Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Speed of Light Exceeded?

kdawson posted more than 7 years ago | from the when-pigs-fly-faster-than-light dept.

Science 393

PreacherTom writes "Scientists at the NEC Research Institute in Princeton, NJ are reporting that they have broken the speed of light. For the experiment, the researchers manipulated a vapor of laser-irradiated atoms, causing a pulse that propagates about 300 times faster than light would travel in a vacuum. The pulse seemed to exit the chamber even before entering it." This research was published in Nature, so presumably it was peer-reviewed. It's impossible from the CBC story to determine what is being claimed. First of all they get the physics wrong by asserting that Einstein's special relativity only decrees that matter cannot exceed the speed of light. Wrong. Matter cannot touch the speed of light in vacuum; energy (e.g. light) cannot exceed it; and information cannot be transferred faster than this limit. What exactly the researchers achieved, and what they claim, can only be determined at this point by subscribers to Nature.

Sorry! There are no comments related to the filter you selected.

It works... (5, Funny)

fortunato (106228) | more than 7 years ago | (#18247368)

I wrote this yesterday.

Re:It works... (5, Funny)

Anonymous Coward | more than 7 years ago | (#18247372)

expect a dupe tomorrow

Re:It works... (2, Funny)

jigyasubalak (308473) | more than 7 years ago | (#18247476)

That's nothing. I will write this tomorrow.

Re:It works... (5, Informative)

AchiIIe (974900) | more than 7 years ago | (#18247510)

It must be true, I read this article months ago....

http://science.slashdot.org/article.pl?sid=05/08/2 0/1440228 [slashdot.org] ..

Now pardon me as I karma whore:

By Trip11

Everyone say it together with me: "Phase velocity vs Group velocity" There are no photons in this experiment that are traveling faster than the speed of light. Only collections of them that 'appear' to be doing so. Think of this as an example: I space people out in a line, each of them two light minutes apart from the people next in line (all at rest with respect to each other). Now I go about talking to them and informing them of my plan. At 12:00 the first person waves, at 12:01 the second person waves, at 12:02 the third person waves, and so forth. My "wave" is propogating, therefore, at twice the speed of light. This is the same thing that this experiment is doing more or less. By spending extra time setting up the experiment, you can make it appear that a light pulse travels faster than c, but like my "wave" it is only an appearance.


By: Justanyone

Information flow (see: Steven Hawking's theories) cannot propogate at faster than the speed of light, or causality is violated and we have (dead virgins/future grandfathers) all over the place.

All 4 basic forces: electromagnatism, gravity, strong nuclear, and weak nuclear (not Nukular; bite me, George) forces propogate at the speed of light in their reference frame. If we switch frames we're not fooling anyone; if we preposition information we're not watching causality violations.

This kind of story is quite irritating, not due to the actual achievement involved (playing with light propogation is actually very cool geek-cred stuff), but the overhype and miscommunication to all the laypersons out there who just go, "Yup, that's an 'oops', they said it was a law and now it ain't. I guess evolution might not really be true, dad-gummit, I don't trust me none o' dem smarty pants anyway."


By: Alwin

Set up say, 1000 domino blocks in a row. Then tip the first one over. Given constant size, weight, spacing of individual blocks, and a horizontal surface, you will observe blocks falling down at a constant rate/speed ('c'). Given that constant rate/speed, tipping over the first block will cause all blocks to fall down, tipping over the last block some time later. Time delay calculates as distance divided by 'c'.

Now, create 'extreme conditions', where the first domino block is down, the last one is still standing, and halfway down the row, blocks are falling, but not quite down on the floor. Then, observe the 'wave front' of falling domino blocks. It will appear to move faster than the previously determined 'c'. How come?

Look more closely: as each block falls down, there's a fixed delay before it hits the next block. But what happens under our 'extreme conditions'? At the exact time a previous block would have hit the next one (under normal circumstances), that next block is already falling down! The time it takes for the 1000 blocks to fall down, is less than what normally would be expected.

Did this 'c' constant get violated? Nope, it still took the same amount of time for each block to fall down. Was the maximum 'c' speed exceeded? Nope. After tipping the first block, it still took the same amount of time before this 'information' was passed on to the next block. With a set of 1000 blocks all standing, the time needed for an initial 'disturbance' to be passed on to the last block, is still limited by 'c'.

So these 'extreme conditions' are like pre-tipping each block, and let you observe something that appeared to move faster than 'c'.
Nice for the lab folks, but other than that, sensationalist journalism. Wake me up when trans-atlantic ping times (sending actual packets with random data) dive below the time dictated by the speed of light.

here is my example (4, Interesting)

deathcow (455995) | more than 7 years ago | (#18247802)


You put a lightbulb inside a spinning coffee can with slits at 4 equally spaced spots around the circumference.
The photons are projecting out of the slits. As the can spins, the pattern of light and shadow turns and projects on the surroundings.

The outside surface of the can is moving at 1 full turn per second.

10 feet away from the can, the pattern of light and shadow is moving at 31.4 feet per second.

100 feet away from the can, the pattern of light and shadow is moving at 314 feet per second.

At just 2 miles from the can (we are using a BRIGHT bulb), the light and shadow is moving 22,619 miles per hour!

Re:It works... (3, Interesting)

BigBuckHunter (722855) | more than 7 years ago | (#18247828)

I was under the impression that they simply used waves within a medium already moving close to the speed of light to overcome the Fitzgerald contraction (avoid addition of velocities). In my mind, it would work like the following....

Drive a bus at .99C. Have the back row stand and sit. Then the next row stand and sit, then the next, so you get a wave going from the back of the bus. If you get people doing the wave fast enough, the wave may exceed the speed of light while the transport mechanism does not.

I can see how this would be useful for faster-than-light communication, but since nothing (well, no "matter")actually exceeds the speed of light, none of the fundamental laws are broken.

I could be totally and absolutely wrong about all of this.
BBH

Not all forces travel at 'c'... (5, Informative)

Roger W Moore (538166) | more than 7 years ago | (#18247880)

All 4 basic forces: electromagnatism, gravity, strong nuclear, and weak nuclear (not Nukular; bite me, George) forces propogate at the speed of light in their reference frame.

