Let's try an experiment. Take a piece of chalk and draw a circle around yourself on the ground. Think of something else for a minute. Now look down. You're in the middle of a circle! Doesn't that make you feel special?
This is the recommended therapy for people suffering from a kind of transgalactic ennui. Blame scientists. Ever since they showed that the Earth goes round the sun and not vice versa, humans' place in the universe has seemed increasingly marginal. As the cosmologist Carl Sagan put it: “We live on a hunk of rock and metal that orbits a humdrum star in the obscure outskirts of an ordinary galaxy comprised of 400 billion stars in a universe of some hundred billion galaxies.” How insignificant we are, on the vast scales of space.
Such is the received wisdom and, like all received wisdom, it is worth challenging. Husband-and-wife team Primack, an astrophysicist, and Abrams, a philosopher of science, understand our pain. They know the temptation of what they call “the existential alternative,” as exemplified by Sagan. They give the feeling a rather beautiful name: “cosmic homelessness.” And they promise to prove, using the latest cosmological discoveries, that the idea is wrong. Science itself, they say, demonstrates that we are actually central to the universe.
The book is a superb pop-science primer on current cosmology. There are gorgeously clear explanations of relativity, dark matter (which Primack was one of the first to propose, and the existence of which seems more likely after recent observations of two distant galaxies colliding), the stages of the universe after the Big Bang and so on. The language is imagistically immediate — “violently relaxed halos of dark matter” — and there are some fruitfully head-spinning thought experiments about reality on galactic scales.
But whenever the authors move from scientific exegesis to the deduction of our centrality, the philosophical rabbit they pull out of their hat crumbles to bits — becomes, as it were, a dust-bunny. We are, for example, said to be at the center of the “cosmic spheres of time.” It turns out that it just means that we are at the center of a time diagram, drawn around planet Earth, now. Well, yes, by definition we are. Along the way there have been some striking concepts, such as this one: “Light and other forms of information are already traveling towards Earth and will arrive in 10 years, a hundred years, a million years from now. That information has been on its way for possibly billions of years. Much of our future already exists — it just hasn't gotten here yet.” That is a pleasingly illuminating thought, but it doesn't prove our centrality to anything except our own viewpoint.
Another argument goes like this: we are all made mostly from stardust — heavy atoms produced in the nuclear furnaces of stars. But actually the vast majority of stuff in the universe is not like us: it's dark matter, or dark energy, or interstellar gas. This means that we are at the top of the “cosmic density pyramid,” represented by a shining eye. Why are we at the top of this pyramid? Well, just because the authors have drawn it that way. They could equally have inverted the pyramid and put us at the bottom; or represented our form of matter as a moldy spot on the surface of a Krispy Kreme doughnut. But that would not have been so inspirational.