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

Flat matter only universe

  1. Oct 4, 2006 #1
    I just finished a problem from ryden's intro to cosmology, but im not sure the answer makes sense here is the problem and my work:

    suppose you are in a flat, matter-only universe that has a hubble constant H0=70 km/s Mpc. you abserve a galaxy with z=1. how long will you have to keep observing the galaxy to see its redshift change by one part in 10^6?

    The equation to use is :

    dz/dt0 = H0(1+z) - H0(1+z)^[3(1+w)/2]

    we know:
    H0=70km/s Mpc
    plugging into the equation we get dt=-7.28E-13 s*Mpc/km
    multiplying (-7.28E-13 s*Mpc/km) * ( 3.1E19 km/Mpc) = -22.6E6 s.

    this seems a bit large and is negative.
    does this seem right?

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

Can you offer guidance or do you also need help?