This story broke a couple of months ago and was kept under wraps but is now hitting the mainstream media...

Getting There Faster: Light's Speed Accelerated

By Deborah Zabarenko

WASHINGTON (Reuters) - Scientists using lasers and specially prepared atoms have managed to make a pulse of light exceed its own top speed of 186,000 miles per second, appearing to leave a laboratory tube before it had fully entered.

This feat might seem more like wizardry than physics to some scientists, who have long assumed that nothing in the universe could go faster than the speed of light in a vacuum.

But researchers at the NEC Research Institute found they could make pulses of light zoom through a tube at a much faster speed, with the peak of the pulse emerging from the tube 62 billionths of a second before the peak had entered.

``It looks as if you've done something magical ... but you can explain this based on physics. This is not a time machine,'' James Chadi, vice president of the institute's science division, said on Thursday in a telephone interview from Princeton, New Jersey.

The NEC team's findings, published in Thursday's issue of the journal Nature, do not contradict Albert Einstein's theory of relativity, in which the great 20th century physicist set the speed of light in a vacuum as the absolute maximum speed for the universe.

According to Einstein's theory of relativity, nothing with mass -- like people or things -- can ever go faster than light, the researchers noted. But something with no mass, like a packet of light waves known as a pulse, can.

``Our experiment is perfectly consistent with Einstein's theory of special relativity,'' said lead researcher Lijun Wang in a telephone interview. ``Precisely speaking, it is the speed of information transfer that is limited by the speed of light in a vacuum.''

EXITING BEFORE IT ENTERS?

All the necessary information about the pulse is contained in its tiny leading edge. As soon as this sliver of the pulse enters the chamber, the specially prepared atoms can begin making another, identical pulse at the chamber's far side.

This finding might have implications for telecommunications, Chadi said.

A telecommunications application may exist even though information cannot move any faster than the speed of light, and it usually moves much more slowly, according to Arthur Dogariu, one of the authors of the Nature paper.

``Information is basically pulses,'' Dogariu said by telephone. ``When you talk about the Internet and fiber optic communications, it's limited by how the pulses can move through the wires, by how many of them there are, how thick the wires are.

``If you can create the medium in which pulses propagate, it would allow them to go through faster as a packet of waves,'' he said.

Any such application will not occur soon, and Dogariu said the environment he and his colleagues created in their laboratory could be re-created in other labs but not in nature.

Researchers at the NEC lab created this medium by using lasers to specially prepare atoms of cesium gas inside a cylindrical chamber about 2.5 inches long, and then shooting pulses of light through it.

Wang said the laser pulse should be thought of as a group of undulating waves of light, with peaks and valleys.

Normally light would pass through a vacuum chamber of that length in 0.2 nanoseconds, or .2 billionths of a second. But the cesium atoms in the chamber shift the light pulse, making it zip through the chamber and exit 62 nanoseconds sooner, or more than 300 times earlier.

As soon as the leading edge of the pulse enters the chamber, the atoms start to reconstruct the pulse at the chamber's far side. This reconstructed pulse can then emerge from the far end of the chamber sooner than it would go through a vacuum.

The NEC Institute is funded by Japan-based NEC Corp., which makes computers and communications products.

---

Think about the implications. Most of our computers and telecommunications are already using fiber optic cable for transmitting information. It could be a very short time before technology allows us to transmit information faster than the speed limit which is believed to apply for physical mass.

This means that you could watch the horse races tomorrow and send the information of which horse won back in time to yourself today, so that you could place a bet that would make you rich. This means that in the very near future, events could be recorded on video and sent into the past, bringing our experience of time to a virtual standstill.

Even if it isn't possible for our physical selves to travel through time, just being able to send information through time would drastically change the motivations of the human race. Would we finally begin to realize that nothing really matters but the present, and become more spiritually evolved? The implications are mind blowing, and this is something that may even become a reality within our lifetimes.

-- Hawk (flyin@hi.again), July 20, 2000

Answers

Just think Hawk, you could replace the faulty embedded chips in the jack screw assembly on Flt 181, then go back and catch the fight and live through it.

Cool huh?

:>)

-- Ra (tion@l.1), July 20, 2000.

That might have been funny if you had paid attention to the article, but instead it just sounds stupid.

A physical person cannot go back in time. However, using this technology, information in the form of light pulses could be sent back in time to let the airlines know that the plane crashed, so they should ground it until they discover the problem.

-- Hawk (flyin@hi.again), July 20, 2000.

Hawk, you are right. I still can't get over it, read it in the Washington Post this morning. I never dreamed this would be possible, thought the speed of light was one of nature's absolute limits.

-- Amazing (cant@believe.it), July 20, 2000.

Nice catch Hawk.

-- Will (righthere@home.now), July 20, 2000.

