Brief Answers to the Big Questions

“I have spent my life travelling across the universe, inside my mind.”

The author’s career changed physics, yet he never visited the black holes that were central to his theories. He didn’t need to venture out into the cosmos to develop the equations that explain many of the biggest events in the universe. Although Hawking’s mobility relied on a wheelchair in his later decades, his mind freely soared through the billions of light years in his intellectual playground.

“[T]he world would soon grind to a halt if we all tried to do theoretical physics. But most people can understand and appreciate the basic ideas if they are presented in a clear way without equations.”

Hawking knows that most people don’t need to understand calculus or trigonometry, or comprehend how a physics lab works, to grasp scientific discoveries. Researchers must know those things, but all can understand the results when they’re put into plain language. The author believes that science has an obligation to communicate important findings to the public.

“[T]he fact that we humans, who are ourselves mere collections of fundamental particles of nature, have been able to come to an understanding of the laws governing us, and our universe, is a great triumph.”

The author, who proved that the universe started as an infinitesimal point and then expanded rapidly outward—a kind of black hole in reverse—believes, as do most scientists, that humans evolved simply from atoms and the laws of physics. People have since done an amazing thing to give meaning to their existence: They’ve begun to figure out how the universe in which they reside actually works. In this achievement, humanity has raised itself from creatures of little obvious importance to surveyors of, and possibly actors upon, that universe. In itself, this is a magnificent achievement.

“The universe is a machine governed by principles or laws—laws that can be understood by the human mind.”

Hawking presents the basic premise of science: that reality operates under strict rules and not because of the decisions of arbitrary deities. This defies ancient religious precepts, so controversy erupts between science-minded and religious-minded people. Hawking doubts that a god created everything behind reality, insisting that the universe runs without such a being’s intervention.

“The laws of science determine the evolution of the universe, given its state at one time. These laws may, or may not, have been decreed by God, but he cannot intervene to break the laws, or they would not be laws. That leaves God with the freedom to choose the initial state of the universe, but even here it seems there may be laws. So God would have no freedom at all.”

If the laws of physics determine the nature of creation, then a god would have nothing to do. Hawking prefers to think, rather poetically, that the laws of nature are the mind of God; otherwise, his notion that a personal God isn’t necessary aggravates religionists. His observations break the truce between religion and science whereby each makes no comments about the other. Hawking isn’t the only scientist to become publicly impatient with religious tenets that directly contradict scientific discoveries.

“[I]t made no sense to talk of a time before the universe began. It would be like asking for a point south of the South Pole. It is not defined.”

Asking what happened before the universe is like asking what happened before “before.” It’s nonsensical because it points toward an undefined concept. Similarly, the universe has no “outside.” This insight is key to our understanding of the nature of reality but is hard to reconcile with common sense. The cosmos is not only weirder than we’ve imagined, but it’s also weirder, perhaps, than we can imagine.

“We are used to the idea that events are caused by earlier events, which in turn are caused by still earlier events. There is a chain of causality, stretching back into the past. But suppose this chain has a beginning, suppose there was a first event. What caused it?”

Scientists are uncomfortable with theories they cannot test. A universe that had a beginning might have had a cause outside itself; if so, it would be very hard to examine, much less run tests on. This is where science and religion cross paths, and the resulting arguments can be uncomfortable for both sides. The author's work has influenced the debate by suggesting that the universe began out of nothing, and did so of its own accord, and therefore needs no creator.

“I think computer viruses should count as life. Maybe it says something about human nature that the only form of life we have created so far is purely destructive. Talk about creating life in our own image.”

Although optimistic about the future of science, Hawking is somewhat pessimistic about the future of humanity. He cites much of human history as evidence that humans can behave in very ignorant ways, and he worries that as technology becomes more powerful, we might use our inventions foolishly and destroy ourselves. When discussing this, his gently humorous way of writing becomes more sardonic. His use of the phrase “in our own image” makes reference to the Bible’s passage that God created humans in His own image. Given that humanity seems to have given God trouble ever since, it’s not surprising that humans, playing with godlike powers, have already created “life” that’s destructive.

“We are more than just our genes. We may be no stronger or inherently more intelligent than our caveman ancestors. But what distinguishes us from them is the knowledge that we have accumulated over the last 10,000 years, and particularly over the last 300. I think it is legitimate to take a broader view and include externally transmitted information, as well as DNA, in the evolution of the human race.”

