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

I Center of the Universe: What! Again!

  1. Jul 13, 2016 #1
    I've recently read that the universe is now estimated to be about 95 billion light years in diameter. This was based on what we now can observe (Hubble Deep Field for example), what is estimated to be seen with new technology (James Webb) and an estimate of what's beyond that which we can't yet image. That being said, doesn't the word "diameter" imply a physical center? I've read many of the threads about how there is NO center to the universe as we now understand it, and then I read a description of the SIZE of the universe implying a physical shape with the normal attributes of shapes about which we are familiar. And then I get completely confused. Furthermore, the latest graphic images that depict the arrangement of local groups, clusters and super clusters again show a universe that is physical with a definable center. Could someone please help me grasp this apparent inconsistency? And that's not even getting into when we do visualize the extremes of our universe, what's beyond that edge.
  2. jcsd
  3. Jul 13, 2016 #2

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The word observable has been left, i.e., it should "the observable universe". Since we can see in all directions, we are at the centre of the part of the universe that we can observe.
  4. Jul 13, 2016 #3
    Is that true? Is the distance to the extremes of our view the same in all directions? If so, then I guess we are the center of the universe. Some people have always acted like they were. Perhaps they were right all along. We haven't taken a deep field view looking in all directions I don't believe. I know it's been done twice looking in the Northern Hemisphere and then in the Southern. Perhaps it should be done in many directions and see what the numbers show regarding the farthest viewed galaxies.
  5. Jul 13, 2016 #4


    User Avatar

    Staff: Mentor

    There is no reason to expect our view to extend to different distances in different directions. While we haven't taken a hubble deep field quality image of the entire sky (it would take something like 10 million years), we have taken plenty of other surveys and our knowledge of the laws of physics appears to hold in all directions. These laws tell us that the observable universe should have the same diameter in all directions and that the diameter is approximately 95 billion light years.
  6. Jul 13, 2016 #5
    There is a limit to how far we can see, it's not based on technology, it's because there was a beginning of time. As you look further out into space, you look backwards in time. There was a time before light could move freely, and then even more time where there was nothing interesting being created.
  7. Jul 13, 2016 #6


    User Avatar
    Science Advisor
    Gold Member

    We have a full sky map of the CMB and found it to have a virtually identical redshift of about 1090 in every direction, A redshift of 1090 corresponds to a proper distance of about 46 billion light years and is a view of the observable universe when it was only a few hundred thousand years old. Only a neutrino or gravitational wave detector can possibily 'see' anything more distant than CMB photons [which are the most ancient of all photons in the universe]. We are still working on those.
  8. Jul 13, 2016 #7


    User Avatar
    Science Advisor

    The situation is similar to standing on the surface of the Earth. The distance to the horizon is the same in all directions (assuming no trees, mountains, etc.). The part of the Earth that you see out to the horizon constitutes the "observable Earth". My "observable Earth" is different from your "observable Earth", but they are both circular regions centered on where we are standing.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted