According to the laws of quantum mechanics, even at absolute zero (0 Kelvin or -273.15 degrees Celsius), a body would still emit some electromagnetic radiation. This phenomenon is known as "zero-point energy" or "vacuum fluctuations."
At temperatures above absolute zero, thermal energy causes particles to move and vibrate, and this motion gives rise to the emission of electromagnetic radiation. However, even at absolute zero, particles do not come to a complete standstill due to the uncertainty principle in quantum mechanics. The uncertainty principle states that there is a fundamental limit to how precisely we can simultaneously know certain pairs of physical properties, such as position and momentum.
As a consequence of the uncertainty principle, there is always some residual energy associated with the zero-point motion of particles, even at absolute zero. This residual energy leads to fluctuations in the electromagnetic field, resulting in the emission of electromagnetic radiation. These fluctuations occur at all frequencies, spanning the entire electromagnetic spectrum.
In practice, the intensity of this radiation at absolute zero is extremely weak, and it becomes more significant as the temperature increases. At everyday temperatures, the contribution of zero-point energy to the total electromagnetic radiation emitted by a body is negligible compared to the thermal radiation emitted due to temperature.