Absolute zero is the lowest theoretical temperature, which scientists define as minus 459.67 degrees Fahrenheit (minus 273.15 degrees Celsius). It’s even colder than space. Nothing we know of so far has reached absolute zero. So is it possible to reach this terrible milestone?

To answer this question, let’s look at what temperature actually is. We tend to think of temperature as how hot or cold something is, but it’s actually a measure of the energy, or vibration, of all the particles in the system. Because hot objects have more energy, their particles can vibrate faster. The point at which particles have no energy and therefore stop moving is defined as absolute zero.

Scientists are interested in reaching such low temperatures because many interesting quantum effects occur when particles slow down. Sankalpa Ghosh, a theoretical condensed matter physicist at the Indian Institute of Technology, said the fundamental principle of quantum mechanics is partial wave dualism, a phenomenon in which a particle such as a photon of light can behave either as a particle or a wave. in Delhi.

When dealing with quantum-mechanical particles, it’s important to remember their “indistinguishability” — “it is not possible to track particles or waves separately as in larger objects,” Ghosh said in an email to LiveScience. “This can be traced back to the famous Heisenberg Uncertainty Principle, which quantifies the probabilistic nature of quantum mechanical measurement. [це означає, що коли положення частинки точно виміряно, її імпульс менш точно відомий, і навпаки]. This probabilistic nature gives the quantum mechanical particle a wave-like character.”

The degree of this quantum wave-like behavior is expressed by the ratio of distances between particles in the system, known as the thermal de Broglie wavelength. At normal temperatures this quantum behavior is negligible, but as the particles cool, strange effects begin to emerge.

“[Це співвідношення] It grows as the temperature decreases and becomes virtually infinite at absolute zero,” said Ghosh. “In this way, quantum phenomena such as superfluidity (frictionless flow), superconductivity (current flowing without any resistance) and ultracold atomic condensation occur.”

Early ultracold experiments in the 1990s used a technique known as laser cooling to begin investigating these effects. “Light exerts a force on atoms that slows them down to very low temperatures of about 1 kelvin (minus 272.15 C, or minus 457.87 F),” said ultracold physicist Christopher Foote of the University of Oxford. “[Це досить мало]”To see the quantum behavior of solids and liquids, but we need temperatures in the 10s of nano-Kelvin to get these quantum effects in the gases we study.”

The lowest temperature ever recorded in the laboratory was achieved by a group in Germany in 2021. The team dropped magnetized gas atoms into a 400-foot-tall (120 meters) tower and slowed the particles almost to a halt by constantly turning the magnetic field on and off. In such experiments, known as magnetic trap cooling, gaseous particles reached an incredible temperature of 38 picokelvins, 38 trillion degrees Celsius above absolute zero, well within the range of starting to observe quantum effects in gases.

So, does it make sense to try to cool the materials even further? Probably not, according to Foote. “We’re more interested in these quantum effects than getting to absolute zero,” he said. “Laser-cooled atoms are already used in atomic standards (atomic clocks) and quantum computers that determine universal time. Working at lower temperatures is still in the research phase, and people are using these techniques to test universal physical theories.”

Cooling the last 38 trillion degrees is currently impossible, and there are many obstacles to overcome before this becomes a reality. In fact, even if we reached absolute zero, we could miss it entirely due to imprecise measurement methods.

“With current tools you can’t tell whether it’s zero or a very, very small number,” Foote said. “To measure absolute zero, you actually need a thermometer with infinite accuracy, and that is beyond the scope of our current measurement systems.”