Einstein's Telescope Authors: Evalyn Gates Publisher: W W Norton ISBN: 978-0-393-06238-0 Price: £18.99 (Hb), 305pp
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One of the predictions of Einstein’s General Theory of Relativity is that gravity bends light. This property has provided astronomers with one of the most powerful ways to probe the cosmos. Massive objects, such as stars, galaxies or even clusters of galaxies, bend the light from far more distant objects, and so act as lenses. The strength of the lens reveals the mass of the massive lensing object and can magnify the images of the more remote objects. This is Einstein’s telescope in operation; the technique is more usually referred to as gravitational lensing. In its various guises it can be used to detect exoplanets, and weigh galaxies so as to map the distribution of dark matter.

At the heart of Evalyn Gates’ exposition is the story of gravitational lensing, and we are in good hands. She writes with authority and clarity. She prepares us in the first three chapters by spelling out some of the central issues in modern cosmology and giving us a whistle stop tour of special and general relativity that is well focused; information is dispensed on a ‘need to know’ basis, so we aren’t bogged down in intricate and puzzling details.

In the last three chapters she concentrates on dark energy, even though gravitational lensing is not really central here, almost as if she feels obliged to tell the complete story of modern cosmology. But it’s a good account. She uses some new analogies to get her ideas across, though not all of them worked for me. However there are nice touches; I loved her account of the equation of state as describing how ‘springy’ a substance is – indeed this concept is well treated throughout. At the start I felt Einstein’s Telescope was a bit pedagogical, but Gates soon won me over, and if you have even the slightest curiosity about gravitational lensing she will win you over too.

Alan Longstaff