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

Is the universe NOT accelerating ?

  1. Oct 12, 2014 #1
    I tweeted neil Tyson, michio kaku and brian green the following:
    [link deleted by moderator]

    no responses yet, would like feedback - does the video make sense?
     
    Last edited by a moderator: Oct 13, 2014
  2. jcsd
  3. Oct 12, 2014 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    What video?

    Even without seeing the video, I'd hazard a guess that no, it does not make sense. The concept of the universe not accelerating is debunked here fairly regularly.
     
    Last edited: Oct 12, 2014
  4. Oct 12, 2014 #3
    on youtube, search hubblesmisinterpretation.
    and I didn't say it's not expanding, it's not accelerating - since the older the galaxy is, the faster it is
     
  5. Oct 12, 2014 #4

    phinds

    User Avatar
    Gold Member
    2016 Award

    Sorry, my post should have the word accelerating where I have expanding. My corrected statement stands. The age of the light from the distant stars is taken into account.
     
  6. Oct 12, 2014 #5
    but hubble's graph is velocity plotted against distance, which is not acceleration - it's velocity plotted against time. from oldest to newest, the graph shows DEceleration
     
  7. Oct 13, 2014 #6

    Drakkith

    User Avatar

    Staff: Mentor

    The acceleration of the universe was not discovered in Hubble's time, but in the 1990's by many observations of specific types of supernovas. You are correct in that Hubble's graph shows velocity, not acceleration, however your argument that the since older galaxies are moving away faster than closer ones means the universe is decelerating is not correct. Objects within expanding space naturally recede at different velocities depending on how far apart they are. The further apart two objects are, the faster they recede from each other. This holds even when the expansion is steady and is neither accelerating nor decelerating. Let's be clear here. In this context, acceleration/deceleration means an increase or decrease in the rate of expansion, not the velocity of objects.

    There are many posts here on PF's cosmology forum explaining this, so I suggest you start there. I believe the link in Phind's signature block may also help.

    Now, since this thread's topic is about a video that inaccurately explains expansion, I have deleted the link to your twitter and am locking the thread. If you have specific questions about expansion, you may start a new thread in the cosmology section.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is the universe NOT accelerating ?
  1. Accelerating universe (Replies: 9)

Loading...