21 May 2014

Scientists work out how create matter from light, to finally prove Einstein’s E=mc2


Physicists in England claim they have discovered how to create matter from light, by smashing together individual massless protons a feat that was first theorized back in 1934, and has been considered practically impossible until now. If this new discovery pans out, the final piece of the physics jigsaw puzzle that describes how light and matter interact would be complete. No one’s quite sure of the repercussions if matter can indeed be produced from photon-photon collision, but I’m sure something awesomely scientific will emerge before long.

Way back in 1930, British theoretical physicist Paul Dirac theorized that an electron and its antimatter counterpart (a positron) could be annihilated (combined) to produce two photons. Then, in 1934, two physicists Breit and Wheeler proposed that the opposite should also be true: That two photons could be smashed together to produce an electron and positron (a Breit-Wheeler pair). In other words, that light can be converted into matter, and vice versa or, to phrase it another way, E=mc2 works in both directions. This would close one of the last gaps in particle physics that has been theorized, but has proven very hard to prove through observation.

Various photon-mass reactions, theorized and proven over the years
Various photon-mass reactions, theorized and proven over the years

The reason it’s proven hard to observe is that photons, a lot like neutrinos or electrons, are incredibly small. Furthermore, photons are massless. These two factors make it very, very hard to collide two photons together. Basically, the only real way of guaranteeing any collisions is to pump some beams of photons up to massive energy levels (think billions of times more energetic than normal visible light), inject them into a small space, and then hope that a few Breit-Wheeler pairs are created.

That is essentially the crux of this new discovery: Steven Rose and Oliver Pike of Imperial College London have come up with a way of getting the photons up to the necessary energy levels to guarantee some collisions. They propose the use of a high-powered laser, which would then slam into a slab of gold, producing a high-intensity gamma ray (photons). Then, further down the line you would have a gold hohlraum (literally hollow space), also excited by a laser to produce a big, fat field of photons. You then smash the gamma ray into the hohlraum (pictured at the top of the story) and, according to Rose and Pike, you get some electrons and positrons flying out the other end. Voila: Proof that Breit and Wheeler knew what they were talking about.

Photon-photon collider

gamma ray burst might look like
What a gamma ray burst might look like

In nature, photon-photon collisions are thought to occur during gamma-ray bursts (GRBs). GRBs are the most violent explosions that our universe can produce that we’ve discovered, anyway and they occur vary rarely, usually during a super or hypernova. A nearby GRB would probably wipe out most of the life on Earth. Perhaps more importantly, though, it’s believed that the Big Bang itself during the first 100 seconds or so of the creation of the universe would’ve also played host to these photon-photon collisions. We desperately want to find out more about the universe’s first few seconds, and recreating some of those primordial processes here on Earth is one of the best ways of doing just that.

For now, this discovery is purely theoretical but Rose and Pike say that there are plenty of laboratories around the world that have the equipment to perform photon-photon collisions. High-power lasers are ten a penny nowadays, and hohlraums are usually used in fusion experiments. ”The race to carry out and complete the experiment is on,” Pike says.

doi:10.1038/nphoton.2014.95 - "A photon-photon collider in a vacuum hohlraum"

Courtesy Extremetech


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