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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.
Time to destination, I think.
.9 LY to get here, its traveling faster than the speed of light
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
I think.
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
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.
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
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
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.
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.
I found this on Greg Egan's (the SF author and programmer) site: Subluminal Applet
-- stream of did I lock the front door consciousness
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
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.
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!"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 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