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When Edwin Hubble decided to study spiral nebulas in the 1920s, he had no idea that he was about to launch the new science of cosmology--the study of the properties of the universe itself. But the unexpectedly rapid recession of most of those enigmatic objects led to a new concept and a new word to describe them: an expanding universe full of galaxies.
When Vera Rubin and William Kent Ford, Jr., decided to study the rotation of galaxies in the 1970s, they had no idea that they were about to launch a revolution in cosmology. But the unexpectedly rapid rotation of galactic outer stars led to a new concept and a new word to explain it: the high-speed rotation would tear the galaxies apart unless their mass was several times as much as that of all the visible stars combined. This missing mass was soon called dark matter.
And in the last decade of the twentieth century, when two competing teams of researchers began analyzing the light of distant supernovae to measure how much gravity was slowing the universe's expansion rate, they had no idea that they were about to produce not just a revolution but an entirely new cosmology.
In 1998, writes Richard Panek in The 4% Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality, both groups discovered that a shared key assumption was wrong.
The expansion wasn't slowing. The universe the two teams observed wasn't one where distant type Ia supernovae were brighter than they should be at this particular redshift or that particular redshift, and therefore nearer. It was one where they were dimmer, and therefore farther. It wasn't a universe that was doing what an expanding universe full of matter acting under the influence of mutual gravitational attraction should be doing. It was doing the opposite.
The expansion of the universe was speeding up.
Scientists soon described the source of this anti-gravitational effect as a "dark energy" that pervaded all of space. Using Einstein's famous equation E=mc2 to compute an equivalent mass, they concluded that the universe contained about three times as much dark energy as matter (dark or otherwise).
That, in brief, describes the scientific pathway to a modern cosmology that is far from a solved problem. The latest estimates, writes Panek, describe a universe "consisting of 72.8 percent dark energy, 22.7 percent dark matter, and 4.56 percent baryonic matter (the stuff of us)--an exquisitely precise accounting of the depth of our ignorance."
And that ignorance is deep indeed. No one knows for certain what dark matter and dark energy are, though fascinating hypotheses-- highly-educated guesses about unresolved questions--abound.
Panek describes the science in accessible language. Non-specialist readers will be able to grasp the significance of key cosmological measurements: the Hubble constant describing the present rate of expansion and the cosmological constant, a term introduced into Einstein's general theory of relativity to allow for a static universe, then deemed unnecessary after Hubble's great discovery, then reintroduced in the present century as one of the most likely explanations for dark energy.
He weaves that science into a compelling narrative of a quest full of technological challenges, unexpected turns, and expected human rivalries over high stakes including perhaps a future Nobel Prize.
Jealousy and arguments over scientific precedence are indeed part of almost every great scientific discovery, but Panek is occasionally guilty of focusing too much on the squabbling and not enough on the scientific breakthroughs. That is especially true for most of the three chapters of Part II ("Getting in the Game," "Staying in the Game," and "The Game") where readers may feel as if they tuned into the Discovery Channel and found a soap opera instead.
Because that overstated drama comes relatively early, a few readers may even be tempted to set the book aside. Doing so would be a mistake. The 4% Universe offers at least 80% scientific adventure and intellectual stimulation, enough even for those who would never watch the soaps.