Astrophysics for People in a Hurry

Neil Degrasse Tyson



Jul 29, 2022

Read time

15 minutes


There's no better guide through mind-expanding questions about the universe. Today, few of us have time to contemplate the cosmos. So Tyson brings the universe down to Earth succinctly and clearly in digestible chapters consumable any time and anywhere in the busy day. I interpreted the book's title a little too seriously because I forgot my copy while commuting the train to a student job. 😕

If you want to read a book that goes more into the math of the concepts of (Astro)physics then I recommend you to read A Brief History of Time by Stephen Hawking as well.

The Greatest Story Ever Told

Tyson starts the book with an introduction to astrophysics 14 billion years in the past with the big bang theory, the origin of which remains unknown to the scientific community.

Everything in the universe at that time was hot and smaller than a dot on paper. Its controlling forces were synchronized (the same). After the big bang, these forces diverged into the gravitational force, electromagnetic force, and strong nuclear force that we are familiar with today. Electrons, neutrinos, and quarks are only a few of the diverse subatomic particles that emerged from matter.

The universe cooled and expanded after the big bang. Hadrons, which were created from quarks, gave rise to neutrons and protons. There was a significant asymmetry in the early activity: more matter than antimatter. If this weren't the case, the equivalent antiparticle would have vaporized all of the matter in a flash of light.

On Earth as in the Heavens

When it comes to physics, the law is the law.

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.

Some theologians condemned Newton for leaving nothing for the Creator to do when he overcame this logical hurdle by making all motion understandable and predictable. Newton discovered that the same force of gravity that pulls ripe apples from their branches also governs the Moon's orbit around the Earth and curves the trajectories of thrown objects. Newton's law of gravity also maintains the orbits of hundreds of billions of stars within our Milky Way galaxy and directs planets, asteroids, and comets in their orbits around the Sun.

Let There Be Light

Some 380,000 years after the big bang, the universal fog lifted and the cosmic background radiation was set free.

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 are made of stuff we don’t yet understand.

Between the Galaxies

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.

Dark Matter

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 scientists 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.

Dark Energy

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.

The Cosmos on the Table

An astrophysicist looks at chemistry’s most famous chart.

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.

On Being Round

Thanks to gravity, stars and planets are spherical. So why are there pizza-shaped galaxies and potato-shaped moons?

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.

It can be shown using freshman-level calculus that the one and only shape that has the smallest surface area for an enclosed volume is a perfect sphere. In fact, billions of dollars could be saved annually on packaging materials if all shipping boxes and all packages of food in the supermarket were spheres. For example, the contents of a super-jumbo box of Cheerios would fit easily into a spherical carton that had a four-and-a-half-inch radius. But practical matters prevail—nobody wants to chase the food down the aisle after it rolls off the shelves.

Invisible Light

In this chapter, Neil tells the story of Sir William Herschel. Herschel was investigating the question of how much heat each hue of visible light could hold. He came up with an experiment in which he divided sunlight into its spectrum of colors using a glass prism. He then set a thermometer beneath each color, with an additional thermometer just beyond the red portion of the spectrum. The thermometer that appeared to be out of the light had the highest temperature, he discovered. Infrared light was thus discovered by him.

Johann Wilhelm Ritter decided to investigate whether there might be light just beyond the purple end of the spectrum a year after Herschel's discovery. Indeed, there was, and Ritter discovered ultraviolet light. In 1867, James Clerk Maxwell predicted that there should be light with even longer wavelengths than infrared light.

Heinrich Hertz created radio waves in his laboratory in 1887 to show that the waves Maxwell prophesied existed.

The higher-energy (shorter wavelength) light in the electromagnetic spectrum was discovered somewhat later and the unit for the speed of the wavelength was named after Hertz.

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.

Between the Planets

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 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.

Exoplanet 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.

Reflections on the Cosmic Perspective

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.