From the diagram it appears that before inflation there was regular spacetime, however small. But that makes no sense to me at all.
From the article which I cited:
The red line in the figure on the left shows that according to Big Bang theory, the Universe had a radius of more than 10^-10 metres at 10^-45 seconds after the Big Bang.
Since the speed of light travels at 3×10^8 m/s, information could only have travelled ~3×10^-37 metres during this time.
Big Bang theory therefore makes it impossible for the whole Universe to have equalised its temperature at these early times, as not all the Universe was in communication.
But the evidence shows that it did expand at greater than 3×10^8 m/s, and that its radius did expand to more than 10^-10 metres equalizing its temprature. I submit this is an indication that before the BB spacetime and its restrictive nature did not exist and universal constants, i.e SOL had no influence for that incredibly small amount of time. Don’t we view quantum as the limiting factor in SOL. But what if the universe exploded in a single mega quantum event, a single universal quanta equalling the limits of inflation, after which the SOL became relevant, and accounts for the subsequent stabilization of expansion.
That is the horizon problem, i.e. we cannot receive information beyond the horizon.
The next problem is the flatness problem
Yes that is our problem, but otoh also an indication that perhaps a different condition existed which prevents us from seeing. We used to think the earth was flat also until we discovered that we could not see the end of it because it was round. Why could such a spatial horizon not exist for the universe.
A flat Universe is one in which the amount of matter present is just sufficient to halt its expansion, but insufficient to re-collapse it. This would represent a very fine balancing act indeed! Imagine the surprise of astronomers to find that, as near as we can tell, the Universe has exactly the required density of matter to be flat. This seems like a truly remarkable coincidence and has become known as the ‘flatness problem’.
A rolled up carpet is still flat and has communication throughout, even when you unroll it very quickly.
Inflation was introduced to resolve both the horizon and flatness problems wrt BB theory.
Perhaps a brilliant insight in the face of convention? And there is some evidence, isn’t there. In fact a violent event is the only evidence we have of a creative process.
But is it not also amazing that the rings around Saturn are flat and have the precise required density to be flat.?
IMO, universal space and time (spacetime) began with inflation of the BB. Before then there was no time or even spatial dimension, other than a single instant of an infinitely small singularity exploding in a single mega quantum event (the creation and beginning of the universe), allowing expansion at FTL, while retaining communication (entanglement?), until the created spacetime as we know it began to order itself in accordance with universal constants (the beginning of spacetime).
A causal singularity at the BB is highly problematic. From the wiki
The classical version of the Big Bang cosmological model of the universe contains a causal singularity at the start of time (t=0), where all time-like geodesics have no extensions into the past. Extrapolating backward to this hypothetical time 0 results in a universe of size 0 in all spatial dimensions, infinite density, infinite temperature, and infinite space-time curvature.
It is incredible that at the start of time, a universe of size 0 spatially with infinite density, temperature and space-time curvature can exist at all.
But is it not equally incredible that an infinitely large universe with an infinitely small density, infinitely cold, and flat could create any expansion and contraction at all? And then not with an orderly gradual (predictable) “breathing” pattern (shades of god), but with great violence and chaos. How can that happen?
There has to be causality and it obviously must be different from our current knowledge. In the end all our theories seem to fail in one or more areas.
Perhaps an infinite large universe could suddenly collapse and create a BB, but that still requires great intial localized force, which does not yet exist at that moment.
However the concept of a zero point (infinitely small) having an infinite density (compression], temperature and inward curvature, begs for a BB and would confirm all we do know of the universe so far. The unrolling of the universal carpet, stretching the fabric flatter and flatter.
I know I am naive, but when/where the universe itself is infinitely smaller than a photon, the concept of a single mega quantum “inflation” at FTL seems to be the simplest and most direct explanation and could be the least of our problems. Drop a rolled up carpet and there is an immediate instantaneous area of flatness of the carpet at one end (inflation), before the carpet continues its unrolling at a more leaisurely pace (expansion @ SOL). In the case of BB, this unrolling starts at the center (the area of inflation) and unrolls @ SOL all directions, curved until stretched flat.