DID YOU EVEN RED THE ARTICLE HAWK, OR DID YOU JUST RANDOMLY PICK ONE IN THE HOPE THAT YOU WOULD LOOK SMART? READ AND THINK BEFORE YOU POST. DO YOU LIKE THESE LARGE LETTERS? I AM THINKING ABOUT WRITING PHIL GREENSPUN AND ASKING HIM FOR BIGGER LETTERS, SO I CAN HAMMER MY POINT ACROSS TO YOU. BUT NO MATTER HOW BIG I GO YOU WILL PROBABLY NOT GET IT. BUT I WILL TRY, AND YOU MIGHT JUST GET AN EDUCATION. TO QUOTE PAUL MILNE "THE NEVER ENDING EDUCATION OF LITTLE HAWK-FLYING@HIGH.AGAIN".

-- (BIG@BIG.BIG), July 20, 2000.

-- - (-@-.-), July 21, 2000.

That anything momentous is being made out of this is a sad comment on the state of public awareness of physics. How hard is it to understand that it's not very difficult for "something" to travel faster than light, as long as that "something" doesn't carry any information (e.g., the intersection of the blades of a very long pair of scissors)? Apparently too hard for the journalists covering this story, and for the posters on this forum.

-- ABC (a@b.c), July 21, 2000.

ABC, your post is the most incredibly stupid, utterly pretentious piece of nonsense I have ever read. For one thing, as the tips of the scissors approach the speed of light, they supposedly attain mass approaching the infinite.

-- Elmo (ee@ff.g), July 21, 2000.

The "C" word Hawk.

Can "YOU" ansure why you like or need to use it?

What is the male word for dirty?

-- BOOBS (itsfake@goingalong.com), July 21, 2000.

Coming soon: Ron Popeil selling "Mr. Pulse-Propigator" on an infomercial (only five easy payments of $71,150,000 -- four, if you call within the next fifteen minutes).

-- I'm Here, I'm There (I'm Everywhere@so.beware), July 21, 2000.

Re: http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v406/n 6793/full/406243a0_r.html&filetype=

Is there a typo? They have c/310 , should it be 310c? No, here's why. It appears that a Shell Game, bait and switch, going on here.

"The experiment by Wang and co-workers creates this type of gain doublet in a six-centimetre cell containing caesium gas by using two laser fields closely spaced in frequency (see Fig. 1a on page 277). They first measured the refractive index of the caesium using a third 'probe' laser, and produced a dispersion curve similar to Fig. 1b, with a steep gradient in the anomalous dispersion region corresponding to an expected vg= - c/310. When they sent a 3.7-microsecond light pulse through the medium, it appeared at the exit of the cell before it arrived at the entrance. Although the pulse itself is only shifted forward in time by a modest fraction (1.7%) of its width, this corresponds to the wavepacket leaving the cell 62 nanoseconds before it arrives  in other words, travelling nearly 20 metres away from the cell before the incoming pulse enters it. Compared with the time to travel six centimetres in a vacuum (about 0.2 nanoseconds), the 62-nanosecond lead means that the group velocity of the pulse inside the medium is - c/310, close to the predicted value."

The Nature write up by Jon Marangos is not as clear as it should be for the lay public. Look at their

"vg = - c/310"

where vg = group speed of the light pulse. Last I heard

|c/310| < c

Again Nature writes

"the 62-nanosecond lead means that the group velocity of the pulse inside the medium is - c/310"

So what's going on?

Formally of course - c < -c/310 < c. So there seems to be a Shell Game going on since many people think the claim is 310c > c, which is not being claimed at all!

Nature writes

"The difference in transit times dT= L/v-L/c is a negative quantity if the velocity is superluminal. If v has a negative value then T can become sufficiently negative that the peak of the pulse emerges from the medium at an instant earlier than when the peak of the pulse enters."

Note that these are two different mathematical cases being garbled.

Case 1. vg = xc > 0

dT = (L/c)[1/x - 1]

If x > 1 (superluminal), 1/x < 1. Therefore, 1/x - 1 < 0, so dT < 0.

Case 2. vg = xc as before.

Let x = -1/310

Note however that |vg| = |xc| = c/310 < c so that the absolute magnitude of the pulse is very slow i.e. subluminal not superluminal. Yet because the group speed is opposite in sign to the phase speeds in the anomalous dispersion region

dT = -311(L/c)

So this quantity is not a real measure of superluminal pulse speed in this case. The fact that dT < 0 by itself is not sufficient to conclude superluminal pulse speed.

For a real transverse polarized photon, the "light cone" mass shell for the pole of the propagator in a material is

f = kc/n

f = frequency

k = wave number

c = speed of light in vacuum

n = real part of the complex material index of refraction

phase speed = f/k

group speed = vg = df/dk = c/n + kc (d/dk)(1/n)

= c/n + kc(d/dn)(1/n) dn/dk

= c/n - (kc/n^2) dn/dk

dn/dk = (dn/df)(df/dk) = (dn/df)vg

vg = c/n - (kc/n^2)(dn/df)vg

vg [1 + (kc/n^2)(dn/df)] = c/n

vg = c/n [1 + (kc/n^2)(dn/df)]

Now look at top picture in

http://www.nature.com/nature/journal/v406/n6793/fig_tab/406243a0_F1.ht ml

The red curve has dn/df < 0 in the region of anomalous dispersion around the material resonance, and this, it seems to me is the key mathematical point.

