Wednesday Books: Heroes of space and time

MEASURING THE UNIVERSE: THE HISTORICAL QUEST TO QUANTIFY SPACE BY KITTY FERGUSON, HEADLINE, pounds 14.99 THE BIRTH OF TIME: HOW WE MEASURED THE AGE OF THE UNIVERSE BY JOHN GRIBBIN, WEIDENFELD & NICOLSON, pounds 18.99

ERATOSTHENES OF Cyrene was chief librarian of the famous library at Alexandria, and a contemporary of Archimedes, from whom he acquired his knowledge of geometry. His eclectic interests included mapping and measuring things. The chance discovery that there was a well in Cyrene to the bottom of which the sun's light penetrated on the summer solstice enabled him to calculate the circumference of the earth, by measuring the angle of the shadow of a stick set up in Alexandria on the same day. His estimation was remarkably close to the modern figure, and Kitty Ferguson calls him the father of "geodesy": the science of earth measurement.

Another prominent figure in the intellectual hothouse of third-century BC Alexandria was Aristarchus of Samos, who published a book of hypotheses that included the "inspired guess" that the earth rotates around the Sun. This wild surmise was flatly contradicted by all observational evidence, and for a further 1,700 years the Earth-centred system of astronomy, most fully formulated by Ptolemy in the second century AD, held sway.

In the black-and-white world of the school textbook, the Ptolemaic system is plain wrong. But Ferguson points out that all motion is relative, and that it is perfectly possible to construct a mathematically coherent model of the universe with, say, your cat at its centre. It merely makes the sums more convoluted.

The Ptolemaic system was highly successful at predicting the movement of heavenly bodies, and until the 16th century was the foundation not just of an educated person's idea of the physical world, but of the human condition. Dante's Divine Comedy is the greatest expression of this world view. The young Galileo, it is intriguing to learn, made something of a name for himself by giving public lectures on the shape, size and location of Dante's hell.

The phrase "Copernican revolution" can sound tired, but Ferguson restores a full sense of the seismic change Copernicus engendered: "No period in the evolution of thought about the universe and humankind's place in it has been more complicated or more ultimately decisive than the century and a half following the publication of De Revolutionibus in 1543."

She is equally good at teasing out the story of Galileo's advocacy of Copernicus, and his trial for heresy. The Catholic Church was not initially greatly bothered by the idea (indeed, it had made use of Copernicus's calculations when producing the new Gregorian calendar in 1582), and Pope Urban VIII was a friend who almost certainly knew that Galileo was right.

The reasons behind the trial remain mysterious, but one thing is sure. Galileo did not help his own cause by deploying the "pitiful defence strategy" of claiming his Dialogo had been misinterpreted and was really pro-Ptolemy. The trial has an iconic status in the history of scientism, and Ferguson makes the sensible observation that the worst they did to him was to hold him under house arrest in his own villa. Stalin's brutal purge of physicists who advocated the Big Bang model of the universe - which implies a beginning, and therefore the possibility of a creator - is less frequently aired.

John Gribbin covers a good deal of the same ground as Ferguson, but in a relatively lacklustre manner. Galileo's trial is covered with a single sentence that sneers vaguely at the Church. Other familiar scientific whipping-boys are paraded, notably Archbishop James Ussher, whose scriptural studies dated the Creation to 4004 BC. In his elegant essay "Fall in the House of Ussher," Stephen Jay Gould observes that Ussher has become "a symbol of ancient and benighted authoritarianism" and that "one can scarcely find a textbook in introductory geology that does not take a swipe at Ussher's date". Gould, like Ferguson, is capable of imagining how the world looked before we discovered certain things about it.

The latter part of The Birth of Time concerns the recent kerfuffle about the age of the universe. It successfully conveys the messy, groping world of modern astronomy - one of statistical probabilities and vast computers processing thousands of gigabytes of data. The main bone of contention was between astrophysicists whose work suggested that some star systems might be as old as 18 billion years, and the cosmological camp, who dated the universe as considerably younger. Initial data from the Hubble Space Telescope in 1994 appeared to support the younger age. Working out the Hubble Constant (the rate of expansion of the universe) was essential to resolving the conflict, and Gribbin was one of the astronomers at Sussex University who achieved this feat - approximately.

Everyone is now agreed that the oldest star systems are between 10 and 13 billion years old, and that the universe itself is between 13 and 16 billion years old - probably. This seems a little indecisive to me. At least Archbishop Ussher had the courage of his convictions.