PLASMAS AND SUPER-LUMINAL GROUP VELOCITIES

You're going to love this article spotted by T.S., and passed along: scientists at Lawrence Livermore have apparently succeeded in breaking the speed limit of the velocity of light, and doing so in a manner that might ring a Bell, using plasmas:

Physicists Broke The Speed of Light With Pulses Inside Hot Plasma

Now, like all such articles, one is left trying to "read between the lines" without having access to the original paper. The original paper is here, but unfortunately behind a paywall:

Slow and Fast Light in Plasma Using Optical Wave Mixing

So I'm going to have to guess what's going on based on the first article's summary, and then indulge in my usual high octane speculation, based on my guesses.

Needless to say, this is a very hazardous procedure, and increases the possibility that I'm completely wrong, so take everything with not just a grain of salt, but with several bags of rock salt.

With that in mind, I want to draw your attention to the following:

While photons themselves are unlikely to ever break this speed limit, there are features of light which don't play by the same rules.

Manipulating them won't hasten our ability to travel to the stars, but they could help us clear the way to a whole new class of laser technology.

Physicists in the US have shown that, under certain conditions, waves made up of groups of photons can move faster than light.

Researchers have been playing hard and fast with the speed limit of light pulses for a while, speeding them up and even slowing them to a virtual stand-still using various materials like cold atomic gases, refractive crystals, and optical fibers.

But impressively, last year, researchers from Lawrence Livermore National Laboratory in California and the University of Rochester in New York managed it inside hot swarms of charged particles, fine-tuning the speed of light waves within plasma to anywhere from around one-tenth of light's usual vacuum speed to more than 30 percent faster.

...

A photon's speed is locked in place by the weave of electrical and magnetic fields referred to as electromagnetism. There's no getting around that, but pulses of photons within narrow frequencies also jostle in ways that create regular waves.

The rhythmic rise and fall of whole groups of light waves moves through stuff at a rate described as group velocity, and it's this 'wave of waves' that can be tweaked to slow down or speed up, depending on the electromagnetic conditions of its surrounds.

By stripping electrons away from a stream of hydrogen and helium ions with a laser, the researchers were able to change the group velocity of light pulses sent through them by a second light source, putting the brakes on or streamlining them by adjusting the gas's ratio and forcing the pulse's features to change shape. (Emphasis added)

Now what I am taking from this are two ways of reading it, and both are in my mind related. The key is in that phrase "groups of waves," which strongly suggests to me the idea of interferometry, which is, indeed, a "group of waves." It's a fancy way of saying that while the individual waves comprising an interferometric pattern move at the standard velocity of light in whatever medium they happen to be moving through, the resulting interferometric pattern itself is moving faster than the waves comprising it. Or another way of putting it would be that the interferometric pattern is a compressional or longitudinal wave pattern resulting from the interference of typical sin waves. Think of it this way, and to use the illustration I've often used: the normal electromagnetic wave is a sin wave, it travels like a jump rope loosely suspended between two people, and one person jerks the rope. The result will be a wave that moves -  slowly - through the rope to the other person, dissipating most of its energy as it does so. The interference pattern of several such waves would be more like a ruler or yardstick placed between two people, and one person pulses the yardstick. All the energy moves "instantaneously" and with little attenuation to the person on the other end.

The group velocity of this interference pattern would itself be quite analogous to a lattice structure in space-time itself, a lattice structure that could, moreover, resemble a compressional wave. Or to put it even more succinctly and provocatively, such an interference pattern or group velocity is the local space-time lattice.

It's notable that all this is being accomplished in a plasma, and by "adjusting the gas's ratio and forcing the pulse's features to change shape," i.e., by adjusting the internal geometry of the plasma and the electromagnetic pulses within it. Or to put the same point even more provocatively, the plasma is being used as an acoustical cavity, and this suggests that it could be used for super-luminal communication and even a kind of non-locality and entanglement. (Transporters, anyone?)

Of course, the article itself is cautioning against such speculations, which probably means I'm completely off target on my guesses, and hence on my speculations.

But it's worth noting that some years back, similar speculations were being advanced by a Brazilian physicist on interferometric patterns and group velocities resulting from finite apertures and squeezing lots of waves through it, with a resulting interferometric pattern of a superluminal velocity.

One can imagine lots of things, like a massive piezo-electric wave guide ending in a very small point with all sorts of plasma-goings-on inside of it, including an optical cavity that looks like it might have been for a maser, and with intriguing indications of acoustic modulation....

... otherwise it's just a big pile of granite and limestone...

See you on the flip side...