Why doesn't light from distant galaxies reach us instantaneously? (Intermediate)

I am a Middle school science teacher and I would like to ask a question. While reading about a recent dicovery of very distant galaxies that may be some of the first to emerge from the "dark ages", I had a thought. If Einstein was correct in his theory that at the speed of light, time stands still, is it possible that no time elapses between the time that the light leaves a distant galaxy and it gets to earth & If this is the case, light from all sources in the universe would get here at the same time, which is the same moment that it left the source. If so, would this affect the "red shift" and "blue shift" theories?

You have to distinguish between time for the photons themselves and time in the outside world. As explained here, it's true that, since a photon moves at the speed of light, it experiences the world with time standing still. (Of course, photons aren't conscious, so don't take the word "experiences" too seriously. :) ) That is, if you were a photon, moving at the speed of light, the trip from a distant galaxy to the Earth would appear to take no time at all.

But in the outside world (not moving at the speed of light), time is *not* standing still. So for us here on Earth, it *does* take time for light to get from Point A to Point B. It's this difference--different observers see the same events as taking different amounts of time because they're in different frames--that's at the heart of relativity.

This page was last updated June 27, 2015.

About the Author

Christopher Springob

Christopher Springob

Chris studies the large scale structure of the universe using the peculiar velocities of galaxies.  He got his PhD from Cornell in 2005, and is now a Research Assistant Professor at the University of Western Australia.

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