The Expanding Nothingness Part I

11/25 - 12/1
by C. Zaitz

In the late 1980's I learned there was a good possibility that we could know the fate of the Universe. There were three choices, and cosmologists were hard at work narrowing it down to one. We knew the Universe was expanding. In 1929, Edwin Hubble had made that clear by showing us the red shifts of countless galaxies. Red shifts meant they were receding, and the farther away they were, the faster they were going. Hubble deduced this meant that space was expanding.

Armed with this information, cosmologists ran the expansion back like a movie to figure out how it began. That’s where the Big Bang Theory came from. And then they ran it forward to see how it would end. Knowing the fate of the Universe seemed within reach. But the fate of the Universe depended on how much stuff there was in it. If there was a lot of mass, gravity would stop the expansion and bring everything together into a Big Crunch. If there was not enough mass, the Universe would expand forever, growing dark and cold into a Big Freeze. Some thought that one day the Big Bang might come together in a Big Bounce, which was an elegant extension of the Big Crunch, wherein the Universe would oscillate forever.

It turns out that the visible Universe, namely the stars that make up galaxies, has only a small percentage of the mass needed for such a fate. The Universe was too light for a Big Crunch or Bounce, and it looked like we were headed toward the Big Freeze. But this is not a happy ending, so cosmologists looked around the Universe for more mass.

We live in the Milky Way, a spiral galaxy home to hundreds of billions of stars. It looks like a big spinning pinwheel. The Milky Way is spinning so fast that the stars in the arms of the galaxy should have wound up around the center a long time ago, like cotton candy winding around a paper cone. But they didn’t; our Milky Way has spun about 20 times in the past 5 billion years and it still looks as pinwheely as it did as a baby galaxy. This doesn’t make sense with the amount of mass calculated from all the stars. There must be mass that we can’t see. Aha!

Cosmologists call it dark matter, and though it is invisible and nothing like regular matter, it accounts for most of the mass in the Universe. The galaxies are embedded in it, and it shapes spacetime. Its existence has changed how we think about the fate of the Universe. In Greek mythology, the three Fates were Clotho, the spinner of the thread of life, Lachesis who measured the thread of fate, and Atropos, who cut the thread to end a life. As the universe spins out its history, it’s easiest to study the past and present. The thread of information left over from the Big Bang is fairly strong. When we look to Atropos, to the end of the Universe, things have gotten cloudy. The fate of the Universe has become uncertain. As we struggle to understand the nature of dark matter, hopefully the answers will become clearer. But there is another piece to the puzzle, an even more enigmatic discovery: dark energy. To be continued…

Until next week, my friends, enjoy the view.