space expansion (almost) explained...

It is somehow evident that any cosmological model must end up with the reality that we are observing around us right now.

So, if we begin to tell the history of the Universe backwards, we can safely begin with our today's observations.

Observation (and Theory) tells us that the Universe is expanding.

But not everywhere: expansion takes place between galaxy clusters because galaxy clusters themselves are gravitationally bound. There is no expansion between galaxies, nor between stars in galaxies.

Only between galaxy clusters.

So, going backward in time, there must have been a moment when galaxy clusters were closer than what they are today. Maybe a moment of the Universe's history when all galaxy clusters were all gravitationally bound alltogether.

And going further backward, what's the next step?

I mean, did expansion penetrate into the galaxy clusters?

Edited November 7, 201213 yr by michel123456