Questions about Physics, Biology and perspective

[Alex K]

Yes, when you do the math of the Standard model living in an expanding universe, you have to make a choice. Either your stick the change of scale which you get from the Friedman equations into the coordinates, which gives you the usual expansion picture, or you absorb it into the fields, forces and masses, which gives you shrinking matter
The latter is much more complicated mathematically, but should be physically equivalent.

As far as I see it, it's a matter of convention without observable differences.

It seems to me there would be at least one important difference: the view on the Big Bang Theory.  If you virtually reverse time, even if you scale all matter to an arbitrarily large size, causing overlap, you'd never arrive at a singularity, since that would require an infinitely large scale.

The past singularity (which is an artifact of using classical theory, but let's run with it for now) would manifest in the masses going to zero and matter and everything tending to grow to infinite size. There would be a singularity in the time coordinate though, I believe. The fact that space isn't "vanishing" in this picture would already tell you that the naive picture of a singularity is not to be trusted - it is an artifact of the maths at a point where the theory is invalid.

The point of the singularity is not so important for Big Bang theory, because we don't have a theory there - all that goes under the name of Big Bang theory and is of a scientific nature, concerns itself with times after the singularity. The thing with the singularity should never have been brought up, there likely is none and we don't know the physics back then.