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The Question

(Submitted February 14, 2013)

In the early universe, during inflation, would not all matter/energy be uniformly distributed and uniformly expanding? If not, why not and at what point during inflation would it no longer be uniform? Would temperature be uniform throughout the early expanding universe? I ask all this to understand how matter would break apart in the first place and form separate stars or objects. I suppose all things being equal, why didn't everything either clump together in one big mass or its opposite, just continue spreading out so that all space with matter be uniform in density & temperature.

The Answer

Excellent question! In the most simple description of the Big Bang and the creation of the universe, you would expect that quantities like temperature, density, etc. would be constant at all points in the universe at a given time. However, if that were really the case, then the universe would be a perfectly smooth distribution of matter and we wouldn't have galaxies, stars, planets, or astronomers to ask such questions. What we think happened is that the early universe had some small pertubations in density and temperature as a result of quantum mechanics. Quantum mechanics treats physics probabilistically and places limits on things like how uniform a distribution of temperature can be. As the universe expanded, these initially tiny fluctuations gave rise to the structure we see today.

What is really fascinating is that we can see the imprint of these fluctuations on the cosmic microwave background (CMB), a signal that fills our universe and is left over from the time that the universe first became transparent to light, around three hundred and eighty thousand years after the big bang. Detailed maps of the CMB by NASA and others provided strong experimental support of the Big Bang model and have allowed us to better understand the early universe. For more, check out this link

Hope that helps,
-Ira & Bernard
for "Ask an Astrophysicist"

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