Spoiler alert: this article is not about the Occupy Wall Street protests. This is about something far more awe-inspiring, in my opinion: exploding stars, dark energy, cosmic expansion, and the startling fact that all the matter we can see in the universe is only 4% of everything that’s out there!
Last week I attended the CIERA lecture "Dark Energy and the Accelerating Universe," given by Robert Kirshner, Clowes Professor of Science at Harvard University and author of “The Extravagant Universe.” He was the graduate advisor of two of the young men who won the 2011 Nobel Prize in physics for “the discovery of the accelerating expansion of the Universe through observations of distant supernovae.” Wait, what? The universe is accelerating? Supernovae?
Let’s start with the Universe. We live in the Milky Way galaxy (right), just one of over 100 billion galaxies in the Universe. Almost all of the information we gather about the Universe comes in the form of light. Modern telescopes like the Hubble Telescope have allowed us to literally look into the past, viewing light from galaxies that are over 10 billion years old. Remember, the Big Bang happened about 13 billion years ago, so 10 billion years ago is getting pretty close to the beginning of the Universe.
These highly advanced telescopes also allow researchers to observe exploding stars called Type I Supernovae, which emit light equivalent to about 4 billion of our suns combined. All visible light is a spectrum of colors running from red to blue, and light shifts slightly toward red if it is moving away from you, and toward blue if it is moving toward you. This shift in the frequency of a wave depending on the relative motion of the source and the observer is called the Doppler Effect, or Doppler Shift. It also applies to sound waves, causing the pitch of a siren to change depending if the ambulance is moving toward or away from you. When scientists measured light from these supernovae they expected some to be shifted toward red and others toward blue, indicating that some were becoming more distant while others moved toward us. Instead, they found that all of the supernovae were shifted toward red, or moving away from us, proving that the Universe is expanding!
That seems crazy: surely eventually the attraction of matter and energy for all other matter and energy in the universe should pull everything back together. The Nobel Prize winners set out to test just that, expecting to find that the expansion of the universe was slowing down. They measured light from supernovae of varying distances. They expected the supernovae farthest away to display less of the “red shift,” indicating that they are moving away from us more slowly, and the expansion of the Universe is slowing down. Surprisingly, they found that distant supernovae are moving away from us more rapidly than closer supernovae. The expansion of the Universe is not slowing down, but actually accelerating!
And it gets even crazier! This expansion acceleration should not happen, because gravity tends to pull mass together. This implies there must be other matter and energy unknown to us, a kind of anti-gravity working to spread things out, or speed up the expansion of the Universe. These have been named dark matter and dark energy, and we have NO IDEA WHAT THEY ARE! And they make up 96% of the Universe! We only know that they must exist in order to explain our scientific observations. We can see the mass of dark matter in action bending the light from galaxies in the Hubble deep field images (below). Dr. Kirshner explained dark matter and energy much like the wind. We cannot see the wind, but we see the leaves moving, so we know the wind must exist.
And so the scientists have done it again. We have taken something as beautiful as the starry night sky, and turned it into depressing graphs and numbers indicating we are on a course of cosmic expansion destined to spread out into nothingness.
Now, when we look up into the night sky, we know that all humans are just a speck on the Earth in the Milky Way, and all the stars and galaxies and nebula that we can and can’t see are still only a tiny fraction of the whole Universe.
But I have to say, what we can see is a magnificent and breathtaking four percent, and it takes a pretty extraordinary speck to become aware of so much more.