Not a constant: The Hubble "constant" changes over time
Big Think -

In all of physics, some of the most important properties inherent to the Universe itself are constants of nature. The speed of light in a vacuum, the strength of the gravitational force between two masses, and the constant inherent to the quantum nature of the Universe, Planck’s constant, are all examples of fundamental parameters that never change, regardless of circumstances. But it’s also plausible that some of the so-called constants aren’t exactly constant, but vary either across space or...

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