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Yes, for the observations we see in the present universe's physical conditions to be upheld, then the BB must be defined as an isotropic and homogeneous expansion on the largest of scales. It's what we see. The universe can be as lumpy as it likes on smaller scales, which it is, but when you average out the matter-energy density of the universe over it's entire volume, the answer come extremely close to zero. Therefore it is isotropic (everything looks the same no matter where you look) and homogeneous (there's no areas which have any more matter-energy than any of the others).
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