MEDIA: Book Review –

August 4, 2020 – The eye of astrophysics reaches a great deal farther now. Cosmologists calculate the curve and complete the figure by employing a potent arsenal of instruments and methodologies. Optical, radio, X-ray and gamma ray telescopes on mountaintops and in space, underground neutrino detectors and gravitational-wave observatories extend our sight to the edges of the universe. But what that really means is that they extend our sight into the past. This is perhaps the most basic fact of cosmology, sometimes taken for granted, and Mack explains it elegantly. Telescope users have a window into time. Light travels at finite speed, so everything comes to us with its own time delay. We see the sun not as it is now but as it was eight minutes ago. All we can know of a galaxy 10 billion light-years away is what it looked like 10 billion years ago, when the universe was young. “We can look even farther back,” she writes, “and see matter swirling into supermassive black holes in a universe less than 500 million years old, when starlight had only just begun to penetrate the darkness between galaxies.”

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