Why do we need inflation to explain the homogeneity of CMB?

Can't we simply assume that the initial condition for the universe is perfectly spherically symmetric, and the problem is solved? In other words, can't we make the CMB homogeneous just by imposing homogeneous initial conditions? The fluctuations can be explained by quantum effects. Of course there are other things such as the flatness problem which seem to be quite naturally explained by inflation, but I never feel sure about the homogeneity problem. After all, we know very little about how the big bang happened, and we can't rule out any particular kind of initial conditions, such as a homogeneous one.
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 Quote by Chronos Inflation nicely explains why the CMB almost perfectly homogenous in every direction. That is one of its more appealing features.
Inflation in turn only begs the question as to why the expansion was uniform.

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Why do we need inflation to explain the homogeneity of CMB?

 Quote by friend Inflation in turn only begs the question as to why the expansion was uniform.
Uniform expansion follows from the requirement that the field driving inflation be uniform in space across the initial inflationary patch. Why do you suggest that the expansion should not have been uniform?

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 Quote by petergreat After all, we know very little about how the big bang happened, and we can't rule out any particular kind of initial conditions, such as a homogeneous one.
I think this is precisely the point. Sure, the initial conditions could have been perfectly homogeneous. There is nothing that forbids this in principle. But, as you say, the IC's could have been inhomogeneous as well. In fact, there are lots more ways of not being homogeneous than there are of being homogeneous. So, given a generic initial state, one would not expect it to be perfectly homogeneous. By just putting such a condition in 'by hand' is considered by many to be a serious fine tuning of initial conditions. Inflation is preferred in this case because, while one still needs a sufficiently homogeneous region of spacetime in order to get inflation started, the region across which we demand such homogeneity is smaller than today's currently observable universe.

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 Quote by bapowell Uniform expansion follows from the requirement that the field driving inflation be uniform in space across the initial inflationary patch. Why do you suggest that the expansion should not have been uniform?
If you're going to suppose that fields can be uniform as the universe grows to astronomical dimensions, then we could just as easily suppose that the matter fields were uniform with a larger universe as well. I fail to see the difference.

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