Wednesday, February 2, 2011
The 4-Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality, by Richard Panek--Book Review
This a highly readable history of the transformation of cosmology from metaphysics to physics, from philosophy and speculation to hard science, and in the process, the discovery of most of the universe.
Historically, astronomy and physics didn't have a great deal to do with each other. Astronomers studied the stars by observation, very patient and detailed observation and record-keeping. Theoretical physicists theorized and calculated, and experimental physicists experimented, and they fed each other's work, very occasionally coming up with something, most notably gravity, that made a real difference to astronomy. Then Einstein gave us general relativity, and began a century of ever-deeper entanglement of physics and astronomy, and the transformation of cosmology--the study of the nature and origins of the entire universe--from something utterly beyond the scope of physics into its core. The questions of how big the universe is, whether it is eternal in space and time or had a beginning and might have an end, became real questions.
Edwin Hubble, early in the century, discovered that the universe is expanding, but also that there are other galaxies beyond our own, and that they're all moving away from us. This was a major, exciting, and initially controversial change in our conception of the universe. In the 1960s, Vera Rubin, looking for a research project she could do within the constraints of raising two young children, studied other astronomers' observations and discovered that the galaxies were rotating as well as moving away from us. Also in the mid-1960s, Robert Dicke, Jim Peebles, and a small group of theoretical physicists had a prediction for which they had no supporting data: If the Big Bang theory of the history of the universe were correct, there should be low-level cosmic microwave radiation, at a temperature of about 3 degrees Kelvin. Then two astronomers at Bell Labs, Arno Penzias and Robert Wilson, had data for which they had no explanation: While trying to calibrate the Bell Labs' Crawford Hill antenna to study radio waves from the fringes of the Milky Way, they found they had a tiny background hiss which no amount of calibration would eliminate. They'd found the background cosmic radiation, echo of the Big Bang.
That's one small step along the way, from Einstein to the discovery that most of our universe is invisible. As the back and forth played out between the theoretical physicists and the experimental and observational scientists, increasingly astronomers, each theoretical question drew forth an observation, a find, a discovery that answered that question, and raised another. The most startling of these was the discovery that visible, directly detectable matter is just over 4% of the total make-up of a universe far larger and more complex than ever suspected at the start of the 20th century. If what we see were all there were, the galaxies would not be, could not be, relatively compact, stable spirals (or their other shapes), but should be torn apart by the speed of their rotation. Outside, among, around, the visible matter of the galaxies was dark matter.
Dark matter was soon joined by the even more mysterious dark energy.
The largest part of Panek's book is devoted to the research to detect and identify dark matter and dark energy, He takes us through not only the science, fascinating enough in itself, but also the human drama as two teams, one primarily physicists and the other primarily astronomers, raced against each other to gather enough observations of sufficiently distant (and therefore ancient) supernovae to answer essential questions about the conditions of the early universe. In the answers to those questions, and questions about changes since that early time, would lie the answers to the reality of dark energy, dark matter, and maybe the ultimate fate of the universe.
The hardcover edition of this book is available from Amazon or Barnes & Noble. A paperback edition will be released in November 2011.
I received a free electronic galley of this book from the publisher via NetGalley.