I take the position that the Universe is about 13.8 billion years old and the Earth is about 4.5 billion years old. In my opinion, one of the larger pieces of evidence against a young Earth, is Hubble's Law.
Hubble's law states that galaxies outside of the Local Group are moving away from earth, and the speed at which they are moving away is proportional to the distance they are from Earth.
In a formula Hubble's Law is the following:
Meaning the speed at which a distant galaxy is moving in km/s is equivalent to its distance from earth in megaparsecs (mpc) multiplied by Hubble's Constant, which is about 71.
With this formula we can calculate the age of the earth.
Distance divided by velocity is time. So we now know the age of the universe is equal to the inverse of Hubble's Constant.
Hubble's Constant is in [km/s]/[mpc] so we can plug that in.
There are 3.0857e19 kilometers in a megaparsec.
We can cancel out the kilometers and get the following:
So the universe is 4.3460563e17 seconds old. Which is 13.78 billion years.
So my question to young earth creationists is:
How do you reconcile a belief that the earth is less than 10,000 years old with Hubble's Law?