How to Take Light and Make Matter

First, you'll need some gold. And also some lasers. 

In 1934, Gregory Breit and John Wheeler—American physicists who would go on to help create the atomic bomb—developed a theory: that, under very particular circumstances, two photons of light could combine to produce an electron and a positron.
It was a daring idea. Electrons form the outer shells of atoms, so the Breit-Wheeler theory suggested that there's a way to turn light into ... stuff. Matter. 
It was also an idea, however, that—as with so much else when you're talking about particle physics—was based on calculations alone. Breit and Wheeler didn't have much hope of having their theory proved in a lab setting. They published their work on the, er, matter, noted that it would be “hopeless to try to observe the pair formation in laboratory experiments,” and then went on with their careers. 
Eighty years later, however, another generation of scientists claims to have taken the hopelessness out of the equation. A team of researchers at Imperial College London has developed a system, they say, for evidencing the Breit-Wheeler theory. It goes by the delightfully descriptive name of the "photon-photon collider," and it would, as that name suggests, offer a way to smash photons (light particles) together to test whether electrons do indeed result from the collision.
The team has just published their work in the journal Nature Photonics. According to their research, you can turn light into matter by recreating, in the lab setting, a process that occurred during the Big Bang. First, as The Guardian's Ian Sample describes it, you fire electrons at a slab of gold, which produces a beam of high-energy photons. Then you create another beam by taking a tiny, gold capsule—a hohlraum, it's called, from the German for “empty room”—and fire a high-energy laser into the capsule, creating an intense brightness. Then you send the first beam of photons into the hohlraum, and the two streams of photons collide. And, boom: electrons. Light into matter. Like Rumplestiltskin with his gold, except in reverse. And ever-so-slightly more high-tech.
Or, you know ... that's how it would work in theory. What the Imperial College team has created is a map for the conversion of light into matter; they're not entirely sure where that map will lead. Their calculations, however, suggest that the photon-photon collider would produce around 100,000 electron-positron pairs.
If so, the collider would also have the capacity, its inventors say, to demonstrate one of the most famous theories in physics: Einstein’s theory of relativity, which claims, among other things, that matter and energy are essentially interchangeable. As Oliver Pike, lead researcher on the Imperial College team, put it: “The Breit-Wheeler process is the simplest way matter can be made from light and one of the purest demonstrations of E=mc2.”
That we now have the technology to evidence Einstein's theory was discovered largely by accident. The Imperial College scientists had started out investigating problems in fusion energy when they realized that their work would have implications for Breit-Wheeler, as well. (They made that realization, an Imperial College press release points out, over coffee.) And there are already several sites, they note, where photon-photon collision could be experimented with. (One of them is the Omega Laser Facility in Rochester, New York.) As Pike puts it“Such a collider could be used to study fundamental physics with a very clean experimental setup: pure light goes in, matter comes out. The experiment would be the first demonstration of this.
And we won't have long to wait for such a high-tech take on ancient alchemy: Pike and his team are hoping to run the experiment within the next year.