Any real superluminal pulse would require

n [1 + (kc/n^2)(dn/df)] < 1

to make vg > 1

n + (kc/n)(dn/df) < 1

n^2 + kc (dn/df) < n

n^2 - n + kc (dn/df) < 0

Solve for the roots of the polynomial

n^2 - n + kc (dn/df)

n(+/-) = { 1 +/- [1 - kc (dn/df)]^1/2}/2

The polynomial is then

n^2 - n + kc (dn/df) = [n - n(+)][n - n(-)]

The superluminal pulse region is then

[n - n(+)][n - n(-)] < 0

Note that in the anomalous dispersion region dn/df < 0 therefore, the square root expression is real.

So the real problem is whether the above condition can be achieved for a real superluminal pulse, not the apparently bogus one being reported in Nature. I may have made a mistake in algebra as I did this fast with phone call interruptions interfering with my attention.

Note that Sommerfeld makes it clear that classical superluminal signal speeds are not possible with transverse EM waves.

"In a region of anomalous dispersion it may happen that n < 1, and hence [phase speed] u > c ... Thus u would be a velocity greater than that of light which cannot exist according to the theory of relativity ... this prohibition is limited to processes which can serve as a signal and are able to initiate material events. A monochromatic light wave without a beginning or end can do no such thing. The Morse signals used in wireless telegraphy are interruped wave trains .... " p. 114 "Optics" V. IV Lectures on Theoretical Physics, Arnod Sommerfeld, Munich (1954 Academic Press).

In computing the propagation of a wave front in a dispersive medium with the Fourier integral "It certainly does not propagate with a velocity greater than that of light" p. 117

Note, however, eq (7) p.90, the fundamental equation is fourth order in time partial differential equation! Sommerfeld then throws away the longitudinal near field solutions in his classical analysis of signal speed in anomalous dispersive material. So Sommerfeld's analysis from many years ago may not be the final word on this subject.

So if something superluminal is going on it has to be an effect of the Bohm quantum potential left out of Sommerfeld's classical analysis - or some kind of non-transverse longitudinal near field effect which might also make superluminal electrical pulses in wires possible with a more immediate application to ultra-fast computing in the solid-state in the mesoscopic near nanometer scale.

The Nature paper itself is

http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v406/n 6793/full/406277a0_fs.html

-- Not quite (@ .), July 21, 2000.

"ABC, your post is the most incredibly stupid, utterly pretentious piece of nonsense I have ever read. For one thing, as the tips of the scissors approach the speed of light, they supposedly attain mass approaching the infinite. "

Sorry, Elmo, you're going to need some reading comprehension lessons. I never said anything about the tips of the scissors approaching the speed of light, only the point of intersection of the two blades. That has no mass and carries no information, and therefore can travel at any velocity, even faster than light. I hope this clears up your confusion.

-- ABC (a@b.c), July 21, 2000.

Elmo (ee@ff.g),

Please re-read ABC's post. It refers to the speed of the blades' intersection (the point where the cutting edges meet), not to the speed of the tips of the blades.

-- No Spam Please (nos_pam_please@hotmail.com), July 21, 2000.

Ah ... I see that ABC was posting his own clarification as I was composing mine. Please excuse the duplication, all.

-- No Spam Please (nos_pam_please@hotmail.com), July 21, 2000.

Hawk: Excellent find. I was sure we weren't going to hear anything about this for years. Thanks

Mar.

-- Not now, not like this (AgentSmith0110@aol.com), July 21, 2000.

I'm Here,
How much is the pulse-progagator if I call within the past 15 minutes?

-- David L (bumpkin@dnet.net), July 21, 2000.

Not quite, A valiant effort there, and hard to follow for those of us not well versed in superluminal pulses...can you give us a description in more laymans terms? Your mathmatical exploration is pertinent, but it would help to have a quick intro...

Having read a few articles about this, I am still trying to determine if the measured light pulse exiting the chamber was the same that entered...and as best as I can determine it was not! Therefore the claim of a pulse exceeding the speed of light would not be an accurate description in such a case.

When the first news of this came out, I understood it to be a wavefront "amplification" with a different wave exiting ....which I took as "information" exceeding the speed of light (much the way electrons flowing in a wire can communicate information far faster than the electrons are actually going). Reading the latest more technical information, it appears that this was incorrect.

Again, thanks for the link to the article, but it will be a while before I can fathom it...information travels much slower than the speed of light in my dense matter, lol...

-- FactFinder (FactFinder@bzn.com), July 22, 2000.