The challenge of the great cosmic unknowns
In The 4% Universe: Dark matter, dark energy, and the race to discover the rest of reality, Richard Panek explains how we came to know so little
It is an embarrassment, to say the least. Scientists have no idea what most of the universe is made of. In fact, a whopping 96 per cent of it is made of something whose very nature we are at a loss to describe - something utterly unlike the ordinary matter that makes up stars and galaxies, planets and moons, birds and bees.
Of that 96 per cent, about one-quarter is that mysterious stuff known as dark matter. Unable to interact with the electromagnetic force, dark matter is invisible. However, it does interact with gravity, so astronomers infer its presence by observing its gravitational pull on the matter we can see.
The remaining three-quarters of the cosmos, dubbed "dark energy", is even more mysterious: rather than pulling it seems to push, flinging every galaxy away from its neighbours and ultimately determining the universe's fate.
In this impeccably researched and highly readable book, journalist Richard Panek gives what is perhaps the most detailed layman's account of how we got ourselves into this predicament. Although he provides a brief tour of astronomy's roots, the emphasis is on 20th-century science, beginning with Edwin Hubble's discovery that we live in an expanding universe. That finding, combined with general relativity - Einstein's theory of gravity - led to what is now the standard model of the universe's origin: the big bang. The model became even more entrenched in the 1960s with the discovery of the cosmic microwave background, a faint echo of the primordial explosion.
As far back as the 1930s, however, it was clear that pieces of the puzzle were missing. When astronomers studied the motion of galaxies relative to one another and the speeds of their rotations, the numbers just didn't add up. In addition to the ordinary, luminous matter they could see with their telescopes, it seemed there had to be some other kind of matter lurking around those galaxies, preventing them from simply flying apart. And so dark matter was born.
As he nears the present day, Panek weaves together two separate yet closely related storylines. In the first, he takes us to sophisticated laboratories around the world where researchers are trying to isolate particles of dark matter. Their best guess is that dark matter is made of WIMPs (weakly interacting massive particles), which were created at the time of the big bang and are now fiendishly difficult to detect.
Dark matter stops galaxies flying apart, but what is it made of?
In the second storyline, we join the hunt for dark energy, which began in the late 1990s when two teams of researchers studying distant supernova explosions reached a stunning conclusion: that the expansion of the universe is not slowing down, but speeding up.
One of Panek's earlier books was a history of the telescope. When Galileo first aimed his scope skyward just over 400 years ago, our world view changed forever. Today's discoveries are again causing a rethink, but this time Panek has a front-row seat, following researchers to their conferences and even gaining access to their emails.
Panek finds considerable drama in the squabbles over which member of which supernova team was actually the first to discover the acceleration of the universe. At the very least, there is a Nobel prize on the line, not to mention a place in history alongside the great astronomers, from Hipparchus to Hubble.
In the final chapter, Panek surveys current opinions regarding the identity of dark energy and gives a brief look at the philosophical underpinnings of modern physics. Comparing today's discoveries to Galileo's, Panek remarks, "It's 1610 all over again." After Galileo, humanity had to wait 75 years before Isaac Newton came along to make sense of it all. Let's hope we won't have to wait as long.
Dan Falk is the author of In Search of Time (Thomas Dunne, 2008)