Quote:
Originally Posted by Ithekro
I wonder if the expansion we think we are seeing is actually the effects of random sub-atomic movements and later gravity on large galatic bodies over several billion years of time. We have only a little over 100 years of reliable data on galactic movements...that's hardly enough to get a clear view of actions that take hundreds of thousands of year to complete.
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Naturally, our measurements aren't of galactic movements in real time (as in, yesterday it was x lightyears away, today it's y lightyears away). The current data on the motion of distant bodies is based largely on redshift. When bright bodies are moving away from us, the light they emit is
redshifted, i.e. the wavelength becomes longer because of the Doppler effect. The faster the galaxy is moving away from us, the greater the redshift.
Also keep in mind that by looking out into the sky we are actually looking into the past. The image of a galaxy that is 100,000 lightyears away is now 100,000 years old by the time it reaches us. If we look a million lightyears away, we are seeing a million years into the past. So cosmologists actually
can know a lot about the movement of galaxies across large time scales.
I believe there's also a way to measure the expansion of the universe based on gravitational lensing (massive objects bend light) but I don't know the details. Combined with other evidence such as the Cosmic Microwave Background (relic radiation from shortly after the Big Bang), it's almost certain that the universe is expanding.