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Electrical Pulses Break Light Speed Record

Posted by chrisd on from the canadians-show-us-the-way-again dept.

J'raxis writes "PhysicsWeb writes that 'Pulses that travel faster than light have been sent over a significant distance for the first time. Alain Haché and Louis Poirier of the University of Moncton in Canada transmitted the pulses through a 120-metre cable made from a coaxial 'photonic crystal.' Haché and Poirier emphasize that their experiment does not break any laws of physics. Although the group velocity exceeds the speed of light - an effect permitted by relativity -- each component of the pulse travels slower than light.'"

68 comments

  1. kinda cool by batkiwi · · Score: 0, Redundant

    This stuff is always cool. Relativity is neat in that it lets you bend rules without breaking anything.

    Hence you can go faster than light, but you're not really....

    All too confusing, but nice to read about.

    1. Re:kinda cool by PD · · Score: 2, Funny

      Yes, relativity is like a willow tree, bending in the wind, not breaking, and it gets all those tiny little leaves all over your yard.

      In other words, WTF are you talking about???

      --
      If tits were wings it'd be flying around.
    2. Re:kinda cool by .sig · · Score: 2, Insightful

      (Meta on)

      Just out of curiosity, how can the first comment on a subject be redundant? That just strikes me as really bizzare.

      (Meta off)

      --
      -Space for rent
    3. Re:kinda cool by hummingtroll · · Score: 2, Funny

      The phenomenon is called the "Crack Mod" effect. When a Slashdot moderator is subjected to the influence of a sufficiently high amount of crack, the laws of nature and even fundamental logic begin to break down and effects such as this can be witnessed.

  2. Well.... by azephrahel · · Score: 2

    They got gigabit off of fiberoptic and onto copper
    (which some said wasn't feasable), and modems up to 56k (which we all said was impossible)
    so we just have to wait a few years until they make ethernet cards out of this ;)

    terabit ethernet anyone?

    /me thinks his pci bus might not handle the throughput this would offer....

    --
    You are only young once, but you can stay immature indefinitely.
    1. Re:Well.... by PhuCknuT · · Score: 4, Informative

      This actually has nothing to do with bandwidth, nor will it make ftl communications possible. Think of it this way. Put in a sine wave, and it shifts it 90 degrees out of phase. So when the leading edge of the wave hits the other end, it makes it a peak, and when the peak gets there, it is at the trough of the output. It looks like the peak got to the output faster than light, but in reality it was just the leading edge of the wave being amplified.

    2. Re:Well.... by PhuCknuT · · Score: 4, Interesting

      I forgot to mention how this IS important. What this type of research will lead to is reduced latency. Instead of information traveling down a cable at 2/3 of the speed of light, they can use methods like this to send data at much closer to the speed of light. Not more data, but slightly lower ping times.

    3. Re:Well.... by .sig · · Score: 2

      But this is a way of sending more data. By sending data faster, more is able to be transmitted in a constant time.

      What I find most impressive about this is the possibility it has with interstellar communication. (Which of course won't be usefull until we have someone to communicate with, but it's a start.) If a message can be sent faster than light, then one of the bigger problems with exploring anything further away than our solar system would be lessened.

      Of course, the real trick would be to figure out how to send solid energy (matter) at such speeds.

      --
      -Space for rent
    4. Re:Well.... by Jester998 · · Score: 1

      "a sine wave, and it shifts it 90 degrees out of phase"

      Uh, wouldn't it be easier to express this as a cosine curve, then?

    5. Re:Well.... by MindStalker · · Score: 2, Insightful

      Umm this example decreases the total time by x regardless of the distance. So you would be able to send the signal 1 nanosecond sooner to the next galaxy that if you used light itself. Its not what your thinking. Basically your creating the wave, then spreading the wave, so that the front of the wave gets there sooner than light, and the back of the wave gets there that same amount of time less than light. Maybe we could figure out how to stretch that wave thousands of light years wide? HAHA

    6. Re:Well.... by PhuCknuT · · Score: 1

      No, I was saying the input looks like a sine wave, and the output looks like a cosine. The peaks of the sine wave get to the output ahead of where they should be.

    7. Re:Well.... by Hal-9001 · · Score: 2

      Since they're using a photonic bandgap fiber, the pulse is already traveling at or very near c. Also, you can't actually use this technique to send information because a) that would actually violate relativity, and b) modulating the pulse screws up the effect by adding or subtracting frequency components to the signal. It's a neat trick, but with no practical use that I can think of...

