INTO THE UNKNOWN

A tour of some of the universe’s inexplicabilities by a genial astrophysicist.

“This is a book about what we don’t know and why we don’t know it,” writes Johnson, an astronomer at the University of Virginia. There’s plenty we don’t know, perched as we are in one infinitesimally small corner of a very large place, from the existential (Why are we us?) to the physical (When will the solar system end?). Undaunted, she encourages all readers, whether or not armed with a doctorate, to ponder matters that range from the meaning of life to the nature of time. On the latter, Einstein may have said it exists so that everything doesn’t happen at once, but Johnson is more cautious: “We interact with it continuously throughout our lives, and much of physics is defined with respect to time, yet we don’t understand what it truly is.” Yet, although she can throw out sentences to make an untested head hurt (“One way to think about imaginary numbers is that they are orthogonal to real numbers in a complex number plane”), she does so in good humor: If in quantum mechanics something that seems to make sense is in fact impossible and something that seems impossible is very much true, then it’s only, she writes, because “‘common sense’ and ‘reality’ are frenemies.” In the end, as Johnson suggests, things are pretty much as they are, whether we understand them or not, and lucky for us: Alter any given law of physics, after all, and “it would profoundly change the properties of the universe, and in almost all cases make the universe inhospitable to life-as-we-know-it.”

Popular science written warmly and accessibly, if not without thought-provoking complexity.