expanding universe question

[TalonD]

reading thru some of the posts I havn't realy found the answer. The univers is expanding but is it a constant rate or is it an accelerating rate?

[Garth]

At present the expansion appears to be accelerating.

This was a major discovery of the 1990's deduced from the fainter than expected distant Supernovae Type 1a.

The acceleration is thought to be due to Dark Energy that has a high negative pressure.

Note: adding positive pressure (the normal kind) acts like adding energy and produces extra gravitation, which counter intuitively increases the deceleration of the universe's expansion. Negative pressure has the opposite effect.

Garth