      --
      "It take 9 months to bear a child, no matter how many women you assign to the job."
    8. Re:Well.... by AgentRavyn · · Score: 1

      Who says that we can't violate relativity? After all, it is still a theory. A damn important one, mind you, but still unproven.

      Remember -- an example of relativity working of not proof, but a counterexample is enough to discard the entire theory.

      --ravyn

      --
      ___
      I'm an exhibit on the mounted animal nature trail.
    9. Re:Well.... by Hal-9001 · · Score: 2

      That's why I qualified statement (a) with statement (b). Trust me, I want superluminal fiber-optic transmission as much as the next geek, maybe even more because that would improve my job outlook as a new graduate optical engineering tremendously, but based on having read the articles and taken quite a few optics classes, all the evidence suggests that this technique will break down upon trying to transmit data because it is basically a trick of wave superposition.

      One of my professors last semester had a really good electrical engineering example of something that works in sort of the same way and also explained why this wouldn't work for data transmission, but unfortunately I can't remember what it was...

      --
      "It take 9 months to bear a child, no matter how many women you assign to the job."
    10. Re:Well.... by Anonymous Coward · · Score: 0

      One of my professors last semester had a Trust me, I want superluminal fiber-optic transmission as much as the next geek, maybe even more because that would improve my job outlook as a new graduate optical engineering tremendously,

      Not to kick you when you're down, but admitting this:

      One of my professors last semester had a really good electrical engineering example of something that works in sort of the same way and also explained why this wouldn't work for data transmission, but unfortunately I can't remember what it was...


      ...is not going to help your prospects any. :-)

    11. Re:Well.... by Anonymous Coward · · Score: 0

      Then again, look at me; I can't even close a stupid italic tag. Never mind?

    12. Re:Well.... by Anonymous Coward · · Score: 0

      Well it's kinda like this:

      if you had a ball that was rolling under a rug, the end of the curvature of the rug at the position of said ball would reach the outside of a rug before said ball came out.

      If you had a 2x4 1 light year long and moved it back and forth you could get a message there faster than light.

    13. Re:Well.... by Rares+Marian · · Score: 1

      Well it's kinda like this:

      if you had a ball that was rolling under a rug, the end of the curvature of the rug at the position of said ball would reach the outside of a rug before said ball came out.

      If you had a 2x4 1 light year long and moved it back and forth you could get a message there faster than light.

      --
      The message on the other side of this sig is false.
  3. Uhhh, this is nothing new. by Mt._Honkey · · Score: 2, Informative

    We have always known that we could send waves "piggybacking" on light that move FTL. When light enters a plasma, such as the ionosphere, the free electrons can cause little ripples to travel along the light wave at significant FTL. However, while you can send information on these waves, the information itself does not move FTL, but at c. This has been known for quite some time, this is just the first time I know of that it has been done in a cable.

    --

    Don't Bogart the fish sticks
    1. Re:Uhhh, this is nothing new. by Linux_ho · · Score: 2
      When light enters a plasma, such as the ionosphere, the free electrons can cause little ripples to travel along the light wave at significant FTL. However, while you can send information on these waves, the information itself does not move FTL, but at c.
      Please forgive my lack of knowledge in this area, but what you said just doesn't make sense to me. If you can send waves FTL, and send information on those waves, then it logically follows that you can send information FTL... What am I missing?

      For example, Bob wants to tell Mary whether he got a research grant today. He has arranged to send her FTL waves at amplitude A if he got it, or at amplitude B if he didn't. If those waves are travelling FTL, so is the information.
      --
      include $sig;
      1;
    2. Re:Uhhh, this is nothing new. by mmontour · · Score: 4, Informative

      Please forgive my lack of knowledge in this area, but what you said just doesn't make sense to me. If you can send waves FTL, and send information on those waves, then it logically follows that you can send information FTL... What am I missing?

      Take a look at this applet and this page. They give a good illustration of the concept:

      [...]If dn(v)/dv is sufficiently negative, it can reduce the denominator in Equation (3) to less than one, yielding a group velocity greater than c. Why is this not a contradiction of special relativity? No energy or information needs to travel at the group velocity in order for the shape of the wave to exhibit features that move at that speed. If you tried to signal someone with a superluminal pulse by dropping a shutter in its path at the last moment, you'd find you were too late: the pulse would happily "pass through" the shutter, because every influence that was actually responsible for its appearance on the other side would have passed through already.

