The following lecture was given by Stephen Hawking
in 1998 as part of the White House
Millennium Council. Some fortunate people at SGI
where able to attend a preview of this lecture when Stephen Hawking spoke there also. (The web page about this is at
- since the writing of this, SGI has removed the page. It is still available at http://clinton2.nara.gov/Initiatives/Millennium/shawking.html
- the National Archives for the Clinton Administration.)
Realize that this is a lecture, and while there is great amounts of useful and interesting information in it, for the best effect it should be read out loud. If you happen to have a 'cheap' voice synthesizer you get much more of the real effect - some of the humor best comes out when it is done in Stephen Hawking's "classic" voice.
My theme tonight is science in the new millennium
. The popular
picture of science in the future
is shown on television every night in science fiction
series like Star Trek
. They even persuaded me to take part, not that it was difficult.
(Clip from StarTrek Shown: Descent, Part I (TNG) (you know, the one with Newton, Einstein and Hawking playing poker with Data.))
Because of the red alert I never collected my winnings. I approached Paramount studios but they didn't know the exchange rate.
The Star Trek appearance was great fun, but I show it to make a serious point. Nearly all the visions of the future that we have been shown from HG Wells onwards have been essentially static. They show a society that is in most cases far in advance of ours, in science, in technology, and in political organization. (The last might not be difficult). There must have been great changes with their accompanying tensions and upsets in the period between now and then. But by the time we are shown the future science, technology, and the organization of society, are supposed to have achieved a level of near perfection.
I want to question this picture and ask if we will ever reach a final steady state of science and technology. At no time in the ten thousand years or so since the last Ice Age has the human race been in a state of constant knowledge and fixed technology. There have been a few set backs like the Dark Ages after the fall of the Roman Empire. But the world's population which is a measure of our technological ability to preserve life and feed ourselves has risen steadily, with a few hiccups like the Black Death. In the last two hundred years the growth has become exponential, that is, the population grows by the same percentage each year. Currently the rate is about 1.9% a year. 1.9% may not sound very much but it means that the world population doubles every 40 years. Other measures of technological development in recent times are electricity consumption, or the number of scientific articles. They also show exponential growth with a doubling time of 40 years or less. Indeed, we now have such heightened expectations that some people feel cheated by politicians and scientists because we have not already achieved the Utopian visions of the future. For example, the film 'Two Thousand and One' showed us with a base on the Moon and launching a manned, or should I say personned, flight to Jupiter. I can't see us managing that in the next three years, whoever wins the
There is no sign that scientific and technological development will slow down and stop in the near future. Certainly not by the time of Star Trek which is only about 300 years away. But the present exponential growth
can not continue for the next millennium. By the year 2600 the world's population would be standing shoulder to shoulder and the electricity consumption would make the Earth glow red hot. If you stacked the new books being published next to each other you would have to move at 90 miles an hour just to keep up with the end of the line. Of course by 2600, new artistic and scientific work will come in electronic forms rather than as physical books and papers. Nevertheless, if the exponential growth continued, there would be ten papers a second in my kind of theoretical physics, and no time to read them.
Clearly the present exponential growth can not continue indefinitely. So what will happen? One possibility is that we wipe ourselves out completely by some disaster such as a nuclear war. There is a sick joke that the reason we have not been contacted by extra-terrestrials is that when a civilization reaches our stage of development it becomes unstable and destroys itself. Of course it is possible that UFO's really do contain aliens, as many people believe, and the government is hushing it up. I couldn't possibly comment!
Personally I believe there's a different explanation why we have not been contacted, but I won't go into it here. However even without that there is a very real danger that we will kill everything on this planet now that we have the technological power to do so. Even if we don't destroy ourselves completely there is the
possibility that we might descend into a state of brutalism and barbarity like the opening scene of Terminator.
But I'm an optimist. I think we have a good chance of avoiding both Armageddon and a new Dark Ages. So how will we develop in science and technology over the next millennium? This is very difficult to answer. But let me stick my neck out and offer my predictions for the future. I will have some chance of being right about the next hundred years, but the rest of the millennium will be wild speculation.
