Physics + Math

01
Apr

Scientists Beam Light in Front of Dolphins, Accidentally Create Rainbow Lasers

In a breakthrough that could upend the technology industry, changing everything from the way cell phones transmit data to how computer chips perform computations, researchers from Fermi National Laboratory and the U.S. Navy announced today a new way to create lasers beams, the tightly-focused beams of narrow-spectrum light. And the key to it all is dolphin sonar.

“When we shined a light in front of a dolphin as it chirped, we had a hunch that something special might happen,” said Michael Greenbaum, a particle physicist at Fermi Lab and lead author on the paper. “What we didn’t know was just how special it would be.”

Navy dolphin
U.S. Navy dolphin K-Dog during training in the Arabian Gulf

The finding confirmed decades of speculation. “Theorists have been predicting the existence of sonically-activated lasers since the mid-1990s,” said Katherine Johnson, a professor of photonics at the University of California, Berkeley. “But we didn’t have any proof. Now we do.”

The experiment coalesced when Greenbaum was golfing last April with Lt. Hank Thompson, his college roommate and a dolphin trainer in the U.S. Navy Marine Mammal Program. Greenbaum was telling Thomspon about his research into the effects of sound waves on photons. Thompson stopped mid-swing. His program was looking for ways to equip dolphins with lasers to disarm underwater mines, but they had run into a problem. Most lasers they tried were unsuitable for use in salt water. “Regular light sources—no problem,” Thompson said. “But lasers? We just haven’t found one that works well.”

While the Navy has been tweaking existing lasers for the purpose, top brass also wanted alternatives. Greenbaum and Thompson’s project was considered a long shot, even by DARPA standards, and the pair had just one year of funding. Initially, they tried shining intense lights in front of echolocating dolphins, but every attempt failed. The beams just weren’t separating. Then in November, about three months before their funding ran out, Greenbaum and Thompson got what they were looking for. There, on their instruments, they saw a faint rainbow of laser beams was bursting from the dolphin’s beak as it echolocated.

“We were shocked to be honest,” Greenbaum recalls. “This is the sort of thing you’d normally see on a fourth-grader’s Trapper Keeper. But in real life? Seriously?”

dolphin-lasers
Greenbaum and Thompson were surprised when their experiment produced not one wavelength of laser light, but an entire rainbow.

Thompson was equally floored. But now the team had a puzzle on their hands and only three months to solve it. What was different about the water that day? It took them weeks, but eventually they got it. By analyzing the isotopic ratios of water samples taken that day, they discovered an abundance of heavy water, or water molecules that consist of at least one deuterium atom. Normally, there are about 150 molecules of heavy water for every million molecules of normal water. Yet that day, there were 300 parts per million. That concentration turned out to be key, and reproducing it allowed Greenbaum and Thompson to quickly replicate their results.

Greenbaum isn’t exactly sure why dolphin chirps can cause light beams to diverge, but he does have a hypothesis. When the sound waves hit molecules of heavy water, he thinks the vibrations excite the deuterium atoms, causing them to release gravitons, the particles thought to cause gravity. The gravitons then interacts with photons and, according to the theory of rainbow gravity, splits white light into its component wavelengths. “Just like a prism,” Greenbaum said. “Well, a dolphin-actuated quantum prism, to be precise.”

Currently, the prism effect isn’t strong enough to see with the naked eye. Greenbaum suspects that Earth’s gravity is interfering, so he and Thompson have submitted a proposal to build a new Marine Mammal Module for the International Space Station, where the gravitational noise should be much less. “Just think,” Thompson said, “not only will we have dolphins shooting rainbow lasers from their beaks—they’ll be doing it in space.”