Most questions about science sound relatively normal: “How can a submarine crew stay underwater for weeks?” “Why do helium balloons rise?” “What causes rainfall?” Scientists can straightforwardly answer these questions. The questions are sometimes downright weird: “How long could a nuclear submarine last in orbit?” (78). “How long of a fall would I need in order for [a helium] balloon to slow me enough that I could land safely?” (150). “What if a rainstorm dropped all of its water in a single giant drop?” (274). The author of What If? specializes in these questions; his answers take advantage of their weirdness to demonstrate interesting aspects of the world that ordinary questions and answers might not reveal.

Chapter 67 answers a question about a bullet made of solid neutrons—a material found only in super-dense neutron stars—saying it would be as heavy as the entire Empire State Building and, within inches of it, would have such concentrated gravity that it would capture a person and not let go. The weird question permits the author to describe the forces involved in neutron stars by describing the effects a thimble-full of the stuff would have on Earth.

A question about daring to swim in a pool containing spent nuclear fuel, asked in Chapter 3, opens up an opportunity for the author to explain that water is an excellent filter for radiation and that a swimming pool keeps a swimmer safer from radiation harm than when she stands next to the pool.