# How to perform experiments near absolute zero temperature when the background temperature of the universe is 2.7 K?

The cosmic microwave background (CMB) radiation as a remnant from an early stage of the universe (Big Bang) is filled all space and has a thermal black body spectrum at a temperature of $$2.72548±0.00057$$ kelvin. Therefore, even the empty scape has an average temperature of 2.7 kelvin, which is greater than the absolute zero temperature (i.e., $$0$$ $${\rm{K}}$$).

Interestingly, the lowest temperature ever recorded in lab is really close to the absolute zero, for example see this link. How is it possible? How can experimental physicists eliminate the thermal effects of CMB noise in such very low-temperature experiments? Is someone here familiar with their experimental techniques or the theoretical basis?

• The thermal radiation in the lab at around 300 kelvin was a much bigger source of heat than the CMB! – Andrew Steane Apr 14 at 17:25
• I don't need an answer anymore because in the answers my mistake was made clear to me. The two answers are good with different viewpoints and they complement each other. I don't know which one is better to be chosen as the most helpful ! Both (+1) from me. – SG8 Apr 14 at 19:09