Not at all correct. First the weak force is transmitted by W and Z bosons which have mass and therefore CANNOT propagate at the speed of light. Secondly in their own reference frame, by definition the weak force bosons will not propagate at all since your own reference frame is defined as the frame you are at rest in. Thirdly massless particles have no reference frame of their own.

I know you were quoting someone else but please pick someone who at least has a clue what they are talking about!

Re:It works... (1)

bowie37 (1068128) | more than 7 years ago | (#18247694)

I think you mean you wrote this tomorrow.

Re:It works... (1)

tigerd (890439) | more than 7 years ago | (#18247888)

Only rumors travels faster than light..

Results of experiment published in the past (5, Insightful)

Epsas (563099) | more than 7 years ago | (#18247374)

This story is from November 2000. If Princeton scientists *did* exceed the light-speed barrier, then it the evidence would only naturally show up in the past. Interesting!

Re:Results of experiment published in the past (5, Funny)

darkitecture (627408) | more than 7 years ago | (#18247404)


This story is from November 2000.

So the dupe will be posted 6 years ago? Awesome! I'm looking forward to it.

Re:Results of experiment published in the past (5, Funny)

unitron (5733) | more than 7 years ago | (#18247500)

So the dupe will be posted 6 years ago? Awesome! I'm looking forward to it.

Shouldn't you be looking backward to it?

Re:Results of experiment published in the past (1)

Tjp($)pjT (266360) | more than 7 years ago | (#18247530)

Some guy named ocaT rednammoC failed to publish it then. Said something about his cat being dead. Last seen walking backwards through red curtains on a checkerboard floor. Well at least that's what they will say on the street in 2000.

Re:Results of experiment published in the past (1)

@madeus (24818) | more than 7 years ago | (#18247626)

Some guy named ocaT rednammoC failed to publish it then. Said something about his cat being dead. Last seen walking backwards through red curtains on a checkerboard floor.
My chances of understanding the science involved in this experiment are still greater than my chances of understanding what the hell was going in that show [wikipedia.org] (funny, I thought it was checkerboard too...).

Re:Results of experiment published in the past (4, Informative)

Siener (139990) | more than 7 years ago | (#18247582)

So the dupe will be posted 6 years ago? Awesome! I'm looking forward to it.


Found it! [slashdot.org]

"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. "

Wow ... we finally have proof that dupes travel faster than the speed of light!

So which one is the dupe? (1)

EmbeddedJanitor (597831) | more than 7 years ago | (#18247448)

This is going to make /. dupe identification pretty hard!

Re:Results of experiment published in the past (1)

Who235 (959706) | more than 7 years ago | (#18247456)

What exactly the researchers achieved, and what they claim, can only be determined at this point by subscribers to Nature.


Well, subscribers who keep their back-issues anyway.

Re:Results of experiment published in the past (1)

acidrain (35064) | more than 7 years ago | (#18247604)

Wow. I'm seriously thinking of filtering kdawson. I mean at least Jon Katz... err nevermind...

Sounds Familiar - (1)

RoffleTheWaffle (916980) | more than 7 years ago | (#18247382)

I think we've heard about this before. Something about atoms reacting in this big wave faster than light would travel, without anything actually moving faster than light.

Anyone got a name for that? I'm lost on it.

Group Velocity Again (5, Informative)

Effugas (2378) | more than 7 years ago | (#18247384)

99% chance it's this again:

You're stuck in traffic, behind an accident. They clear the accident. Slowly, every car speeds up now that the blockage is gone. If you're looking from above, you'll see a "wave" move through the line of cars, as each takes a few seconds to realize he can accelerate.

This wave is the group velocity, and very much has nothing to do with the speed of each individual car.

Suppose all the cars were wired electronically to know that they could all accelerate at once. That knowledge would move at nearly the speed of light.

No car would be moving at the speed of light. Everyone would just hit their gas pedal at almost the same time.

Almost every time we see these stories, this is the type of speed they're talking about.

Re:Group Velocity Again (3, Informative)

julesh (229690) | more than 7 years ago | (#18247408)

Exactly. It's exactly the same experiment we've seen time & time again, and it's meaningless because no information is transmitted.

Re:Group Velocity Again (1)

TapeCutter (624760) | more than 7 years ago | (#18247454)

I agree, debunking the same psudeo-scientific crap over and over again is boring.

no information? (1)

someone1234 (830754) | more than 7 years ago | (#18247498)

I just don't understand the following: the pulse/no pulse thing is itself a bit of information.

Re:no information? (3, Informative)

julesh (229690) | more than 7 years ago | (#18247560)

I just don't understand the following: the pulse/no pulse thing is itself a bit of information.

Because of the way the experiment is set up, the pulse has to arrive; you can predict that it will arrive because of previous things that have happened. Basically, as I understand the experiment, a sequence of short pulses of light are sent down the chamber, with known gaps between them. The 'faster than light' wave results from the phase motion of these normal speed light waves. By the time it starts propogating, you can already tell that it will do so from observations you can make at the end of its run.

Re:Group Velocity Again (3, Insightful)

Anonymous Cowled (917825) | more than 7 years ago | (#18247554)

Ah... the good old /. car analogy ;-)

Re:Group Velocity Again (1)

gingerTabs (532664) | more than 7 years ago | (#18247602)

Thanks for that - the clearest explanation of group velocity I've heard. /notes

Re:Group Velocity Again (3, Informative)

physicsnick (1031656) | more than 7 years ago | (#18247614)

Exactly.

There are plenty of examples of arbitrary "things" that move faster than the speed of light. For example, take a laser pointer and point it at the moon. As you move your hand, you can get that dot moving across the surface of the moon way faster than the speed of light. However, this can't be used to transmit information faster than c; it still takes a few seconds for the light to get from your moving hand to the surface of the moon.

The group velocity of photons is just another one of those things. The summary refers to a "pulse" that "propagates"; they almost certainly mean the group velocity, which is useless to transmit information.

