Entry 483, on 2007-02-27 at 19:51:17 (Rating 3, Science)
After my tirade against Creationism in this blog yesterday I have been thinking further about a simple way to prove the world isn't less than 10,000 years old. I have been an amateur astronomer for many years so I decided to take an astronomical approach. Its an approach that anyone can confirm is true - if they have a telescope and some observing skills - so it doesn't rely on taking any scientist's word on anything controversial.
First we have to establish the speed of light. This can be done using the approach of timing mutual phenomena of Jupiter's moons, and using some relatively simple maths. I won't go into the details here, but will try to find some time to expand my web page on this subject.
If we know the speed of light we can say how long it takes for light to travel any distance. Let's be conventional and use the light year as the measure of distance. the light from an object one light year away took one year to get here, which means the object existed one year ago.
Now we have to find a star which is more than 10,000 light years away. If the star's light has taken over 10,000 years to get here, it must have existed over 10,000 years ago. Since Genesis says the stars were created after the Earth that means the Earth must also be over 10,000 years old.
The problem is that it is difficult to measure distances to stars. There is only one direct method, known as parallax, but that doesn't work at such great distances (I'll also explain this on the web page when its done). We have used parallax to measure distances of stars which are up to about 100 light years away.
Luckily there is a type of star called a Cephied variable which is bright and has a characteristic which makes it possible to know its real brightness. These stars change brightness over time, and the time taken to change can be used to tell how bright they really are. If we compare how bright they look and how bright they really are we can estimate how far away they are. By the way, the calibration necessary can be done by using parallax on a close Cepheid.
These stars are visible at 100s of thousands, or even millions of light years. Their light took millions of years to get here. The stars are millions of years old (at least) and so is the Earth.
Some Creationists counter this by saying god created the Universe with the light already on its way from the stars. This isn't impossible, but its a fairly desperate tactic to try to get away from the problem. If we are going to allow people to invoke improbable, arbitrary ideas like that we could set out to prove anything is true!
Another counter is to say that the speed of light has changed over time, but this wouldn't work either, because we would notice this effect when viewing distant objects (which are also distant in time).
So, unless god tried to fool us all by deliberately making the light from stars look exactly like it left those stars millions of years ago (is he some sort of cosmic fraudster?), the young Earth idea is dead.
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