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Brief Answers to the Big Questions - Stephen Hawking

Last updated Aug 29, 2023


# Metadata

# Highlights

# Foreword Eddie Redmayne

He also insisted that I call him Stephen and stop referring to him as Professor. I had been told… (Location 54)

# An Introduction Professor Kip S. Thorne

Over the next decade, Stephen and Roger, combining forces, would go on to prove, ever more convincingly, this singular beginning of time, and also prove ever more convincingly that the core of every black hole is inhabited by a singularity where time ends. (Location 85)

the great value of conversations like this is that they can trigger new directions of thought. (Location 103)

This “Hawking temperature” of a black hole and its “Hawking radiation” (as they came to be called) were truly radical—perhaps the most radical theoretical physics discovery in the second half of the twentieth century. They opened our eyes to profound connections between general relativity (black holes), thermodynamics (the physics of heat) and quantum physics (the creation of particles where before there were none). (Location 109)

I became convinced that the prospects for success were great enough that I should devote most of my own career, and my future students’ research, to helping Rai and other experimenters achieve our gravitational-wave vision. (Location 150)

Newton gave us answers. Hawking gave us questions. And Hawking’s questions themselves keep on giving, generating breakthroughs decades later. (Location 172)

I have shied away from big questions. I don’t have enough skills, wisdom or self-confidence to tackle them. Stephen, by contrast, was always attracted to big questions, whether they were deeply rooted in his science or not. He did have the necessary skills, wisdom and self-confidence. (Location 179)


most people can understand and appreciate the basic ideas if they are presented in a clear way without equations, which I believe is possible and which is something I have enjoyed trying to do throughout my life. (Location 206)

I want to add my voice to those who demand immediate action on the key challenges for our global community. I hope that going forward, even when I am no longer here, people with power can show creativity, courage and leadership. Let them rise to the challenge of the sustainable development goals, and act, not out of self-interest, but out of common interest. I am very aware of the preciousness of time. Seize the moment. Act now. (Location 211)

I grew up in a tall, narrow Victorian house in Highgate, London, which my parents had bought very cheaply during the Second World War when everyone thought London was going to be bombed flat. (Location 219)

I was always very interested in how things operated, and I used to take them apart to see how they worked, but I was not so good at putting them back together again. My practical abilities never matched up to my theoretical qualities. (Location 234)

In the long vacation following my final exam, the college offered a number of small travel grants. I thought my chances of getting one would be greater the further I proposed to go, so I said I wanted to go to Iran. (Location 247)

As a father, I would try to instill the importance of asking questions, always. (Location 287)

I told him never to be afraid to come up with an idea or a hypothesis no matter how daft (his words not mine) it might seem. (Location 289)

there I was able to enjoy full-time use of an electric wheelchair for the first time. It gave me a considerable degree of independence, especially as in the United States buildings and sidewalks are much more accessible for the disabled than they are in Britain. (Location 326)

In 1985, I caught pneumonia on a trip to CERN, the European Organisation for Nuclear Research, in Switzerland. This was a life-altering moment. I was rushed to the Lucerne Cantonal Hospital and put on to a ventilator. The doctors suggested to Jane that things had progressed to the stage where nothing could be done and that they turn off my ventilator to end my life. But Jane refused and had me flown back to Addenbrooke’s Hospital in Cambridge by air ambulance. (Location 337)

because my larynx was still allowing food and saliva into my lungs, they had to perform a tracheostomy. As most of you will know, a tracheostomy takes away the ability to speak. Your voice is very important. If it is slurred, as mine was, people can think you are mentally deficient and treat you accordingly. (Location 341)

Today I use a program called Acat, developed by Intel, which I control by a small sensor in my glasses via my cheek movements. It has a mobile phone, which gives me access to the internet. I can claim to be the most connected person in the world. (Location 348)

We are all time travellers, journeying together into the future. But let us work together to make that future a place we want to visit. Be brave, be curious, be determined, overcome the odds. It can be done. (Location 380)


Science is increasingly answering questions that used to be the province of religion. (Location 393)

But I don’t have a grudge against God. I do not want to give the impression that my work is about proving or disproving the existence of God. My work is about finding a rational framework to understand the universe around us. (Location 399)

One could define God as the embodiment of the laws of nature. However, this is not what most people would think of as God. They mean a human-like being, with whom one can have a personal relationship. When you look at the vast size of the universe, and how insignificant and accidental human life is in it, that seems most implausible. (Location 423)

I use the word “God” in an impersonal sense, like Einstein did, for the laws of nature, so knowing the mind of God is knowing the laws of nature. My prediction is that we will know the mind of God by the end of this century. (Location 426)

His famous equation E = mc2 simply means that mass can be thought of as a kind of energy, and vice versa. So instead of three ingredients, we can now say that the universe has just two: energy and space. (Location 449)

where did all this energy and space come from? The answer was found after decades of work by scientists: space and energy were spontaneously invented in an event we now call the Big Bang. (Location 450)

travel down into this coffee cup—through the milk particles, down to the atomic level and right down to the sub-atomic level, and you enter a world where conjuring something out of nothing is possible. At least, for a short while. That’s because, at this scale, particles such as protons behave according to the laws of nature we call quantum mechanics. And they really can appear at random, stick around for a while and then vanish again, to reappear somewhere else. (Location 481)

Since we know the universe itself was once very small—perhaps smaller than a proton—this means something quite remarkable. It means the universe itself, in all its mind-boggling vastness and complexity, could simply have popped into existence without violating the known laws of nature. (Location 484)

Our everyday experience makes us think that everything that happens must be caused by something that occurred earlier in time, (Location 490)

You can’t get to a time before the Big Bang because there was no time before the Big Bang. We have finally found something that doesn’t have a cause, because there was no time for a cause to exist in. For me this means that there is no possibility of a creator, because there is no time for a creator to have existed in. (Location 512)


Edwin Hubble discovered that many faint patches of light, called nebulae, were in fact other galaxies, vast collections of stars like our Sun, but at a great distance. In order for them to appear so small and faint, the distances had to be so great that light from them would have taken millions or even billions of years to reach us. This indicated that the beginning of the universe couldn’t have been just a few thousand years ago. (Location 586)

Two Russians, Evgeny Lifshitz and Isaak Khalatnikov, actually claimed to have proved that a general contraction without exact symmetry would always lead to a bounce, with the density remaining finite. This result was very convenient for Marxist–Leninist dialectical materialism, because it avoided awkward questions about the creation of the universe. It therefore became an article of faith for Soviet scientists. (Location 611)

If the laws of science are suspended at the beginning of the universe, might not they also fail at other times? A law is not a law if it only holds sometimes. I believe that we should try to understand the beginning of the universe on the basis of science. It may be a task beyond our powers, but at least we should make the attempt. (Location 621)

It is difficult to argue with a mathematical theorem, so in the end Lifshitz and Khalatnikov conceded that the universe should have a beginning. Although the idea of a beginning to the universe might not be very welcome to communist ideas, ideology was never allowed to stand in the way of science in physics. Physics was needed for the bomb, and it was important that it worked. However, Soviet ideology did prevent progress in biology by denying the truth of genetics. (Location 625)

In order to understand the origin of the universe, one therefore has to incorporate the Uncertainty Principle into Einstein’s general theory of relativity. This has been the great challenge in theoretical physics for at least the last thirty years. We haven’t solved it yet, but we have made a lot of progress. (Location 656)

Thus the very fact that we exist as beings that can ask the question “Why is the universe the way it is?” is a restriction on the history we live in. It implies it is one of the minority of histories that have galaxies and stars. This is an example of what is called the Anthropic Principle. The Anthropic Principle says that the universe has to be more or less as we see it, because if it were different there wouldn’t be anyone here to observe it. (Location 687)

This intelligent life need not be anything like humans. Little green men would do as well. In fact, they might do rather better. The human race does not have a very good record of intelligent behaviour. (Location 697)

in M-theory space has ten dimensions (as well as the theory having one dimension of time), but it is thought that seven of the ten spatial directions are curled up very small, leaving three directions that are large and nearly flat. (Location 702)

Why don’t we live in a history in which eight of the dimensions are curled up small, leaving only two dimensions that we notice? A two-dimensional animal would have a hard job digesting food. If it had a gut that went right through, like we have, it would divide the animal in two, and the poor creature would fall apart. So two flat directions are not enough for anything as complicated as intelligent life. There is something special about three space dimensions. In three dimensions, planets can have stable orbits around stars. This is a consequence of gravitation obeying the inverse square law, as discovered by Robert Hooke in 1665 and elaborated on by Isaac Newton. (Location 705)

Quantum fluctuations occur as a consequence of the Uncertainty Principle. Furthermore, these fluctuations were the seeds for structures in our universe: galaxies, stars and us. This idea is basically the same mechanism as so-called Hawking radiation from a black hole horizon, which I had predicted a decade earlier, except that now it comes from a cosmological horizon, the surface that divided the universe between the parts that we can see and the parts that we cannot observe. (Location 726)

in 2003, with the first results from the WMAP satellite. WMAP produced a wonderful map of the temperature of the cosmic microwave sky, a snapshot of the universe at about one-hundredth of its present age. The irregularities you see are predicted by inflation, and they mean that some regions of the universe had a slightly higher density than others. The gravitational attraction of the extra density slows the expansion of that region, and can eventually cause it to collapse to form galaxies and stars. So look carefully at the map of the microwave sky. It is the blueprint for all the structure in the universe. We are the product of quantum fluctuations in the very early universe. God really does play dice. (Location 733)

There may be other universes. M-theory predicts that a great many universes were created out of nothing, corresponding to the many different possible histories. Each universe has many possible histories and many possible states as they age to the present and beyond into the future. Most of these states will be quite unlike the universe we observe. (Location 740)

The universe in the past was small and dense and so it is quite like the nutshell with which I began. Yet this nut encodes everything that happens in real time. So Hamlet was quite right. We could be bounded in a nutshell and count ourselves kings of infinite space. (Location 764)


It is a matter of common experience that things get more disordered and chaotic with time. This observation even has its own law, the so-called second law of thermodynamics. This law says that the total amount of disorder, or entropy, in the universe always increases with time. (Location 779)

We can define life as an ordered system that can keep itself going against the tendency to disorder and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form—like food, sunlight or electric power—into disordered energy, in the form of heat. (Location 783)

A living being like you or me usually has two elements: a set of instructions that tell the system how to keep going and how to reproduce itself, and a mechanism to carry out the instructions. In biology, these two parts are called genes and metabolism. But it is worth emphasising that there need be nothing bio-logical about them. (Location 788)

the Anthropic Principle, the idea that our theories about the universe must be compatible with our own existence. This is based on the self-evident truth that if the universe had not been suitable for life we wouldn’t be asking why it is so finely adjusted. (Location 803)

by now a few thousand planets have been discovered orbiting distant stars. It is estimated that one star in five has an Earth-like planet orbiting it at a distance from the star to be compatible with life as we know it. (Location 832)

The DNA in a human egg or sperm contains about three billion base pairs of nitrogenous bases. However, much of the information coded in this sequence seems to be redundant or is inactive. So the total amount of useful information in our genes is probably something like a hundred million bits. (Location 873)

Even more important is the fact that the information in books can be changed, and updated, much more rapidly. It has taken us several million years to evolve from less advanced, earlier apes. During that time, the useful information in our DNA has probably changed by only a few million bits, so the rate of biological evolution in humans is about a bit a year. (Location 878)

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. (Location 890)

This has meant that no one person can be the master of more than a small corner of human knowledge. People have to specialise, in narrower and narrower fields. This is likely to be a major limitation in the future. (Location 898)

An even greater limitation and danger for future generations is that we still have the instincts, and in particular the aggressive impulses, that we had in caveman days. 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. (Location 900)

I am sure that during this century people will discover how to modify both intelligence and instincts like aggression. (Location 909)

If the human race manages to redesign itself, to reduce or eliminate the risk of self-destruction, it will probably spread out and colonise other planets and stars. However, long-distance space travel will be difficult for chemically based life forms—like us—based on DNA. The natural lifetime for such beings is short compared with the travel time. (Location 914)

In science fiction, they overcome this difficulty by space warps, or travel through extra dimensions. But I don’t think these will ever be possible, no matter how intelligent life becomes. In the theory of relativity, if one can travel faster than light, one can also travel back in time, and this would lead to problems with people going back and changing the past. (Location 918)

I discount suggestions that UFOs contain beings from outer space, as I think that any visits by aliens would be much more obvious—and probably also much more unpleasant. (Location 931)

But we need to be wary of answering back until we have developed a bit further. Meeting a more advanced civilisation, at our present stage, might be a bit like the original inhabitants of America meeting Columbus—and I don’t think they thought they were better off for it. (Location 956)


“God does not play dice.” He seemed to have felt that the uncertainty was only provisional and that there was an underlying reality, in which particles would have well-defined positions and speeds and would evolve according to deterministic laws in the spirit of Laplace. This reality might be known to God, but the quantum nature of light would prevent us seeing it, except through a glass darkly. (Location 1020)

The wave function contains all that one can know of the particle, both its position and its speed. If you know the wave function at one time, then its values at other times are determined by what is called the Schrödinger equation. (Location 1039)

it still allows us to predict, with certainty, one combination of position and speed. However, even this degree of certainty seems to be threatened by more recent developments. The problem arises because gravity can warp space–time so much that there can be regions of space that we can’t observe. (Location 1043)

we cannot, even in principle, observe the particles inside a black hole. (Location 1046)

