# The Ascent of Gravity: The Quest to Understand the Force that Explains Everything, by Marcus Chown

## Deft hands make light work of the incomplete ‘jigsaw’ that is physics, says Cait MacPhee

June 15, 2017
Source: Alamy

I once tried to teach my children about the effect of the Moon on our tides. They were learning about gravity in school and I’d had some success describing the planets and the Moon. But the tides; oh the tides. My children looked at me as if they doubted that I should be given a job in any reputable university, muttered “uh-huh”, and went back to Minecraft so that they could turn physics off.

You’ll be pleased to know that Marcus Chown does a much better job in The Ascent of Gravity. As is to be expected in a book on gravity, Chown starts in the age of Isaac Newton and the dreaded – and likely apocryphal – apple, but quickly moves on to what Newton’s ideas tell us about the world around us and the worlds around the Sun. His chapter on the tides, from the water in the River Severn to the squeezing and stretching of Jupiter’s moon Io, is lovely.

After Newton, we move to Einstein and one of the nicest explanations that I’ve read of the fact that objects of different mass fall at the same rate. We’re taught this in secondary school, typically with reference to the Leaning Tower of Pisa, but you’d be surprised how many students carry misconceptions about this idea into first-year physics. As a consequence, when asked about a problem that invokes the same concept but looks unfamiliar, their (our!) instinctive Newtonian idea of what happens in the “real” world rebels and sometimes provides the wrong answer. However, these misconceptions fall away if we discuss Einstein’s equivalence principle first. There is a case to be made for introducing the idea of Einstein’s warped space-time earlier in the curriculum – this is what is now happening in Scotland – and Chown’s book has convinced me that this is a good approach.

He then expands on what Einstein’s gravity tells us about the universe, from gravitational waves, directly detected only recently, to black holes and the Big Bang. We end with the current attempt to reconcile gravity and quantum theory and a surprisingly accessible and enjoyable discussion of string theory and multidimensional space.

For the most part, The Ascent of Gravity focuses on the physics, and provides interesting examples of how it has helped to explain the previously inexplicable. There are some curious fictional vignettes, particularly in the section on Einstein: in one, I had the sense that his Einstein character was about to don a fedora and tap dance down a rain-soaked street à la Gene Kelly. These “fly on the wall” perspectives are fun, but a change in focus from the rest of the book.

Enjoyably, though, Chown’s book doesn’t give the sense that “physics is broken” that I’ve come across elsewhere; it’s more that we’re on the cusp of an exciting step change in our understanding. We now know that the jigsaw is incomplete, which is an advance on not realising that any of the pieces are missing. It may take hundreds of years for understanding to dawn, or dark matter may hold all the answers. And who knows? Maybe one day we might be able to switch off physics and build our castles in the air.

Cait MacPhee is professor of biological physics, University of Edinburgh.

The Ascent of Gravity: The Quest to Understand the Force that Explains Everything
By Marcus Chown
Weidenfeld & Nicolson, 288pp, £16.99
ISBN 9781474601863
Published 6 April 2017

## POSTSCRIPT:

Print headline: It's all starting to fall into place

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