That's not quite right - the quark-gluon plasma that formed after about a millionth of a second was very much a fluid - it behaved as a nearly frictionless liquid.The Big Bang was neither big nor a bang. It started from a tiny singularity and there was no fluid in existence to carry sound.![]()
Also, the singularity is just the point where general relativity breaks down, it just means we can't say what there was or what was happening at that point, and a measure of size is only relevant with respect to our observable universe, which is a small part of the whole (the default assumption is that the universe is spatially infinite, and was at the big bang). It was not an expansion of a point in space, but an expansion of all space, which may have been infinitely large. Singularities are points in time, not points in space.
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