Cosmology's sole "rate of expansion" is declining

[PeterDonis]

I thought, ∞ (infinite) is undefined. Isn't that a problem?

$\infty$ is just being used as a handy label in this case; the physical meaning is "the value that the Hubble constant approaches in the very far future".

 

[timmdeeg]

I'd rather say that accelerated expansion means the universe is approaching exponential expansion.
Here's the plot:
View attachment 91581

Thanks. The inflection point of the a-curve separates deceleration and acceleration. In case inflation is included the H-curve also should show an inflection point. But how would you describe its physical meaning? I don't see any.

I think that accelerated expansion means that the second derivative of the scale factor is positive, which includes exponential expansion.

 

[Pizza]

Thank you, Peter!