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Scientists confirm the incredible existence of a ‘second sound’
This phenomenon has been observed before, but never imaged.
Updated: February 17, 2024 9:33 AM ET
In the average everyday material world, heat tends to spread from local sources. If you drop a burning coal into a pot of water, the temperature of the liquid will slowly rise until the heat dissipates. However, the world is full of rare and exotic substances to which these thermal laws do not apply precisely. Rather than spreading out as expected, these superfluid quantum gases “slosh” their heat from side to side, essentially propagating as waves. Scientists call this behavior the “second sound” of matter (the first is the normal sound caused by density waves). This phenomenon has been observed before, but never imaged. But recently, scientists at the Massachusetts Institute of Technology (MIT) were finally able to capture this movement of pure heat by developing a new method of thermography (also known as heat mapping). The results of the study were published last week in the journal Science and were also announced in a university press release highlighting the findings. MIT assistant professor and co-author Richard Fletcher continued with the boiling pot analogy to explain the inherent strangeness of the “second sounds” contained in these exotic superfluids. “It’s like you have a tank of water and half of it is about to boil,” Fletcher said. “Then you observe it, and the water itself may seem perfectly calm, but then all of a sudden it gets hot on the other side, and then the other side gets hot, and the heat goes back and forth, while the water stays perfectly still. These superfluids are produced. When a cloud of atoms is exposed to extremely low temperatures close to absolute zero (-459.67 °F). In this rare state, atoms behave differently because they create an essentially frictionless fluid. In this frictionless state, heat is theorized to propagate like waves. “The second sound is a signature of superfluidity, but until now we have only been able to see it in cryogenic gases through faint reflections of the accompanying density ripples,” said lead author Martin. Zwierlein said in a press statement. “The nature of heat waves has never been proven.” To really capture this second of his sounds, Zweerlein and his team had to think outside the usual heat box. That’s because there are big problems in trying to track the heat of ultra-cold objects. — Does not emit normal infrared radiation. So scientists at the Massachusetts Institute of Technology have designed a way to use radio frequencies to track a particular subatomic particle known as a “lithium-6 fermion.” The particles can be captured at different frequencies depending on the temperature (i.e. the higher the temperature the higher the frequency and vice versa). . This new technique allowed the researchers to zero in on essentially “hotter” frequencies (which are still very cold) and track the resulting second wave over time. After all, when was the last time we had a close encounter with a superfluid quantum gas? But ask any materials scientist or astronomer and you’ll get a very different answer. Exotic superfluids may not fill our lives (yet), but understanding the properties of second-wave motion may help answer questions about high-temperature superconductors (repeatedly (but still at very low temperatures), or the messy physics at the heart of a neutron star.
In the average everyday material world, heat tends to spread from local sources. If you drop a burning coal into a pot of water, the temperature of the liquid will slowly rise until the heat dissipates. However, there are many rare and exotic materials in the world that do not exactly fit into these thermal laws.
Rather than spreading out as expected, these superfluid quantum gases “bounce” heat from side to side, essentially propagating as waves. Scientists call this behavior the “second sound” of matter (the first is the normal sound caused by density waves). This phenomenon has been observed before, but never imaged. But recently, scientists at the Massachusetts Institute of Technology (MIT) were finally able to capture this movement of pure heat by developing a new method of thermography (also known as heat mapping).
The study results were published last week in a diary science, and highlighted the results in a university press release. MIT assistant professor and co-author Richard Fletcher continued with the boiling pot analogy to explain the inherent strangeness of the “second sounds” contained in these exotic superfluids.
“It’s like you have a tank of water and half of it is about to boil,” Fletcher said. “Then you look and the water itself may seem perfectly calm, but then all of a sudden it gets hot on the other side, and then the other side gets hot, and the heat goes back and forth, while the water stays perfectly still. It looks like it is.”
These superfluids are created when clouds of atoms are exposed to extremely low temperatures near absolute zero (-459.67 °F). In this rare state, atoms behave differently because they create an essentially frictionless fluid. In this frictionless state, heat is theorized to propagate like waves.
“Secondary sounds are a feature of superfluidity, but until now in ultracold gases they have only been visible in faint reflections of the associated density ripples,” lead author Martin Zwierlein said in a press release. said in a statement. “The nature of heat waves has never been proven.”
To actually capture this second sound, Zweerlein and his team had to think outside the usual thermal box. There is a big problem with tracking the heat of ultra-cold objects, which do not emit normal infrared radiation. So scientists at the Massachusetts Institute of Technology have designed a way to use radio frequencies to track a particular subatomic particle known as a “lithium-6 fermion.” The particles can be captured at different frequencies depending on the temperature (i.e. the higher the temperature the higher the frequency and vice versa). . This new technique essentially allowed the researchers to focus on “hotter” frequencies (which are still very cold) and track the resulting second wave over time.
This may feel like a big “so what?” After all, when was the last time you had a close encounter with a superfluid quantum gas? But ask any materials scientist or astronomer and you’ll get a very different answer.
Exotic superfluids may not fill our lives (yet), but understanding the properties of second-wave motion could lead to the creation of hot superconductors (which are also at very low temperatures) and neutron stars. The thorny physics questions at the heart of may be answered. .
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