# Accelerating universe != conservation of energy?

1. Jun 16, 2008

### Denton

I'm sorry if this sounds as a very simplistic view but my main underlying belief that the universe is not accelerating and will not expand to infinity but indeed collapse on itself eventually arises from the fact that the kinetic energy of the expansion will be met by the gravitational attraction.

The universe is the universe, there is nothing else outside it therefore its a closed system with a limited amount of energy, no new energy is coming in. So if a universe such as this continues to expand indefinitely, KE + U != 0.

Does general relativity have anything to explain about this, or do astronomers blatantly ignore one of the most fundamental laws?

2. Jun 16, 2008

### MeJennifer

You are wrong in your reasoning.
Irrespective of it size the total energy of the universe is always 0, this is because negative gravitational potential energy balances the energy of matter.

3. Jun 16, 2008

### Adonis

well classick physics say the energy of the universe is balanced.......
cause when energy turns of a form to another it will stay
energy (potential or kinetic or....)
so.....we cansay KE+U= constant
btw the universe is limited but with no boundaries (by GR)

4. Jun 17, 2008

### DemTings

Am I wrong in saying dark matter holds the answer to that one? I remember Stephen Hawking saying that should the universe be made up of simply the matter we see around us, it will likely expand forever. But, should the universe be made up of mostly dark matter, on top of all the matter we can see, the gravitational force will become too much and it will initiate the big crunch.

5. Jun 17, 2008

### shalayka

The $\Lambda$CDM model is something to look into. In it you will find that dark matter and luminous matter only make up about 1/4 of the required total energy needed to explain the apparent spatial flatness of the universe -- google for "angular size of microwave anisotropies". It's real science, I promise.

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