|HPS 0410||Einstein for Everyone||Spring 2010| Back to main
course page We can use Hubble's law to arrive at a crude
estimate of the age of the universe. That is, we will calculate
how long ago all the galaxies were crammed into our neighborhood
of space. This time will be our estimate of how long ago the big
bang happened. We will assume that each galaxy has moved at a
constant speed for all time, although this speed will vary from
galaxy to galaxy. We will use the value of 20 km/sec per
1,000,000 light-years for Hubble's constant. 1. (a) If a galaxy
is 1,000,000 light-years away from us now, according to Hubble's
law, how fast is it receding from us? (b) A galaxy traveling at
1 km/sec will travel one light-year in 300,000 years. How long
does the galaxy of (a) require to travel a light-year? (c) How
long did it take the galaxy of (a) to get to its position
1,000,000 light-years distant from us? 2. Repeat the calculation
of 1. for a galaxy now 2,000,000 light years distant from us. 3.
Repeat the calculation