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

Understanding the accelerating expansion of the universe based on redshift

  1. Jun 19, 2010 #1
    Understanding the accelerating/decelerating expansion of universe based on redshift..

    I am trying to understand how the expansion of the universe is accelerating, if indeed it is. It's confusing, as some people say that the expansion is accelerating, whereas I have a video lecture where the professor says that the expansion is decelerating. My question is how do you conclude that expansion is accelerating/decelerating based on these numbers, given that the more distant galaxy is seen as it was much longer ago than the closer one?

    Circinus Galaxy.

    Distance from earth: 1.23x10^20 km (13 million ly)

    speed: 426 km/s

    IOK-1 galaxy.

    Distance from earth: 1.23x10^23 km (13 billion ly)

    speed: 290 477 km/s

    Last edited: Jun 19, 2010
  2. jcsd
  3. Jun 19, 2010 #2


    User Avatar
    Science Advisor
    Gold Member

    The Perlmutter supernova legacy study confirmed expansion.
  4. Jun 20, 2010 #3


    User Avatar
    Science Advisor

    In the early universe, the expansion was decelerating. It's only within the last few billion years that it's been accelerating. So I guess it depends upon what epoch you're looking at.

    But in any case today we have hundreds of supernovae, as well as large galaxy surveys and cosmic microwave background observations that all confirm the same story. Two individual galaxy observations aren't going to overturn this (or even add much to it, because two single galaxies are just two small data points among thousands).
  5. Jun 20, 2010 #4
    Tests of Big Bang: Expansion from NASA by Official: Dr. Gary F. Hinshaw,
    Updated: Friday, 04-16-2010

    Universe is Expanding - "Red Shift" is Proof of Einstein's General Theory from "Cosmic Times is a product of the Imagine the Universe! website. Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan P. Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center. . .
    Last Updated: Tuesday, 05-Jan-2010 16:34:49 EST"
    Best to review the contents online from the link (url) below:
    Last edited: Jun 20, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook