The Five Biggest Unsolved Problems in Science

The preface presents the book as the last of a three-book project. The first book covered the big ideas scientists trust on the strength of evidence, the second covered pseudoscience with no evidence at all. This one takes the middle ground: problems with plenty of evidence where no hypothesis has yet won. The problems were chosen for their explanatory power, difficulty and long-term impact, and each comes with drawings by Sidney Harris, America's best-known science cartoonist. In the authors' words, science has become the «400-pound gorilla» of our culture: research consumes vast amounts of time, labour and money, while its technological applications give rise to global industries.

«A Look at Science» starts with the difference between science and technology. Science springs from the wish to understand the world, technology from the wish to change the human condition. The authors recall Faraday's famous reply: asked by Chancellor Gladstone «what use is it?», Faraday answered, «I don't know, sir, but one day you will tax it». Then the scientific method is explained step by step (observation, hypothesis, prediction, experiment), with Thomson's «plum pudding» model of the atom as the example.

The chapter's best example shows how science cleans itself up. In 1999 the Berkeley laboratory announced that it had synthesised element 118. Laboratories in Germany, France and Japan could not reproduce the result, nor could an expanded Berkeley team, and in the end the lab withdrew its claim. As the authors put it, the final word always belongs to experimental evidence, not to the reputation of whoever proposed the idea.

The physics chapter calls mass a property «everyone knows and nobody can explain» and opens the problem through history: Planck's quanta, Einstein's photoelectric effect, Heisenberg's uncertainty principle, the positron predicted by Dirac and found by Anderson in cosmic rays, and the muon, greeted with «who ordered that?». Then come accelerators, the interruption of the Manhattan Project and more than a hundred new particles. Fermi told a student, «If I could remember the names of all these particles, I'd be a botanist». Gell-Mann names the quarks, and in the 1970s the Standard Model is born.

The authors show with numbers how precise the Standard Model is. In 1947 Willis Lamb measured a transition between two close energy levels of hydrogen at 1057.845 MHz; the model predicts 1057.860 MHz, a difference of about one part in 100,000. An even nicer proof comes from the universe itself. The share of helium made in the first minutes after the Big Bang depends on the number of particle families: four families would give more than 26 per cent, three give 25 per cent, and the measured value is exactly 25. The neutrino's «ghostly» nature is memorable too: stopping half of a batch of neutrinos would take eight light-years of lead.

The heart of the chapter is a critique of the Standard Model. It produces infinities in calculations that have to be removed by «renormalisation», it does not explain why electroweak symmetry is broken, and it ignores gravity altogether. The Higgs field proposed as the origin of mass is explained with two lovely analogies: soldiers marching through mud, and cocktail guests crowding around a famous visitor. The chapter ends with M-theory, supersymmetry, technicolor and twistor theory.

• Sidney Harris cartoons that bring every chapter to life
• The scientific method explained through real episodes (element 118, the Lamb shift)
• A «How, Who, Where and When?» summary at the end of each chapter
• A structure that makes the questions, not the physicists, the heroes