To answer the OP: Asimov was a writer with a PhD in biochemistry, not a cosmologist.
One problem is that not many people understood the equations and consequences of general relativity for a few decades after it was proposed and popular treatments didn't catch up until quite a bit after that. Your book by Asimov is a popular account that, unfortunately, was not up to the best descriptions even of the time the book was written.
Pretty much any serious treatment of the BB past about 1930 would have NOT had a 'cosmic egg'. At best, that is a poor characterization of an idea LeMaitre had, but it is NOT at all in the basic equations for the Big Bang model and never was. The problem is that the equations are KNOWN to break down at some point, and early writers tended to 'start' things with some sort of 'egg'. But even with that, it did NOT explode in any standard sense. The Big Bang has *always* been about the expansion of space with the galaxies 'at rest', at least approximately, in the local expansion.
So what lead to the idea that the BB is NOT an explosion? Well, the equations of general relativity (Einstein's theory of gravity) describe gravity as a curvature of spacetime. The degree of curvature is determined by the density of mass and energy. If we apply these equations to the universe as a whole, and assume a uniform density of mass and energy, we get the expansion of space directly out of the equations. This is where the expansion of space description comes from: directly out of general relativity. Later, thermodynamics and nuclear physics were added to the mix and the 'hot Big bang' model was proposed. This is the one that predicted the background radiation and is the core of modern descriptions.
One problem is that not many people understood the equations and consequences of general relativity for a few decades after it was proposed and popular treatments didn't catch up until quite a bit after that. Your book by Asimov is a popular account that, unfortunately, was not up to the best descriptions even of the time the book was written.
Pretty much any serious treatment of the BB past about 1930 would have NOT had a 'cosmic egg'. At best, that is a poor characterization of an idea LeMaitre had, but it is NOT at all in the basic equations for the Big Bang model and never was. The problem is that the equations are KNOWN to break down at some point, and early writers tended to 'start' things with some sort of 'egg'. But even with that, it did NOT explode in any standard sense. The Big Bang has *always* been about the expansion of space with the galaxies 'at rest', at least approximately, in the local expansion.
So what lead to the idea that the BB is NOT an explosion? Well, the equations of general relativity (Einstein's theory of gravity) describe gravity as a curvature of spacetime. The degree of curvature is determined by the density of mass and energy. If we apply these equations to the universe as a whole, and assume a uniform density of mass and energy, we get the expansion of space directly out of the equations. This is where the expansion of space description comes from: directly out of general relativity. Later, thermodynamics and nuclear physics were added to the mix and the 'hot Big bang' model was proposed. This is the one that predicted the background radiation and is the core of modern descriptions.
