Seed Question: You have probably heard that the universe is expanding. What does this mean? Select all that apply.

A) Everything is getting further apart

B) Galaxies are getting bigger

C) Galaxies are getting further apart

Exploration: Most galaxies look like they are moving away from us. Check out this Hubble graph of galactic recession velocity versus distance away from us. Tape in this graphic.

What can we conclude from Hubble’s graph? Write v as a function of r…

Find the slope of this graph.

The slope is called H0, Hubble’s Constant.

Write down Hubble’s Law:

Hurray! We are the center of the universe again. Or are we? What would it look like if we looked from somewhere else in the universe? Hoberman Sphere Demo.

The Big Bang

Based on data from Kristian, Sandage and Westphal with added distance scale. From Alan Guth’s The Inflationary Universe, p. 38

Recession Velocity vs Distance

Draw a graph of Average Galaxy Separation vs Time. Label “Now”

Thecurrent best value of H0 is68 kms

/megaparsec

If the universe always expanded at this same constant rate (H0), how old is it now? To figure this out, look at your graph above. What would tnow be in terms of r and v? Now, what is r/v according to Hubble?

1 parsec = 3.09 x 1016 m

Big Idea: Hubble’s Expansion Law:

The current best value of Hubble Constant is

H 0=68 kms

/megaparsec

The Hubble Time is 1/H0 = 14 billion years

Discussion:

vrec=H0 r