Re:Group Velocity Again (5, Funny)

jez9999 (618189) | more than 7 years ago | (#18247726)

So YOU were the one causing that damn red blob when I was trying to watch the eclipse? Go test out your new laser toy elsewhere!

Re:Group Velocity Again (1)

Deliveranc3 (629997) | more than 7 years ago | (#18247620)

Um then some force or energy is passing through the mass, moving faster than light...

Also I believe a group of scientists sucessfully proved that you can go faster than light using super cooled Cesium or something like that.

I don't understand why people are so hung up on this absolute speed of light thing, Einstein was a smart guy but so were Galileo, Newton and more recently Hawkings, and Hawkings says something > SOL.

String theory is all based around the concept that nothing can go faster than light.

I appreciate the whole shooting light off the back of a moving car thing (It goes the same speed forward or backwards regardless of your momentum) but that isn't nescessarily proof that it's the fastest anything can go.

Quarks don't rotate together with nothing between them.

Re:Group Velocity Again (1)

fonik (776566) | more than 7 years ago | (#18247776)

Physicists get hung up on that whole faster-than-light thing because going faster than the speed of light and going backwards in time are the same thing, just from different relative perspectives.

Re:Group Velocity Again (1)

jmv (93421) | more than 7 years ago | (#18247640)

Actually, your analogy is bad because in the case of cars in a traffic jam, if wave of cars did indeed move faster than light (even if the individual ones didn't), that would still violate special relativity because there would be information (there's no more blockage) transmitted faster than the speed of light.

Re:Group Velocity Again (1)

physicsnick (1031656) | more than 7 years ago | (#18247678)

Actually, your analogy is bad because in the case of cars in a traffic jam, if wave of cars did indeed move faster than light (even if the individual ones didn't), that would still violate special relativity because there would be information (there's no more blockage) transmitted faster than the speed of light.
The correct analogy is not that the wave moves faster than the speed of light, it's that the wave moves faster than the top speed of a car. In this case the analogy is slightly flawed because you could use it to transmit information faster than the top speed of a car; the only reason this is possible is because the drivers are using light to see when to accelerate :D

Re:Group Velocity Again (1)

ArsenneLupin (766289) | more than 7 years ago | (#18247798)

The correct analogy is not that the wave moves faster than the speed of light, it's that the wave moves faster than the top speed of a car. In this case the analogy is slightly flawed because you could use it to transmit information faster than the top speed of a car; the only reason this is possible is because the drivers are using light to see when to accelerate :D
The speed of the wave has pretty much nothing to do with the speed of the car. It doesn't even go into the same direction (the cars go forward, the wave travels backward). And actually, many wave phenomena (except light in vacuum) involve the same basic phenomenon: they involve movement of some medium (water molecules for surface waves, O2 and N2 molecules for sound, pieces of rope, electrons in a wire, ...) which may move slower or faster than the wave. Relativity says that neither the particles of the medium (mass), nor the wave (information) may be faster than c.

The correct way to use the car analogy would be that the experimenters told each driver beforehand at exactly which time the obstruction would be cleared, and so everybody would be accelerating blindly at that predetermined time, even before seeing the previous car move. In such conditions the wave could move faster than reaction times of drivers normally would allow, or even faster than c.

However, it would carry no information: the information would already have been prepositioned before the experiment.

Re:Group Velocity Again (1)

OhBoy! (842699) | more than 7 years ago | (#18247664)

Suppose all the cars were wired electronically to know that they could all accelerate at once... ...Everyone would just hit their gas pedal at almost the same time.
I don't know anything about physics desicribed in the main article, but this is such a botched up analogy. Imagine what would happen if all these cars, presumably stopped within 2-3 feet from each other, were to hit the gas pedal at the same time. Transferring knowledge at the speed of light or not, they wouldn't want to accelerate at the same time, thus making this analogy just psychologically feel wrong, and kind of defeating the whole point of making an analogy.

Re:Group Velocity Again (1)

fabs64 (657132) | more than 7 years ago | (#18247754)

... I think you have missed the whole point in ANY analogy

Information? (5, Informative)

Jugalator (259273) | more than 7 years ago | (#18247390)

So, was any information transmitted? Then it's big news I suppose, otherwise not? From the sound of it, a "pulse" make me suspicious, but I lack the full physics geekdom to completely dismiss the story. Anyway, speed of light only applies to transmission of information, not group velocity [wikipedia.org] .

Re:Information? (1)

NOLFXceptMe (1013903) | more than 7 years ago | (#18247870)

"I lack the full physics geekdom" ... Its simple...nothin can ever exceed speed of light, not even information,as proved by Hawking.And someone else says itz from 2000...huh? Excuse me, proof please, we're talkin about science.

You can beat it! (0, Redundant)

feyhunde (700477) | more than 7 years ago | (#18247396)

You can beat the speed of light in vacuum if it goes in a material with an N less than 1. A few already exist.It's the same trick as slowing the speed of light in a material with a huge N.

Re:You can beat it! (1)

someone1234 (830754) | more than 7 years ago | (#18247480)

I thought vacuum means there is no material. Surely physics evolved beyond me :)

Re:You can beat it! (1)

feyhunde (700477) | more than 7 years ago | (#18247546)

Vacuum has an N of 1. It's possible to be faster than vacuum, but in terms of Group Velocity, which is useless to send encoded information on.

Re:You can beat it! (4, Insightful)

cyclop (780354) | more than 7 years ago | (#18247662)

Well, to be honest the today conception of vacuum is not that of a space completely devoid of everything. Vacuum has an energy, and literally boils of instantly-annihilating particle-antiparticle couples. This has observable effects that have been measured, like the Casimir effect. See http://en.wikipedia.org/wiki/Vacuum_energy [wikipedia.org] for an explanation.

Re:You can beat it! (1)

gripen40k (957933) | more than 7 years ago | (#18247548)

I believe that this has something to do with why those heavy water tanks in nuclear reactors glow blue. I'm far too lazy too look it up right now (it's 1AM) but it shouldn't be too hard to find on wiki or something...

Re:You can beat it! (1)

feyhunde (700477) | more than 7 years ago | (#18247584)

Thats what happens when particles that are traveling faster than the speed of light in one material enter another. It's faster in Uranium than water, resulting in the particles having to give up the extra energy.