Our modern understanding of science began about the same time as the European settlement of North America. In 1687 Isaac Newton, the second Lucasian professor at Cambridge, published his theory of gravity and in 1864 Clerk Maxwell, another Cambridge man, discovered the equations that govern electricity and magnetism. By the end of the 19th century it seemed that we were about to achieve a complete understanding of the universe in terms of what are now known as classical laws. These correspond to what might seem the common sense notion that physical quantities such as position, speed, and rate of rotation, should be both well defined and continuously variable. But common sense is just another name for the prejudices that we have been brought up with. Common sense might lead us to expect quantities like energy to be continuous. But from the beginning of the 20th century observations began to show that energy came in discrete packets called quanta. It seems that Nature is grainy not smooth.
A new kind of theory called quantum mechanics was formulated in the early years of the 20th century. Quantum theory is a completely different picture of reality so it should concern us all but it is hardly known outside physics and chemistry and not even properly understood by many in those fields. Yet if, as I hope basic science becomes part of general awareness what now appear as the paradoxes of quantum theory will seem as just common sense to our children's' children.
In quantum theory things don't have a single unique history as our
present day common sense would suggest. Instead they have every possible
history each with its own probability. There must have been a history in
which the Chicago Cubs won the World Series, though maybe the probability
was low. However for large scale systems like base ball games the
probability is normally peaked around a single history so there is very little uncertainty. But when one goes to the small lengths scales of individual particles the uncertainty can become very large. For example, if one knows that a particle is at a point A at a certain time then at a later time it can be anywhere because it can have any path or history. To calculate the probability that it is at a point B one has to add up the probabilities for all the paths or histories that take it from A to B. This idea of a sum over all possible histories is due to the American physicist and one time bongo drum player Richard Feynman.
The possible particle histories have to include paths that travel faster than light and even paths that go back in time. Before anyone rushes out to patent a time machine let me say that in normal circumstances at least, one can not use this for time travel. However paths that go back in time are not just like angels dancing on a pin. They have real observational consequences. Even what we think of as empty space is full of particles moving in closed loops in space and time. That is they move forward in time on one side of the loop and backwards in time on the other side. These closed loops are said to be virtual particles because they can not be measured directly with a particle detector. However their effects can be measured indirectly. One way is to have a pair of metal plates close together. The effect of the plates is to reduce slightly the number of closed loops in the region between the plates relative to the number outside. There are thus more closed loops hitting the outside edges of the plates and bouncing off than there are hitting the inside edges. One would therefore expect there to be a small force pushing the plates together. This force, which was first predicted by the Turkish physicist Hendrick Casimir, has been observed experimentally. So we can be confident that closed particle loops really exist.
The awkward thing is that because there's an infinite number of points in space and time there are an infinite number of possible closed loops of particles. This infinite number of loops didn't matter in the calculation of the force between two plates because the numbers between the plates and outside them are both infinite. There is a well defined way in which one can subtract one infinity from the other and get a finite answer. It is a bit like the American budget. Both the government tax revenue, and its expenditure, are very large sums, almost infinite. Yet if one is careful one can subtract one from another and get a small surplus, at least until the next election.
Where the infinite number of closed loops caused trouble was when people tried to combine quantum theory with Einstein's General Theory of Relativity. This is the other great scientific revolution of the first half of the 20th century. It says that space and time are not flat like common sense once told us that the Earth was flat. Instead, they are warped and distorted by the matter and energy in them. An infinite number of closed loops of particles would have an infinite amount of energy and would curl space and time up to a single point.
To deal with this infinite energy requires some really creative accounting. The key concept was a new kind of balance or symmetry in nature called super symmetry, which was first proposed by two Russians, Golfand and Likhtman, in 1971. The idea was that as well as the ordinary dimensions of space and time with which we are familiar, there were extra dimensions that were measured in what are called Grassmann numbers. Of course, science fiction has been telling us for years that there are extra dimensions. But even science fiction did not think of anything as odd as Grassmann dimensions. Here the word "odd" has a technical use as well as the usual meaning of peculiar. Ordinary numbers are said to be even because it doesn't matter in what order one multiplies them. 6 times 4 is the same as 4 times 6. But Grassmann numbers are odd in the sense that x times y, is minus y times x.
