Sorry, Astronomy Fans, The Hubble Constant Isn’t A Constant At All
“The fact that the Hubble expansion rate of the Universe changes over time teaches us that the expanding Universe isn’t a constant phenomenon. In fact, by measuring how that rate changes over time, we can learn what our Universe is made from: this was exactly how dark energy was first discovered.
But the “Hubble constant” itself is a misnomer. It has a value today that’s the same everywhere in the Universe, making it a constant in space, but it’s not a constant in time. In fact, so long as matter remains in our Universe, it will never become a constant, as increasing the volume will always make the density (and, a la Friedmann, the expansion rate) decrease. Perhaps it’s time to call it by its more accurate but rarely used name: the Hubble parameter. As it changes with time, it continues to reveal the very nature of our expanding Universe.”
Have you heard about the recent controversy over the Hubble constant? That some astronomers are arguing for a lower value while others are arguing for a higher value? Although that puzzle does present a legitimate conundrum, a very real issue is that this “constant” isn’t a constant at all, because it changes over time as the Universe expands!
I’d much prefer it to be called the Hubble parameter (and that its present value be called the Hubble parameter today), and that we relegate “Hubble constant” to where it belongs: the dustbin of history.