Breakthrough: Heat Mimics Sound in Superfluid, Say Scientists

Researchers have discovered that under certain exotic conditions, heat can mimic the properties of sound, echoing back and forth in a manner referred to as “second sound.” This intriguing behavior has been captured in images for the first time by scientists at the Massachusetts Institute of Technology (MIT), showcasing how heat propagates like sound waves within a superfluid—a unique state of matter characterized by frictionless atomic flow.

In this groundbreaking study, the team observed how heat interacts with the superfluid, causing both to oscillate against each other in a manner akin to sound waves. “Imagine having a tank of water where one side is nearly boiling,” explained Richard Fletcher, an assistant professor of physics at MIT and co-author of the study. “While the water may appear undisturbed, you would suddenly find one side hot, then the other, as the heat oscillates back and forth.”

The implications of this research, detailed in the journal Science, extend far beyond the lab. Understanding the dynamics of heat in superfluids could shed light on the properties of superconductors and the extreme conditions within neutron stars.

Martin Zwierlein, the Thomas A. Frank Professor of Physics at MIT and the research team’s leader, highlighted the broader significance of their findings. He noted, “Our experiment, which involves a gas a million times thinner than air, connects to the behavior of electrons in high-temperature superconductors and the dense environment of neutron stars.”

To conduct their experiment, the researchers cooled a group of lithium-6 atoms—fermions known for their repulsive interactions—to near absolute zero. A magnetic field was then applied, coaxing the atoms into pairs to form a superfluid. Using a laser, they created a hot spot within this state and utilized another laser to document the heat’s movement.

The resulting images showed that the heat moved in a periodic manner, akin to sound waves, but was desynchronized with the superfluid’s matter waves. This discrepancy highlighted a distinct separation between the movements of heat and matter, a hallmark of the “second sound,” differing from conventional sound where both elements move in unison.