Absolute Zero
Absolute Zero is the holy grail of temperatures But even that we know exactly how cold that is -273.15 degrees celsius Reaching it has alluded us for centuries and will continue to allude us probably forever For this frustration we have to thank Sir William Thomson, First Baron Kelvin when in the mid 1800 tested a new theory that heat is just molecules moving around in a substance So we wanted to get stuff as cold as he could get it So he conducted experiments that drew heat from a warm substance toward a cooler one and found that at some point all the kinetic energy could be drained from the warm substance It could no longer be cooled any further This temperature wasn't like melting points or boiling points which change for every substance It was the same for everything So Kelvin created a Thermodynamic temperature scale that measured the amount of kinetic energy within any given material And we still use his Kelvin scale today But ever since Kelvin's day, scientists have been trying to chill stuff to Absolute Zero and no one has succeeded All a bunch of failures, because it turns out quantum mechanics is involved which means it´s really complicated Physicists know that Absolute Zero does not mean a complete abscence of motion in a substance Instead, zero degrees Kelvin marks the state of minimum motion of a substance's particles That's because of Heinsenberg's uncertainty principle Which says that for any ever loved particle in the universe is impossible to know both it's momentum and it's exact position at the same time So suppose you chill a lump of lead down to the point where there's no motion going on within Even at a subatomic level If you could do that, you know both the particle´s positions and their momentum which would be zero but measuring this, is, impossible, it's forbidden by the uncertainty principle So it cannot be done So you can't reach true Zero Kelvin but you can get pretty darn close, like a billionth of a degree away And when you get that cold, some pretty weird stuff starts happening Below about thirty Kelvin some substances can become superconductive Meaning that they can carry an electrical current with no resistance Which is super useful when you are making particle accelerators or really powerful electromagnets to put in your MRI machine And those superconductors have been discovered that operated at much warmer temperatures The development of the field was thanks to work at very, very cold temperatures measured on the Kelvin scale And you might be wondering, because I was, how cold is the coldest place in the universe? You'd think like deep space, right? Well, yeah, space is cold, but is pretty uniformly filled with microwave radiation leftover from the Big Bang This actually heats up space to a balmy 2.73 Kelvin The coldest natural place in the known universe is the Boomerang Nebula which has been spitting out gas for so long that it's cool down to only about 1 Kelvin And all of this means, that, in fact, the coldest place in the known universe Is in laboratories right here on planet Earth, pretty cool.