Evolution

[Cyberman]

I only took 1 astronomy class. They said the universe was about 15 billion years old by measuring Doppler shift (or something like that). I just went along with it at the time since that's what they taught us. I never really thought much about it nor did I even know that people actually believed in a young earth at the time. To be honest I never actually thought to question science (or really anything else) when I was younger.

Actually, light from distant stars and galaxies is old not because of the Doppler effect, but because of the travel time of the light itself. Light, obviously and by definition, travels at the speed of light. The time that light takes to reach our eyes depends on the distance it has to travel. So the light from the Sun takes around eight and a half minutes to reach us. If we were in a spacecraft sitting roughly 9,500,000,000,000 km (about 5,900,000,000,000 miles) from the Sun, a photon leaving it would take one year to reach us. To make things simpler, that distance is classed as one lightyear.

Thus the light from a star that is, say, 10 ly away would take ten years to reach us. Our nearest neighbouring large galaxy*, the Andromeda galaxy (classified as M31) is almost three million ly away. And that's one of the closer ones; we've found more galaxies than there are stars in our own, the most distant ones (so far) being over 13,000,000,000 ly away (sorry, I hate and detest the 'new' definition of billion and refuse to use it unless I absolutely have no choice but to do so). Clearly, over such vast distances the expansion of space is going to have a profound effect, increasing with distance. But that's not what causes the light to be old.

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* M31 is only our nearest large neighbour, not the nearest galaxy to our own. That honour goes to the Canis Major Dwarf Galaxy, which took the title from the Sagittarius Dwarf galaxy - which we are in the process of 'eating' - in 2003. That one itself usurped the throne from the long-reigning Large and Small Magellanic Clouds in 1994. All of them are far, far closer to us than poor old Andromeda.