Sound Pulses Exceed Speed of Light

Hi fellows

I believe that light travels faster than the speed of sound.

One Sight a jet aircraft in the sky then weight for the sound.

Two send a radio signal from point A to point B and send the same signal to point C simultaneously which is to the side of point A and the singal from point A to B will arrive before the signal from point C. Now turn a light on at point A and you will see the light from point A and C at the same time if you reflect this light with a mirror at point C and you are located at point B.

This sounds almost as 'spooky' as particle/anti-particle pair production. Look at the diagram from the LiveScience article.

One way of explaining the superluminal transmission speed is that just before a pulse enters a medium (wave-guide, pipe, glass, or whatever), a new pulse and it's 'anti-pulse' is formed by borrowing some energy from the medium or environment. The new pulse exits the medium even before the original pulse enters it. The 'anti-pulse' rushes back to annihilate the original pulse and so pay back the energy loan to the medium.

One apparent problem is that all information contained in the original pulse dies with it at annihilation and no info exists in the new pulse. However, what if we send a lot of these pulses and phase-modulate them? I suppose the darn Heisenberg uncertainty will make it impossible to retain the modulation...

Jorrie

So far as I could see, the explanation in the article didn't say how the medium was prepared. However, there are a number of possibilities; below, I describe one that can look as if the new pulse appeared spontaneously without preparation; personally, I would view the article's presentation as trickery if it related to the process I'm about to describe, so it is to be hoped that this is not the case.

In all cases I might consider, the "New Pulse" of the figures is simply the result of initial conditioning - it would exit at the same time regardless of whether the "initial pulse" actually follows. However, the conditioning can be a by product of the generation of the "initial pulse".

Ultra-short pulses that are generated in non-linear media often have long precursors at relatively low power and apparently unrelated frequencies. If such a pulse meets a suitable non-linear material, the apparently unrelated signals can indeed produce a pulse that behaves as described. In the usual case the cancellation shown in the third figure results in a signal being generated at a different wavelength, but it can be arranged that this signal is in the absorption band.

BTW, on the basis that I don't find particle/antiparticle pair production particularly spooky, it would appear that I have turned partway into a vampire

Fyz

Hi nighthawk. The reason that I connot beleive that sound travels faster that light in any medium is that many years ago I watched a display of old 18th century cannons shooting at targets, I watched this from a distance of 300 yards. I could clearly see the flash of fire at the muzzle before I heard the sound of the shot. This lead me to retreat to one mile up the hill to observe the difference in speed between the sound and the light. Armed with a good set of binoculars I watched the light flare from one of the cannons, then counted the seconds until I heard the shot. The answer was about 4 seconds difference per mile. Since then I have spoken to many people about this, and one old man said that everytime he obseved lightning from his house he would count the seconds between seeing the flash and hearing the sound of thunder. This he told me indicated the distance from his house of the lightning strike, and he had calculated it at 4 seconds per mile. I chalenge you to prove otherwise.

Hi Scapolie, you wrote: "This he told me indicated the distance from his house of the lightning strike, and he had calculated it at 4 seconds per mile. I chalenge you to prove otherwise."

This discovery does not mean that sound travel anywhere near the speed of light! It simply says that in a specific experiment, it appears as if the sound wave exits a particular enclosure before it properly entered it.

My feeling is that this is a misinterpretation of "simultaneity", in the special relativity sense (or in other words, a confusion between different coordinate systems).

Jorrie

Hi Scrapolie. Just because you've never seen sound travel as fast as light, it doesn't mean that it can't appear to if, as others have mentioned, it is simply considered to be a result of relativistic phenomenon, just like it doesn't appear to a mideival king that we're travelling around the sun or that the earth is spherical. Let's give an example:

Two galaxies are travelling in opposite directions at 3/4 of the speed of light. An observer, using redshift phenomena, on one galaxy believes that the other is traveling at 1.5 times the speed of light , seeing the light reach her many many years in the future. Now, according to a neutral frame of reference, neither is travelling faster than the speed of light, however it can appear otherwise.

I personally don't believe there's any true frame of reference in our universe. Does anything, including space, ever truly "stand still" such that it could be considered an objective frame of reference? (For instance, we know space expands)

What was the medium that was used to carry the sound??

Would there not have been any type of resistance against the sound wave??

Hi Guest. The medium that the sound and light travelled through was air at normal atmospheric pressure, it was a warm very still day and there was nothing between myself and these cannons. The following year I concocted an explosive charge together with a half a pound of magnesium in powder form to see if I could replicate what I had experience. I put the charge on the top of a 15ft wooden stake at the same location of my first experience. I then retreated to the original observation position and signalled to my friend below to light the fuse. The results were utterly fantastic, a burst of brilliant white light followed by a large bang about 4 seconds after. I replicated this experiment twice during the following winter when the temperature was -15 degrees celsius, the results were the same as before.

Liquid unobtainium? 2,2,4-trimethylchickenwire?

The description in the article is inadequate to know exactly what was the original experiment, but I can immediately think of three situations where this can happen:

The first is a multi-moded situation where several acoustic waves at the different frequencies are travelling along different paths. Because the frequencies are discrete, you can measure a timing difference that looks like the group velocity is whatever value you wish. Of course, this only works for repetitive signals - the instant that the propagating pulses are modulated, you can see the length of time that the information (or energy) takes to propagate.

The second condition is possibly more interesting, and can occur under conditions known as "anomalous dispersion". Here, we have continuous ranges of frequency where the group velocity exceeds C. But the loss is changing rapidly. As the theory that relates group velocity to the propagation velocity of information/energy is developed under the assumption of constant loss, we can see again that this high group velocity does not have any implications for the velocity of energy/data transmission.

The final area (which is in reality equivalent to the first) is the area of meta-materials (details in another blog). I believe that awareness of this implication is important, in that it represents a fundamental limit to the performance of these materials.

Fyz

The only way I see this happening is if somehow an INERTIALESS transfer of sound took place ... which, theoretically, should take no time.

Maybe we are on the verge of discovering Anti-Gravity and an Inertialess Travel mode.

Silver.

... On second thought ... Inertialess Sound would not be heard as it would stick to the mass of air or its atomic level electromagnetic waves ... now that would require some deep thinking!

Ha ! nothing new here. I've accomplished a similar phenomena in my checking account, i.e., money with negative value and FTL rejection of my debit card. I'm sure the secret of their negative inertial vibratory transmissions FTL have something to do with ufo's Phlosmagon, and cold fusion or that old stanby; slow light.