In principle, the laws allow us to predict the future. But in practice the calculations are often too difficult. (Location 1055)


Although gravity is by far the weakest of the known forces of nature, it has two crucial advantages over other forces. First, it acts over a long range. The Earth is held in orbit by the Sun, ninety-three million miles away, and the Sun is held in orbit around the centre of the galaxy, about 10,000 light years away. The second advantage is that gravity is always attractive, unlike electric forces which can be either attractive or repulsive. (Location 1074)

if one neglected pressure, a uniform spherically systematic symmetric star would contract to a single point of infinite density. Such a point is called a singularity. All our theories of space are formulated on the assumption that space–time is smooth and nearly flat, so they break down at the singularity, where the curvature of space–time is infinite. (Location 1091)

singularities formed by the collapse of stars or other bodies are hidden from view inside black holes. A black hole is a region where gravity is so strong that light cannot escape. (Location 1106)

A black hole has a boundary called the event horizon. It is where gravity is just strong enough to drag light back and prevent it from escaping. (Location 1112)

As you get nearer the Falls, the current gets faster. This means it pulls harder on the front of the canoe than the back. There’s a danger that the canoe will be pulled apart. (Location 1116)

if you fell into a much larger black hole, with a mass of more than a million times the Sun, the gravitational pull would be the same on the whole of your body and you would reach the horizon without difficulty. So, if you want to explore the inside of a black hole, make sure you choose a big one. There is a black hole with a mass of about four million times that of the Sun at the centre of our Milky Way galaxy. (Location 1119)

only objects heavier than a particular weight can form black holes. That weight is about the same as that of a grain of salt. (Location 1163)

calculations predicted that a black hole creates and emits particles and radiation, just as if it were an ordinary hot body, with a temperature that is proportional to the surface gravity and inversely proportional to the mass. (Location 1189)

Quantum mechanics implies that the whole of space is filled with pairs of virtual particles and antiparticles that are constantly materialising in pairs, separating and then coming together again, and annihilating each other. These particles are called virtual, because, unlike real particles, they cannot be observed directly with a particle detector. (Location 1194)

A mountain-sized black hole would give off X-rays and gamma rays, at a rate of about ten million megawatts, enough to power the world’s electricity supply. (Location 1206)

Another possibility, however, is that we might be able to create micro black holes in the extra dimensions of space–time. According to some theories, the universe we experience is just a four-dimensional surface in a ten- or eleven-dimensional space. The movie Interstellar gives some idea of what this is like. (Location 1210)

For more than 200 years, we have believed in scientific determinism—that is, that the laws of science determine the evolution of the universe. (Location 1223)


In conclusion, rapid space travel and travel back in time can’t be ruled out according to our present understanding. (Location 1453)


The universe is a violent place. (Location 1509)

we are, by nature, explorers. Motivated by curiosity. This is a uniquely human quality. (Location 1524)

Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth. If we stay, we risk being annihilated. (Location 1529)

There has been relatively little change in human DNA in the last 10,000 years. But it is likely that we will be able to redesign it completely in the next thousand. (Location 1608)

In a way, the human race needs to improve its mental and physical qualities if it is to deal with the increasingly complex world around it and meet new challenges like space travel. (Location 1615)

it seems to me that if very complicated chemical molecules can operate in humans to make them intelligent, then equally complicated electronic circuits can also make computers act in an intelligent way. And if they are intelligent they can presumably design computers that have even greater complexity and intelligence. (Location 1622)

I think the present world order has a future, but it will be very different. (Location 1629)


I’m not denying the importance of fighting climate change and global warming, but we can do that and still spare a quarter of a per cent of world GDP for space. Isn’t our future worth a quarter of a per cent? (Location 1657)

A goal of a base on the Moon by 2050, and of a manned landing on Mars by 2070, would reignite the space programme, and give it a sense of purpose, in the same way that President Kennedy’s Moon target did in the 1960s. (Location 1671)

the distance to Alpha Centauri is so great that to reach it in a human lifetime a spacecraft would have to carry fuel with roughly the mass of all the stars in the galaxy. (Location 1732)


The establishment of shared theoretical frameworks, combined with the availability of data and processing power, has yielded remarkable successes in various component tasks, such as speech recognition, image classification, autonomous vehicles, machine translation, legged locomotion and question-answering systems. (Location 1812)