    3. Re:Uhhh, this is nothing new. by MindStalker · · Score: 2, Insightful

      I think the point is, you can create the signal faster than light, but you simply can't manipulate the signal to put information in it faster than light.

    4. Re:Uhhh, this is nothing new. by Mt._Honkey · · Score: 1

      No, you can put information on it, but the information moves allong the FTL wave at light speed. Odd, huh?

      --

      Don't Bogart the fish sticks
    5. Re:Uhhh, this is nothing new. by Hercynium · · Score: 2

      OK, now IANAP (IANA Physicist,) but I think it goes something like this:

      Think of yourself as a piece of information. You are standing on a train. Think of the train as the light wave, travelling at the speed of light. You are now walking from the back of the train to the front. Relative to the earth, you are travelling faster than the train, thus faster than the speed of light. However, relative to the train, you are travelling at walking speed. The problem is, in order to minimize your time on the train, you start your journey by jumping onto the last car as the train leaves the terminal, and jumping out of the first car as the train approaches the destination platform. Given a sufficiently long train, you could send a large amount of data that would begin to arrive quickly, however you must first establish the carrier (the train) and then you must offload the information. Your net gain should be a faster arrival of the data, but most likely the data will be offloaded at the same speed as usual. Ar you as confused as I am yet?

      OK, I think I'll go read the article now. :^)

      --
      I'm done with sigs. Sigs are lame.
  4. What an LPB... by Anonymous Coward · · Score: 0

    Think of the gaming ping times!

  5. Sounds familiar by codeButcher · · Score: 4, Funny
    Although the group velocity exceeds the speed of light ... each component of the pulse travels slower than light.

    My team words just the opposite: Each individual working at breakneck speeds, but the group never gets there fast enough.

    Now if they only could stop posting to /.

    --
    Free, as in your money being freed from the confines of your account.
  6. Measure? by Noodlenose · · Score: 1
    As I am not a physicist, I wonder how you can measure something that's faster than light???

    D

    1. Re:Measure? by AnalogBoy · · Score: 2

      Time to destination, I think.

      if object A is sent from 1 LY away and takes 1 LY to get here, it's traveling at the speed of light.

      if object B is sent from 1 LY away and takes .9 LY to get here, its traveling faster than the speed of light

      I think.

    2. Re:Measure? by SIGFPE · · Score: 2

      As a bit of a physicist I can't help but wonder why you think there's a difficulty with measuring a velocity faster than that of light???

      --
      -- SIGFPE
    3. Re:Measure? by Anonymous Coward · · Score: 0

      As a bit of a physicist I can't help but wonder why you think there's a difficulty with measuring a velocity faster than that of light???

      That is as silly a response as this one:

      As a brain surgeon, I am wondering why you can not perform brain surgery.

      Perhaps a more helpful response would have been warranted, since the poster was stating his/her ignorance to the subject and asking for help rather than an arrogant bit of self-induced ego inflation.

    4. Re:Measure? by SIGFPE · · Score: 2
      Er...no. You don't need to be a physicist to measure the velocity or understand the concept of a velocity and I strongly suspect the original poster understands these ideas quite well.


      I think you are missing a point. The original poster seems to think that not only is there some speed limit at c but also a limit to your ability to measure speeds greater than c. There's some interesting idea in the guy's head that makes him think this even though no popular (or unpopular) article on science says any such thing. I'd love to know where this idea came from.


      To follow through with your analogy: if someone had said to a brain surgeon "how can you possibly operate on that person they weigh more that 100kg?" I suspect that not a few people would be very curious to know what the questioner was talking about.

      --
      -- SIGFPE
    5. Re:Measure? by jokrswild · · Score: 1

      You mean "1 year" and ".9 year" to get here. cause A light year is a distance, not a time. So, um. Yeah. Agreeing with alot of the above, this will just decrease ping times. We still can't send information faster than c.

    6. Re:Measure? by Transcendent · · Score: 1

      Chill out... just because the guy didn't understand completely how exactly they measured the speed of light doesn't mean you have to get on his case. So now we all know that you're some bigshot (well... a bit of a) physicist with a huge ego. You're original statement "As a bit of a physicist I can't help but wonder why you think there's a difficulty with measuring a velocity faster than that of light???" is really really stupid. I mean, it's like a math professor (don't get me wrong, I'm not saying you're anywhere near the intelligence of a math professor) wondering why the hell some 8th grader can't do third derivatives in their head, or find the area under the curve of 1/x [1,infinity) spun around the x-axis to create a cone.

