Wednesday, February 05, 2014

The International Space Station will soon become the coldest place in the known universe… for science!

Below, below zero...

Here’s one of the coolest sentences you’ll ever read: The International Space Station will soon be the coldest place in the known universe. A new instrument that will be sent to the ISS, called the Cold Atom Lab, will reach temperatures as low as 100 picokelvin — 100 trillionths of a degree above absolute zero. As matter approaches absolute zero, it starts to exhibit some very odd, rather quantum behaviour.
Because it’s so hard to reach these temperatures, and because the material universe acts so weirdly when you get down that low, no one actually knows what the Cold Atom Lab will discover — but NASA seems to be pretty certain that the findings will be fascinating, in any case.

Dilution refrigerator that gets to around 1K. Each platform gets a little bit cooler, with the bottom one being the coldest.

As you probably know, space is already very, very cold — roughly 2.7 Kelvin (-270.45 Celsius, -454.81 Fahrenheit). This is mostly due to a lack of atmosphere and the vacuum-like nature of space — with very few molecules to energetically bounce around, there can be no heat. At 2.7 Kelvin, though, nothing weird happens; classical physics are still completely in control. To go quantum, you need to go colder — a lot colder. (Read: Negative temperature: Understanding what happens below absolute zero.)

Now, getting to say, 1 Kelvin (-272C) isn’t all that hard. A multi-stage dilution refrigerator (pictured right), which mixes helium-3 and helium-4, will happily get you to around 0.3 Kelvin. This is the method that most quantum computers currently use. Another option is laser cooling — but here on Earth, where the nagging force of gravity on the cooled sample has to be counteracted with strong magnetic traps, there are fairly strict limits on just how cold you can get. In the International Space Station’s microgravity climate, however, laser cooling can be very effective indeed. Only weak traps are needed to hold the sample in place while the laser cools it — and less power means lower temperatures can be reached. 100 picokelvin in this case, or 100 trillionths of a degree above absolute zero.

NASA says the Cold Atom Lab, which will launch to the International Space Station in 2016, will be the coldest place in the known universe. To be fair, one group hit 100 picokelvin way back in 1999. That experiment isn’t running any more, though, and it also had a very different purpose — while they were looking at the magnetism of rubidium atoms, NASA will be investigating something far more interesting: Bose-Einstein condensates. Basically, when you cool a very dilute gas of bosons (force-carrying particles, as opposed to matter-carrying fermions), a large number of the bosons start to exhibit quantum behavior on the macroscopic scale. That’s the important part — macroscopic scale means that these quantum effects will be visible to the naked eye.

In short, this coldest spot in the universe is expected to be the first time that quantum physics makes the jump from the realm of quarks and gluons and other phantasmal forces, into the real world that you and I occupy. The crazy thing is, though, no one even knows what this Bose-Einstein condensate will actually do once we cool it down to 100 picokelvin. No one’s ever done it before, and no one knows where it will lead. How exciting!

Source: ExtremeTech

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