I’m Not talking about coronavirus. Not talking about conspiracy theories that are a constant presence…you know, comet Z, asteroid A, or heaven forbid, planet Nibiru might threaten life on Earth. Because even if they don’t hit us, they are poisonous or will cause some extreme disruption of our planet as it zips past. And of course, the government knows about it and is taking steps to save itself and let the rest of us suffer.
No, I’m talking about the expansion of our universe.
From the get-go (Big Bang) our universe has been puffing out like someone blowing a balloon that just won’t fill. Just keeps getting bigger and bigger. Will it ever end? The expansion, that is.
A few astronomers in the early 20th century noted something peculiar about galaxy motion. Their measurements showed galaxies appear to be moving away from us, also called redshifted. At that time, we didn’t know galaxies were like the Milky Way, island universes so the importance of this was not appreciated. Galaxies were thought to be nebulae within the Milky Way and the Milky Way was our universe.
In 1929 Edwin Hubble confirmed the results of those astronomers, Silpher, Friedmann, and Lemaitre and discovered that galaxies are like the Milky Way, each with billions of stars. Our universe got way bigger. This discovery led to his hypothesis of the universe’s expansion. For many years, cosmologists (physicists/astronomers who look at the big picture of how our universe works) thought the expansion would slow and one day stop due to gravitational forces. After a period of no expansion, gravity would then draw everything back, faster and faster until the entire universe collapses into a singularity. Then, maybe, start all over. Well, that idea went into the trashcan when cosmologists realized the expansion was accelerating. Based on gravity theory the expansion should be slowing. Back to the chalkboard.
Hubble had developed a value for the universe’s expansion rate, we now call the Hubble Constant. His value was 500 km/s/Mpc (500 kilometers per second per mega parsec). Many attempts have been made to refine that figure and the best thing discovered was that Hubble made a big error. His value was nearly 10 times too large due to the error, but recent measurements have also stirred the pot of uncertainty with a mixed bag of results. One group determined a value of 67 km/s/Mpc, and another group 73 km/s/Mpc. Even at the closest ends of their margins of error they do not agree. Something’s amiss.
Well, we do know our universe is expanding, and the expansion is accelerating. Will it stop? Right now, it does not seem so. Maybe it will just rip apart in a trillion years! What would that be like?
Oh, how can a continuously changing value be a constant?