Re:You can beat it! (1)

smaddox (928261) | more than 7 years ago | (#18247596)

I have never heard of a material with N less than 1 and greater than 0. Can you give an example?

There ARE, so called, metamaterials with N less than 0. However, my understanding is that these still only work on group velocity.

Leap second (0)

Anonymous Coward | more than 7 years ago | (#18247398)

Everything is faster during a leap second.

Fair enough... (1)

im_thatoneguy (819432) | more than 7 years ago | (#18247406)

The poster can't figure out exactly what their news item is about. What the author of TFA claiming, or what conclusions we should reach. Sounds like just another day on Slashdot.

Re:Fair enough... (0)

Anonymous Coward | more than 7 years ago | (#18247426)

I can't wait until the dupe three days from now.

Re:Fair enough... (1)

Tim C (15259) | more than 7 years ago | (#18247496)

That's not the poster saying that, that's kdawson - all of PreacherTom's words are in the blockquoted section.

Besides, kdawson's wrong. The article does not say that SR says that matter can't travel faster than light, it says that "The result appears to be at odds with one of the basic principles of Albert Einstein's theory of relativity, that nothing can go faster than the speed of light in a vacuum". Further down the article it then says "The scientific statement "nothing with mass can travel faster than the speed of light" is an entirely different belief, one that has yet to be proven wrong.".

Other than that, I agree - there seems to be little point to posting this until more information is available. I just wish that the editors would realise that slashdot isn't (or shouldn't be) about scoops and breaking news, and only post when it's worth posting.

From 2000 (0)

Anonymous Coward | more than 7 years ago | (#18247418)

WTF, PreacherTom? Why would you submit a link to an article over six years old?? In any case, I too certainly would expect that this article was peer reviewed. If I remember correctly, this research presented a method whereby the group velocity of a light pulse was impressively high but the signal velocity still remained less than the speed of light in a vacuum.

Time . . . (5, Funny)

OverlordQ (264228) | more than 7 years ago | (#18247436)

"Good. No, the answer is an orange and two lemons."

"Lemons?"

"If I have three lemons and three oranges and I lose two oranges and a lemon, what do I have left?"

"Huh?"

"Okay, so you think that time flows that way, do you?"

-Mostly Harmless

Check dates on stories please (1)

deadlock911 (629647) | more than 7 years ago | (#18247438)

Come on Eds! We have seen this happen way too much lately, its at the top of the page!

No time travel imminent... (1)

kimmop (121096) | more than 7 years ago | (#18247440)

at least back in time.

"This week" (when the Nature article was published) was 7 years ago: http://scholar.google.com/scholar?sourceid=Mozilla -search&q=Gain-assisted+superluminal+light+propaga tion [google.com]

Back in time vs forward in time (1)

EmbeddedJanitor (597831) | more than 7 years ago | (#18247462)

"at least back in time."

If x travels forward in time isn't that equivalent to (universe - x) travelling back in time?

Re:Back in time vs forward in time (1)

sumdumass (711423) | more than 7 years ago | (#18247684)

Only to the perspective of the one moving forward wich means :depends on who you ask.".

If this is true then (1)

bgibby9 (614547) | more than 7 years ago | (#18247446)

everything else we know of could potentially have flaws, enough to cause the fundamentals we rely upon to also potentially be wrong.

I was only a matter of time (forgive the pun) until we found a way to do it. Light is potentially the lowest form of energy that we can detect. What if there is some form of energy higher that we can't detect which has properties beyond that of light.

Who knows what additional properties the universe has that we could one day tap into!

Here's hoping q:)

Re:If this is true then (0)

Anonymous Coward | more than 7 years ago | (#18247524)

We may not know the additional properties, but we can at least access the methods in python:

import universe
print dir(universe)

['ArticleIsSevenYearsOldError']

Slashdot is not the proper forum for speculation. (3, Informative)

Futurepower(R) (558542) | more than 7 years ago | (#18247458)

kdawson: You said, and I quote: "What exactly the researchers achieved, and what they claim, can only be determined at this point by subscribers to Nature."

The linked article says, and I quote: "Last Updated: Friday, November 10, 2000 | 11:57 PM ET" (My emphasis.)

Please consider that Slashdot is not the proper forum for speculation about Physics, especially when it is not clear what happened, and the article is over 6 YEARS old.

Please consider that perhaps you should not be a Slashdot editor. It amazes me that Slashdot editors are still, after all these years, not very good at what they do. What social processes prevented even the most simple learning?

--
Is U.S. government violence a good in the world, or does violence just cause more violence?

Re:Slashdot is not the proper forum for speculatio (2, Funny)

JRHelgeson (576325) | more than 7 years ago | (#18247574)

You moron! Can't you see that the information contained in the article appeared back in November 2000 yet the test was conducted on March 2007? This is further PROOF that they have exceeded the speed of light as the information contained in the article appeared six years prior to the tests being reported at Slashdot.

So: kdawson's integrity remains intact. :)

Re:Slashdot is not the proper forum for speculatio (0)

Anonymous Coward | more than 7 years ago | (#18247598)

Please consider that Slashdot is not the proper forum for speculation about Physics, especially when it is not clear what happened, and the article is over 6 YEARS old.
No, it just means the experiment works as advertised. It was posted today, and after it's done propagating it will show up 6 years ago.

Re:Slashdot is not the proper forum for speculatio (1)

Danny Rathjens (8471) | more than 7 years ago | (#18247610)

You can't even figure out where your .sig is supposed to go and you are whining about editors? Just filter his stories in your preferences if you can't stand his article selections or frequent mistakes.

Then what is it? (1)

Flying pig (925874) | more than 7 years ago | (#18247716)

Slashdot is, I believe, Rob Malda's blog and as such whatever he sees fit to include is proper content. In fact, the parent post is so completely up itself that it is looking at its kidneys from the inside. +5 informative? -5 troll more like. And I've just fallen for it - so it works!

Re:Slashdot is not the proper forum for speculatio (-1, Troll)

Anonymous Coward | more than 7 years ago | (#18247728)

"Is U.S. government violence a good in the world, or does violence just cause more violence?"

