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

That’s an easy one, ironically. The total energy of the universe is 0. In physics terms, we say the universe is flat. They mean the same thing.

It seems strange, considering that matter, radiation, and dark energy all contribute to positive energy terms. Worse yet, the amount of energy in our visible universe due to dark energy is increasing! However, gravitational potential is negative, and exactly balances with all the positive energy terms. Even as the total amount of dark energy increases, the negative potential of gravity gets larger as well.

The other thing to remember is that the energy of a CLOSED system is constant. But the universe is not necessarily a closed system.