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Upside the Head

Started by Recusant, May 21, 2021, 09:26:25 AM

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Recusant

A smack, that is. Upside the head of the headline editor who excreted this meretricious bilge. "Broken the speed of light" is an obvious and completely unnecessary falsehood. The story is interesting and not too bad: A possible step forward in developing more powerful lasers, which would prove useful in a number of ways, not least being the advancement of workable fusion power.

The picture I have of this phenomenon is as a sort of harmonic secondary wave imposed on the beam of light. It's probably not a particularly accurate picture, but I can at least grasp it.  :sidesmile:

"Physicists Have Broken The Speed of Light With Pulses Inside Hot Plasma" | Science Alert

QuoteSailing through the smooth waters of vacuum, a photon of light moves at around 300 thousand kilometers (186 thousand miles) a second. This sets a firm limit on how quickly a whisper of information can travel anywhere in the Universe.

While this law isn't likely to ever be broken, 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 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.

This time, researchers from Lawrence Livermore National Laboratory in California and the University of Rochester in New York have 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.

This is both more – and less – impressive than it sounds.

To break the hearts of those hoping it'll fly us to Proxima Centauri and back in time for tea, this superluminal travel is well within the laws of physics. Sorry.

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.

The overall effect was due to refraction from the plasma's fields and the polarized light from the primary laser used to strip them down. The individual light waves still zoomed along at their usual pace, even as their collective dance appeared to accelerate.

[Continues . . .]

The paper ("Slow and Fast Light in Plasma Using Optical Wave Mixing"} is behind a paywall. Here's the pleasantly succinct if not downright laconic--

QuoteAbstract:

Slow and fast light, or large changes in the group velocity of light, have been observed in a range of optical media, but the fine optical control necessary to induce an observable effect has not been achieved in a plasma. Here, we describe how the ion-acoustic response in a fully ionized plasma can produce large and measurable changes in the group velocity of light. We show the first experimental demonstration of slow and fast light in a plasma, measuring group velocities between 0.12c and −0.34c
"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken


Icarus

That is some heady stuff to be sure.