What is the coldest thing in the world

The Coldest Materials in the World

The coldest materials in the world aren’t located in the icy landscapes of Antarctica, the peak of Mount Everest, or buried deep within a glacier. Instead, they exist within the confines of physics labs. Here, clouds of gases are held just fractions of a degree above absolute zero. To put this into perspective, that’s 395 million times colder than your refrigerator, 100 million times colder than liquid nitrogen, and 4 million times colder than outer space.

Creating Extreme Temperatures

These extreme temperatures provide scientists with a unique window into the inner workings of matter. They also allow engineers to construct incredibly sensitive instruments that can reveal more about everything from our exact position on the planet to the happenings in the farthest reaches of the universe. But how do we create such extreme temperatures? The answer lies in slowing down moving particles.

When we talk about temperature, we’re essentially talking about motion. The atoms that make up solids, liquids, and gases are always in motion. When atoms move more rapidly, we perceive that matter as hot. Conversely, when they move more slowly, we perceive it as cold. In everyday life, to make a hot object or gas cold, we place it in a colder environment, like a refrigerator. Some of the atomic motion in the hot object is transferred to the surroundings, and it cools down. However, even outer space is too warm to create ultra-low temperatures. Therefore, scientists have devised a way to slow the atoms down directly – with a laser beam.

The Role of Laser Beams

Under normal circumstances, the energy in a laser beam heats things up. But when used in a very precise way, the beam’s momentum can stall moving atoms, cooling them down. This is what happens in a device called a magneto-optical trap. Atoms are injected into a vacuum chamber, and a magnetic field draws them towards the center. A laser beam aimed at the middle of the chamber is tuned to just the right frequency that an atom moving towards it will absorb a photon of the laser beam and slow down. The slow down effect comes from the transfer of momentum between the atom and the photon. A total of six beams, in a perpendicular arrangement, ensure that atoms traveling in all directions will be intercepted. At the center, where the beams intersect, the atoms move sluggishly, as if trapped in a thick liquid — an effect the researchers who invented it described as “optical molasses.”

The Importance of Cooling Atoms

A magneto-optical trap like this can cool atoms down to just a few microkelvins — about -273 degrees Celsius. This technique was developed in the 1980s, and the scientists who contributed to it won the Nobel Prize in Physics in 1997 for the discovery. Since then, laser cooling has been improved to reach even lower temperatures. But why would you want to cool atoms down that much?

Firstly, cold atoms can make very good detectors. With so little energy, they’re incredibly sensitive to fluctuations in the environment. So they’re used in devices that find underground oil and mineral deposits, and they also make highly accurate atomic clocks, like the ones used in global positioning satellites.

Secondly, cold atoms hold enormous potential for probing the frontiers of physics. Their extreme sensitivity makes them candidates to be used to detect gravitational waves in future space-based detectors. They’re also useful for the study of atomic and subatomic phenomena, which requires measuring incredibly tiny fluctuations in the energy of atoms. These fluctuations are drowned out at normal temperatures, when atoms speed around at hundreds of meters per second. Laser cooling can slow atoms to just a few centimeters per second—enough for the motion caused by atomic quantum effects to become obvious.

Ultracold atoms have already allowed scientists to study phenomena like Bose-Einstein condensation, in which atoms are cooled almost to absolute zero and become a rare new state of matter. So as researchers continue in their quest to understand the laws of physics and unravel the mysteries of the universe, they’ll do so with the help of the very coldest atoms in it.