People have been measuring the speed of light for a few hundred years, but the universe is nearly 14 billion years old. If the speed of light changes very slowly – say a small percentage every 10,000 years – how could we tell?
• If the speed of light varied over time, we would see supposedly constant astronomical processes taking place at the wrong rate, or even changing their rate.
Imagine a small star orbiting a larger one, and that someone close by measures the orbital period as being exactly one Earth year. What would astronomers 100 light years away observe?
If…
