Slashdot Mirror
Electrical Pulses Break Light Speed Record
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.'"
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.
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.
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
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.
D
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
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.
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
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.
(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
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.
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.
There's nothing unusual or fantastical about this claim. Group velocity/phase velocity 'n' all that stuff is basic undergrad material.
-- SIGFPE
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.
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.
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.
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.
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
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Cerenkov radiation, that's been known for decades?
"Provided by the management for your protection."
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.
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.
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.
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!
I found this on Greg Egan's (the SF author and programmer) site: Subluminal Applet
-- stream of did I lock the front door consciousness
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.
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.
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.
Actually, I may be the dope - I never verified if this was true. Anyone know?
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 < 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!
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
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