US Government violence is good, because all foreigners are sub-human. Soon we will have eliminated all foreigners/enemies. Then the world will be OURS!

Iraqis should be HAPPY to be killed by Americans. (0)

Anonymous Coward | more than 7 years ago | (#18247836)

Parent comment posted by a humorist who has seen the result of people playing too many video games.

More ugly humor: Iraqis should be proud to be killed by those superior Americans.

Tag it ... (1)

CaptainMunchies (458558) | more than 7 years ago | (#18247466)

blastfromthepast.

Obligitory Futurama (5, Funny)

Rik Sweeney (471717) | more than 7 years ago | (#18247472)

Farnsworth: These are the dark matter engines I invented. They allow my starship to travel between galaxies in mere hours.
Cubert: That's impossible. You can't go faster than the speed of light.
Farnsworth: Of course not. That's why scientists increased the speed of light in 2208.

Re:Obligitory Futurama (1)

sumdumass (711423) | more than 7 years ago | (#18247696)

I get it know. The ship's engines don't move the ship at all, It moves the universe around the ship.

Ok, lemme take a poke at what is might be (2, Interesting)

realcoolguy425 (587426) | more than 7 years ago | (#18247492)

I've been hearing group velocity. I understand nothing, but I remember from a class, no idea which one now, that you can seem to exceed the speed of light, but you're not really doing it. For example take a tube of balls, packed end to end. There is no more room for any of the balls, so the moment you put one in on one end, the other one immediatly pops out. Now, if that tube of balls was empty, then it would take n amount of time for that ball to roll the length of the tube. Is this the same conceptionally or is it different?

Old news (2, Informative)

sdxxx (471771) | more than 7 years ago | (#18247494)

This is old news.

If you shined a flashlight or a laser beam at a wall very far away and quickly turned the angle of the beam, the lit spot on the wall might move faster than the speed of light. It doesn't mean you can transmit information faster than the speed of light in a vacuum.

Re:Old news (0)

Anonymous Coward | more than 7 years ago | (#18247536)

There are so many things wrong with that assumption I don't know where to begin.
Where is the "false", "mistaken" or "just plain wrong" moderation?

Old, Old News (1)

Frodrick (666941) | more than 7 years ago | (#18247522)

From the article:

Last Updated: Friday, November 10, 2000 | 11:57 PM ET

Maybe I don't get it (1)

Kaeles (971982) | more than 7 years ago | (#18247526)

and i didn't read the article, but if group movement works like cars, or electrons in a curcuit (the pulse being the electricity and the cars being the electrons) couldn't you send a steady laser beam somewhere (assuming you could keep it perfectly targeted) and use this to send a pulse faster than light along the photons or somesort?

Or not.

Funny (4, Funny)

MarsDude (74832) | more than 7 years ago | (#18247528)

On my google startpage I have the 'quotes of the day'. Just now I noticed there was a quote from Woody Allen : "It is impossible to travel faster than the speed of light, and certainly not desirable, as one's hat keeps blowing off."

How do I mod down kdawson and the /. editors? (5, Insightful)

osu-neko (2604) | more than 7 years ago | (#18247532)

I have mod points, but I can't figure out how to dole out some negative karma to either the person sending in a link for an over six year old story, or the editor who approved it. >:(

Re:How do I mod down kdawson and the /. editors? (1)

Lord Aurora (969557) | more than 7 years ago | (#18247622)

Well, now that you posted in the story, all hope is lost.

Quick! Travel backwards and reverse what you've done so you can mod kdawson down!

Re:How do I mod down kdawson and the /. editors? (1)

sumdumass (711423) | more than 7 years ago | (#18247710)

Simple. Troll like the others. Goto their user page, find articles they have posted in that you havn't and start modding comments troll and flaim bate.

Ever wonder how a person can be moded troll, explain himself a few posts later and be moded insightfull or interesting? It is freaks going after freaks.

Re:How do I mod down kdawson and the /. editors? (1)

jez9999 (618189) | more than 7 years ago | (#18247734)

You might have been able to contribute to its not being considered by modding it down in the Firehose beforehand...

A small thought experiment (1)

Fjodor42 (181415) | more than 7 years ago | (#18247562)

I seem to remember reading about the following hypothetical experiment:

Let 2 enormously rigid "rods" of astronomical length be parallel. Let the one set of endpoints be fixed, and accelerate the other ends towards each other until crossing, and let them continue moving, now apart, with the rods intersecting. Even if the individual endpoints are moving at sub-c, one could easily imagine having the intersection point moving faster than c, however the intersection point is a logical construct, carrying neither mass nor information, and thus would this setup not contradict relativity, but merely present a challenge of engineering for anyone interested in carrying it out. /F

Re:A small thought experiment (1)

Lazarian (906722) | more than 7 years ago | (#18247718)

Okay...

If a person at one end of the two parallel rods were to cross the rods by taking one (let's call it rod A) and passing it over the other (rod B), as opposed to crossing rod B over rod A, would it not transmit to an observer at the other end one of the two states faster than the crossing motion (which for this instance would be referred to being slower than light)?

(I realize that this thought experiment has logical faults - crossing the rods and having them still straight would assume that the rods themselves would be impervious to the effects of forces upon them like bending, and in some way invalidates the experiment. But it's an interesting puzzle nonetheless, since the point of the rods crossing would travel faster than light, and in this case could transmit the state of either "over" or "under".)

Re:A small thought experiment (1)

Fjodor42 (181415) | more than 7 years ago | (#18247788)

Well, the states "over the other" or "under the other" are relative to the coordinate systems used by the two observers, and that information could not be transferred merely by the crossing itself. Either they would have to agree beforehand, in which case no transfer of information takes place, or they would have to compare notes afterwards, and nothing still suggests that this comparison could be carried out faster than the time taken to transfer the information of the coordinate systems used via conventional ways, at sub-c speeds. Also, given the proposed length of the rods, even fairly large movements at one end would probably be immeasurable at the other end for quite some time.

The "differing coordinate systems" is, by the way, a main point in relativity.

