Gerolamo Cardano (1501-1576) was an Italian polymath. He studied medicine and earned reputation and wealth as a physician, but he was also gifted mathematically and he used negative numbers and imaginary numbers as square roots of negative numbers well before they were more generally accepted. As a gambler, he also laid foundations of probability theory a century before Fermat and Pascal worked it out and 200 years before Laplace finished the job.

Michael Brooks has a PhD in quantum physics from the University of Sussex, but he switched career and became a journalist and most of all a science writer. In this book (his seventh) we learn how his science is entangled with what Cardano (or Jerome as Brooks calls him) did. It has been remarked before by the authors of the papers collected in The Art of Science. From Perspective Drawing to Quantum Randomness (Springer 2014) that Cardano's findings (complex numbers and probability) laid the foundations for the elements that are so essential for the development of quantum theory. Brooks is exploring this trace by writing a novel-like biography of Cardano, and at the same time explaining his own field by discussing the history and the subtleties of quantum physics and the many questions that it has raised and that still remain unsolved even today.

Collecting the data for a biography of Cardano is not a major problem since he wrote an autobiography near the end of his life. Born as an illegitimate son of Frazio Cardano, a jurist and mathematician, his birth is almost a miracle because his mother tried abortion, but he got born anyway and survived frequent illness and the plague to which his three siblings succumbed. He decided to study medicine against his father's desire. He applied several times to be accepted as a physician in Milan, but it was repeatedly refused which caused him to live in poverty. By the mediation of some influential friends he got eventually a professorship in mathematics in Milan and got his medical licence. He was now a respected scientist and the most popular physician of Milan. He got offers from kings of Denmark, France, and the Queen of Scotland, that he all refused. He did travel to Scotland though where he also treated the archbishop John Hamilton, whom would later save Cardano from the inquisition. With his wife, Lucia Brandini, who was the love of his life, he had three children but his oldest son got executed for poisoning his own wife, and he disinherited his youngest who was a gambler stealing from his father. His outspoken confrontational ideas (his book On the Bad Practice of Medicine in Common Use was a success but not gracefully accepted by colleagues) and influential jealousy of his success brought his reputation down and allegations about his behaviour made the inquisition decide to imprison him at the age of 69 for the obscure reason of having cast an horoscope of Jesus Christ. So he had to spend several months in jail. By an intervention of John Hamilton he got out but he lost his professorship and was forbidden to publish his work. Not feeling accepted in Milan anymore, he moved to Rome where he wrote his biography. He predicted his own death on September 21, 1576 presumably by committing suicide.

Brooks has interwoven this biography with the evolution of quantum physics by using a fictional component in which he is visiting Cardano while he is imprisoned waiting for his release or conviction. Cardano writes in his biography that he was visited by a guardian angel, and Brooks is taking up this role and they have a conversation of which this book is a reflection. We learn about the ups and downs in Cardano's life, the love of his life, the misery he has with his children, and the well known dispute with Tartagli and del Ferro about revealing the formula to solve a cubic equation. At the same time Brooks explains to Cardano (and thus also to the reader) the principles of quantum physics. He writes:

Jerome's views on astrology mirror our own on quantum physics. In quantum experiments we see things appear in two different places at once, or an instantaneous influence over something that is half a world away. We cannot make sense of it, but we don't dismiss it as ridiculous. We have the evidence of our experiments, after all, just as the astrologers have the 'evidence' of experience. (p.22-23).

Quantum physics is real as Brooks describes his history and evolution, but we still do not understand why the experiments give the results they do. He goes through all the possible interpretations from the Copenhagen interpretation to the multiverse theory and the superdeterministic interpretation, the pilot wave theory, the Penrose interpretation, etc. Cardano (and the reader) learns all about the main protagonists, the double slit experiment, Schrödinger's equation, the EPR thought experiment and its verification, and even some particle physics and string theory.

Because in his conversation with Cardano, Brooks, coming from the future, knows things that did not happen yet. However, using the mysterious possibilities that quantum physics provides, Brooks can convince the reader to accept these anomalies. So the following twist comes as a surprise, and I think it is an amusing find. Brooks suggests to Cardano in prison that all this misfortune is the result of Tartaglia's doing. But Cardano answers that he doubts that because Tartaglia is dead for more than a decade. Then Brooks realizes that he read that in a book by Alan Wykes Doctor Cardano (1969) but Wykes may have used this historical flaw for the sake of his story. So it leaves Brooks blushing with shame in front of Cardano. At this moment Brooks is simultaneously a character in his own book and the biographer of Cardano who is correcting another biographer about historical facts. Later a similar trick is used when Brooks suggests that Cardano should write to Hamilton for help. It is then Cardano who doubts that Hamilton is still alive. But Brooks insists since he knows who has helped Cardano to get out of prison.

The parallels between Cardano and Brooks, and the similarities between Cardano's science, inventions, and philosophy and the modern quest to explain quantum physics is very inspiring. Many of the findings that Cardano pioneered were way ahead of his time. For example his idea of the aevium even hints at a higher dimensional universe. Whatever the eventual faith or the proper interpretation of quantum physics may be, currently we are still in the dark. Perhaps we shall look in a century upon our present guesses and beliefs like we now look upon Cardano's astrology and his horoscopes, that were fully rational to him, as much as they are unscientific to us. So it may be symbolic when near the end of the book, Cardano steps out of his prison cell, leaving Brooks behind sitting on the bed.

As far as I know, there is no biography-novel-popular-science-or whatever-you-call-it book produced that mixes all these ingredients in a marvelous plot. There are of course very good historical novels that sketch a biography of some scientist or another historical figure (and some exist some for Cardano already), but none has mixed this with popularizing science in such an harmonic and entertaining way as Brooks has achieved here. A novel, a biography and a popular science book, none of these in a strict classical sense, and yet all of them at the same time. Its format is certainly original. A recommended read.