A team of researchers has cooled matter to less than a billionth of a degree from absolute zero, colder than even the deepest depths of space, far from any star.
Interstellar space never gets that cold due to the fact that it is evenly filled with cosmic microwave background (CMB), a form of radiation left over from an event that occurred shortly after the big Bang when the universe was in its infancy. Cooled matter is even colder than the coldest known region of space, the Boomerang Nebulalocated 3,000 Light years Earth, which has a temperature just one degree above absolute zero.
The experiment, conducted at Kyoto University in Japan, used fermions, what particle physicists call any particle that makes up matter, including electrons, protons and neutrons. The team cooled their fermions – atoms of the element ytterbium – to about a billionth of a degree above absolute zero, the hypothetical temperature at which all atomic movement would cease.
“Unless an extraterrestrial civilization is doing experiments like these right now, every time this experiment happens at Kyoto University, it produces the coldest fermions in the universe,” Kaden said. Hazzard, a researcher at Rice University, who participated in the study. statement (opens in a new tab).
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The team used lasers to cool matter by limiting the movement of 300,000 atoms in an optical lattice. The experiment simulates a model of quantum physics first proposed in 1963 by theoretical physicist John Hubbard. The so-called Hubbard model allows atoms to demonstrate unusual quantum properties, including collective behavior between electrons such as superconduction (the ability to conduct electricity without loss of energy).
“The payoff of having that cold is that the physics really change,” Hazzard said. “Physics is starting to get more quantum mechanical, and it’s letting you see new phenomena.”
The “fossil” radiation that keeps space warm
Interstellar space can never be this cold because of the presence of the CMB. This evenly distributed and uniform radiation was created by an event during the rapid initial expansion of the universe shortly after the Big Bang, the so-called last scatter.
During the last scattering, electrons began to bond with protons, forming the first atoms of hydrogen, the lightest element in existence. As a result of this formation of atoms, the universe rapidly lost its free electrons. And because electrons scatter photons, the universe was opaque to light before the last scattering. With electrons bound to protons in those early hydrogen atoms, photons could suddenly travel freely, making the universe transparent to light. The last scattering also marked the last time when fermions like protons and photons had the same temperature.
Following the last scatter, photons filled the universe at a specific temperature of 2.73 Kelvin, which is equivalent to minus 454.76 degrees Fahrenheit (minus 270.42 degrees Celsius), or just 2.73 degrees above absolute zero – 0 Kelvin or minus 459.67 degrees F (minus 273.15 degrees Celsius).
There is a region in the known universe, the Boomerang Nebula, a cloud of gas that surrounds a dying being star in the constellation Centaurus, which is even colder than the rest of the universe – around 1 Kelvin or minus 457.6⁰F (minus 272⁰C). Astronomers believe the Boomerang Nebula is being cooled by cold, expanding gas spewed out by the dying star at the center of the nebula. But even the Boomerang Nebula can’t match the temperatures of the ytterbium atom in the latest experiment.
The team behind this experiment is currently working on developing the first tools capable of measuring the behavior that occurs at a billionth of a degree above absolute zero.
“These systems are quite exotic and special, but the hope is that by studying and understanding them, we can identify the key ingredients that must be present in real materials,” Hazzard concluded.
The team’s research is published September 1 in Natural Physics (opens in a new tab).
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