Ask Dr. SETI ®
by Dan Duda
from the June/July, 2017 issue of Penn Central,
the monthly newsletter of Central PA Mensa,
used by permission
“Science progresses best when observations force us to alter our preconceptions.”
Particle Physics and Cosmology tend to crash into each other now and then. And that causes problems because each has its own science that works extremely well within its own sphere. However, when we try to mix them they’re like oil and water—they just don’t play well together. The two disciplines are currently trying to coordinate theories that could explain some very weird observations in the heavens.
Let’s start with the late Vera Rubin, an American astronomer who pioneered work on galaxy rotation and contributed greatly to the hypothesis of Dark Matter.
In our Solar System, the revolution time of Mercury (closest planet to the Sun) is very fast (88 Earth days). The revolution of Earth, of course, takes one year. And it takes Pluto 248 Earth years to make its way around the Sun. Taken together with all the planets this is called the “Rotation Curve” because it accounts for the action in the entire Solar System.
The reason for this difference in speed is simple, If Mercury revolved any slower solar gravity would pull it into a fiery extinction. And, if Pluto revolved as fast as Mercury or Earth it would overcome the relatively weak solar gravity at that distance and fly right out of the Solar System.
Enter Vera Rubin. She decided to test this universal (or so we thought) rotation curve on galaxies. Like the Solar System, she expected she would find that the farther away from the core of a galaxy a star is situated the slower would be its speed. That would allow gravity to keep it in orbit. However, the world of cosmology was stunned to learn that Vera’s results showed that stars have a relatively constant speed no matter where they’re situated relative to the core. Why aren’t most stars flying off into empty space as the theory of gravity says they should? Why indeed.
Enter Particle Physics. The mystery of the uncooperative Galactic Rotation Curve totally stumped cosmologists. There just isn’t enough matter in galaxies to generate the gravity needed to account for our observations. So, a combi-nation of physicists and cosmologists invented the term “Dark Matter.” Voila! Problem solved. Or maybe not. The word “dark” really means we have no idea what is going on, but we think we need a lot more mass to generate the gravity we think ought to be there so that we can resolve what we see with what we think we know. (Whew! That’s a mouthful.)
But wait, there’s more! The other shock still rattling cosmologists to the core is the stunning discovery that the universe itself is not just expanding, but expanding at an ever-increasing rate of speed. Here again what we think we know about gravity says this isn’t supposed to happen. Can’t cosmologists ever catch a break? They think dark matter is holding galaxies together and dark energy is pushing them apart. But they have absolutely no idea what this “dark” stuff is. It’s an idea that just seems to fit what we see. Greek drama had a term for this type of solution: Deus Ex Machina which means God by Machine. This technique is still used today—when our movie hero is facing the imminent detonation of a bomb a few feet away, he suddenly finds a bomb proof closet that no one knew about. It really looks like the dark substances are science’s technique for saving the hero (in this case our observations).
OK, let’s look at the whole picture. Baryonic matter (that’s the stuff that we think we understand) makes up only 5% of the universe we see. Given our observations and what we think we understand about the universal laws of physics (especially gravity) 95% of the universe is missing. Scientist think that the 95% is dark matter and dark energy. But they (and we) don’t really know.
To quote Vera Rubin, “In a spiral galaxy, the ratio of dark-to-light matter is about a factor of ten. That’s probably a good number for the ratio of our ignorance-to-knowledge. We’re out of kindergarten, but only in about third grade.”
Disclaimer: The opinions expressed in editorials are those of the individual authors, and do not necessarily reflect the position of The SETI League, Inc., its Trustees, officers, Advisory Board, members, donors, or commercial sponsors.
Editor's Note: This editorial is dedicated to the memory of our friend and colleague Vera Cooper Rubin (23 July 1928 - 25 December 2016). Dr. Rubin's academic advisors were a who's who of modern astrophysics: George Gamow, Richard Feynman, Hanse Bethe, and Philip Morrison. Many (including this editor) believe that Rubin's research and discoveries were worthy of a Nobel Prize, one of the few honors she was denied.
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this page last updated 3 June 2017
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