Lambda, No longer on the Lam?

Lambda (Λ) came into use by Albert Einstein in 1917. His General Relativity equations described a dynamic universe, an expanding universe, and, well, that didn’t fit his notion of a static universe. His theory of Relativity was a theory of gravity, building on and refining Sir Issac Newton’s equations. And gravity supposedly ruled the universe. Oh, our universe at that time was just the Milky Way galaxy and gravity seemed to rule on that scale.  Einstein inserted Lambda to compensate for this strange, anti-gravity force.

Lambda, aka the Cosmological Constant, kept our universe, and Einstein’s convictions, together until Vesto Slipher, Edwin Hubble, Georges Lemaitre, Alexander Friedmann, and Knut Lundmark shook things up. This group of unrelated physicists provided observational data and solved some of Einstein’s field equations. Something was afoot.

Vesto’s, Hubble’s, Lemaitre’s, Friedmann’s, and Lundmark’s work made it clear that our universe was way bigger than believed…and expanding! Philosophically, Einstein didn’t like the concept of an expanding universe, but he couldn’t ignore the data. So much for beliefs. Even the smartest ones get fooled occasionally.

So, Einstein dropped lambda and moved on, calling lambda his “biggest blunder”. That was that for decades…until…

Two astrophysicists walk into a bar. One says “I’m bored”. The other says “let’s solve the fate of the universe”.

It wasn’t quite like that, but in 1994 it seems the wheels started turning for two groups of scientists. What was the excitement about? They felt the need to figure out if our universe will just expand forever, expand violently and destroy spacetime, or, as had been once thought, expand to a point, then gravity takes over and we come crashing back into singularity. After all, dark energy had just been elevated to a significant influence within our universe. This was good stuff to study even if we didn’t/don’t know what dark energy is.

For several years the investigators toiled independently, trying to get a handle on the expansion rate. They used data collected from type Ia supernovae and the Baryon (subatomic particles) Acoustic Oscillations (BAO) within the Cosmic Microwave Background. If that’s a bit too pithy for you, it’s too pithy for me too.

The big takeaway from this hard work is that our universe’s expansion rate seems to be non-stable. Right now the expansion rate is accelerating, but in the distant past (>5billion years) it appears to have been decelerating. Is that a red herring or something important? Maybe it partially explains why the two very precise measurement tools (supernovae and BAO) disagree on the rate of expansion.

So, until scientists get a handle on the expansion acceleration rate we are stuck with, you guessed it, Einstein’s Cosmological Constant – an estimate, a place filler. We’re getting there but we still don’t know what dark energy is. Figuring that out will help…a lot!

What’s in the Sky?

January 13: Bob Keyser Astronomy Night at Tye Preston Memorial Library 6pm, including a dedication of the Keyser-Stevens telescope and other astronomical gear.

January 13; 45 minutes after sunset; southwest: A waxing crescent Moon hangs below Saturn in the evening sky