The first law of thermodynamics states that the energy of the universe is constant, but the universe is constantly expanding, so how does the energy stay constant considering the expansion?

Question

I think this is physics based(?), but I thought of this question during my summer chemistry course, so I wasn’t sure of the flair.

In: Physics

Answer 1

I don’t think these two concepts really play nice together. The first law does require the system to be constant, because energy depends on your reference point. For everyone on Earth it’s stationary in space and Earth’s kinetic energy would be zero. Look at Earth from the sun and it would be moving very fast, I’m gonna guess it like 40,000 m/s something, suddenly the Earth has a lot of kinetic energy.

Look at the sun from the Milky Way’s center and suddenly the sun is moving at like 200 km/s something and the Earth would be moving at speeds up to 240 km/s, a insane amount of kinetic energy.

Has the kinetic energy of the Earth changed? Yes it went from none, to a lot, to a ton. However, your system also changed and those numbers are in no way comparable. The easiest way of getting out of answering this question would be that if the system is expanding, your system isn’t constant. (Energy is being added in the form of dark energy).

Physicists really hate this question though, it’s always been a pain in the ass for them. This is because thermodynamics is built on quantum mechanics and in quantum in nature. The universe mostly just functions with gravity. Quantum and gravity don’t play nice together. A working theory of Quantum Gravity is what physicist have been trying to find for the past 50 years and so far they’ve been very unsuccessful.