2019-07-01_Discover

Celsius

(°C)

Kelvin

(K)

Water

boils 100 212

32

-459.67

0

-273.15

273.15

373.15

0

Water

freezes

Absolute

zero

Fahrenheit

(°F)

EVERYTHING

WORTH

KNOWING

7676 DISCOVERMAGAZINE.COMDISCOVERMAGAZINE.COM

TEMPERATURE TENDS TO BE RELATIVE — the air is

below freezing, her fever is above normal. But scientists

probe the extreme ends of the spectrum of what’s called

absolute temperature: At the upper limit, absolute hot

is a theoretical furnace where the laws of physics melt

away. On the flip side, absolute zero — cold so cold there’s

nowhere to go but up — is almost within scientists’ grasp.

To understand it, you first need some Physics 101.

The atoms that make up matter are always moving.

Temperature measures those atoms’ kinetic energy, or

energy of motion. The faster they move, the higher their

temperature. Absolute zero, though, is almost perfect

stillness.

Nothing in the universe — or in a lab — has ever reached

absolute zero as far as we know. Even space has a back-

ground temperature of 2.7 kelvins.

But we do now have a precise

number for it: -459.67 Fahrenheit,

or -273.15 degrees Celsius, both of

which equal 0 kelvin.

Different materials vary in how

cold they can get, and theory sug-

gests we’ll never get to absolute

zero. But with an arsenal of new

tools and techniques, scientists

inch ever closer to reaching that

rock bottom.

How low you can go.

BY STEPHEN ORNES

Absolute

Zero

WHY IT MATTERS

Superfluids and Other Material Gains

Bose-Einstein Condensate (BEC): In 1995, University of Colorado

Boulder physicists observed BEC, a fifth state of matter that only

exists within a sliver of absolute zero. At such a low temperature,

individual atoms overlap so much that they collapse into a single

quantum state where they collectively act as a single entity. The

discovery of BEC opened a new field of science in which physicists

can probe quantum behaviors.

Quantum computing: Instead of relying on bits, the 1s and 0s that

regular computers use, quantum computers use qubits to make

calculations. In theory, these machines can conquer problems much

faster than today’s computers. But to work, their atoms or molecules

must be cooled to a couple hundredths of a degree above absolute

zero, a realm where quantum features aren’t lost in the electrical

noise that heat can create.

Material weirdness: When helium gets cold, it gets weird: It can glide

friction-free through narrow tubes, sustain currents for long periods

of time and flow up and over a container’s sides. Scientists describe

it — and some ultracold gases, like BEC — as a superfluid. In recent

years, they’ve suggested superfluids might exist in neutron stars,

the small, dense relics of supernovas not massive enough to form a

black hole. Superfluids have also led to the discovery of supersolids,

which have the odd property of being able to flow through

themselves. These materials let scientists probe fundamental

mysteries of nature.

THE COLDEST NATURAL

PLACE IN THE UNIVERSE

Although temperatures

plummet on the dark

side of the moon and

the shadowy craters of

Pluto, those locales look

balmy compared with the

Boomerang Nebula. About

5,000 light-years away, this

star system is just 1 kelvin

above absolute zero.

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Bose-Einstein Condensate (BEC),

a fifth state of matter, consists of

atoms so cold, they condense into

a quantum state, acting as one.

Here, a graph shows atoms’ density

increasing as they get colder,

eventually forming BEC (right).

Cold atoms move slowly.

Ultracold atoms

barely move at all.

Hot atoms move fast.