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

Hubble Constant

  1. May 2, 2009 #1
    The hubble constant v = Hd tells us recessional velocity of galaxies is proportional to distance. But distance is equivalent to looking back in time. So what we are seeing is the recessional velocities of galaxies at different times in the universe? This surely can't be right, because for an expanding universe, recessional velocity should be proportional to physical distance, not time.
  2. jcsd
  3. May 3, 2009 #2


    User Avatar
    Science Advisor

    The above equation only holds when you have a constant expansion rate. When the expansion rate changes with time, you have to use an integral.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook