|MadSci Network: Physics|
Every atom gives off radiation at its own characteristic frequencies. If the atom is moving towards or away from us, this frequency will be shifted. By looking at the frequencies of distant stars, scientists have observed that these distant stars are all traveling away from us, and that their velocities are roughly proportional to their distance from us. From this we can deduce that the universe is expanding. By measuring how far away distant galaxies are, and how fast they're traveling you can figure out how long ago they must have started traveling from some common point (or roughly how old the universe is). If your friend is trying to say that the shift in frequency is due to the speed of light being different in the past, I've got a simple experiment for them to try. Point a telescope at some distant galaxy and measure the speed of light. Although its difficult to measure the speed of light accurately, in order for it to be responsible for the large shifts in frequencies that we observe the effect should be noticeable. Its my guess that your friend will not attempt this experiment. In order to believe that the universe is only 5000 years old, one must disbelieve thousands and thousands of experiments carried out in field after field. One must disbelieve physics, astronomy, biology, chemistry, geology, and probably several other fields of science that I'm leaving out. Its one thing to suggest that a varying speed of light is responsible for the shift in frequencies that we observe, but this suggestion must be logically extended and its consequences must be examined. The speed of light is a fundamental constant that appears in all sorts of equations. What consequence does the speed of light being different have on all those equations? Why do galaxies in every direction have the same frequency shift and the shift get larger according to their distance from us? According to his suggestion, this would be determined solely by the age of the galaxies so this would suggest that the universe was created in layers, like the layers of a onion, with the outermost layers created first, and the earth smack-dab in the middle!
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