Published in 2018, Brief Answers to the Big Questions is a popular science book that explains what scientists have learned about the birth and history of the universe and the future of human technological civilization. As the final published writing by physicist Stephen Hawking, the work became a bestseller and landed on several best-book lists. Hawking, author of the best-selling work A Brief History of Time, was a chief contributor to many of the discoveries that the book discusses. Widely considered the greatest scientist since Albert Einstein, Hawking made major contributions to theory about the black holes that lie at the center of most galaxies and to human understanding of the beginnings of space and time. Each chapter of Brief Answers begins with a question that the author’s audiences often asked; the rest of the chapter provides an answer, drawing from the extensive archive of Hawking’s lectures, speeches, and essays. Hawking’s colleagues finished and published the work in the months following his death.

The e-book version of the original edition forms the basis for this study guide.

Summary

In the Foreword and Introduction, Eddie Redmayne—who portrayed Hawking in the film The Theory of Everything—and Kip Thorne, a Caltech professor of astrophysics who worked with Hawking on the theory of gravitational waves, offer their appreciations of the author. They describe him as a brilliant, determined, humorous, and compassionate man whose work changed the world of physics.

Hawking adds his own Introduction as well. He admits that he was indifferent in school until he was diagnosed with a motor neuron disease that threatened to take his life in a few years. Thereafter, he worked hard to complete as much physics work as he could, assisted by the love and support of friends, colleagues, and family, without whom the entire project would have seemed pointless to him. Hawking exhorts readers to support continued scientific developments in understanding the universe. In addition, he encourages them to stand up for a society that takes care of the planet and makes it a secure and healthy home.

The author first tackles the question of whether God exists. He concludes that the laws of nature are sufficient to explain everything that happens in the universe and that no god interferes. He believes that the cosmos was created out of nothing, which was possible because the positive energy of the universe is perfectly balanced by the negative energy of space. This belief, coupled with his contention that time doesn’t exist outside the universe, forces him to conclude that no god is necessary and that perhaps that no god exists.

The early universe left hints about itself. Hawking notes how reddened light from faraway galaxies proves that the universe is expanding, and microwave radiation from all directions is the stretched-out remnant of the extreme heat in the early dense universe; its slight variations help explain the clumping of galaxies that we see today. Only some universes are compatible with life, according to the anthropic principle, which limits the huge number of possible states that a universe might adopt.

Hawking notes that although life likely exists on other planets, advanced intelligence—which took billions of years to evolve on Earth—is unlikely to exist on nearby planets at the same moment in evolutionary history. Scientists constantly search for possible signals from advanced civilizations on distant planets. The author is skeptical of attempts to communicate with them, however, since they might be hostile.

Another thing the author considers unlikely is the ability to predict humanity’s future. He concludes that although the laws of the universe make predictions possible, especially regarding the future of natural systems like star systems, galaxies, and the universe, two obstacles block accurate predictions regarding systems that humanity influences or creates: chaos and quantum mechanics. Chaos theory describes how the tiniest changes in complex systems—for example, life forms or the weather—quickly balloon into uncountable possible outcomes. Quantum mechanics theory further complicates things by proving that it’s impossible to know the exact position and momentum of any particle at the outset.

Next, the author explores the complex mystery of black holes, which crush mass to an infinitesimal point; they contain mass so dense that, within a certain distance, even light cannot escape their gravity. The dense point at the center, called a singularity, contains all the mass and related information. Black holes eventually evaporate, but if the mass and energy return to space without the original information, this would break fundamental laws of physics. Fortunately, researchers have reasoned that black holes contain traits that may permit them to release the information alongside the evaporating mass.

The author holds that time travel might be possible through the warpage of space and time—if it uses negative mass and energy, which are difficult to collect. Such material could be fashioned into wormholes to connect one place in the universe with another. Travel through a wormhole could transport users across vast distances far more quickly than the speed of light. Returning through a second wormhole might permit users to arrive back home before they left, however, which could create paradoxes forbidden by physics.

Hawking reflects on how modern technology has put humanity in the crosshairs of multiple possible disasters, such as a devastating nuclear war, environmental collapse, and domination by artificial intelligence, adding threats beyond a life-ending asteroid strike. His solution is to colonize the moon, nearby planets, and, later, the planets circling faraway stars. Human destiny, he believes, lies in space, where dispersed colonies can be protected from the devastation of Earth that he considers likely. Artificial intelligence (AI) may someday outsmart humans; whether it does so for our benefit or to sideline or destroy us is an open question. AI could provide wondrous boons to humanity or cause a terrible disaster; people must carefully nurture this new technology so that it serves us harmlessly.

Humanity’s future, Hawking concludes, depends on imagination, curiosity, and a widely held interest in science and technology. Instead of de-emphasizing science education, as has been a recent trend, institutions should increase funding for it and cease demoralizing budding scientists via rote studies. The internet is revolutionizing education and may itself nurture future scientists. The world will rise or fall depending on scientific development in the coming decades; people must take the initiative in discovering ways to solve problems on Earth and explore and colonize space.

The book’s Afterword by Lucy Hawking (one of the author’s children) describes the joy she experienced as his daughter and the grief she felt at his death. Her heartfelt love parallels the admiration of people throughout the world for her father, who could barely move yet shifted humanity’s view of the universe.