Thursday, April 17, 2014

Dark Energy

In case you want an entertaining lesson or information on Dark Energy and why we think it is there, here's a nice video on it.



This video, in conjunction of the earlier video on Dark Matter, should give you some idea on what these "dark" entities are based on what we currently know.

Zz.

1 comment:

johnduffieldblog said...

Not bad. It was nice to see Don give some caveats and mention alternatives such as quintessence. But what puzzles me is that we never seem to hear about the obvious alternative.

The universe expands like the balloon analogy we’ve all seen on the Discovery Channel. And a balloon is the size it is because the internal pressure is counterbalanced by the tension in the skin. Now, how do you make that balloon bigger? You can blow some more air into it. That’s like adding more energy, increasing the pressure. The trouble is it drives a coach and horses through conservation of energy. But there is another way to make that balloon bigger: reduce the tensile strength of the skin. Tension is negative pressure and when you reduce the tension the balloon gets bigger until the internal pressure is reduced and balances the tension again. But the balloon got bigger so the skin is now thinner so the tensile strength is reduced, so the balloon gets bigger again.

See page 5 of http://arxiv.org/abs/0912.2678 where Milgrom mentions the elasticity and strength of space re f(R) gravity, and don't forget the bag model.