Whereas the short-term impact of AI depends on who controls it, the long-term impact depends on whether it can be controlled at all. (Location 1839)

We spend a great deal of time studying history, which, let’s face it, is mostly the history of stupidity. So it’s a welcome change that people are studying instead the future of intelligence. (Location 1860)

The report acknowledges the possibility that within a few decades AI could surpass human intellectual capacity and challenge the human–robot relationship. (Location 1872)

Creating realistic digital surrogates of ourselves is an ambitious dream, but the latest technology suggests that it may not be as far-fetched an idea as it sounds. (Location 1879)

Interactive tutors could prove useful for massive open online courses (MOOCs) and for entertainment. (Location 1884)

How we connect with the digital world is key to the progress we’ll make in the future. (Location 1886)

I believe the future of communication is brain–computer interfaces. (Location 1897)

Intelligence is characterised as the ability to adapt to change. Human intelligence is the result of generations of natural selection of those with the ability to adapt to changed circumstances. We must not fear change. We need to make it work to our advantage. (Location 1906)

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. (Location 1915)


A key element for Einstein was imagination. Many of his discoveries came from his ability to reimagine the universe through thought experiments. (Location 1930)

If you know how something works, you can control it. (Location 1940)

for each mind to achieve its full potential, it needs a spark. The spark of enquiry and wonder. Often that spark comes from a teacher. (Location 1945)

If you look behind every exceptional person there is an exceptional teacher. When each of us thinks about what we can do in life, chances are we can do it because of a teacher. (Location 1948)

Most people respond to a qualitative, rather than a quantitative, understanding, without the need for complicated equations. Popular science books and articles can also put across ideas about the way we live. However, only a small percentage of the population read even the most successful books. Science documentaries and films reach a mass audience, but it is only one-way communication. (Location 1959)

Among the problems I count global warming, finding space and resources for the massive increase in the Earth’s human population, rapid extinction of other species, the need to develop renewable energy sources, the degradation of the oceans, deforestation and epidemic diseases—just to name a few. (Location 1968)

The huge questions of existence still remain unanswered—how did life begin on Earth? What is consciousness? Is there anyone out there or are we alone in the universe? (Location 1973)

As an optimist, I believe that we can create AI for the good of the world, that it can work in harmony with us. We simply need to be aware of the dangers, identify them, employ the best possible practice and management and prepare for its consequences well in advance. (Location 1993)

our future world will be equally transformed in ways we are only beginning to conceive. Information on its own will not take us there, but its intelligent and creative use will. (Location 2009)

I believe the future of learning and education is the internet. People can answer back and interact. In a way, the internet connects us all together like the neurons in a giant brain. And with such an IQ, what cannot we be capable of? (Location 2013)

I am advocating that all young people should be familiar with and confident around scientific subjects, whatever they choose to do. They need to be scientifically literate, and inspired to engage with developments in science and technology in order to learn more. (Location 2018)

Through scientific endeavour and technological innovation, we must look outwards to the wider universe, while also striving to fix the problems on Earth. (Location 2028)

point—we never really know where the next great scientific discovery will come from, nor who will make it. Opening up the thrill and wonder of scientific discovery, creating innovative and accessible ways to reach out to the widest young audience possible, greatly increases the chances of finding and inspiring the new Einstein. Wherever she might be. (Location 2032)

So remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious. And however difficult life may seem, there is always something you can do and succeed at. It matters that you don’t just give up. Unleash your imagination. Shape the future. (Location 2035)

# Afterword Lucy Hawking

It was effortful for him to communicate—but he made that effort, constantly adapting his equipment as he further lost mobility. He selected his words precisely so that they would have maximum impact when spoken in that flat electronic voice which became so oddly expressive when used by him. (Location 2066)

As a small child, I intensely disliked the way strangers felt free to stare at us, sometimes with open mouths, as my father piloted his wheelchair at insane speeds through Cambridge, accompanied by two mop-haired blond children, often running alongside while trying to eat an ice cream. (Location 2072)

I thought it was perfectly normal to ask grown-ups lots of challenging questions because this is what we did at home. (Location 2076)

As time dulls the raw grief, I have reflected that it could take me for ever to process our experiences. In a way, I’m not even sure I want to. Sometimes, I just want to hold on to the last words my father said to me, that I had been a lovely daughter and that I should be unafraid. (Location 2086)

I will never be as brave as him—I’m not by nature a particularly courageous person—but he showed me that I could try. And that trying might turn out to be the most important part of courage. (Location 2088)