This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Standing on the sandy, windswept shores of Provincetown, Massachusetts, people may find themselves squinting at the horizon, waiting for a whale to make its grand entrance with a spectacular breach. On a good day, they might spot a couple.
But for a more precise and consistent way to detect the presence of whales, oceanographers like John Spiesberger, a visiting scholar in the Department of Earth and Environmental Sciences in the School of Arts & Sciences, rarely rely on sight. "Sound from a fin whale can be heard from 100 kilometers (62 miles) away underwater with a single hydrophone," Spiesberger says. "Because those calls travel so far, we can use them to pinpoint where an animal is by comparing when its sound reaches receivers spread across the seafloor." But there's a catch: If they were trying to track a nearby whale using just standard physics, they'd probably place the animal in the wrong spot—off by hundreds of meters.
In a paper recently published in the journal Physical Review E, Spiesberger and colleague Eugene Terray of the Woods Hole Oceanographic Institution offer a potential explanation for why this occurs: The humble whale call is, improbably, tangled up with the same speed limits Einstein deduced from the universe. Their findings could improve whale tracking for conservationists. "Most of us don't hear a whale call and think, 'Wow, look at the special theory of relativity in action,'" says Spiesberger.
"I would have never guessed any connection existed." When a whale calls, Spiesberger explains, the sound doesn't take a single path to each receiver. Some of the sound travels directly to a receiver, while some of it ricochets off the ocean surface first, arriving fashionably late. That delay can put the two signals out of phase, causing them to interfere with one another and shifting when sound appears to arrive at a receiver.
Spiesberger stumbled onto this while refining a computer program meant to calculate the correct speed of sound for his whale-tracking equations. The results were surprising. "The first time, we got a number that was around 1,000 meters per second," he says, well below the roughly 1,500 meters per second that sound normally travels in seawater.
"And then, further on, I got values that were sometimes 3,000 meters per second. I immediately thought there was a bug in my program." After examining his software for a few hours, he discovered that the behavior wasn't a coding error, but a physical effect caused when a receiver picked up both the direct signal and its reflected echo when a whale was near the ocean's surface. Physicists call this "temporal interference," the same phenomenon that causes TV broadcasts at your home antenna to fade out because two paths arrive out of phase or out of sync.
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