I’ve heard the theory that universal expansion may actually be speeding up. What mechanism allows that? It seems like that violates some energy conservation laws.
It’s been a long time since I took my one physics class. Can anyone explain it to a layman?
Well it’s not only a theory. Recent tests seem to show that it’s actually happening.
It doesn’t have to violate any conservation of energy laws. Like when you put two electrons together they’ll fly apart, the energy was stored as potential before.
Oh yeah, as to why it’s happening, who knows? That’s the big mystery they’re trying to figure out.
There is no conservation law that says there is some limit to the size of the universe. If there is not enough mass-energy in the universe to stop the pull of gravity, the universe will expand forever just getting less and less dense. If the mass-energy is greater than some critical value, it will collapse back on itself.
Or, the third possibility, that the forces and masses are necessarily balanced by reason of some relationship not presently understood. In that case the expansion slows, over time, approaching a rest state as an asymptote, but never really stopping. This is the so-called “flat universe” theory.
<p align=“center”>Tris</p>
I understand the idea about not enough mass/energy to stop the expansion (the Big Freeze), and I understand that if they “found” enough mass/energy, the universe would eventually collapse (the Big Crunch).
BUT WHAT IS MAKING THE CURRENT EXPANSION SPEED UP!?! How can that be? Is there some kind of nuclear repellant force operating on a cosmic level?
Rysdad: BUT WHAT IS MAKING THE CURRENT EXPANSION SPEED UP!?! How can that be? Is there some kind of nuclear repellant force operating on a cosmic level?
Maybe the mass of the universe is now closer to the sides of the giant shoebox that contains our universe. 
AWB, that would be a hypershoebox, since it would by definition be in four spatial dimensions. Which leads to the question of what a hypershoebox would contain?
And while we’re at it, is the universe bigger than a hyperbreadbox?
No, the Universe is actually contained within a glass marble owned by a really big alien. Didn’t you see Men in Black?
Those who do not learn from the past are condemned to relive it. Georges Santayana