# Internal energy and total heat of universe

Hello. I am starting to learn about thermodynamics. (i'm going to use lower case "d" for delta)

Energy is neither created nor destroyed. So dU = 0 for the universe as a whole.

If the universe is constantly expanding, then it must be doing work on the vacuum around it, right? So W is a positive number

dU = Q - W
0 = Q - a positive number

So Q is a positive number.

So heat is being added to the universe constantly.

Is this correct?

## Answers and Replies

phinds
Gold Member
Hello. I am starting to learn about thermodynamics. (i'm going to use lower case "d" for delta)

Energy is neither created nor destroyed. So dU = 0 for the universe as a whole.

If the universe is constantly expanding, then it must be doing work on the vacuum around it, right? So W is a positive number

dU = Q - W
0 = Q - a positive number

So Q is a positive number.

So heat is being added to the universe constantly.

Is this correct?
Energy is not conserved at cosmological scales

http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

Dale
Mentor
2020 Award
Energy is neither created nor destroyed. So dU = 0 for the universe as a whole.
Unfortunately, the energy of the universe is not a well defined quantity. http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

A globally conserved energy is only defined for a class of spacetimes that does not include the usual model of the universe.

If the universe is constantly expanding, then it must be doing work on the vacuum around it, right?
There is no vacuum around the universe in the usual cosmological models.