And yes, I stated "enormously rigid" as a premise. This is mostly to do away with pesky details of material physics that is of no interest of the idea put forth. In reality, however, that requirement is blatantly unattainable :-)

Superluminal Scissors (1)

7bit (1031746) | more than 7 years ago | (#18247874)

Fjodor42 said:
"I seem to remember reading about the following hypothetical experiment:

Let 2 enormously rigid "rods" of astronomical length be parallel. Let the one set of endpoints be fixed, and accelerate the other ends towards each other until crossing, and let them continue moving, now apart, with the rods intersecting. Even if the individual endpoints are moving at sub-c, one could easily imagine having the intersection point moving faster than c, however the intersection point is a logical construct, carrying neither mass nor information, and thus would this setup not contradict relativity, but merely present a challenge of engineering for anyone interested in carrying it out."

    Another, simple, way to envision the above idea is to think of a giant pair of scissors. The head of the scissors rests on the surface of the earth and the two blade tips reach into orbit but are open and at an angle to each other. Now, air resistance etc aside (Do it on the moon instead); when the scissors are "closed", each half moving at sub-luminal speeds, the virtual point of intersection between the two blades can in fact end up "moving" faster than the speed of light. It's movement of an abstraction though.

    But there's a problem if you make the scissors too long; they cease to act as a rigid body due to the electromagnetic force binding it's atoms propagating at the speed of light. Say the scissors were one light year long and the arms only a couple degrees apart then suddenly closed. You would think that would create an obvious sudden signal one light year away. But, even if the scissors were made of material far stronger than we can make now, the far ends wouldn't actually close that fast. The scissors would in fact close "suddenly" in the visible distance, but the closing (not refering to the contact point mentioned earlier) would be occurring along the length of the scissors at a speed less than light, in a bending wave. The far tips would finally close a year or more later.

    I would love to see FTL achieved. Perhaps subatomic particles/waves of some sort and some extraordinarly small scale could be coaxed into moving FTL?

Has your enormous, rigid rod gone floppy? (1)

Pfhorrest (545131) | more than 7 years ago | (#18247890)

I seem to remember reading about the following hypothetical experiment:

Let 2 enormously rigid "rods" of astronomical length be parallel. Let the one set of endpoints be fixed, and accelerate the other ends towards each other until crossing, and let them continue moving, now apart, with the rods intersecting. Even if the individual endpoints are moving at sub-c, one could easily imagine having the intersection point moving faster than c, however the intersection point is a logical construct, carrying neither mass nor information, and thus would this setup not contradict relativity, but merely present a challenge of engineering for anyone interested in carrying it out. /F


If you could construct an astronomically large rod rigid enough that it stayed perfectly straight as you wiggled one end of it, you could transmit information faster than light. The people at the other (fixed) end of the rod could just measure the rotation on that end, and thus tell how you were wiggling the other end. The reason this isn't a practical way to send information faster than light is because you cannot build rods that rigid; the energy you impart on the atoms at one end would have to be imparted in turn to the other particles in the rod faster than the speed of light. Since they cannot do that, the compression wave caused in such a rod can travel no faster than the speed of light.

Thus, your enormous rods would be extremely floppy if viewed altogether, no matter how rigidly you tried to build them; you would move the ends of them, and the middle portions would take, at the very least, a number of seconds equal to their distance in light-seconds away from you to move in response. So you uncross your ends, and three years later, the portions of the rods three lightyears away from you would uncross (assuming these rods were as rigid as theoretically possible, transmitting compression at c).

Even at mundane scales, if you grab a stiff piece of rebar (the heavy iron reinforcement bar used in stone/brick/block construction), about an inch thick and maybe three feet long, and wave it around... it may appear incredibly rigid to you, and there will certainly be no visible compression waves in it, but when you wave it around, it is still flopping about ever so slightly, just as a floppy car antenna would if you waved it around likewise. If you got a longer piece of rebar and waved it around you'd even be able to see it flopping. You could make it thicker and it would flop less again (to the point of not being noticeable), but at no point does it actually cease to flop entirely. In fact, that's a good mundane model of this. Grab two long pieces of half inch rebar, say 50ft long, and fix one end of each at some point, like your setup. Note that if you move the loose ends fast enough, you can cross and uncross them before the crossing has propagated all the way down their lengths. The longer or thinner the rebar, the more noticeable this is, and the shorter and thicker (and therefore more rigid) it is, the less noticeable - in fact you'll quickly get to proportions where you simple can't, as a mere human, move the ends faster than the compression travels - but those compressions waves are always there, and still limited to the speed of light.

In short, to surmount your "challenge of engineering" would itself require that relativity be violated, for energy would need to be transmitted faster than c for any rods to be so rigid; and perfect rigidity would require instantaneous transmission of energy.

it seems April Fools is a little early this year.. (1)

haggis_breath (686734) | more than 7 years ago | (#18247632)

this comment body is here just to waste your time. Please move along.

Sub-space communications? (1)

cablepokerface (718716) | more than 7 years ago | (#18247648)

I always wondered how they did that on star-trek.

One way (1)

edwardpickman (965122) | more than 7 years ago | (#18247652)

Physics wouldn't allow it unless the light travelled 1/300 the distance. Gas wouldn't do it but within known physics it could happen with severely warped space. No laws are broken if the distance is shortened. Obviously that isn't what happened in this case.

little info (0)

Anonymous Coward | more than 7 years ago | (#18247672)

if i recall matter cannot be accelerated to the speed of light

notinhg saying it cant start there or faster

oh wow (0)

Anonymous Coward | more than 7 years ago | (#18247682)

What an utterly USELESS POST!

A few misconceptions (3, Insightful)

jandersen (462034) | more than 7 years ago | (#18247686)

First of all - it is a fundamental assumption in Einstein's theory that the speed of light is the same in EVERY frame of reference; ie. two observers moving at some speed relative to each other will see the same lightwave moving at the same speed. One consequence of this is that all (rest-) massless particles move at the speed of light - in a way they only exist as movement or a disturbance of some field or other. Photons are disturbances in the electro-magnetic field, gravitons are disturbances in the gravity field (or the 'structure of space', if you like). Another consequence of the constance of the speed of light is that particles with real restmass > 0 get heavier when they move faster and the perceived mass goes to infinity as the relative speed approaches the speed of light.

