Hubble constant, despite what its name suggests, has been shown to not be a constant already, we know it's increasing.
Dark matter is 99.9% a certainty, we observe it's consequences and interactions. We only need to experience it first hand to say it's real, that's called being prudent.
We can actually explain lots of constants in physics.
MisterLupov t1_j1di9mu wrote
Reply to comment by pete_68 in Can we truly know the age of the universe? by Geodad478
It is not "just theoretical"
Hubble constant, despite what its name suggests, has been shown to not be a constant already, we know it's increasing. Dark matter is 99.9% a certainty, we observe it's consequences and interactions. We only need to experience it first hand to say it's real, that's called being prudent. We can actually explain lots of constants in physics.