By all appearances, there are five steps to transforming light into matter—and the fifth one hasn’t happened yet.
The first step took place on July 16th, 1717, when Isaac Newton published the second English edition of his Opticks: Or, a Treatise of the Reflections, Refractions, Inflections and Colours of Light. This new edition contained some fresh suggestions for further research, and one of them (Query 30) stands out:
“Are not gross Bodies and Light convertible into one another, and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition? For all fix’d Bodies being heated emit Light so long as they continue sufficiently hot, and Light mutually stops in Bodies as often as its Rays strike upon their Parts … The changing of Bodies into Light, and Light into Bodies, is very conformable to the Course of Nature, which seems delighted with Transmutations.”
The second took place on September 27th, 1905, when Albert Einstein published his paper titled “Does the Inertia of a Body Depend Upon Its Energy-Content?” It was the first of Einstein’s papers to clearly suggest a proportional relationship between matter and energy, with the implication that one can in fact become the other. And since Einstein had also suggested that light was made up of particles called photons, the idea that energy behaves more like matter than his predecessors had realized began to point towards the equation that would define his career: E = mc2.
The third step came on December 15th, 1934, when New York University physicists Gregory Breit and John Wheeler published a paper describing in general terms a means by which light could be turned into matter, writing that it would in any case be “hopeless to try to observe [the process] in laboratory experiments” given the then-current state of technology.
The fourth came on May 18th, 2014, when a team of European physicists published a method by which we can actually test the Breit-Wheeler theory by engineering a photon-photon collider that creates matter out of pure light.
And by the end of the year, it is likely that a physics laboratory will have tested this theory and, assuming it’s valid, created matter out of light.
This is often what science often means: a question asked three centuries ago, a vague answer given over a century ago, a more specific answer proposed 80 years ago, a viable plan of action published over the weekend, and an experiment conducted in a matter of months. It’s a long, slow process punctuated by unexpected breakthroughs, and these breakthroughs in turn create new questions, beginning a fresh cycle of inquiry. And if the fifth step happens—if we are able to confirm that light can, in fact, be transformed into matter—we will finally be able to answer Newton’s question by demonstration. He would have enjoyed being able to do that during his lifetime. Let’s enjoy it on his behalf.