Actually, the CMB affirmed the Big Bang scenario implied by Friedmann-LemaƮtre's solution to Einstein's field equations.
Recall that before the unvarnished ramifications of Einstein's theory of general relativity (1915) were disclosed, most scientists held that the universe was infinitely static (or stationary), i.e., temporarily and spatially infinite, and neither expanding nor contracting. However, Einstein proposed a static universe that was temporarily infinite and spatially finite in 1917 when he applied the field equations of general relativity to cosmology. Ironically, he added a positive cosmological constant to the calculi of the spacetime metric tensor as his preferred cosmology would otherwise collapse or expand forever. In 1922, Alexander Friedmann was the first to take the field equations of general relativity at face value cosmologically and in 1924 published an exact solution giving a homogeneous, isotropic and expanding universe. See "About the possibility of a world with constant negative curvature."
In 1927, Georges LemaƮtre independently derived the same solution as Friedmann and posited that the galactic recession first observed by the astronomer Vesto Slipher is explained by an expanding universe. (Slipher discovered the Doppler effects of redshift in 1912 before Einstein posited his revolutionary theory of gravity, so he never made the connection and assumed spiral nebulae were moving within the fixed background of space.) Accordingly, LemaƮtre was actually the first to posit the essence of Hubble's law: galaxies are receding in every direction at velocities directly proportional to their distance from each other; i.e., the greater the distance between any two galaxies, the greater their relative speed of separation. In other words, these galaxies are not moving away from one another under their own steam within the fixed background of space; they're moving away from one another as the fabric of space itself expands. LemaƮtre also made the first estimation of the rate of expansion, which is known today as the Hubble constant. Finally, he posited what became known as the Big Bang theory, what he called "the hypothesis of the primƦval atom", which he elaborated on in 1931:
https://www.nature.com/articles/127706b0.
However, like Friedmann's paper, LemaƮtre's "A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae" of 1927 was published in an obscure journal. It was translated into English in 1931 and republished by the Royal Astronomical Society, but in 1929 Edwin Hubble published his paper on the velocity-distance relation with a more precise constant for the rate of expansion: "A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae". Notwithstanding, Hubble used virtually the same input data as that previously used by LemaƮtre, and, once again, LemaƮtre was the first to unequivocally attribute the pertinent astronomical observations to the expanding universe described by the field equations of general relativity!
LemaĆ®tre got his due in 1931 for connecting galactic recession directly to an expanding universe per the pertinent calculi of general relativity, and the velocity-distance relation is sometimes more properly referred to as Hubble-LemaĆ®tre's law in the literature. (LemaĆ®tre struck his estimation of the expansion rate from his translated paper in deference to Hubble's more accurate calculations.) The myth that Hubble was the first to discover that the universe is expanding persists because Hubble's 1929 calculi for the rate of expansion were more accurate and because his and Milton Humason's follow-up paper "The Velocity-Distance Relation among Extra-Galactic Nebulae" (1931) provided an even more decisively comprehensive observational foundation for an expanding universe, which put the matter beyond all reasonable doubt. What Einstein's relativity theories were to physics, LemaĆ®tre and Hubble's discovery was to cosmologyāa seismic event. Finally, in this wise, physicists Howard Robertson and Arthur Walker working together but independently of Friedmann and LemaĆ®tre, derived a variant of Friedmann's solution in 1934. Hence, the classic solution of the Einstein field equations giving a dynamically homogeneous and isotropic universe is referred to as the FriedmannāLemaĆ®treāRobertsonāWalker (FLRW) space-time metric (or the standard model of modern cosmology). In the face of the findings of Hubble-Humason of 1931, Einstein finally accepted that the universe was expanding, of course, but rejected LemaĆ®tre's apparent beginning.
Einstein and others briefly considered the possibility of an oscillatory/cyclic universe predicated on the notion that the universe would expand for a period of time before the gravitational attraction of matter caused it to collapse, but then Richard C. Tolman showed in 1934 that entropy would only increase with each cycle. (Beginning in the later 1960s, the oscillatory/cyclic scenario was revived and has since been variously tweaked by the theoretical mechanisms of some form of quantum or inflationary theory, but as we have seen thus far to no avail in terms of past-eternality.) In the meantime, the Big Bang theory's main rival was the Steady State theory, which also depicted a homogeneous, isotropic and expanding universe. However, it is said to be past-eternally expanding everywhere as matter is continuously created via the intrinsic energy of space. Thus, while the amount of matter increases over time, the density of matter is everywhere constant.