      Er...no. You don't need to be a physicist to measure the velocity or understand the concept of a velocity and I strongly suspect the original poster understands these ideas quite well.

      Of course you don't need to be a physicist to understand velocity. Sure someone might have a concept of velocity, but it doesn't mean that they know the methods and formulas used in wave motion to calculate the velocity of a particle.

      The original poster seems to think that not only is there some speed limit at c but also a limit to your ability to measure speeds greater than c. There's some interesting idea in the guy's head that makes him think this even though no popular (or unpopular) article on science says any such thing. I'd love to know where this idea came from.

      And without being a physicist, I too thought that there was a universal speed limit (without getting into relativity)... the speed of light. Usually that's taught in gradeschools and highschools, so I'm guessing that's where "some interesting idea in the guy's head" came from.

  7. must've been.... by Snafoo · · Score: 1, Flamebait

    carrying a Microsoft press release, or other bad news ;)

    Either that, or the scientists crunched the numbers over a nice Italian meal at some bistro...

    --
    - undoware.ca
  8. Beating Carrier Waves Against One Another by Anonymous Coward · · Score: 1, Informative

    Send a signal. Compare it with a reference signal. Compare times. The comparision of one against the other is "beating" one signal against another. So comparing sines. The two signals combine and/or cancel, and produce a new signal. That signal correlates to a time.

    That's the same way that radar worked back when it was just an oscilloscope hooked to a radio. (Oscillation Scope.) You don't actually run a clock to see how far the signal has travelled, rather you compare it against another signal for a time difference. Very easy to do with analog.

  9. "Laser smashes light speed record" by richie2000 · · Score: 2, Interesting
    The other article linked to from the one in the submission says:

    Next they send a 3.7-microsecond long laser pulse into the caesium cell, which is 6 centimetres long, and show that, at the correct wavelength, it emerges from the cell 62 nanoseconds sooner than would be expected if it had travelled at the speed of light. 62 nanoseconds might not sound like much, but since it should only take 0.2 nanoseconds for the pulse to pass through the cell, this means that the pulse has been travelling at 310 times the speed of light. Moreover, unlike previous superluminal experiments, the input and output pulse shapes are essentially the same.

    Correct me when I'm wrong, but doesn't this mean that the pulse went out of the cell 61.8 ns before it went in? When I try to picture this phenomena my brain just overloads and dumps the core.

    --
    Money for nothing, pix for free
    1. Re:"Laser smashes light speed record" by justinstreufert · · Score: 1

      No, under normal circumstances the pulse would have gotten there many ns later. It's an increase in speed, not time travel. There is still a delay involved in getting the photons to their destination, it's just shorter.

      If you put one of these setups next to a light bulb and turned them on at the same time, the laser pulse would get there first.

      Justin

      --
      "Why would God give us a waist if we wasn't supposed to rest our pants on it?" - Rev. Roy McDaniels
  10. FTL - information backwards in time by kippy · · Score: 0, Offtopic

    I'm not a physicist or anything but doesn't faster than light communication allow for information to be sent backwards in time?

    Also, will this allow me in any way to go to my parents' home town and get into a chance with the local bully, resulting with a dump truck of manure being dumped on him?

    --
    Blaze a trail to the New World
    1. Re:FTL - information backwards in time by scott1853 · · Score: 2

      I've heard this my whole life. I'm not a physicist though, but it doesn't seem like light and time are one in the same, or even have any effect on the other.

      It's not like we calculate time in relation to light except when measuring the distance to stars. Even then it's still light YEARS, so it's being converted to a time unit we understand. It would be like miles per hour, it's just that it's such a large number we use a conversion factor that makes it relatively small.

      FTL means faster than light, not backwards through time.

    2. Re:FTL - information backwards in time by Captoo · · Score: 2, Informative

      If you look closely at the equation used to describe time dialation in the theory of reletivity, you will see that it is simply a variation of the famous a^2 + b^2 = c^2, where a is your velocity through space and b is your velocity through time. What it boils down to is that your speed in four dimensions always equals c.

