The term cooling is associated with loss of energy, while the law of conservation of energy states that the energy the universe had just after the Big Bang is still the same today. Can one more scientifically formulate the statement about cooling, which as I understand it actually refers to temperature?
Answer
Conservation of energy is just about the most important law of physics, and the cosmological background radiation also complies with it.
According to the first law of thermodynamics, total energy is conserved. But that total energy is the sum of the internal energy and the work done. Mathematically expressed: dE = dU + P dV = 0.
The internal energy U is the energy of the radiation itself; it does indeed decrease as the temperature decreases. But the radiation also has a pressure P and due to the increase in the volume dV as a result of the expansion, that pressure therefore performs work. And both effects together lead to a constant total energy E.
Answered by
Prof. dr. Christopher Waelkens
Astronomy
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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