Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

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

In a documentary written in collaboration with Stephen Hawking, the narrator (supposedly Stephen Hawkings) says that by the time the cosmos was 10 minutes old, it had already expanded thousands of light years in diameter. How is it possible that matter was traveling faster than light?

share|cite|improve this question

migrated from Dec 16 '13 at 23:10

This question came from our site for scientific skepticism.

Related: – Alfred Centauri Dec 16 '13 at 23:32

The metric expansion of space is a fundamentally different phenomenon than the relative motion of two objects in the flat spacetime of Special Relativity:

While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, it places no theoretical constraint on changes to the scale of space itself. It is thus possible for two objects to be stationary or moving at speeds below that of light, and yet to become separated in space by more than the distance light could have travelled,

Also, see this question and the accepted answer.

share|cite|improve this answer
In fact, the accepted answer is not as thorough or accurate as the one given by "Pulsar" below it (which also has more upvotes). One problem about the accepted answer is that it equates the Cosmic Event Horizon with the Hubble Sphere, which is only true for a pure, empty De Sitter space, but not generally true. – Thriveth Jan 14 '14 at 11:18

Because space itself was expanding faster than the speed of light.

Which is perfectly acceptable by the way with Special Relativity, because the speed of light is only a barrier for matter traveling through space. There is no such limit for the speed with which space itself can expand (or contract), as far as I know.

share|cite|improve this answer

protected by Kyle Kanos Mar 28 '15 at 0:43

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?