Newton's Third law and a big Crunch?

According to Newton's one law of motion "Every action has an equal and opposite reaction" the universe started with a big bang then will it also have a big crunch ?
- Rahul Agarwal (age 17)
Siliguri,West Bengal, India

Newton's third  law doesn't mean anything at all like the vague ideas often suggested by that way of phrasing it. What it says is that in an isolated system momentum is conserved. That has no direct implications for whether or not there's going to be a big crunch. Unless the universe changes in a deep way, there won't be, since the expansion is now accelerating, not slowing.

Mike W.

(published on 09/18/2012)