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

Size of the universe

  1. Apr 15, 2005 #1
    How does one figure something like this out? As well as its rate of change, and such things?
  2. jcsd
  3. Apr 15, 2005 #2
    Another question, I've heard velocities of stellar objects can be/are measured relative to the stars, how does this work if the stars themselves rae moving? Is it that their movement is so minute relative to the object that they can be considered stationary?
  4. Apr 15, 2005 #3
    I wish we knew the topology of the universe. According to standard cosmology, the universe should be a closed system.

    Check out this report.
    Last edited: Apr 15, 2005
  5. Apr 15, 2005 #4
    There is no way

    There is no way to figure this out considering the universe has not been discoverd for its full extent and probably never will be...
  6. Apr 16, 2005 #5
    There are some approximations out there,and I'm asing how those came about.
  7. Apr 16, 2005 #6


    User Avatar
    Science Advisor
    Gold Member

    The universe has a very distinct, and finite size observationally.
  8. Apr 16, 2005 #7
    Well I know this, do you have an answer to my question?
  9. Apr 16, 2005 #8
    the universe is expanding and it is actually accelerating in its rate of expansion.
    we can tell this from the red shift in the spectrum of galaxies as seen from Earth.
    It is not of constant size.
    love and peace,
    peace and love,
    (kirk) kirk gregory czuhai
    owner/ceo Heaven Sense
  10. Apr 16, 2005 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The observable universe is approximately 47 billion light-years in radius. The light from objects further than 47 billion light-years away has not yet had time to reach us.

    - Warren
  11. Apr 16, 2005 #10
    :bugeye: That's quite a radius for the observable universe. Then again I'm not all that surprised because it is the universe we are talking about. Warren, do you know how scientists arrived at that figure? I mean how did they calculate it?
  12. Apr 16, 2005 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member


    Using instruments like WMAP, cosmologists can fit the universe around us to one of a number of candidate models. The models produce, among other data, the rate of expansion of space at each moment in time. You can use that function to determine the present-day radius.

    - Warren
  13. Apr 16, 2005 #12
    That is really cool. I hadn't heard about it. Would it be possible to predict the diameter of the universe based on that data? Might it be possible to predict the radius of the whole thing?
  14. Apr 17, 2005 #13
    Thanks chroot. Its kind of an obvious way now that I think about it.

    misskitty: Divide by two :)
  15. Apr 18, 2005 #14
    Whozum, i know how to find the radius of the circle. :smile: I meant predicting the diameter of the entire universe.
  16. Apr 19, 2005 #15
    can we use the formula of the gamma particle when desiontegrated from uranium to know the age of the universe?
    because as i know it travells throughout space and nothing can stop it!?
  17. Apr 19, 2005 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This would assume that there was a noticable and large supply of uranium at the beginning of time. However, uranium is generally created in supernova explosions and, since there weren't any stars around at the beginning of time, there was no uranium either. As far as I know, even at the present time there is no strong source of uranium emission in space. A lot of the radiation we see from supernovae, however, is from the radioactive decay of titanium-44 and aluminum-26.

    Also, it's not true that nothing can stop gamma-rays. In fact, the reason we can't observe them from the ground is that they're absorbed and scattered in the atmosphere.
  18. Apr 19, 2005 #17
    The universe is infinite and cannot be measured or modelled.
    This is why mathematicians do not like the infinite universe.
    They cannot meaure it. Except in terms of the big bang that theoretically happened and is finite. Maths teachers can then work. :!!)
  19. Apr 19, 2005 #18


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    PF readers may find http://www.eso.org/outreach/press-rel/pr-2001/pr-02-01.html [Broken] of some interest (it's only indirectly related to what SpaceTiger said above) ... "They* measured for the first time the amount of the radioactive isotope Uranium-238 in a star that was born when the Milky Way, the galaxy in which we live, was still forming. It is the first measurement ever of uranium outside the Solar System"

    *Roger Cayrel (P.I.), Francois Spite and Monique Spite (all Observatoire de Paris, France), Vanessa Hill and Francesca Primas (ESO), Johannes Andersen and Birgitta Nordström (Copenhagen and Lund Observatories, Denmark and Sweden), Timothy C. Beers (Michigan State Univ., USA), Piercarlo Bonifacio and Paolo Molaro (Trieste, Italy), Bertrand Plez (Montpellier, France), and Beatriz Barbuy (Univ. of Sao Paulo, Brazil).
    Last edited by a moderator: May 2, 2017
  20. Apr 19, 2005 #19


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Lots of details here - Ned Wright's Cosmology website (includes a calculator).
    Last edited: Apr 19, 2005
  21. Apr 19, 2005 #20
    Lot's of details is an understatement dear. :smile:

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook