrong or right...

[yuggoth]

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.

They are comparing to speed of light in vacuum.

[Mr Z]

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.

--Joe
--

Re:Less confusing, but little more info

[kinkie]

Short answer: evanescent waves can't carry information because thery convey no power.

Long answer (I'll try to keep it simple): when a beam of EMW (electro-magnetic waves) hits the interface between two materials, it gets partially reflected (and thus returns to the side where it came from), and partially refracted (that is, "goes forward"). Think of the effect you have when you look at a stick through the water's surface. How much of the incoming power is reflected and how much is refracted depends on the two materials involved.
We're mainly interested in the refraction part at this point, and particularly at the angle the EMW beam has with the interface surface. Under certain conditions, the propagation angle of the refracted ("forward") beam with the perpendicular to the interface's surface is bigger than the one of the incoming beam. If we increase the incoming beam's angle, so does the "forward" beam's, until it is completely parallel to the interface. At this angle ("critical angle") the physics of the whole setup change abruptly, and all the incoming power gets reflected. But some kind of EMF is still present in the "forward" part of the interface, generating some field patterns named "evanescent waves".
Those waves don't carry power "forward" (because it's all being reflected), but _can_ carry power along the interface.
This effect has also been studied for long-distance communications using the earth-to-air interface as a carrier.

Old News

[fred_the_slow]

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

Santa Cruz, CA - A rift in the space-time continuum was created today when overclocker Jamie Aperman ran a 750 MHz Coppermine Pentium III at 1.6 GHz. Overclocking has long been blamed for causing global warming, but this is the first occasion that the fabric of space-time has been damaged.

MIT Professor George Greznowski said, "It appears that the CPU was operating so fast that it began to execute instructions before they arrived. This execution of future instructions created a small tear in the fabric of space-time itself through which part of the motherboard passed into a parallel universe."

No one was injured in the accident, but a computer motherboard was partially damaged. Mr. Aperman better known as SpeedPhreeek said, "I'm pissed. I lost a brand new Alpha Cooler and Coppermine to a parallel universe. I called my insurance company and they don't cover losses to rifts in the space-time continuum."

Intel researchers have long warned of such damage to the space-time continuum, and added clock multiplier locks to their CPUs before they were required by Congress. A bill is now in the US Senate which would require a three day waiting period for purchasers of Alpha Cooling Fans and Peltier cooling devices. The bill would also require clock multiplier locks on all new processors.

Overclocking advocate Horace Spencer said, "This bill before Congress won't prevent overclocking. They'll just create a black market for non-locked processors. Most of the top overclockers already get their goods from Taiwan." (link no registration req. here: http://bbspot.com/News/2000/5/clock_rift.html)

Re:E=mc^2

[Dust Puppy]

They were talking about rest mass.

Rest mass is the mass something would have if it wasn't moving.

Only things which have zero rest mass (such as photons) can travel at the speed of light.

If something which had non-zero rest mass was moving at the speed of light it would have infinite kinetic energy.

The correct equation is E=mc^2/sqrt(1-v^2/c^2) where v is the velocity, m is the rest mass and E is the energy (which is the sum of the rest mass energy mc^2 and the kinetic energy).

Re:E=mc^2

[EricWright]

This is just a statement of the *equivalence* of mass and energy. This equation just specifies how much energy you can get out of the destruction/conversion of a particular amount of mass.

The energy of anything is correctly E = sqrt((pc)^2 + (m_0*c^2)^2). Thus, when an object has no rest mass m_0, it's energy reduces to E = pc. Since photons fall into this category, and since the momentum p of a photon is h/lambda (Planck's constant over wavelength), E = pc = hc/lambda = hf (where f*lambda=c) is more appropriate for massless particles like photons.

Eric

T=0

[Effugas]

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,

Dan Kaminsky
DoxPara Research
http://www.doxpara.com

Re:Eh?

[JohnnyCannuk]

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.

Speed of Light -- Physics Major

[BWS]

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

This isn't time travel

[wowbagger]

Sorry, but even if we assume the light pulse traversed the chamber at V=300*Cvacuum, this is still not time travel. The light did not traverse an interval with a negative timelike value, it traversed a spacelike interval with a positive timelike component, to use relatavistic terms.

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.

ASCII art description

[Remus Shepherd]

I am a physicist, but not an optical physicist, so take the following with a grain of salt.

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. :)

hmmm

[the_other_one]

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.

Special Relativity 101

[p3d0]

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

Resublimated Thiotimoline

[pq]

This whole news article reminds me of the Asimov story, "The Endochronic Properties of Resublimated Thiotimoline". (Astounding SF, March 1948, republished in The Early Asimov.)

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?

Re:But...

[Nehemiah S.]

but...

the formula used in the original Star Trek series for warp travel is

v = (W ^ 3) * c

where v = velocity, c = speed of light in vacuum, and W = Warp factor. So 300c would be warp 6.69433- easily within the range of any Federation vessel. Warp 300 would be 27e6*c!

Don't ask me why I felt compelled to share this; I don't even like ST.

Rev Neh

According to my Prof

[Ex Machina]

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.

What's so special about c?

[lingsb]

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:

1. The laws of physics are the same in any inertial (ie. non-accelerating) frame of reference. This means that the laws of physics are the same on earth (technicall only without gravity) and if your on a (hypothetical) spaceship traveling at half the speed of light a million light-years away from earth.
2. There is a speed, which when you 'transform' from one frame of reference to annother, remains the same. 'Tranforming' your frame of reference is simply looking at what the other person would see.

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.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:Waves with no energy, undetectable?

[spectecjr]

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

Faster than c IS backward in time.

[Ungrounded Lightning]

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.