# I Spacetime & Dark Energy

1. Jul 4, 2016

### allen1966

I have a question. Please excuse me if this seems naive as I am not a physicist. This thing dark energy has been proposed to explain the acceleration of the expansion of the universe. From what I understand, it is everywhere. Could it be possible that dark energy really does not exist, but the effects that we are seeing are the result of the properties of space time itself, the geometry of the universe, and the distribution of mass throughout the universe?

2. Jul 4, 2016

### rootone

'Dark energy' might be anything.
The term is just a place-holder name for something which we don't know what it is, but is causing accelerating expansion.

3. Jul 4, 2016

### Staff: Mentor

I once have been answered to the same question here, that this is one possibility among others.
Personally, I think according to Occam's razor a likely one.

4. Jul 4, 2016

### phinds

Yes, it could, at least as far as being a property of spacetime. I don't think mass distribution is a factor. As rootone pointed out, we don't know WHAT it is, but there are various theories including, I believe, at least one that basically encompass your thought.

5. Jul 4, 2016

### Chalnoth

The simplest explanation for the accelerated expansion is a cosmological constant.

One way to describe gravity is to do a series expansion in the curvature parameter R, so that gravity is defined by the expression:

$$a_0 + a_1 R + a_2 R^2 + a_3 R^3 ...$$

The simplest theory of gravity that isn't completely trivial is just using the constant and linear terms:

$$a_0 + a_1 R$$

This is General Relativity. By convention, $a_1 = 1$ and $a_0 = \Lambda$, the latter of which is the cosmological constant.

This is usually considered to be one possible model of dark energy because a cosmological constant acts exactly as if there was a constant energy density through the universe.