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:(adsbygoogle = window.adsbygoogle || []).push({});

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

z=1

w=0

dz=1/10^6

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?

thanks

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# Flat matter only universe

Can you offer guidance or do you also need help?

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