Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Speed of light vs. the universe's inflation

  1. Aug 10, 2011 #1
    I understand that the Speed of light is the universal speed limit (I do not believe this is in question). However, I watched Steven Hawking's show this weekend on TV where they stated "10 minutes after the big bang the universe was thousands of light years across."

    How is this possible if the speed of light is the "speed limit?" How could anything be light years across if it has only been 10 minutes? I would think that at most it could be 20 "light minutes" across. I am sure there is an answer, I am just now aware of one.
  2. jcsd
  3. Aug 10, 2011 #2


    User Avatar

    Staff: Mentor

    Space is not a thing that moves, so the speed of light does not apply to its expansion.
  4. Aug 10, 2011 #3
    Russ, thanks for the reply. I understand that space does not move but the things in the "space" of the early universe did move namely radiation. Was there empty universe expanding faster than radiation? The expanding radiation is what made up the universe as there was no space yet. I appreciate your thoughts.
  5. Aug 10, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    2018 Award

    Spacetime existed at the beginning of the universe. All radiation, matter, and everything occupies spacetime. The expansion between points in spacetime has no limit and as such it can, and does, cause objects to move faster than c. The key is that the objects don't move WITHIN spacetime greater than c, but that spacetime itself is expanding.
  6. Aug 10, 2011 #5
    Drakkith ~

    Thank you VERY much that makes a lot of sense. Thank you so much for your help.
  7. Aug 12, 2011 #6
    If you had a Cartesian planes that you "placed" upon the Universe the size that it is right now, from an external vantage point, then yes, however, matter would have traveled a fair bit faster than c. But the speed is only in reference to an already expanding reference point, and so the example is not valid.

    I generally think of it as an expanding polka dot balloon, but how it works in my head would probably confuse most.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook