Brief Answers to the Big Questions

by Stephen Hawking

After my expectations had been reduced to zero, every new day became a bonus, and I began to appreciate everything I did have. While there’s life, there is hope.

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.

To my colleagues, I’m just another physicist, but to the wider public I became possibly the best-known scientist in the world. This is partly because scientists, apart from Einstein, are not widely known rock stars, and partly because I fit the stereotype of a disabled genius. I can’t disguise myself with a wig and dark glasses—the wheelchair gives me away.

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

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.

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.

I think the universe was spontaneously created out of nothing, according to the laws of science.

The great mystery at the heart of the Big Bang is to explain how an entire, fantastically enormous universe of space and energy can materialise out of nothing. The secret lies in one of the strangest facts about our cosmos. The laws of physics demand the existence of something called “negative energy.”

When the Big Bang produced a massive amount of positive energy, it simultaneously produced the same amount of negative energy. In this way, the positive and the negative add up to zero, always. It’s another law of nature. So where is all this negative energy today? It’s in the third ingredient in our cosmic cookbook: it’s in space.

The laws of nature itself tell us that not only could the universe have popped into existence without any assistance, like a proton, and have required nothing in terms of energy, but also that it is possible that nothing caused the Big Bang. Nothing.

As we travel back in time towards the moment of the Big Bang, the universe gets smaller and smaller and smaller, until it finally comes to a point where the whole universe is a space so small that it is in effect a single infinitesimally small, infinitesimally dense black hole. And just as with modern-day black holes, floating around in space, the laws of nature dictate something quite extraordinary. They tell us that here too time itself must come to a stop. 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.

Do I have faith? We are each free to believe what we want, and it’s my view that the simplest explanation is that there is no God. No one created the universe and no one directs our fate. This leads me to a profound realisation: there is probably no heaven and afterlife either. I think belief in an afterlife is just wishful thinking. There is no reliable evidence for it, and it flies in the face of everything we know in science. I think that when we die we return to dust. But there’s a sense in which we live on, in our influence, and in our genes that we pass on to our children. We have this one life to appreciate the grand design of the universe, and for that I am extremely grateful.

Is the universe actually infinite, or just very large? Did it have a beginning? Will it last for ever or just a long time?

Roger Penrose and I managed to prove geometrical theorems to show that the universe must have had a beginning if Einstein’s general theory of relativity was correct, and certain reasonable conditions were satisfied.

That the universe began with a singularity was not an idea that I or a number of other people were happy with. The reason Einstein’s general relativity breaks down near the Big Bang is that it is what is called a classical theory.

dictum “God does not play dice.”

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.

So there may well be other universes, but unfortunately we will never be able to explore them. We have seen something about the origin of the universe. But that leaves two big questions. Will the universe end? Is the universe unique?

If there is more than a certain critical amount, the gravitational attraction between the galaxies will slow down the expansion. Eventually they will then start falling towards each other and will all come together in a Big Crunch. That will be the end of the history of the universe, in real time.

If the density of the universe is below the critical value, gravity is too weak to stop the galaxies flying apart for ever. All the stars will burn out, and the universe will get emptier and emptier, and colder and colder. So, again, things will come to an end, but in a less dramatic way. Still, we have a few billion years in hand.

What came before the Big Bang? According to the no-boundary proposal, asking what came before the Big Bang is meaningless—like asking what is south of the South Pole—because there is no notion of time available to refer to. The concept of time only exists within our universe.

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.

There is fossil evidence that there was some form of life on Earth about three and a half billion years ago. This may have been only 500 million years after the Earth became stable and cool enough for life to develop. But life could have taken seven billion years to develop in the universe and still have left time to evolve to beings like us, who could ask about the origin of life. If the probability of life developing on a given planet is very small, why did it happen on Earth in about one-fourteenth of the time available?

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. By contrast, there are about 50,000 new books published in the English language each year, containing of the order of a hundred billion bits of information. Of course, the great majority of this information is garbage and no use to any form of life.

Nevertheless, I am sure that during this century people will discover how to modify both intelligence and instincts like aggression.

Laws will probably be passed against genetic engineering with humans. But some people won’t be able to resist the temptation to improve human characteristics, such as size of memory, resistance to disease and length of life. Once such superhumans appear, there are going to be major political problems with the unimproved humans, who won’t be able to compete. Presumably, they will die out, or become unimportant. Instead, there will be a race of self-designing beings, who are improving themselves at an ever-increasing rate.

It might be possible to use genetic engineering to make DNA-based life survive indefinitely, or at least for 100,000 years. But an easier way, which is almost within our capabilities already, would be to send machines. These could be designed to last long enough for interstellar travel. When they arrived at a new star, they could land on a suitable planet and mine material to produce more machines, which could be sent on to yet more stars. These machines would be a new form of life, based on mechanical and electronic components rather than macromolecules. They could eventually replace DNA-based life, just as DNA may have replaced an earlier form of life.

It is difficult to say how often such collisions occur, but a reasonable guess might be every twenty million years, on average. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last sixty-six million years. Other planets in the galaxy, on which life has developed, may not have had a long enough collision-free period to evolve intelligent beings.

Planck showed one could avoid this disaster if one gave up the idea that the amount of radiation could have just any value, and said instead that radiation came only in packets or quanta of a certain size. It is a bit like saying that you can’t buy sugar loose in the supermarket, it has to be in kilogram bags. The energy in the packets or quanta is higher for ultra-violet and X-rays than for infra-red or visible light. It means that unless a body is very hot, like the Sun, it will not have enough energy to give off even a single quantum of ultra-violet or X-rays. That is why we don’t get sunburn from a cup of coffee.

Albert Einstein even wrote a paper in 1939 claiming that stars could not collapse under gravity, because matter could not be compressed beyond a certain point.

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. In fact, it marks the end of space and time itself. That is what Einstein found so objectionable.

If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole. The result is that you will be stretched out lengthwise, and squashed in sideways.

If the black hole has a mass of a few times our Sun, you would be torn apart and made into spaghetti before you reached the horizon. However, 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.

If information were really lost in black holes, we wouldn’t be able to predict the future, because a black hole could emit any collection of particles. It could emit a working television set or a leather-bound volume of the complete works of Shakespeare, though the chance of such exotic emissions is very low. It is much more likely to emit thermal radiation, like the glow from red-hot metal. It might seem that it wouldn’t matter very much if we couldn’t predict what comes out of black holes. There aren’t any black holes near us. But it is a matter of principle. If determinism, the predictability of the universe, breaks down with black holes, it could break down in other situations. There could be virtual black holes that appear as fluctuations out of the vacuum, absorb one set of particles, emit another and disappear into the vacuum again. Even worse, if determinism breaks down, we can’t be sure of our past history either. The history books and our memories could just be illusions. It is the past that tells us who we are. Without it, we lose our identity.

Instead the universe has every single possible history, each with its own probability. There must be a possible history in which there is a lasting peace in the Middle East, though maybe the probability is low.

if general relativity is correct and energy density is positive, time travel is not possible.

The last big such collision with us was about sixty-six million years ago and that is thought to have killed the dinosaurs, and it will happen again. This is not science fiction; it is guaranteed by the laws of physics and probability.

For example, the film 2001: A Space Odyssey showed us with a base on the Moon and launching a manned, or should I say personned, flight to Jupiter.

What we do know is that by three and a half billion years ago the highly complicated molecule DNA had emerged. DNA is the basis for all life on Earth. It has a double-helix structure, like a spiral staircase, which was discovered by Francis Crick and James Watson in the Cavendish lab at Cambridge in 1953. The two strands of the double helix are linked by pairs of nitrogenous bases like the treads in a spiral staircase. There are four kinds of nitrogenous bases: cytosine, guanine, adenine and thymine. The order in which the different nitrogenous bases occur along the spiral staircase carries the genetic information that enables the DNA molecule to assemble an organism around it and reproduce itself.

For the first two billion years or so the rate of increase in complexity must have been of the order of one bit of information every hundred years. The rate of increase of DNA complexity gradually rose to about one bit a year over the last few million years. But now we are at the beginning of a new era in which we will be able to increase the complexity of our DNA without having to wait for the slow process of biological evolution. 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. Of course, many people will say that genetic engineering on humans should be banned. But I rather doubt that they will be able to prevent it.

Clearly developing improved humans will create great social and political problems with respect to unimproved humans. I’m not advocating human genetic engineering as a good thing, I’m just saying that it is likely to happen in the next millennium, whether we want it or not.

Some people say that computers can never show true intelligence, whatever that may be. But 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.

However, the zero gravity of orbit causes a number of undesirable physiological changes, including a weakening of the bones, as well as creating practical problems with liquids and so on. One would therefore want any long-term base for human beings to be on a planet or moon. By digging into the surface, one would get thermal insulation, and protection from meteors and cosmic rays. The planet or moon could also serve as a source of the raw materials that would be needed if the extra-terrestrial community was to be self-sustaining, independent of Earth.

In fact, 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. In other words, with current technology interstellar travel is utterly impractical. Alpha Centauri can never become a holiday destination.

I believe the future of communication is brain–computer interfaces. There are two ways: electrodes on the skull and implants. The first is like looking through frosted glass, the second is better but risks infection. If we can connect a human brain to the internet it will have all of Wikipedia as its resource.

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.

We could be mining rare metals on the Moon, establishing a human outpost on Mars and finding cures and treatments for conditions which currently offer no hope. 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? These are questions for the next generation to work on.

But the advent of super-intelligent AI would be either the best or the worst thing ever to happen to humanity.

And one final 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.

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.