Physicists Broke The Speed of Light With Pulses Inside Hot Plasma

Most of us grow up knowing that the speed of light, which tops out at 300,000 kilometers (186,000 miles) per second, is the prevailing law that limits how quickly information can travel through empty space.

While photons are unlikely to ever exceed this speed limit, there are some features of light that do not follow the same rules.

Manipulation of them will not speed up our ability to travel to the stars, but it may pave the way for a whole new class of laser technology.

Under certain conditions, waves made up of groups of photons can move faster than light, according to physicists in the United States.

For a number of years, researchers have been experimenting with the speed limit of light pulses, speeding them up and even slowing them to a halt using materials such as 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.

This is both more and less impressive than it sounds.

Physicists Broke The Speed of Light With Pulses Inside Hot Plasma
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To the disappointment of those hoping it will transport us to Proxima Centauri and back in time for tea, superluminal travel is well within the laws of physics. Sorry.

The weave of electrical and magnetic fields known as electromagnetism holds a photon’s speed in place. There’s no getting around it, but photon pulses at specific frequencies jostle in ways that produce regular waves.

The rhythmic rise and fall of entire groups of light waves moves through matter at a rate known as group velocity, and it is this ‘wave of waves’ that can be slowed or sped up depending on the electromagnetic conditions of its surroundings.

The researchers were able to change the group velocity of light pulses sent through them by a second light source by stripping electrons away from a stream of hydrogen and helium ions with a laser, 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 caused by refraction of the plasma fields and the use of polarized light from the primary laser to strip them down. Even as their collective dance appeared to speed up, the individual light waves continued to zoom along at their usual rate.

From a theoretical standpoint, the experiment contributes to the understanding of plasma physics and places new constraints on the accuracy of current models.

In practice, this is good news for advanced technologies waiting in the wings for clues on how to overcome obstacles that are preventing them from becoming a reality.

Lasers, particularly the insanely powerful variety, would be the big winners here. Old-school lasers rely on solid-state optical materials, which degrade as the energy increases. Using plasma streams to amplify or change light characteristics would circumvent this problem, but to make the most of it, we would need to model their electromagnetic properties.

It’s no coincidence that Lawrence Livermore National Laboratory, which is home to some of the world’s most impressive laser technology, is interested in understanding the optical nature of plasmas.

More powerful lasers are exactly what we need for a wide range of applications, from increasing the efficiency of particle accelerators to improving clean fusion technology.

It may not help us travel through space faster, but it is precisely these discoveries that will push us towards the kind of future we all desire.

This study was published in the journal Physical Review Letters.

READ MORE: Speed Of Light – How Fast is That?

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