# Electromagnetic waves vs the laws

1. Dec 16, 2013

### drew737

Does the law of the conservation of energy apply to the light in our universe?
If yes, is our universe a closed system?
If no, is our universe losing energy?

2. Dec 16, 2013

### ChrisVer

the conservation of energy applies everywhere.
As far as we know, since the way you "define" the universe is the region where the spacetime is defined, yes it is a closed system. If it was an open one, you'd be able to determine that loss of energy...
I think until now, everything works fine adiabatically

3. Dec 16, 2013

### WannabeNewton

Global conservation of energy can't be defined for non-stationary systems like an expanding universe. However locally conservation of energy always applies.

4. Dec 16, 2013

### drew737

Since this universe is a closed system of energy, is the universe expanding?
If yes, is the expansion rate increasing?
If no, does the universe have a finite mass/energy?

5. Dec 16, 2013

### ChrisVer

Isn't the universe expanding adiabatically? If it does, there is no energy loss...

6. Dec 16, 2013

### ChrisVer

7. Dec 16, 2013

### drew737

Since the universe is accelerating at an increasing rate, will we eventually have our own isolated/closed systems when the distance between galactic masses (bound by gravity) grows to an accelerated rate beyond the speed of light?
If yes, will our new system collapse into a singularity due to contraction?
If no, would we continually lose energy from light escaping into the void between what we can see and what we can't see (our old system)?

8. Dec 16, 2013

### ChrisVer

there is no matter speed greater than the speed of light, you should read the link I posted to understand what acceleration means.
What is the future of the Universe is still, if I recall well, an open question. Probably the universe will stop expanding one day and start collapsing, maybe it will keep expanding, maybe it never began and it will never cease to exist. But whatever the situation, I think we are around the critical level...

9. Dec 16, 2013

### Staff: Mentor

In the model in which the universe remains dark-energy dominated forever, yes. However, although that is the current best-fit model, our measurements are not accurate enough to rule out other possibilities, such as an eventual recollapse.

No. First, to an extremely good approximation, the large-scale expansion of the universe does not affect systems which are gravitationally bound on smaller scales, such as galaxies, solar systems, planets, or humans. The Usenet Physics FAQ has a good article on this (including a great Woody Allen quote):

http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.html

Second, to the extent that the large-scale expansion of the universe does have any effect, it is to make small-scale systems *less* gravitationally bound, not more.

This is happening regardless of what the universe is doing on a large scale; any system which is at a temperature greater than that of the cosmic microwave background radiation (currently 2.7K) is losing energy, on net, to the universe. But the timescales involved are very long compared to ordinary timescales.

John Baez has a good article on the *really* long term fate of ordinary objects if the universe's expansion does continue to accelerate:

http://math.ucr.edu/home/baez/end.html

10. Dec 16, 2013

### Staff: Mentor

It is still technically an open question, because our measurements are not accurate enough to tell for certain (because we are, as you say, very close to the critical density for the universe as a whole), but as I noted in my previous post, our current best-fit model says that the universe's expansion will continue to accelerate forever.

11. Dec 16, 2013

### TumblingDice

There's a recent thread that covers these questions and includes more good info and links:
Conservation of Energy in GR

12. Dec 17, 2013

### Chronos

1. You assume facts not in evidence.
2. Irrelevant. The universe can expand at any rate it desires, regardless if it is finite or infinite.
3. Assuming the universe is finite, the answer is definitely yes.