Astrophysics for People in a Hurry

Astrophysics for People in a Hurry by Neil deGrasse Tyson, PhD, is a popular science book about astronomy, astrophysics, and cosmology. The book outlines our current knowledge about the creation of the universe, supernovas, black holes, the mysteries of dark matter and dark energy, invisible light, and how Earth and its materials came to be. On its release in 2017, the book became a #1 New York Times bestseller; it remained on the list for more than a year and sold over one million copies.

Astrophysicist Tyson is an award-winning science writer and educator and the director of New York’s Hayden Planetarium. Tyson hosts the popular podcast and TV show StarTalk and hosted TV’s Nova Science Now and Cosmos: A Spacetime Odyssey. Other works by Tyson include Starry Messenger: Cosmic Perspectives on Civilization (2022) and To Infinity and Beyond (2023).

The eBook version of the original 2017 edition forms the basis for this study guide.

Summary

No one knows what existed before the universe, but scientists understand it began as an infinitesimally small dot that contained everything and expanded rapidly. In the first trillionth of a second, the laws of physics emerged, but it took 380,000 years before light could separate from matter and things became visible. Today, nearly 14 billion years later, the universe contains 100 billion galaxies that each contain up to hundreds of billions of stars. One is our own Sun and its planets—including Earth, which is not too warm and not too cold, so life can thrive on it and evolve to create humans, who wonder about the universe.

Newton’s laws of gravity function everywhere, not just on Earth. The theory offered the first proof that the laws of physics apply to the entire universe and that the realm beyond our planet isn’t a separate, heavenly space but instead is made of the same materials and follows the same rules as on Earth.

Cosmologists could only speculate on the nature of the universe until they discovered the cosmic microwave background, which is ancient light that gives evidence of the early universe. With that information, scientists now know the age, size, and shape of our cosmos and that most of its matter and energy is made of stuff we don’t yet understand.

Spread across the cosmos like lit-up cities, the billions of galaxies capture our attention, but between them lie vast areas filled with hydrogen gas and other matter that weigh up to 10 times as much as the galaxies themselves.

Only one-sixth of the mass in the universe is made of the galaxies and gas clouds we can observe. The rest consists of something we cannot detect, except it exerts a huge gravitational influence on everything around it. This dark matter has puzzled science for decades, but the inability to detect it through ordinary means suggests it represents an entirely new principle about the universe yet to be discovered.

The universe is expanding, and it’s doing so much faster than expected. Einstein thought the universe was stable, so he added a constant to his equations that kept gravity from collapsing everything. The discovery that the universe is expanding made Einstein’s constant obsolete, but still later observations showed the cosmos expands at an ever-increasing rate, so Einstein’s constant once again makes sense. No one yet knows what this expansive force is, but it alone is two-thirds of the universe’s total makeup. Scientists call it dark energy.

Many of the atomic elements were discovered or their description enhanced by astrophysicists. Helium was found in the Sun before it was found on Earth; gallium and aluminum are used in astronomical detectors; technetium appears in nuclear reactors but also in stars, where it shouldn’t be. Iridium is common in asteroids, and a streak of it in the Earth’s crust hints that it was an asteroid that struck our planet and killed off the dinosaurs. Some elements—mercury, neptunium, and plutonium—are named for planets; cerium and palladium honor the asteroids Ceres and Pallas.

Many large objects in space are spherical. A sphere is an efficient way to enclose a large volume, and the gravity of large planets and stars tends to smooth them down into nearly perfect spheres. The universe itself can be thought of as a sphere, though its outer reaches are unknowable to us because those regions are expanding faster than their light can travel to reach us.

Light arrives in the form of packets of energy called photons, but most photons have energies our eyes can’t detect. These invisible forms of light range from low-energy radio waves, microwaves, and infrared to high-energy ultraviolet, X-ray, and gamma rays. Photons from every part of this electromagnetic spectrum are emitted by objects in space; scientists use detectors tuned to every type of photon, from giant radio antennas to small gamma-ray sensors, to learn about the cosmos.

If our solar system were contained in a sphere, all the mass from the Sun, planets, and moons would take up only one trillionth of the space. There’s plenty of dust and rocks in the system, though, including a belt of asteroids between Mars and Jupiter. Some of this detritus falls onto planets, with big objects occasionally crashing catastrophically on Earth. The Moon was created from such a splash, and it’s possible life here got started on an early, wet Mars and then was knocked into space, eventually landing on Earth.

If aliens with detectors focused on our Sun, they might notice a tiny dot nearby, the blue of its oceans and the oxygen and methane in its atmosphere hinting at life. This would be Earth, where our own scientists observe nearby stars and their planets’ planets, first by the planets’ tiny effects on their own suns and then by the light that passes through planetary atmospheres and brings clues about those planets to us.

The study of the universe might seem like an idle pursuit in an era filled with poverty and oppression, but scientists need people everywhere to contribute to that project, and the wonder it creates can help unite us. When we appreciate how unique and fragile our planetary oasis is in this gigantic universe, we can work together to make it a safer and more beautiful home for everyone.