It will be interesting to see in what sense they have exceeded the speed of light; so far all examples of this have proven to be tricks of the circumstances rather than actual physics - eg. it is easy, at least in theory, to make a shadow move faster than the speed of light, but it doesn't represent actual, physical motion; I'm sure most have heard about this one.

Question (2, Interesting)

Lord Aurora (969557) | more than 7 years ago | (#18247688)

Ok, so all this nonsense about group velocity and whatnot tickles inside of me like so much uncooked rice, and I have a little question. Say you set up a couple million little blocks across the Atlantic Ocean. Block 1 is set to pop up at 12:00, Block 2 at a time just the tiniest bit afterwards, and so on, so eventually what you have is a wave of blocks popping up, and let's say this 'wave' 'moves' faster than the speed of light. Follow? Now, put the blocks inside a perfect vacuum, slope their tops toward the next block, and put a bouncy ball filled with old love letters on top of Block 1. Press Start. All things being equal, isn't the little bouncy ball gonna move faster than the speed of light? And since we get to read the old love letters at the end, we're transmitting information, right? Now, that obviously doesn't solve the problem of information moving faster than light (as I'm relatively (no pun intended) sure it has to move of its own recognizance), but it's kinda fun, and the bouncy ball IS moving faster than light. Someone clear me up here.

(Oh. No friction, by the way. Let's assume everything's soaked in WD40 or whatever.)

Re:Question (2, Informative)

Skrynkelberg (910137) | more than 7 years ago | (#18247840)

Briefly explained: As the ball's velocity increases, so does it's mass, thanks to special relativity. That means it will take more time to accelerate and you will never actually reach the speed of light, no matter how long the slope.

Wrong, sorry (1)

Moraelin (679338) | more than 7 years ago | (#18247884)

Well, no. The short answer is that there still is no way to make the bouncy ball move faster than light, or even at the speed of light.

Just because there are some falling blocks, doesn't mean the ball will jump on the head of the next block just because it's there. You'd still need to accelerate the ball from zero velocity (in your frame of reference) to reaching the head of the next block just in time. It would take infinite energy to even reach the speed of light, and may the elder gods help you in getting above that. Doing it in the tiny space between two domino blocks, heh.

It has nothing to do with friction. Even without friction, you still need to apply a force to accelerate an object. That's why you still need thrusters to change a satellite's orbit, even though friction and drag are negligible up there. If you don't apply enough force, the object just doesn't accelerate fast enough. At this point there isn't even anything relativistic about it, it's just plain elementary Newtonian mechanics, as you may have learned it in school.

Additionally, your wave is an artifficial construct. Just because the next block is a little tilted already, doesn't make the current block also fall faster. Any particular block falls just as fast as if it were alone, with the other blocks not even existing at all, until the point of impact with the next. Just because block 2 is already tilted, doesn't mean block 1 will accelerate faster.

So the ball you've put on top of block 1 also won't accelerate any faster. Just because block 2 was already tilted, doesn't mean the ball will be forced to keep up with the wave. It will still fall at the same speed, and probably fail to transfer to the top of block 2, since block 2 will have fallen earlier and it's top will be some way ahead of the ball. So at most the ball will keep on rolling at a lower speed over the already fallen blocks.

Or think of another analogy, someone else used it already, but let's use it again here since it makes a good illustration. Think of a traffic congestion. All cars are standing still, then the first car moves, the next driver takes some time to notice he can step on it, so he starts at a tiny delay, the third car does the same, etc. Better yet, let's say they're pre-timed to start at uniformly spaced intervals, so no particular transfer of information is involved in getting them started. So basically although the cars are moving forward, viewed from above there is a wave travelling backwards. (It's an uncanny similarity with the "it appeared to exit before it entered" claim in the summary. Viewed from above, the car wave too is seen at the front of the congestion before it reaches the back of the congestion.)

It also can appear to move faster than the individual cars. If every driver only needs 0.5 seconds to notice that he can hit the gas, and the cars are stopped, say, every 3m (10 ft), the wave will move at 20 m/s or 72 km/h backwards. Although this may happen in a town where the speed limit is only 50 km/h, so the individual cars won't exceed that by much.

Now imagine you give the first car in the pack your ball filled with love letters. Will it travel backwards together with the wave? Well, nope, that particular car still travel forward at 50 km/h. Let's say you give the last car in the pack your ball. Will the ball appear to exit the congestion before the last car even started? Well, no, not really.

Basically just because you can set up one particular kind of wave doesn't mean you can actually use it to transfer information between two points. Whichever car you give your ball of letters, still moves at 50 km/h, and the "wave" is just an artifficial illusion or construct.

Or think you have some people 1 km apart, with stopwatches and really big speakers and amplifiers, and they're told to shout "geronimo!" in 1 second intervals. The "wave" is faster than the speed of sound, but it can't carry any information that way faster than sound. At the end point you don't get any information the last guy didn't already have. (He already had the "geronimo!" information.) If you tried to use it to transfer information, e.g., tell the first guy to shout "the king is dead!" instead, the next guy will still shout "geronimo!" and only 2 seconds later hear "the king is dead!". To actually transfer information that way you'd have to have guy number 2 wait until he hears "the king is dead!" and then shout that to guy number 3, and so on. However, at that point you've braked it all to the speed of sound (in fact, a bit less.) Now each guy has to wait 3 seconds, so they can hear what the previous guy shouted, before they can relay that to the next one. You can't, by sound alone, transfer the information _and_ keep the 1 second per km tempo.

Yay (0)

Anonymous Coward | more than 7 years ago | (#18247690)

Time for the annual Slashdot story dedicated to people who don't understand the difference between phase velocity and group velocity.

