Whale Calls Can Appear to Outrun Sound, Without Breaking Einstein’s Theory of Special Relativity

A new study published in Physical Review E reveals how ocean echoes can make whale calls appear to travel faster than anticipated, without breaking the laws of physics. Oceanographer John Spiesberger noticed an unexpected speed in sound waves through seawater, initially suspecting a coding error. However, the phenomenon was traced back to an echo from the ocean's surface.

Spiesberger and co-author Eugene Terray discovered that the echo can alter the strongest part of a whale call, causing it to seem like it's moving faster than sound. This observation aligns with Einstein's theory of special relativity, which states that information cannot surpass the speed of light. The researchers suggest that the same effect could occur with light signals, although this has yet to be tested.

The findings could improve whale tracking methods, as multiple hydrophones can detect a whale's call from up to 62 miles (100 kilometers) away. By analyzing the arrival times of the call at different microphones, scientists can calculate the whale's position, even when it's not visible. The effect arises from interference between direct and reflected sound waves near the ocean's surface.

When these waves overlap, their peaks and troughs can either enhance or cancel each other out, shifting the signal's strongest peak. This causes the recorded arrival time to change, potentially placing the whale several hundred yards (hundreds of meters) away from its actual location. To distinguish between the peak's movement and the information's movement, the researchers modeled two signals representing a zero and a one.

The signals initially matched before diverging in different ways. Although the strongest peak was shifted by interference, the receiver couldn't accurately determine which signal was sent first. Consequently, the information remained slower than the normal speed of sound in the simulations. While the results are theoretical, the possibility of extending this effect to light has not been ruled out.

The researchers anticipate testing the effect using microphones and a hard floor as a substitute for the ocean's surface. A future experiment may recreate the two paths using light, potentially revealing more about this intriguing phenomenon.