Dispatches from Planet Three
In the tradition of Carlo Rovelli’s Seven Brief Lessons on Physics and Neil Tyson’s Astrophysics for People in a Hurry, an anthology of perfectly crafted stories about our unfolding understanding of the Universe, based on the author’s ‘Cosmic Background’ columns for Natural History magazine.
Early astronomers spent much of their time devoted to our local celestial neighbourhood. They aimed their telescopes at our Solar System and prominent stars in the nighttime sky. Armed with Newton’s law of gravitation, they were able to predict the motions of the Moon, planets and comets and detect new and unexpected objects such as asteroids. They found rings around Saturn and canal-like features on Mars. Could that mean there is water on the red planet? Is their other life in the Solar System or even on planets circling other stars? And what about those stars? They soon found these ranged in size from huge red giants to tiny white dwarfs no bigger than Earth. And then there were even weirder possibilities such as neutron stars no bigger than cities.
Astronomers then moved outwards. They traced how galaxies are uniquely arranged through the cosmos and evolve over time. They learned what elements reside in both stars and interstellar space, and realized that regular matter – the stuff of stars, planets and us – is not the major component of the Universe. Instead, some unknown ‘dark matter’ is five times more abundant. Meanwhile, Einstein’s theories recast our vision of the Universe as violent rather than serene, powered by objects with amazing energies. New tools arrived for exploring the cosmos, taking us beyond the visible-light spectrum – and recently even allowing us to detect the ripples generated in the very fabric of spacetime as black holes collide more than a billion light-years away.
Shortly after learning that our own galaxy, the Milky Way, is accompanied by billions of other galaxies, cosmologists were astounded to find out that spacetime was expanding, with galaxies surfing outward on the wave. It didn’t take long for them to imagine this ballooning in reverse, leading to the conception of the Big Bang – a prediction not firmly proven for nearly two decades. Since then, we have added new details to the story of our cosmic creation. The Universe may have begun with a brief moment of super-accelerated expansion, called inflation. What’s more, parallel universes might be generated in a similar way, meaning we live in a ‘multiverse’, side-by-side with other universes. But to prove that, theorists must first wrestle with the nature of time.