Nothing can travel faster than light, i.e. 299,792,458 meters per second. But a particular group of particles behave as if they could, a team of physicists recently concluded, potentially paving the way for a powerful light source that could reveal new types of science.
When electrons are excited and pushed around, they produce light of varying energies that can be used to study phenomena far beyond the limits of the naked eye or typical microscopes. Scientists have learned how to create and correct electrons in machines to get the particles to produce high-energy light. These light sources – from synchrotrons and cyclotrons to linear accelerators – allow scientists to see incredibly small things like the structure of a molecule. The knowledge gained from this technology has enabled the development of new medicines, the production of better computer chips and the non-destructive exploration of fossils. The waves emitted by electrons literally shed light on what would otherwise be invisible.
But these light sources are not common. Construction is expensive, requires a lot of land and can be booked out by scientists months in advance. Now a team of physicists believe that quasiparticles—groups of electrons that behave as if they were one particle—can be used as light sources in smaller laboratory and industrial settings, making it easier for scientists to make discoveries anywhere. The team’s research describing their findings is published today in nature photonics.
“No individual particles move faster than the speed of light, but features in the collection of particles can and do learn,” said John Palastro, a physicist at the University of Rochester’s Laser Energetics Laboratory and co-author of the new study, in a video call with Gizmodo. “This violates no rules or laws of physics.”
“I think that relaxing these electron beam requirements and moving away from the idea that every electron has to move in unison to produce this very coherent radiation really democratizes these sources – it makes them more widely accessible,” Palastro added added.
In their work, the team is investigating the possibility of making plasma accelerator-based light sources as bright as larger free-electron lasers by making their light more coherent compared to quasiparticles. According to a University of Rochester, the team carried out simulations of the properties of quasiparticles in a plasma using supercomputers provided by the European High Performance Computing Joint Undertaking (EuroHPC JU). release.
Large linear accelerators are among the most powerful light sources on Earth. Consider the $1 billion upgrade to SLAC National Accelerator Laboratory’s Linac Coherent Light Source – simply called LCLS-II – that reached first light last month. LCLS-II can produce a million X-ray pulses per second, up from the original LCLS’s tiny 120 pulses per second. The new X-ray pulses are 10,000 times brighter than those produced by LCLS, paving the way for scientists to study previously unseen phenomena, from molecules in plant cells to the phase change of materials. All of these X-rays are created by intentionally moving groups of fast-moving electrons back and forth using large magnets. You can read a full breakdown of how linear accelerators like LCLS-II work Here.
In a linear accelerator, “each electron does the same thing as the collective,” said Bernardo Malaca, a physicist at the Instituto Superior Técnico in Portugal and lead author of the study, in a video call with Gizmodo. “In our case, there is no electron that is wave-shaped, but we still create an undulator-like spectrum.”
The researchers compare quasiparticles with that Mexican wave, a popular collective behavior in which sports fans stand up and sit down one at a time. A stadium full of people can give the impression of a wave moving around the venue, even though no person is moving sideways.
“You can clearly see that the wave could, in principle, spread faster than any human being if the audience cooperates. Quasiparticles are very similar, but the dynamics can be more extreme,” said co-author Jorge Vieira, also a physicist at the Instituto Superior Técnico, in an email to Gizmodo. “For example, individual particles cannot travel faster than the speed of light, but quasiparticles can travel at any speed, including superluminal speed.”
“Since quasiparticles are the result of collective behavior, there are no limits to their acceleration,” Vieira added. “In principle, this acceleration could be just as strong as, for example, near a black hole.”
To be clear: the electrons in the bundle that make up the quasiparticle do not move faster than light. But the quasiparticle can effectively travel faster than light, the researchers say, if the wavelengths involved are larger than the quasiparticle itself.
The difference between what is perceived to be happening and what is actually happening when it comes to faster-than-light travel is an “unnecessary distinction,” Malaca said. “There are actually things that travel faster than light that are not individual particles, but rather waves or airfoils. These move faster than light and can create real faster-than-light effects. So you measure things that you only associate with superluminal particles.”
The group found that the collective quality of the electrons need not be as pristine as that of the beams produced by large facilities and that it could be practically implemented in more “tabletop” environments, Palastro said. In other words, scientists could conduct experiments on site using very bright light sources instead of having to wait for an opening at a coveted linear accelerator.
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