The evolution of life proceeds slowly, but the evolution of human knowledge has accelerated. With this acceleration is a massive advancement of technology. Without it, we’re no more than cave people; technology multiplies our powers—including our intelligence. Already, it has enabled us to do things that would have taken thousands or millions of years to evolve. This revolution has barely begun; the acceleration will feed on itself and hurtle us forward into a future filled with both promise and danger. We might even meet aliens.

“Aggression, in the form of subjugating or killing other men and taking their women and food, has had definite survival advantage up to the present time. But now it could destroy the entire human race and much of the rest of life on Earth. A nuclear war is still the most immediate danger, but there are others, such as the release of a genetically engineered virus. Or the greenhouse effect becoming unstable.”

One of the author’s purposes in writing this book is to warn people of the dangers they face in a future where our prehistoric emotions combine with dangerous new technical powers to cause a disaster. He wants the discoveries of science to help civilization, not destroy it. If science and technology caused destruction, all Hawking’s work—as well as his hopes and dreams for humanity—would fall to ruin.

“Do the laws governing the universe allow us to predict exactly what is going to happen to us in the future? The short answer is no, and yes. In principle, the laws allow us to predict the future. But in practice the calculations are often too difficult.”

The author notes that the laws of the universe make the future of star systems, galaxies, and the general universe relatively predictable compared to human-influenced systems, like the weather, or human-created systems, like stock markets. These systems present significant uncertainties because of chaos theory and quantum mechanics, both of which introduce variables that can’t be pinned down with precision. Thus, we can know how long the sun will last but can’t predict with any accuracy how long we as a species will last. This unpredictability is built into the laws of the universe, so surprises are inevitable.

“There was a young lady of Wight

Who travelled much faster than light

She departed one day

In a relative way

And arrived on the previous night.”

Hawking quotes a limerick that amusingly illustrates how faster-than-light travel, were it possible, could take a traveler backward in time. This might cause all sorts of logical problems (reminiscent of the Back to the Future films): Time travelers could go way into the past, kill their own grandparents, and cease to exist, whereupon they wouldn’t have been alive to kill their grandparents, who survive and whose grandchildren become time travelers who go into the past to kill the grandparents, in an endless loop.

“In 2009 I held a party for time travellers in my college, Gonville and Caius in Cambridge, for a film about time travel. To ensure that only genuine time travellers came, I didn’t send out the invitations until after the party. On the day of the party, I sat in college hoping, but no one came. I was disappointed, but not surprised, because I had shown that if general relativity is correct and energy density is positive, time travel is not possible. I would have been delighted if one of my assumptions had turned out to be wrong.”

This passage captures the author’s mischievous sense of humor alongside his curiosity. He describes how he invited people to a party after it occurred to test whether time travel existed. It didn’t work, which suggested to Hawking that time travel isn’t possible. (On the other hand, maybe time travelers simply hadn’t yet visited the time when they could read the invitation.) Hawking expected that his results would be negative yet felt disappointment. As a scientist, he’s prepared to abandon his carefully worked-out theories if evidence appears that overturns them. He hoped someone would show up from the future, prove him wrong, and open up vast new possibilities for science.

“I am uncomfortably, acutely aware of the passage of time, and have lived much of my life with a sense that the time that I have been granted is, as they say, borrowed.”

The author made excellent use of his time on Earth. Despite his having a debilitating and usually rapidly fatal disease, his extraordinary lifespan set a record: No one has lived longer under such conditions. With help from advanced medical care and dedicated assistants, Hawking was able to concentrate on physics, to which he contributed multiple theories that garnered him much recognition. His life was well spent despite trying conditions.

“As we stand on the brink of a Second Nuclear Age and a period of unprecedented climate change, scientists have a special responsibility, once again, to inform the public and to advise leaders about the perils that humanity faces.”

Besides explaining to a general audience the discoveries he and other scientists have made during his lifetime, Hawking wants to warn humanity of the dangers it faces. He feels that it’s his responsibility—as a researcher intimately familiar with the science that supports deep concerns about climate change and the risks posed by the technology of mass warfare—to sound the alert in his final publication for the public. In addition to climate and war dangers, he warns about the dangers associated with uncontrolled artificial intelligence (AI).