Friedmann's solution is equally compatible with both the Big Bang and Steady State theories, but the later has always been held by many to be a faux alternative in terms of origin given that it implies, not a past-eternally expanding universe at all, but a universe with an even more decisive beginning than that depicted by the former. As extrapolated backwards, the Big Bang model implies either "a primƦval atom of maximum compaction" or an initial point of zero volume and infinite density, while the Steady State model implies an initial point of zero volume
and density. In other words, the Steady State model is not so much a paradox as a scenario that implies the opposite of what it asserts. It was assumed that some future discovery would somehow resolve this apparent contradiction. This was thought to be necessarily so because the absolute beginning implied by the Big Bang violated the perfect cosmological principle, which states that the spatial distribution of matter in the universe is homogeneously and isotropically changeless when viewed on a large scale. While the long-held principle is arguably consistent with a static universe, imposing it on an expanding universe is utterly arbitrary. Hence, the key distinction between them: Big Bang theory predicts an evolving universe that is homogeneous and isotropic in the sense that matter density is uniformly changing, while Steady State theory predicts a changeless universe that is homogeneous and isotropic in the sense that matter density is uniformly constant.
Einstein briefly regarded a steady state scenario of his own in 1931. Long before the discovery of the CMB in 1964 and its increasingly detailed analyses drove the final nail into its coffin, he insightfully understood then what would become increasingly obvious over the next few decades from astronomical observations in general: the Steady State model is an arbitrary contrivance and entails an improbable degree of ad hoc fine-tuning. As for the decades of astronomical observations prior to the discovery of the CMB, the universe was definitely observed to have undergone evolutionary material change in the past.
While virtually all of the predictions of an expanding universe with a beginning in the finite past were affirmed over the next few decadesāincluding the prediction regarding the existence of the CMB itself!āit became apparent that an arbitrary "explosion" of energy and matter was not entirely compatible with the observed conditions of the CMB. As discussed in the above, these discrepancies were resolved by inflationary theory beginning in 1980 ("The Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems", Alan H. Guth), whereby the epoch of the Big Bang state, as discussed in the above, is actually a big conversion of energy following the epoch of rapid, exponential inflation of space itself:
http://tucana.astro.physik.uni-potsdam.de/~cfech/lectures/galkos/guth1981.pdf.
Alexei Starobinsky, Andreas Albrecht and Andrei Linde further developed the theory of cosmic inflation in the early 1980s. They resolved the "unacceptable consequences" for which "modifications must be sought" by elaborating on the microscopic inflationary region of Guth's scenario. They posited a coherent, natural mechanism for cosmic inflation and the metric expansion of space, specifically, a causal and regulatory scalar field which permeates the universe. This eliminated the reliance on the percolation of a large number of small bubbles to end the inflationary epoch so that the Big Bang epoch could begin. In Guth's scenario, inflation tunnels out of a false vacuum state, which happily sets up the condition that naturally leads to the percolation of the bubbles. Alas, while this condition and the bubbles thereof would solve the transitional problem, it's incompatible with the condition that would solve two of the three cosmic problems. Guth showed that inflation solved the transitional problem and, if he suppressed the condition that facilitated this, the cosmic problems. Hence, inflation was key, but his quantum-tunneling mechanism was either incomplete or entirely wrong. On the Starobinsky-Albrecht-Linde scenario coupled with the quantum fluctuations in the underlying field of space: inflation smoothly ensues via a "slow roll" of a scalar field along a relatively flat potential, which gradually increases, ends exponential inflation, ignites the transitional epoch of the Big Bang and resolves all three of the cosmic problems, including the magnetic monopole problem, in one stroke. Despite the guff of its occasional detractors, inflationary theory has not only held up against numerous challenges over the years, but has been strengthened by the proofs for several, likely scalar fields. This fact was recently underscored again by Mishra-Sahni-Toporensky (2018):
https://arxiv.org/pdf/1801.04948.pdf.
Cosmological evolution from the Big Bang doesn't necessarily imply biological evolution at all, and while none of this necessarily proves that our spacetime is the first and only to have ever existed, all of the evidence tells us that
spacetime most certainly began to exist in the finite past. Also, LemaƮtre's cosmogony was already known as the Big Bang before the discovery of the CMB, and, as I pointed out in the above, actually predicted it's discovery. I don't know what
theology is, but I do know that he, like me, believes that the cosmos was created
nothing.
strikes me as a pantheist of the Hindu tradition, though, I might be wrong about that. But he does hold to the Hindu notion of an eternally cycling cosmogony.
