1. It's common to read that the total energy of the universe is constant - the classical-physics conservation of energy story. However, since it's now thought that the total energy content is actually increasing as the universe expands (although the energy density is decreasing) I'm left wondering how to understand this. If the universe decides to expand for an inordinate length of time, then that's a heck of a lot of extra energy pulled out of nowhere. Does gravity fit in here somewhere to balance things out (since gravity is seen as -ve)? Or do we not need to worry if things don't balance out?

2.

3. I probably worded this question in a confusing way (because I'm confused about what it is I'm asking) , so I'll put it more clearly:

1) The universe is expanding.
2) Empty space is not really empty, as such. It contains energy.
3) That energy comes from a "froth" of virtual particles winking in and out of existence, apparently.
4) The amount of empty space is increasing (as the universe expands). So...
5) The amount of energy in the universe is going up. More space = more vacuum energy.

What I'm wondering is this: does this extra energy actually increase the amount of energy in the universe; that is, are we getting something for nothing?. Or, is it transferred somehow to the gravitational field of the universe, and canceled out?

A second, wider, related question is this: does it matter if the universe is increasing its energy content? Are any fundamental principles of physics violated? Does it have to cancel out to keep us all sane?

4. Energy and matter have a property known as mass. If you want to send a heavy mass to the moon, you need to expend a lot of energy. So in a way, mass behaves like negative energy. Alan Guth, who described how inflation could explain the Big Bang, thinks that if you could add up all the energy and matter in the universe plus the negative energy of its mass, the result might be zero. Perhaps Dark Energy has a co-property that zeros it out as well so that the overall effect is nil.

5. Originally Posted by Zwirko
I probably worded this question in a confusing way (because I'm confused about what it is I'm asking) , so I'll put it more clearly:

1) The universe is expanding.
2) Empty space is not really empty, as such. It contains energy.
3) That energy comes from a "froth" of virtual particles winking in and out of existence, apparently.
4) The amount of empty space is increasing (as the universe expands). So...
5) The amount of energy in the universe is going up. More space = more vacuum energy.

What I'm wondering is this: does this extra energy actually increase the amount of energy in the universe; that is, are we getting something for nothing?. Or, is it transferred somehow to the gravitational field of the universe, and canceled out?

A second, wider, related question is this: does it matter if the universe is increasing its energy content? Are any fundamental principles of physics violated? Does it have to cancel out to keep us all sane?
Some thoughts. It would depend on the "froth". We have only detected it on Earth and not in space. If it exists in space, then unless it is a property of space itself, as the universe expanded it would decrease to the point where it would now be undetectable.

If space however can produce endless amounts of particles popping in and out of existence, that would mean that a black hole would continually gain mass (and energy) as it sucked in all such particles in it's gravitational area as it moved around a galaxy, which would either leave an area of space at a lower energy, to be bumped up by other areas of space around it, so to speak.

However, how does space "infinitely" expand from quantum size to present size, onwards? If some kind of medium as warping space and energy level would suggest, there would have to be a process of continuous creation to make ever more of it, and supply the energy needed, which would suggest a loss of matter and energy "elsewhere" to compensate for it.

6. Well is it now accepted that dark energy is the vacuum energy? Could it be that space is simply compressed like a spring and is just expanding?

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