Scientists have created a new type of matter in which light actually acts like it has mass.
"The physics of what’s happening in these molecules is similar to what we see in the movies," Harvard physics professor Mikhail Lukin told the Harvard Gazette. "It’s not an inapt analogy to compare this to lightsabers."
Normally light doesn't interact with other light — when two lasers collide, nothing happens. By cooling light and shooting it through a cloud of atoms, however, the researchers were able to get the light to interact, even binding together to create molecules. Before this finding, the state of matter was only theoretical.
They did it by supercooling a bunch of rubidium atoms in a vacuum then hitting them with two photons of light. The photons entered separately but left the cloud of atoms together, having pushed and pulled each other through the cloud and bound into one packet.
As the individual photons moved through the atoms they excited then, then took that energy back as it moves away from the atom. The energy level transferred to the atoms is at level called a Rydberg state. Two atoms can't be in the same Rydberg state, so this slows the photon down as it passed from one atom to the next.
The photon traveling behind the first has to wait for the next atom to be ready to accept its energy and reenter the Rydberg state, so it is essentially twinned with the first photon, linking the two together.
They compared this to lightsabers from the Star Wars series of films, because the light in those make-believe weapons is able to interact with the physical world, cutting quickly through flesh. They actually aren't fully sure what kind of physics it would take to make a real lightsaber.
When The Guardian's Ian Sample asked study first author Ofer Firstenberg about the lightsaber connection, he said: "I don't know what to say. The lightsaber is fictitious," he said. "We don't know what the physics is behind a lightsaber."
The matter is only created at very cold temperatures, and the machine weighs about a ton so don't expect lightsabers any time soon. The researchers aren't even sure what this new matter could be used for — they still need to study it.
"What it will be useful for we don’t know yet," Lukin said. "But it’s a new state of matter, so we are hopeful that new applications may emerge as we continue to investigate these photonic molecules’ properties."
One potential application is in quantum computing. And Lukin even said that in the future we might be able to make 3-D structures, like crystals, out of light. The finding was published Sept. 25 in the journal Nature.
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