    3. Re:FTL - information backwards in time by progbuc · · Score: 1

      So if the magnitude of your velocity in the 3 spacial dimensions is greater than c, wouldn't that require you're velocity through time to be negative? Hence, going back in time.

      --
      Go ahead and waste your life with your inhibitions, just don't ruin other people's lives with your intolerances.
    4. Re:FTL - information backwards in time by mmontour · · Score: 2

      I'm not a physicist or anything but doesn't faster than light communication allow for information to be sent backwards in time?

      If you can send faster than light communication in two different reference frames that are moving past each other at a high (but sub-c) velocity, then the basic equations of special relativity (length contraction, etc) say that you'd be able to relay a signal back to its starting point before it was originally transmitted.

    5. Re:FTL - information backwards in time by Not2Bryt64 · · Score: 1

      Yes, which is why Physicists say that it isn't possible to go faster than c. This thinking is the basis for many sci-fi time travel stories. This has always seemed to me to have problems, since if you go deeper you will see that just as you reach the speed of light, according to this thinking, your velocity through time would have to cross over 0, at which point you would "Stop".

      --
      -These aren't my pants.
    6. Re:FTL - information backwards in time by SIGFPE · · Score: 2

      Your comment is a bit of a non sequitur as the original 'pulses' are not a form of communication. However what you say is otherwise an accurate statement - within the context of relativity FTL is the same as travel back in time.

      --
      -- SIGFPE
    7. Re:FTL - information backwards in time by Captoo · · Score: 1

      That is one reason. The other is that as you approach the speed of light, your mass increases towards infinity. In other words, even if time didn't slow down, it would take an infinite amount of energy to accelerate you to the speed ot light. The only way to reach the speed of light is if you come into existence already traveling that speed, or if you have zero mass.

    8. Re:FTL - information backwards in time by spike+hay · · Score: 2, Informative

      There is no such thing as faster than light. In this experiment, nothing is moving faster than light (just ignore common sense, it does not apply here). From my understanding, it's just the peak of the wave that travels FTL. The photon is not going FTL.
      Though this isnt really travel, as such, the only FTL phenomenon we know of is quantum teleportation. This is when you "entangle" two particles. When you entangle 2 particles, they act as one. If you changed the polarity of one, the other would instantly change to the opposite polarity, even if it is accross the galaxy. However, this still does not allow FTL star-trek teleportation or communication. Due to good old Heisenberg's Uncertainty Principle, you cannot measure a particle's properties exactly, because doing so would disrupt the particle.
      If you and your friend Bob both had entangled photons, and you were at Alpha Centauri, you could vertically polarize your photon. Bob's photon back at Earth would instantly become horizontally polarized. But it Bob tried to measure his photon by sending it though a polarizing filter, he would only have a 1 in 4 chance of correctly measuring the photon. It's essentialy random.
      The only way around this is for you to tell Bob that you polarized your photon vertically. This can only be done at light speed with a radio signal. Then Bob can send the photon through a horizontal filter.

      --
      If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
    9. Re:FTL - information backwards in time by DahGhostfacedFiddlah · · Score: 2

      Okay - this I never understood, so could someone help me out?
      Taking :
      A^2 + B^2 = C^2
      Therefore C^2 - A^2 = B^2
      And assuming that A (velocity through space) > C
      C^2 - A^2 &lt 0
      B^2 < 0
      B = (Something) x (Root of -1)

      That's not "backwards in time", that's moving through a complex plane of time or something. I'm not claiming to know what that means, just that "backwards in time" doesn't make sense. Can someone help me understand this?

      --
      Last post!
    10. Re:FTL - information backwards in time by Xilman · · Score: 1

      I'll try. There are two things wrong.

      First, the a^2+b^2=c^2 thing is for calculating with lengths, not velocities.

      Secondly, you, (and the original poster), are using good old Euclidean geometry to calculate a "length". Your algebra is fine, it's just that space-time doesn't work the same way. The rule (for flat space-time) is that s^2 = x^2+y^2+z^2-t^2. Note the minus sign before the t. It's the presence of this minus sign that leads to many of the apparently counter-intuitive results of Special Relativity.

      In General Relativity, not even the simple (+1 +1 +1 -1) metric works. The simple constants are, in general, replaced with functions involving the space-time co-ordinates. The effect is the same as curving the geometry; the curvature has an effect on test particles which is the same as the observed effects of gravity.

