Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Time flows one way...cause creates effect.

Could the expansion of the universe also cause an expansion of space time in a similar fashion?...and if so, would this phenomenon explain the one way direction of time?

I read a article about EST (expanding spacetime theory) that seemed to back this up.

share|cite|improve this question
Can you share a link to this article? – Bernhard Jul 21 '12 at 5:45
OP is presumably referring to this website. – Qmechanic Aug 21 '12 at 12:52

You mention the expansion of the universe, so I'm assuming your question is in the context of General Relativity.

The first thing to make clear is that the expansion of the universe is an expansion in spacetime and not just an expansion in space. We see it as an expansion in space because we are comoving observers, but this is an accident of the co-ordinate system we're using rather than a fundamental split between space and time.

In fact, in General Relativity the difference between the spatial co-ordinates and the time co-ordinate is not fundamental, and different observers will find their views of what constitutes time and what constitutes space will differ. There is not really a flow of time in GR any more than there is a flow of space.

So the expansion of space does not explain the one way direction of time. Over the decades (millenia if you include St Augustine!) there has been much discussion over why there is a directional flow of time but no-one has reached any satisafctory conclusions. If you're interested I recommend Googling for Sean Carroll's articles on the subject as he's particularly interested in this area. See for example this video for a popular science level introduction to the subject.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.