Filling in the gaps

The story of astronomy has plenty of highlights. Galileo’s observations. Kepler’s calculations. Henrietta Leavitt’s Cepheid variables. Hubble’s receding galaxies. And so on, up through Arno Penzias and Robert Wilson’s puzzling detector noise (“the echo of the Big Bang”) and the still-mysterious discovery that the expansion of the universe is accelerating. All of these highlights could (and in most cases do) have entire books written about them, but it is rare to find all of them in a single volume, let alone one as accessible as Ethan Siegel’s Beyond the Galaxy. An astrophysicist and teacher, Siegel is best known for his blog Starts with a Bang (see October 2011 “Web life”), which has given him plenty of practice at explaining complex concepts to a general audience. This is fortunate, because the story he tells here is an intricate one, taking in elements of nuclear and atomic physics as well as astronomy and the history of science. In this methodical account, how we came to know things about cosmology is almost as important as the knowledge itself, and Siegel’s tale is distinguished by the respectful way he treats hypotheses that fell out of favour after new data emerged to discredit them. “When two explanations can account for the same phenomenon, it is not simply enough to choose the simpler one or the one that you feel better about,” he writes. “Instead, you need to look a little deeper, and find where the explanations differ from one another in their predictions for something you can then go and look for, either observationally or experimentally.” (Sometimes, of course, individual astronomers have clung to their preferred explanations even after the compass needle of evidence had swung in another direction; Siegel is much less forgiving of this.) The book is pitched at a level somewhere between popular science and beginners’ astronomy textbooks, and it contains few equations, but plenty of graphs containing real astrophysical data. It also offers detailed explanations of concepts such as the r-process, which describes how giant stars kick out huge quantities of heavy elements in their death throes. In the book’s later chapters, there are a few lapses; objects such as “cosmic strings” and “domain walls” play important roles in Siegel’s discussion of dark matter but are defined only briefly, while analyses of the three possible fates of our universe (a “big crunch”, limitless expansion in a “big freeze” or a finely balanced “Goldilocks” universe where expansion eventually slows to zero but never reverses) appear three separate times. Overall, though, Beyond the Galaxy is an excellent way for less cosmically minded physicists to fill in the gaps in their astronomy knowledge, and thereby transform “things I’ve vaguely heard about” into “things I actually know something about”.

• 2015 World Scientific £29.00/$38.00pb 388pp

The Planck problem

For a physicist whose most important insight came in the year 1900 – and who by his own admission fell short of true scientific brilliance – Max Planck is remarkably well known. Physics students learn the value of his famous constant h (or its variant, ħ) by heart. Historians of science trace the quantum era back to Planck’s 1900 paper on black-body radiation, which suggested that light might exist in discrete packets. In Planck’s native Germany, his name is attached to a network of prestigious research institutions. And as Brandon Brown points out in his fine new biography Planck: Driven by Vision, Broken by War, this stern old-fashioned Prussian gentleman was also responsible for “Planck’s principle”, the darkly comic observation that a new scientific idea becomes accepted “because its opponents eventually die and a new generation grows up that is familiar with it”. Early in the book, Brown argues that Planck was an exception to this rule, pointing out that when Albert Einstein came on the scene, Planck (unlike most of his similarly middle-aged contemporaries) eagerly adopted the younger man’s revolutionary ideas about light and gravity. But Planck’s adaptability had limits. As the quantum revolution gathered pace, Brown writes, “Planck would play the role of a worried parent asking everyone to slow down, to be careful please”. Tragically, this innate conservatism also applied to Planck’s politics. In the opening weeks of the First World War, Planck was among the 93 Germans intellectuals who signed an “Appeal to the Cultured Peoples of the World” protesting against supposed “lies and calumnies” about the German army’s conduct in Belgium. His Dutch colleague Hendrik Lorentz (who Brown memorably describes as “the kindly papa bear of physics”) eventually managed to convince him that some of the atrocity stories were true, but he remained deeply patriotic. This stance led him, for the most part, to adopt a strategy of accommodation after the Nazis came to power in 1933. “Flanked by swastikas, he praised his Führer to start speeches [and] executed the Nazi salute,” Brown writes. “When asked to bar Jewish students from his classrooms and then fire Jewish staff, he did as he was told.” Planck’s chosen path, which Brown describes as “working within the new system, however deranged, and trying to make a positive difference, however small”, dealt a severe blow to his reputation. His sporadic attempts to ingratiate himself with the Nazis were also not enough to save his son Erwin, who was hanged for his alleged involvement in the 1944 plot to kill Adolf Hitler. After the war, some of his former colleagues forgave him; Brown quotes a postwar letter from Lise Meitner in which she writes of Planck’s “unusually pure disposition and inner rectitude”. Thanks to an Allied bombing raid that destroyed his home and library, there are big gaps in what we know about Planck; accordingly, Brown’s biography often strays from its central character. Many of these diversions are interesting in their own right, but the book’s nonlinear structure can be disorienting. In one especially jarring passage, Planck’s granddaughter survives a difficult birth on one page, then appears on the next page some 20 years later as a survivor of an apparent suicide attempt. Overall, though, Planck is an illuminating and thought-provoking book about one of physics’ near-greats and his troubled times.

• 2015 Oxford University Press £20.00/$29.95hb 280pp

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