Light so fast it goes backwards?

math.ucr.edu...

Quantum Tunnelling is the quantum mechanical effect which permits a particle to escape through a barrier when it does not have enough energy to do so classically. You can do a calculation of the time it takes a particle to tunnel through. The answer you get can come out less than the time it takes light to cover the distance at speed c. Does this provide a means of FTL communication?
ref:T. E. Hartman, J. Appl. Phys. 33, 3427 (1962).

The answer must surely be "No!" otherwise our understanding of QED is very suspect. Yet a group of physicists have performed experiments which seem to suggest that FTL communication by quantum tunneling is possible. They claim to have transmitted Mozart's 40th Symphony through a barrier 11.4cm wide at a speed of 4.7c. Their interpretation is, of course, very controversial. Most physicists say this is a quantum effect where no information can actually be passed at FTL speeds because of the Heisenberg uncertainty principle. If the effect is real it is difficult to see why it should not be possible to transmit signals into the past by placing the apparatus in a fast moving frame of reference.
ref:
W. Heitmann and G. Nimtz, Phys Lett A196, 154 (1994);
A. Enders and G. Nimtz, Phys Rev E48, 632 (1993).

Terence Tao has pointed out that apparent FTL transmission of an audio signal over such a short distance is not very impressive. The signal takes less than 0.4ns to travel the 11.4cm at light speed, but it is quite easy to anticipate an audio signal ahead of time by up to 1000ns simply by extrapolating the signal waveform. Although this is not what is being done in the above experiments it does illustrate that they will have to use a much higher frequency random signal or transmit over much larger distances if they are to convincingly demonstrate FTL information transfer.

The likely conclusion is that there is no real FTL communication taking place and that the effect is another manifestation of the Heisenberg uncertainty principle.


Also couldnt you possible transfer information through pulsating gravity waves? since they go faster than the speed of light one could rig a time device that would be able to transfer information faster than the speed of light.

Ok let me give it a shot. The way I would explain what they are saying is as follows:

Say particle A representing a photon is released at C the speed of light and experiences a linear acceleration over a distance X

Particle B representing a photon is released at time t after particle A and also experiences the same linear acceleration over same distance X.

So for particle A

T1 representing the time of particle A to travel the distance

" In equation A represents whatever acceleration the particles experience" Sorry I forgot to clarrify hope it's not too confusing I was in a hurry.

X = [A(T1)^2]/2 + C(T1)

For particle B

X = [A(T2)^2]/2 + C(T2)

Thus:


A and C are the same so when setting equations equal for same distance fall out of the equation leaving
(T1)^2 + T1 = (T2)^2 + T2

which makes it Clear that T1 = T2 which intuition would support.

So if T1 = T2... the time elapsed from the time the First particle A arrives at distance X and particle B arrives at distance X is time t which represents the time after particle A's release that particle B was released.


Since information transfer as we know it requires a sequence of releases or bits the rate at which the bits of information can be recieved is at the same frequency the bits are transmitted at. So the speed of date transfer would be time T + t basicly the time between release and the time T it takes to travel distance X. If we say that faster than the speed of light the particle A would arrive at distance X instantaneously then T approaches 0 and t is the only factor left to deal with or the time between the release of the two particles.

It can be visualised as a waterhose. The same ammount of water will come out that goes in assuming no leaks or stretching of the hose. If the hose is really big but the water spicot can only flow a very small volume the ammount of water out of the hose is limited by the ammount of water flowing into the hose from the spicot.

Interestingly enough the same holds true if the hose is fixed in a veritcal position with the water put in from top and a bucket under the bottom. You may assume gravity would make the water fill the bucket at the bottom faster because the water accelerates. This however is false. The bucket will only fill at the same rate the water enters the top of the hose.

There is a loophole that may be exploited. And that is the bucket will fill at a faster rate than the water goes in the top of the hose if the bucket is raised at some velocity. However this will only work for a short time at that because the bucket can only be lifted a finite distance before it hits the hose.

So what I am saying is that the only way data could be recieved at a faster rate than it was transmitted is if the the observer was moving toward the source of transmission at a high velocity"low velocity would work also but it would be too small of an effect to measure" The problem is that if the observer moves towards the source of transmission at a velocity a distance X is traveled so it could only be sustained for a period of time. At which point the observer would coincident with the point of transmission so at that point once again the limiting rate of the transfer of data if the observer is coincident with the transmitter is the rate the data is transmitted since there is no distance to be traversed.

Hopefully this makes a little bit of sense to someone.

to summarize if there is zero time elapsed between the release of particle A and particle B the particles will arive at the same time. But particle B can never arrive before particle A unless it is released initially before particle A, stating both particles behave the same. It seems almost too obvious to talk about but I wanted to add my input never the less incase someone happened to be interested.

Thanks,
Flipside





[edit on 16-5-2006 by flipside]

[edit on 16-5-2006 by flipside]

This again reminds me of a comment I've heard most of my life.

We only know how consistent both time and light is, close to us. Everything further out is outside of our persoanl experience.

All the changing of light speed by man means that there is a possibility that under certain circumstances, a natural phenomenom can change the speed of light.

This makes me want to get close to a black hole and see what it really does to light.