      I realise that the above is over simplified and the purists are probably shuddering already, but to do the subject justice requires much more space and time than I have available right now.

      Paul

      --
      Lasciate ogne speranza, voi ch'intrate
    11. Re:FTL - information backwards in time by TheLink · · Score: 2

      I am not a physicist but is it possible to store these entangled photons for later use of FTL communication?

      Say you send half of a large number of these photons somewhere.

      Then at a predetermined time (war say) you start using them in a particular prearranged way and Bob measures them accordingly. So that any changes in expected result would be the information (plus error correction of course), which is now transferred FTL and not easily jammable.

      So is this possible? There's probably something I'm missing right? Can't be as easy as that :).

      --
  11. What bugs me about this by renehollan · · Score: 3, Interesting
    is a problem akin to Shannon's Theorem: you know, the maximum data rate of a channel is related to the bandwidth and noise floor?

    In this case, the effect occurs close to the intentional absorbtion band, where signals get reflected because of impedance mismatch. So, the signal gets strongly attenuated. Gets there faster, but is much weaker, yes?

    The effect of the thermal noise of the receiver in the band of interest thus gets more significant. More relative noise, less bits per pulse (think AM).

    So, what would be a 1 km cable capable of carrying 100 mb/s (for example -- I'm pulling these numbers outa my...) now looks like a 100 m cable capable of carrying 1 Mb/s... great for wire latency, lousy for bandwidth.

    Now, we all know that for typical packet sizes, wire latency is insignificant to data serialization latency: the time it takes for the last bit in a packet to leave the transmitter, compared to the first bit. So, you've cut wire latency by 90% and increased data latency by much more.

    What am I missing here? Or, is there, as I suspect, NSTASFL

    --
    You could've hired me.
  12. FTL Pulse = Science; Perpetual Motion = Hoax??? by Cy+Guy · · Score: 0, Redundant


    How is it that Wednesday's story on a machine that purports to generate more energy than it consumes, replenishing its fuel, is posted to /. as bogus hoax poorly understood and reported by the (aparently defrauded) mainstream press, the /. story garnering over 900 comments. But this story on sending an electrical pulse is relegated to the Science section, gets under 20 posts, all of which seem to accept the claim at face value.

    Note that both discoverers clearly noted that while the results seems fantastical, no fundemental rules of physics were broken (despite Michael's interpretation of the 'perpetual motion machine' inventors claims as being just that).

    I accept that Applied Physics Letters is a much more repected source of science news than CNN, but why did the /. response have to be disparate? As far as I can tell the only difference is that the Perpetual Motion Machine inventor hasn't yet had a chance to publish their results, as the story was broken in the press based on a patent application before any thought of scientific publication could be pursued.

    --
    Work for Change & GET PAID!
    1. Re:FTL Pulse = Science; Perpetual Motion = Hoax??? by SIGFPE · · Score: 3, Informative

      There's nothing unusual or fantastical about this claim. Group velocity/phase velocity 'n' all that stuff is basic undergrad material.

      --
      -- SIGFPE
    2. Re:FTL Pulse = Science; Perpetual Motion = Hoax??? by hubie · · Score: 3, Informative
      This is straight-up physics of waves, and as such is not unexpected. From time to time another experiment is done and it gets widely reported and misunderstood (even by scientists that should know better, but who have forgot their freshman/sophomore level physics).

      This is the basic misunderstanding of what the phase, group, and signal velocities of a wave system are. The bottom line is that you cannot send information using these superluminal signals, so there are no time travel/relativity problems. A nice Java applet showing this is here.

  13. Einstein wins again by p3d0 · · Score: 2
    at the group velocity reached three times the speed of light for frequencies in the absorption band.
    Great. Just when they get a signal to travel faster than light, it gets absorbed.
    --
    Patrick Doyle
    I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
  14. Isn't this just - by 4of12 · · Score: 2



    Cerenkov radiation, that's been known for decades?

    --
    "Provided by the management for your protection."
    1. Re:Isn't this just - by Crispy+Critters · · Score: 1
      Cerenkov radiation


      I believe it is not at all related. Cerenkov radiation is the result of a charged particle moving through a medium at a speed faster then the speed of light in that medium, like a proton moving through water at 0.9c. This generates photons, but they move at the speed of light in the medium.

