Using Hubble’s Law to determine the age of the universe
● The expansion rate appears to be the same everywhere in space.
● The universe has no center and no edge (as far as we can tell).
● One example of something that expands but has no center or edge is the surface of a
● The universe looks the same no matter where you are within it.
● Matter is evenly distributed on very large scales in the universe
● It has no center or edges
● The cosmological principle has not been proven beyond a doubt, but it is consistent with
all observations to date.
● Hubble’s constant tells us the age of the universe because it relates the velocities and
distances of all galaxies.
○ Age = Distance / Velocity ~ 1/H0
How does expansion affect distance measurements?
● Distance between far-away galaxies change while light travels.
● Astronomers think in terms of lookback time rather than distance,
● Lookback Time: how long it takes light to reach us.
● Expansion stretches photon wavelengths, causing a cosmological redshift directly related