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Q & A: light and matter in the big bang

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Most recent answer: 03/05/2016
Q:
As the Universe expanded after the Big Bang, both matter and light traveled outward. Assuming matter does not travel at the speed of light, the light would reach any given spot before matter condensed and formed planets. So if the light has passed us, how do we now look back to see light coming from the Big Bang.
- Jon Hammersberg (age 73)
Virginia Beach, VA USA
A:

The picture isn't that at some spot in space there was light and matter and they blew outward like in a normal explosion. It's that all of space was filled very densely with hot matter and light. The whole space expanded, staying approximately uniformly filled. It cooled as it expanded. After it cooled enough, electrons and protons combined to make atoms, and these are almost transparent to light. So since then as the universe keeps expanding the light and the matter have gotten much less dense (more space to fill) but they are still approximately uniformly distributed on a large scale. On a smaller scale, the matter has formed lumps (like our galaxy) but the old light has stayed almost uniformly spread out. So wherever you are, there's some of it there. It's coming from all directions because it was always everywhere.  There never was an "outside" where it was missing.

Mike W.


(published on 03/05/2016)

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