  15. It's the shape of the pulse... by Crispy+Critters · · Score: 5, Informative
    What is happening here is that they are sending a pulse of light, and the envelope or shape of the pulse changes as it travels. Previous papers have shown a pulse that starts out as a Gaussian and becomes progressively more skewed as it propagates.

    This allows the peak of the pulse to move faster than light speed. However, the leading edge of the pulse does not.

    This is why this is not a technique for sending information faster than the speed of light.

  16. Isn't this old news? by zenyu · · Score: 1

    I think the Science Times ran something about moving the group velocity faster than c a year ago.

    Plus my reading of this article leaves me thinking they were actually moving their signal at 2/3 c since they were working in a medium where you'd only expect light to travel 8"/ns instead of the 12"/ns in vacum.

  17. Speeding up time by archnerd · · Score: 1

    If time is a fourth dimension, then we can set up the equation x^2 + y^2 + z^2 + t^2 = C^2, where x,y,z, and t are the magnitudes of the vectors in each dimension and C is the speed of light. So all we need to do is travel at an imaginary speed in x, y, and z and x^2 + y^2 + z^2 will be negative so we'll be able to speed up time. Woohoo!

    1. Re:Speeding up time by WolfWithoutAClause · · Score: 2

      FWIW you're close, but no cigar, actually the invariant relativistic equation is:

      Dx^2 + Dy^2 + Dz^2 - Dt^2 = constant

      Where Dx, Dy, Dz and Dt are distances in x,y,z,t directions.

      But noone knows how to get an imaginary velocity...

      --

      -WolfWithoutAClause

      "Gravity is only a theory, not a fact!"
  18. Applet that Illustrates This by cmpalmer · · Score: 2, Informative

    I found this on Greg Egan's (the SF author and programmer) site: Subluminal Applet

    --
    -- stream of did I lock the front door consciousness
  19. More FTL "tricks" by Cade144 · · Score: 1, Informative

    Slightly off topic, but you can perform your own FTL demo at home.
    The classic example uses a bright searchlight reflecting of the clouds at night, but I suppose a laser pointer in a large auditiourm would work well too. The bright spot can be "moved" faster than light accross the clouds, just by moving the light source through a few minutes of arc.
    Unfortunatly the spot is not a physical thing, just an image. No real information is moved FTL.

  20. Brain Teaser by Mignon · · Score: 3, Interesting
    As a youngun', I was told by an adult friend that if you closed a pair of scisors fast enough, the point where the two blades crossed would move faster than the speed of light. It was presented as a sort of paradox about how something could go faster than light. (Note to Marilyn Vos Savant: it's 'cause the thing moving faster than light has no mass, not 'cause Einstein was wrong.)

    Actually, I may be the dope - I never verified if this was true. Anyone know?

    1. Re:Brain Teaser by Farang · · Score: 1

      This was mentioned and illustrated in Scientific American years ago. I think you are right: the point moves FTL. -- Can any information move faster than light? Suppose you put a four inch long wooden dowel between your finger and the doorbell, and push the bell. Pressure from your finger is passed to the doorbell button. Now imagine a dowel a few million kilometers long; push it, and -- will the push arrive at the doorbell instantaneously, as if the dowel were not there, or at the speed of light? Anyone?

    2. Re:Brain Teaser by -douggy · · Score: 2

      Actually the scissors dont close instantly. The clsoing action propergates along the metal at the speed of sound in the metal. Same with waggling a long rod. Speed of sound in steel = 5000m/s ish right? (i dunno the real number)

      Same with tugging on a lightyear long rope doesn't "instantly" send information to the otherend

    3. Re:Brain Teaser by lightray · · Score: 1

      The push (which is a compression wave) travels at the speed of sound in the dowel, much slower than the speed of light.

    4. Re:Brain Teaser by DahGhostfacedFiddlah · · Score: 2

      That's where the whole time-slowdown comes in.

      There are no laws stating that two things cannot appear to move faster than light relative to each other to *an observer*. Two spaceships moving at the speed of light towards each other, and starting 2 light seconds apart, will hit in 1 second. From your point of view.

      On the interior of the spaceship, time dilation will take effect, and it will be much longer.

      --
      Last post!
    5. Re:Brain Teaser by SIGFPE · · Score: 2

      That's kinda missing the point. You could push the blade simultaneously (in the scissors rest frame) all the way along its length rather than have a signal from the handles propagate at the speed of sound in steel.

      --
      -- SIGFPE