Not in Nature... (3, Interesting)

tgv (254536) | more than 7 years ago | (#18247738)

Well, it's from Nature 406 (6793): 277-279 Jul 20 2000. The article is cited 315 times and seems dispted. Here is the abstract for those poor souls without access to Nature, Web of Science, Scopus, etc.:

Einstein's theory of special relativity and the principle of causality(1-4) imply that the speed of any moving object cannot exceed that of light in a vacuum (c). Nevertheless, there exist various proposals(5-18) for observing faster-than-c propagation of light pulses, using anomalous dispersion near an absorption line(4,6-8), nonlinear(9) and linear gain lines(10-18), or tunnelling barriers(19). However, in all previous experimental demonstrations, the light pulses experienced either very large absorption(7) or severe reshaping(9,19), resulting in controversies over the interpretation. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light propagation in atomic caesium gas. The group velocity of a laser pulse in this region exceeds c and can even become negative(16,17), while the shape of the pulse is preserved. We measure a group-velocity index of n(g) = -310(+/-5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears to leave the cell before entering it. The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.

For another, more understandable report, here is a BBC website: http://www.whyevolution.com/einstein.html [whyevolution.com] (search for Wang).

E = m (* Unit converter) (1)

CleverNickedName (644160) | more than 7 years ago | (#18247750)

"Matter cannot touch the speed of light in vacuum; energy (e.g. light) cannot exceed it"

"Matter" and "energy" are two analogies for the same entity.

Not trying to sound preachy, but our clumsy language should describe concepts, not define them.

Just Horrible (3, Insightful)

fonik (776566) | more than 7 years ago | (#18247758)

For those who want to see how this REALLY works...
http://gregegan.customer.netspace.net.au/APPLETS/2 0/20.html [netspace.net.au]

This is probably the worst article I've ever read. The journalist's dubious explanation of the findings and complete lack of understanding of how these findings fit into known science is a perfect example of how modern journalism is often at odds with the spread of knowledge.

The findings are IN NO WAY "at odds" with relativity.

The team did not "change the state of a vapour in a way that light travelling(sic) through it would travel faster than normal." They created a pattern of interfering waves that made a pulse that traveled faster than normal. This is like saying that swinging the end of a jump-rope changes the state of the surrounding air to make the rope move faster, when in reality the ends of the rope are stationary and only a pulse is moving down the rope.

This was on Fark yesterday and it was even lower than THEIR scientific standards. I'm waiting for it to hit Digg so 500 people can comment that there is a massive conspiracy to suppress FTL technologies.

Cerenkov Radiation (0)

Anonymous Coward | more than 7 years ago | (#18247780)

I don't know if any of this is possible, but Cerenkov radiation is very cool to look at.

http://campus.umr.edu/reactor/cerenkov.html [umr.edu]

Re:Cerenkov Radiation (1)

Fjodor42 (181415) | more than 7 years ago | (#18247808)

Cherenkov radiation is indeed an interesting phenomenon, and is a good reminder that c is set to be the maximal velocity in vacuum, and not an invariant figure when other things come into play.

Speed of light (0)

Anonymous Coward | more than 7 years ago | (#18247794)

Wrong. Matter cannot touch the speed of light in vacuum; energy (e.g. light) cannot exceed it; and information cannot be transferred faster than this limit.

I think there's a basic fallacy in the summary's logic. How is it possible for light to exceed the speed of light? There's such a thing called the reflexive property of equality. Perhaps what's being violated in this article is the postulate that the speed of light is constant.

Group speed (1)

Shalcker (989572) | more than 7 years ago | (#18247826)

While you cannot exceed speed of light, sure having faster-then-light group speed can help in some applications!
Look at it from a simple example - a sattelite flying above the Earth that sends some file. As long as it covers large area, you can propagate this file faster then it'd took sending it through wires. Yes, it'll require "preparation" (you need to upload file to satellite first), but you'll get faster file distribution in the end. Each recipient gets his file at a speed of light, but group bandwidth increases immersely.

This research was done in 2000 (5, Informative)

Anonymous Coward | more than 7 years ago | (#18247842)

In fact, this research is so old that Dr. Lijun Wang's FAQ page describing the experiment is no longer on the Internet. It has to be located through the Internet Archive: http://web.archive.org/web/20041012175312/www.neci .nj.nec.com/homepages/lwan/faq.htm [archive.org]

Here's what he said:

Q. How to interpret those earlier press coverage?

A. It has been mistakenly reported that we have observed a light pulse's group velocity exceeding c by a factor of 300. This is erroneous. In the experiment, the light pulse emerges on the far side of the atomic cell sooner than if it had traveled through the same thickness in vacuum by a time difference that is 310 folds of the vacuum transit time.

In our experiment, a smooth light pulse of about 3-microsecond duration propagates through a specially prepared cesium atomic chamber of 6-cm length. It takes 0.2 nanosecond for a light pulse to traverse a 6-cm length in vacuum. In our experiment, we measured that the light pulse traversing through the specially-prepared atomic cell emerges 62 nanosecond sooner than if it propagate through the same thickness in vacuum. In other words, the net effect can be viewed as that the time it takes a light pulse to traverse through the specially prepared atomic medium is a negative one. This negative delay, or a pulse advance, is 310 times the "vacuum transit time" (time it takes light to traverse the 6-cm length in vacuum).

Q. Is Einstein's Relativity violated?

A. Our experiment is not at odds with Einstein's special relativity. The experiment can be well explained using existing physics theories that are consistent with Relativity. In fact, the experiment was designed based on calculations using existing physics theories.

However, our experiment does show that the generally held misconception "nothing can move faster than the speed of light" is wrong. The statement only applies to objects with a rest mass. Light can be viewed as waves and has no mass. Therefore, it is not limited by its speed inside a vacuum.

Information coded using a light pulse cannot be transmitted faster than c using this effect. Hence, it is still true to say that "Information carried by a light pulse cannot be transmitted faster than c." The detailed reasons are very complex and are still under debate. However, using this effect, one might be able to increase information transfer speed up to c. In present day technology, information is transmitted at speed far slower than c in most cases such as through the Internet and inside a computer.


The page also contains an "intuitive" explanation of the phenonmenon. A careful reading and some high school level physics make it simple to understand in a logical sense, but it remains completely incomprehensible intuitively (at least to me).
Load More Comments
Slashdot Login

Need an Account?

Forgot your password?