PhilKravitz said:
Explosion is not that bad a phrase. The universe at some time close to t=0 is small and hot as time goes on it is big and cooler just like the plasma of a chemical explosion.
This seems at least somewhat reasonable, assuming that our universe is spatially and temporally finite. It could, presumably, be modeled as an expanding wave shell in some preexisting medium with the wavefront determining its spatial extent, a finite kinetic energy (imparted via initial disturbance and decreasing with time evolution) powering the expansion (accounting for 'dark energy'), with periodic anomalous accelerations/decelerations determined by topological irregularities in the preexisting medium. The original extent of our universe in such a picture would necessarily be smaller than it's current, and ultimate, extent, but it could involve all points in, say, a 10 or 100 or 1000 light year diameter volume (assuming, for simplicity, at least a roughly spherical original shape and evolution).
But I don't know if this sort of picture is compatible with current mainstream cosmological models, and since the OP seems to be referring to the relationship between current mainstream models and the term 'big bang', and insofar as the terms 'big bang', as referring to an explosive initial event, and, therefore, 'explosion' are incompatible with current mainstream models, then the answers generally given here at PF wrt questions akin to "Big Bang, explosion or what?" would seem to be correct.
Dmitry67 said:
... if Universe is infinite now (very likely), it was infinite at any time. It never was 'small'.
Ok, except for the "very likely" part, but I don't think PhilKravitz was assuming that our universe is, in any sense, infinite.
In another thread you stated:
Dmitry67 said:
Observational data proves that universe is the same in any direction. No center, no edges.
Maybe that's what's generally inferred from the current mainstream models. Observational data, afaik, indicates only that there's an observational boundary. As for no center, well, that would depend on how things are modeled.
The fact that our universe appears roughly the same in all directions doesn't, by itself, rule out the notion that it might be an expanding disturbance in a preexisting medium. In which case it would have 'edges', and there would be some volume within its boundary corresponding to its center.
In that other thread ("Why was the big bang not an explosion?") you also stated, as requirements for an 'explosion':
Dmitry67 said:
1. Pre-existing space/time (before the explosion).
2. High pressure at the center and empty space around
3. Pressure accelerated matter outside.
All that is not correct for the BB.
I'll have to take your word for it that the term 'big bang' (and the 'explosion' that that term would seem to imply) doesn't really apply to current mainstream cosmological models. It's just a misnomer -- one of many in the popularization of physics.
Of course, the possibility remains that those models are wrong in some way or other. It doesn't seem unreasonable to suppose that GR is a simplification of a more fundamental wave mechanics (with much of this wave activity being undetectable via our senses, and, to large extent, via the instruments that we employ to augment our senses), that our universe might be an expanding disturbance in a preexisting medium, that the more or less isotropic expansion is powered by energy imparted via an initial disturbance (a 'big bang' as it were), that the dominant force is therefore the expansion, and that the archetypal wave dynamic, evident wrt all particulate media at all scales, is the dynamic of the boundary of our universe.
And while that view might also be wrong, it does solve a lot of 'conceptual' problems that the current mainstream views don't, with the added plus for, say, PF that it might reduce the number of threads asking whether the origin of the universe was an explosion of sorts (because, in that view, it actually would be an explosion, of sorts). Of course, if a model based on that sort of conceptual approach is ever developed and accepted into the mainstream, then it would probably not be called a 'big bang' model -- thereby increasing the confusion associated with this topic (and, along with that, the number of 'big bang and explosion' threads at PF).