“Not to leave planet Earth would be like castaways on a desert island not trying to escape. We need to explore the solar system to find out where humans could live.”

Because Hawking is fairly certain that humanity will largely destroy itself sometime during the next 1,000 years, he believes it’s crucially important that we explore space in search of new homes for people. Having humans on other worlds wouldn’t save Earth from destruction but could protect the human species from annihilation. To insist that people must first solve problems here before spending resources on trips into space is to ignore the dangers that threaten our descendants.

“[E]ngineers’ challenges tend, eventually, to be solved.”

Although pessimistic about humanity’s ability to avoid upcoming disasters, Hawking is optimistic about technology: He believes that technological problems will fall to the relentlessly logical brains of scientists and engineers, and he puts his faith on their shoulders, hoping that they’ll overcome the difficulties of space exploration in time to help colonize other worlds and thereby populate places beyond the endangered Earth.

“Human colonisation on other planets is no longer science fiction. It can be science fact. The human race has existed as a separate species for about two million years. Civilisation began about 10,000 years ago, and the rate of development has been steadily increasing. If humanity is to continue for another million years, our future lies in boldly going where no one else has gone before. I hope for the best. I have to. We have no other option.”

Hawking’s great hope is that humanity travels into space to establish new homes on other planets and moons. He considers Earth doomed because of human foolishness; his hopes for our future lie among the stars. People living on other planets will continue to be foolish, but at least they’ll be spread out. For Hawking, our destiny, and perhaps our greatness, lies beyond Earth.

“Intelligence is central to what it means to be human. Everything that civilisation has to offer is a product of human intelligence.”

People might argue that brainpower isn’t as important as love or dedication to a great cause, but Hawking would argue that it’s brains that make love and commitment possible. One can easily see why intelligence mattered so much to Hawking, whose life of the mind became all the more important to him as his body failed. Civilization depends on intelligence; people pride themselves on it, and it’s part of how we define ourselves as members of the family of life on Earth. Thus, brainpower and the creative use of our minds is vital to our future, both to solve the problems we face and to advance our civilization.

“At some point during our 13.8 billion years of cosmic history, something beautiful happened […] information processing got so intelligent that life forms became conscious. Our universe has now awoken, becoming aware of itself. I regard it a triumph that we, who are ourselves mere stardust, have come to such a detailed understanding of the universe in which we live.”

For Hawking, humankind’s greatest achievement is science. By applying it, people have walked on the moon, discovered the shape of the universe, and learned much about its workings. The evolution of protoplasm, over billions of years, into beings who ask big questions and answer them seems to Hawking a monumental achievement. He implies that the credit should go to the universe itself; in any case, it’s a wonder of reality that dust from interstellar space organized itself into brains that can look back at their origins and see forward to even greater possibilities.

“When we invented fire, we messed up repeatedly, then invented the fire extinguisher. With more powerful technologies such as nuclear weapons, synthetic biology and strong artificial intelligence, we should instead plan ahead and aim to get things right the first time, because it may be the only chance we will get. Our future is a race between the growing power of our technology and the wisdom with which we use it. Let’s make sure that wisdom wins.”

The future of AI, like the future of nuclear power or environmental change, can be handled well or poorly. Each holds the promise both of great benefits and terrible disasters. The author worries that, at the moment when humanity stands to benefit the most from its inventions, it will instead destroy itself. He wants us not to abandon technology but to use it wisely and with care, anticipating problems early and preventing them, so that all people can benefit from it and the world remain safe for everyone.

“People asked a computer, ‘Is there a God?’ And the computer said, ‘There is now,’ and fused the plug.”

Many people assume that we can control AI simply by unplugging it. However, such machines may eventually figure out how to prevent humans from stopping them. As AI machines become smarter, they may begin to transcend human demands. The author implies that AI will eventually have godlike powers and that we’ll be lucky if it continues to serve us rather than ultimately controlling us.

“If you know how something works, you can control it. It sounds so simple when I say it like that! It is an absorbing and complex endeavour that has fascinated and thrilled me throughout my adult life.”

The author gets to the essence of his motivations: He wants to know how the universe works. A man who had progressively less control over his body instead acquired an increasingly vast knowledge of the cosmos. Others may build on his discoveries, learn further to control the processes that enable them to visit the stars, and perhaps make constructive use of Hawking’s work.