[HKMk23]

If I add up all of the energy in the unverse, convert all matter (and anti-matter) to energy and add that in, and express that grand sum as E_all is that a constant or a variable?

[NicknamedBob]

"... express that grand sum as E_all is that a constant or a variable?"

It depends.

Even though the steady state theory is out of favor, there could be the occasional spontaneous generation of matter because of quantum wobbles, or something.

Then there's also the matter, so to speak, of dark matter. Depending on its nature, and where it comes from, (and when!), perhaps not All matter is accounted for at any one time.

From the standpoint, or view, of most astrophysicists, it probably doesn't make much difference.

I'm inclined to partake of a tiny bit of steady-statism, just to keep things spicy.