I can get that we may have created something (quark-gluon plasma) at 4 trillion degrees Celsius that is hotter than a supernova, but…
How could we have created the coldest thing ever, at 100pK (less than 1 K), and that there is nothing colder? Might a single atom in deep space not have less energy? Apparently some nebula is the coldest thing out there.
In: Physics
As far as we can tell, the entire universe is filled with something called the Cosmic Microwave Background (CMB), which is sort of a leftover from the early universe when everything was much hotter and denser. Basically in the earliest moments of the universe, all space was taken up by huge amounts of hot plasma made up of subatomic particles. As the universe has expanded and become much much larger over billions of years, that energy has dissipated over the much larger volume of the current universe (compared to the early universe) and since temperature is basically the average amount of energy within a specified volume of whatever you’re measuring, that ‘background’ energy has cooled a lot since those early days, and now mainly exists as low energy radio waves. Primarily in the microwave part of the radio spectrum, hence the name Cosmic Microwave Background.
Anyways, the CMB is pretty darn uniform, and has an average temperature of about 2.725 K today. So basically everything in the universe is surrounded by ‘ambient’ energy levels of that temperature, so stuff in the universe can’t really radiate away energy to a lower temperature than that, because if it did, the CMB would radiate some its energy back into that object and warm it up to that temperature.
It does seem like there are some natural phenomena that can actively cool things below that temperature (for example in a nebula like you mentioned), but so far we haven’t seen anything as cold as what we can manage to do in purpose-built experiments.
Latest Answers