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Emma Chapman
John Murray

When he was 16 years old, Albert Einstein imagined chasing after a beam of light and, as the story goes, this feat of imagination helped him develop the now-famous theory of special relativity.

Physicist Emma Chapman also chases a light signal through the known universe and up to its very edges in her new book, Radio Universe: How to explore space without leaving Earth (in the US, its title is The Echoing Universe and it is out on 19 May). But while Einstein wanted to hop onto the light beam and experience the cosmos’s fastest speed, the light Chapman is after plays the role not of a carrier, but of an explorer, guide and messenger. “The universe already speaks the language of light,” she writes, and her book offers a wonderful insight into how humans have used radio telescopes to learn and become fluent in that language, too.

As a wave of electromagnetism, light can have many different wavelengths. For example, ultraviolet light (UV) has a relatively short wavelength, with its peaks and valleys scrunched up much closer together than those of visible light. Chapman is a radio astronomer, so the light signals she works with are on the opposite end of the electromagnetic spectrum. Radio waves can have adjacent peaks, or valleys, as far apart as several metres.

Because they are so stretched out, radio waves can travel longer distances than all of their electromagnetic relatives, which means that telescopes that either emit or collect them can see and probe deeper into the cosmos than other telescopes. Unlike telescopes that collect visible light, radio telescopes can work during both night and day, buying astronomers extra time. They are astonishingly versatile machines, Chapman asserts, before joyously chasing their signals from our moon to the possible cosmic dwellings of extraterrestrials.

Radio Universe is organised into three sections – Our Solar System, Our Galaxy and Our Universe – following a radio signal’s journey to each. For example, in the first chapter, Chapman explores how the first time humankind touched the moon was not via Neil Armstrong’s foot, but rather with a radio wave, as well as how contemporary radio studies play a central role in investigating our satellite’s origin and history.

In another chapter, the focus is on Venus, which is so inhospitable that most light-based observation techniques can’t access it – except for radio waves. Their superpower, says Chapman, is communicating with otherwise unknowable environments.

In later chapters, she tackles how the most famous images of black holes are based on radio data, how the first indirect evidence of ripples in spacetime known as gravitational waves was obtained by radio astronomers, and how radio waves uncovered some of the first exoplanets.

In the chapter on the role radio astronomy may play in searching for alien civilizations, Chapman writes, “Far more likely than any invasion is contact by radio signal.” Later, she adds: “Whether that planet has a yellow-green sky, whether it has five moons, or its people five legs, radio waves will be the form of light that is used for long-distance communication.”

The last two chapters of Radio Universe are dedicated to the biggest mysteries of modern physics: dark matter and dark energy. These two substances fill much of our cosmos, and yet we are terribly unsure of exactly what they are, in part because we don’t know how to directly detect them. Chapman points to all the ways in which radio telescopes can help, for instance, by detecting radiation from interstellar hydrogen gas that allows astronomers to infer exactly where in those areas dark matter ought to be.

Throughout, Chapman’s writing is accessible, imaginative and compelling. When she described the speed with which Mercury travels around the sun, which makes it hard to land on but doesn’t deter investigations via radio signals, I felt the planet buzzing through my mental map of the solar system.

And when she discussed the asteroid belt, I felt like I was getting a master class not only in radio astronomy, but also in plain old astronomy – and not delivered by a professor, but by someone who could be a very knowledgeable friend or the absolute best seatmate on a long flight. I also chuckled at most of Chapman’s jokes, and marvelled at how her sincere love for her craft as a radio astronomer permeated every page. The book even has an appendix listing all the radio telescopes you can visit as a tourist.

It is this great, inviting and optimistic tone that then made me somewhat disappointed when Chapman discussed, fairly uncritically, the colonisation of Mars and the efforts towards commercial exploration of the moon. She writes that “a new generation of tech billionaires has sparked a second space age”. But she then goes on to ask whether researchers who want to put their telescopes on the moon will actually be welcome there “amidst those who wish to mine it, settle on it and use it as a springboard to Mars” – without ever questioning whether the future of space exploration absolutely must be this way. Shouldn’t an ardent astronomer be advocating for a far more democratic and egalitarian future for cosmic travel and research?

Similarly, while several American and British radio astronomers are namechecked and spotlighted in Chapman’s narrative, there is far less room and detail devoted to researchers from other parts of the world, even though some of the most important radio telescopes were built and operated for years in places such as Puerto Rico and, more recently, Chile.

Ultimately, however, Chapman is effective in illustrating a beautiful and powerful point – that our universe is nowhere near quiet. “Wherever you are, you are surrounded by radio waves,” she explains. “Some have escaped black holes, some are the echoes from asteroids. Some have even travelled to us from the Era of the First Stars. We just have to close our eyes, and listen.”

The next time I find myself underneath a night sky, even if it is crowded with city lights and the din of people, I will certainly remember that suggestion to just close my eyes, and listen.

Two more great books on astronomy

by Stephon Alexander

Here we have a complex telling of the history and future of our universe from the perspective of an outsider, a dreamer and a musician. Alexander, a working cosmologist and theorist, doesn’t shy away from being inspired by, for instance, experiences at a Zen centre he visited in graduate school, or influences such as the artist Jean-Michel Basquiat. This is a book where mathematical tools, such as Feynman diagrams, don’t just coexist but also cross-pollinate with stories from Alexander’s life as a Black man.

by Chanda Prescod-Weinstein

This is a potent blend of the scientific and the personal from the Â鶹´«Ã½ columnist, offering both rigorous detail on phenomena, such as dark matter, and a meaningful analysis of sociopolitical circumstances that have shaped how we talk about the mysteries of modern physics. Notably, Prescod-Weinstein also explicitly addresses the tensions and controversies surrounding where telescopes are built and with consent from whom, conveying that scientific rigour can transcend activities like collecting and analysing light.