Scientists discovered that in some exotic states of matter, heat behaves like sound and bounces back and forth. The phenomenon is not new and is referred to as “second sound.” However, scientists at MIT have for the first time acquired photographs of the second sound’. The photos demonstrate how heat can move like sound waves when generated within a superfluid, a state of matter in which atoms flow without friction. The physicists discovered that heat and matter may “slosh” against one another, resulting in oscillations comparable to sound waves. Richard Fletcher, an assistant professor of physics at MIT and a research co-author, was reported as saying in media reports, “It’s like if you took a tank of water and made one half almost boiling.”
Their findings revealed that the heat patterns moved in a periodic manner similar to sound waves but were out of sync with the matter waves
“If you then watched, the water itself might look calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks still,” he added. The study, published in Science, can help physicists ascertain how heat behaves in superfluids and other related materials, such as superconductors and neutron stars. “There are strong connections between our puff of gas, which is a million times thinner than air, and the behaviour of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars,” says Martin Zwierlein, the Thomas A Frank, Professor of Physics at MIT and the leader of the research team.
“Now we can probe pristinely the temperature response of our system, which teaches us about things that are very difficult to understand or even reach,” he adds. The scientists employed a cluster of lithium-6 atoms, which are fermions that generally resist each other. They caused the atoms to couple together and form a superfluid by cooling them near absolute zero and applying a magnetic field. They used a laser beam to create a hot spot within the superfluid and then used another laser beam to capture the heat patterns that emerged. Their findings revealed that the heat patterns moved in a periodic manner similar to sound waves but were out of sync with the matter waves, indicating oscillation in different directions for heat and matter. This phenomenon, known as second sound, differs from regular sound in that heat and matter travel simultaneously.