Chicago in January may feel like the coldest place in the universe, but it’s colder at the South Pole. Scientists there, including some from Fermilab, are looking out into space and observing microwaves that have been travelling at the speed of light for 13.6 billion years. Once they were ultraviolet rays, but as the universe expanded their wavelengths stretched, and they became blue, then red, then infrared (heat) and now they are microwaves, which you may have in an oven in your kitchen. Radio waves have even longer wavelengths.
Just after the Big Bang at the beginning of our universe – I say “our” because ours may be one of many, we don’t yet know – everything was inconceivably hot. It cooled as it expanded, and now “space” is at about 2.7 Kelvin above absolute zero temperature. (Zero Kelvin is minus 460 degrees Fahrenheit, or minus 260 degrees Celsius.)
The universe is full of hot stars, and planets may be hot, warm or cold, but a rock in the depths of space would be bathed in microwaves at 2.7 K and be that cold. Nothing natural in the universe can be colder.
At absolute zero temperature all atoms would stop jiggling and be still. According to quantum physics that is not possible, and nothing can get as cold as absolute zero. In physics laboratories, scientists have reached a millionth of a degree above absolute zero, but we can never quite get there.
The scientists at the South Pole use a microwave telescope to make maps of this “cosmic microwave background” to learn about the Big Bang. They are in Antarctica because the atmosphere there is transparent to microwaves, being thin, cold and dry since water vapor freezes out. Also, they are far from civilization’s annoying background radiation. Thousands of tiny thermometers in this telescope are kept even colder as they are extremely sensitive at only 0.4 K, at what is called a “superconducting phase transition”.
We think only a complicated physical apparatus can make anything colder than that 2.7 K bath, and scientists have reached that temperature only in the last 110 years. For how many centuries will science continue to be done? While there may be life on millions of planets, how many have active scientists? Only one? We could be unique.
So, if there are no other scientifically advanced civilizations in the Milky Way galaxy, there is no place as cold as in our laboratories. Not even Chicago in January.
