When oceanographer John Spiesberger’s whale-tracking program calculated that sound was moving through seawater at nearly twice its expected speed, he assumed something had gone wrong.
He checked the code, but found no mistake. The impossible-looking result instead pointed to an echo from the ocean’s surface.
In a new study published in Physical Review E, Spiesberger and Eugene Terray of the Woods Hole Oceanographic Institution found that an echo can shift the strongest part of a whale call, making it appear to move faster than sound even though the information within it does not.
That is where the whale call meets Einstein. His theory of special relativity holds that information cannot travel faster than light. Because sound and light are both waves, the researchers think the same effect could make part of a light signal appear to move faster than light. Its information, however, would remain within the light-speed limit, leaving Einstein’s theory intact. The findings could also help researchers locate whales more accurately.
“Most of us don’t hear a whale call and think, ‘Wow, look at the special theory of relativity in action,” Spiesberger said in a press release. “I would have never guessed any connection existed.”
Why Whale Calls Can Confuse Underwater Receivers
A single hydrophone can detect a fin whale calling from about 62 miles (100 kilometers) away. By comparing arrival times at several microphones across the seafloor, researchers can calculate the whale’s position, even when the animal never comes into view.
Near the ocean’s surface, however, a call may follow two routes. Some sound travels directly to a receiver, while another portion bounces off the surface and takes a slightly longer path.
If the two versions arrive close together, their peaks and troughs overlap, reinforcing or partially canceling one another. This process, called temporal interference, changes the combined signal and can move its strongest peak forward or backward.
By changing the recorded arrival time, the effect could place a nearby whale several hundred yards (hundreds of meters) from its actual position.
Read More: Birdsong and Whale Songs Share a Surprising Similarity With Human Language
How a Whale Call Appears to Outrun Sound
In one simulation, the researchers set the normal speed of sound in water at approximately 4,900 feet (1,500 meters) per second. After interference reshaped two test signals, their peaks arrived at times corresponding to apparent speeds of about 5,560 feet (1,694.5 meters) and 9,130 feet (2,782.5 meters) per second.
The waves themselves did not accelerate. Their overlap shifted the signal’s most intense point, producing the supersonic calculation.
“The effect sounds like a violation of physics,” Spiesberger said in the press release, “but it isn't.”
To separate the movement of the peak from the movement of information, the researchers modeled two signals representing a zero and a one. The signals initially matched before changing in different ways.
Although interference advanced the strongest peak, the receiver could not reliably identify which signal had been sent before the new information traveling along the direct path arrived. Information therefore remained slower than the normal speed of sound in the simulations.
From Whale Calls to the Speed of Light
The results remain theoretical, and the possible extension to light has not been tested. The researchers think direct and reflected light waves could interfere, making the signal’s strongest point appear to move faster than light. Because the reflected wave travels farther, however, it could not deliver information before the direct signal.
“You can’t use this trick to send a message to your past self to bet on the stock market,” Spiesberger joked in the press release. “Causality isn’t overturned.”
Spiesberger will first test the effect using microphones and a hard floor as a stand-in for the ocean’s surface. A later experiment could recreate the two paths with light. A question that began with whales may therefore find its next answer on a tabletop in his lab.
Read More: Whales Once Rare Along East Greenland Now Gather by the Thousands in Feeding Frenzies
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in Physical Review E:Supersonic and superluminal energy and speed of information via temporal interference in a dispersionless environment