What's not possible, and what was assumed with this statement is if

the total amount of the energy in the universe is a constant.

It's not possible to know the total amount of energy in the universe.

There's way too many complicating factors, down to the atomic level and

the electrons moving about having energy associated with them.

Molecules flying through the air, having energy associated with that.

A car driving down the street having energy associated with that.

It's not possible to know the total amount of energy in the universe, but

we can determine the change in energy as a process takes place.

Now it's not the change in the energy of the universe because that's not changing.

But when a process takes place, we could study that system and

we can know its change of energy, which is abbreviated delta E.

Okay, so the total amount of energy change with any process in the universe is

gotta be 0, because the amount of energy in the universe is a constant.

But whatever the system is doing,

the surroundings has to be doing just the opposite.

So if the system is losing, let's say 10 Joules of heat,

the surroundings must be gaining 10 Joules of heat.

Whatever the one is doing, the other's doing just the opposite.

So if it's losing, it's going down.

If it's gaining, it's a positive value, but overall the universe is not changing.

The other way I like to think of this equation, and

more commonly I think of it this way, is that whatever the delta E,

the change in energy of the system is, that would have to be

equal in magnitude but opposite in sign of the delta E of the surroundings.

So I usually think of it this way, so

this is been stated exactly the same with this equation here.