The International Space Station (ISS) is slated to become the coldest spot in space as NASA's Cold Atom Laboratory (CAL) begins producing ultra-cold atoms. Called Bose-Einstein condensates, these atoms are cooled to 10 millionth of one Kelvin above absolute zero as part of microgravity experiments to study quantum mechanics and the fundamental nature of matter.
On the everyday scale, the universe makes sense, but when you start poking around in extreme conditions like the very large, the very small, or the very fast, things start to get a little weird. One example is when an object is cooled to very close to absolute zero – the lowest temperature that is theoretically possible (0 K,-459º F, -273º C).
At its most basic, temperature is a measurement of the movement of molecules in a substance. If the molecules move very slowly, then the substance is solid. If they move more quickly, it's a liquid. A little more quickly and it's a gas. Even quicker and the electrons start to strip away, it's a plasma.
At the other end of the scale, if these molecules stop completely, then they've reached the point of absolute zero. The weirdness comes in because it isn't actually possible to reach absolute zero. No matter how much energy you suck out of a molecule, it will still move slightly, because you're now in the realm of quantum mechanics where the everyday laws of physics start to break down.
This is why supercooled helium remains a liquid under normal pressures when it's reduced to near absolute zero. The interatomic bonds that would make other substances freeze don't work and the helium becomes a superfluid with all kinds of odd properties, like being able to creep up and out of any cup it's stored in like some freakish living soup.
Roughly speaking, supercooled liquid helium is a type of Bose-Einstein Condensate (BEC). First predicted in the 1920s by Satyendra Nath Bose and Albert Einstein, BECs are a fifth state of matter where atoms reach their lowest energy level and become a type of collective super-atom that can act like a wave instead of a particle. This is a phenomenon that is well known in subatomic particles like photons, but BECs exhibit this on a macroscopic level.
To reduce things to more practical terms, BECs make excellent tools for studying quantum mechanics. However, producing such BECs isn't easy. To bring atoms down to a temperature of 0.00000000001 K is already a tricky affair that involves suspending atoms in frictionless magnetic containers as they're subjected to a complex series of steps involving lasers, magnetic fields, and evaporative cooling to reach the quantum level of cryogenics.
That was only managed on Earth in 1995, but the annoying thing is that once the magnetic field is shut off, scientists have only a fraction of a second to study the BECs because gravity takes over and the atoms drop and warm up.
The new Cold Atom Lab has the advantage of being in the microgravity environment of the ISS. Already the CAL has cooled atoms of rubidium down to 100 nanoKelvin above absolute zero, which is one ten-millionth of a Kelvin above absolute zero. That's colder than the average temperature of space, which is about 3 K (-454º F, -270º C).
In fact, when CAL is fully operational, it will be the coldest spot in the known universe – one where scientists can observe BECs at their leisure for up to 10 seconds and repeat experiments up to six hours a day. It's not only the first device of its kind to be installed in space, but it's also the coldest and the most compact yet built. This is because the longer the chilled atom cloud stays in the trap, the colder it gets, much in the same way if you use one of those aerosol keyboard cleaners it becomes too cold to hold after a couple of minutes.
"CAL is an extremely complicated instrument," says Robert Shotwell, chief engineer of the Jet Propulsion Laboratory's astronomy and physics directorate. "Typically, BEC experiments involve enough equipment to fill a room and require near-constant monitoring by scientists, whereas CAL is about the size of a small refrigerator and can be operated remotely from Earth. It was a struggle and required significant effort to overcome all the hurdles necessary to produce the sophisticated facility that's operating on the space station today."
The CAL was sent to the ISS aboard a Northrop Grumman Cygnus unmanned cargo ship on May 21, 2018. Installed in one of the US science modules on the station, it's currently in its commissioning phase and will become operational in September, when it will work with two isotopes of potassium in addition to rubidium atoms.
The video below discusses the CAL.
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