Page 3, Cosmology Part II: [Previous Page] [Next Page] [Class Home Page] Text Pages 416

In the 1920s, Hubble first noted that the further a galaxy was from us, the faster it was moving away from us. This is in ALL DIRECTIONS. The "Hubble Law" suggested an expanding universe.


The Age of the Universe from Hubble's Law
Consider this.. you tell your friends you've been traveling 40 miles per hour for the last 80 miles. So, when did you leave? You know to divide 80 miles / 40 miles per hour.. giving you 2 hours.

Hubble said the Universe was expanding at 500 km/s for every 1 Mpc (1 Mpc = 3 x 10¹⁹ km and 3 x 107 seconds = 1 year).

SO: 3 x 10¹⁹ km / 500 km per second.. gives you 6 x 10¹⁶ seconds. That's equal to 2 x 10⁹ yrs ago! (2 billion yrs) WRONG!

They KNEW the earth and stars were more than several billion years old. Many people bought into a STEADY STATE universe because Hubble's Constant didn't give the right age! The Hubble Constant is now thought to be 70 km/s/Mpc, giving an age of 15 Billion Years (in agreement with the oldest known stars).

Other factors effecting our Age Calculation
What if in our example of the car above, we didn't travel 40 mph the entire time? What if we had been on the freeway first? Or had been forced to drive slowly in a residentail area first? The density of our universe has effected the speed of the Universe's expansion, and thus, our age determination will be off depending on whether we are going slower or faster now versus earlier.