The universe around us is not what it appears to be. The stars make up less than 1 percent of its mass; all the loose gas and other forms of ordinary matter, less than 5 percent. The motions of this visible material reveal that it is mere flotsam on an unseen sea of unknown material.
We know little about that sea. The terms we use to describe its components, “dark matter” and “dark energy,” serve mainly as expressions of our ignorance.
David Cline, professor of Physics and Astrophysics at UCLA
A Bracing Look at the Unseen Universe
Back in the 1920s, Edwin Hubble laid the groundwork for an expanding universe. Hubble used the period/luminosity relation in Cepheid variables (this was Henrietta Swan Leavitt’s work) to find the distances to nearby galaxies. He took the redshift for those galaxies as equivalent to their velocities.
Panek explains how he graphed the distances he found against the galactic velocities, concluding they were directly proportional to each other. The relation seemed straightforward: The greater the distance, the greater the velocity. That was a relationship, one-to-one, that you could plot on a graph as a straight line on a 45-degree angle. Assume a constant rate of expansion and the straight line would continue no matter how far you looked.
But of course we also know that the universe is full of matter, and that matter attracts other matter by virtue of gravity. So it’s perfectly understandable to think that the expansion of the universe should be slowing, and the question becomes, what is the density of matter, and can we, by showing how fast the expansion is slowing, see what lies ahead for the cosmos? Can we push that straight line graph until it bends by using distant supernovae as our standard candles?
These are sound questions, but the scientists studying them had no reason to believe that by 1998, they would have changed our view of the cosmos. It was a breakthrough the likes of which astronomy has rarely seen, with two teams of passionate, committed scientists — working with their own agendas, each battling feverishly to get their work out ahead of the other guys — coming to the same startling conclusion. The straight line on the graph was bending the wrong way, and that meant the expansion wasn’t slowing. Type 1a supernovae at great distances were dimmer than they ought to be at their particular redshift, and thus further away than our theories said. The expansion of the universe was, in fact, speeding up.
And what do you do when you run into a result like that? Panek excels in following up the question, and if you ever wanted to see science at the level of everyday head-banging research, theories butting against each other, observations failing at critical, hair-pulling moments only to be replaced by serendipitous discoveries, this is the book for you. It says something that two combative teams working with mostly independent data sets and relying on different methods of analysis arrived at a conclusion that neither team had expected. Yet this is precisely what the High-z Supernova team and the Supernova Cosmology Project proceeded to do in 1998.
The Dark Energy Follow-Up
Re dark energy, the answer to the question of what to do next is, you set out to prove the effect doesn’t exist. Two possibilities immediately surfaced, the first being a new kind of dust. Astronomers already know how to correct for the dust within galaxies that makes light from them redder, but perhaps there was a different kind of dust — call it ‘gray dust,’ even if no one has a clue what it is — and posit that it exists between the galaxies. Or consider another possibility: Maybe Type 1a supernovae in the early universe were intrinsically fainter. Perhaps the supernova process was slightly different then, creating astronomical events that make us think they were more distant, when we are actually looking at a slightly different kind of object.
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