The existence of these extra odd dimensions implies that every species of particle must have a super partner species. The super partner species will also have closed loops of particles. But the energy of the super partner loops will have the opposite sign to those of the original species. Thus the infinite energies tend to cancel out. But as the President knows, balancing the budget is a very delicate business. Even if one removes the main deficit smaller deficits have a nasty habit of appearing. Much of the work in theoretical physics in the last twenty years has been looking for a theory in which the infinities cancel completely. Only then will we be able to unify Quantum Theory with Einstein's General Relativity and achieve a complete theory of the basic laws of the universe.
What are the prospects that we will discover this complete theory in the next millennium. I would say they were very good but then I'm an optimist. In 1980 I said I thought there was a 50-50 chance that we would discover a complete unified theory in the next twenty years. We have made some remarkable progress in the period since then but the final theory seems about the same distance away. Will the Holy Grail of physics be always just beyond our reach? I think not. At the beginning of the 20th century we understood the workings of nature on the scales ofclassical physics which is good down to about a hundredth of a millimeter. The work on atomic physics in the first thirty years of the century took our understanding down to lengths of a millionth of a millimeter. Since then, research on nuclear and high energy physics has taken us to length scales that are smaller by a further factor of a billion. It might seem that we could go on forever discovering structures on smaller and smaller length scales. However there is a limit to this series as there is to the series of Russian dolls within Russian dolls. Eventually one gets down to a smallest doll, which can't be taken apart any more. In physics the smallest doll is called the Planck length and is a millimeter divided by a hundred thousand billion billion billion. We are not about to build particle accelerators that can probe to distances that small. They would have to be larger than the solar system and they are not likely to be approved in the present financial climate. However, there are consequences of our theories that can be tested by much more modest
machines. By far the most important of these is super symmetry which is fundamental to most attempts to unify Einstein's General Relativity with Quantum Theory. This would be confirmed by the discovery of super
partners to the particles that we already know. The Superconducting Super Collider (the SSC) was being built in Texas and would have reached the energies at which super partners were expected. However, the United States went through a fit of feeling poor and canceled the project half way. At the risk of causing embarrassment, I have to say I think this was a very short sighted decision. I hope that the US, and other governments will do better in the next millennium.
I expect super symmetry will be confirmed eventually by experiments at CERN in Geneva. But it won't be possible to probe down to the Planck length in the laboratory. We can study the Big Bang to get observational evidence at higher energies and shorter length scales than we can achieve on Earth. However, to a large extent we shall have to rely on mathematical beauty and consistency to find the ultimate Theory of Everything. Nevertheless I am confident we will discover it by the end of the 21st century and probably much sooner. I would take a bet at 50-50 odds that it will be within twenty years starting now.
The Star Trek vision of the future that we achieve an advanced but essentially static level may come true in respect of our knowledge of the basic laws that govern the universe. But I don't think we will ever reach a steady state in the uses we make of these laws. The ultimate theory will place no limit on the complexity of systems that we can produce and it is in this complexity that I think the most important developments of the next millennium will be.
By far the most complex systems that we have are our own bodies. Life seems to have originated in the primordial oceans that covered the Earth four billion years ago. How this happened we don't know. It may be that random collisions between atoms built up macro-molecules that could reproduce themselves and assemble themselves into more complicated structures. 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 Cavendishlab at Cambridge in 1953. The two strands of the double helix are linked by pairs of nucleic acids like the treads in a spiral staircase. There are four kinds of nucleic acids. I won't try to pronounce their names because my speech synthesizer makes a mess of them. Obviously it was not designed for molecular biologists. But I can refer to them by their initials, C, G, A, and T. The order in which the different nucleic acids occur along the spiral staircase carries the genetic information that enables the DNA molecule to assemble an organism around it and reproduce itself. As the DNA made copies of itself there would have been occasional errors in the order of the nucleic acids along the spiral. In most cases the mistakes in copying would have made the DNA unable to reproduce itself. Such genetic errors, or mutations as they are called, would die out. But in a few cases the error or mutation would increase the chances of the DNA surviving and reproducing. This natural selection of mutations was first proposed by another Cambridge man, Charles Darwin, in 1857, though he didn't know the mechanism for it. Thus the information content in the sequence of nucleic acids would gradually evolve and increase in complexity.
Because biological evolution is basically a random walk in the space of all genetic possibilities it has been very slow. The complexity, or number of bits of information that are coded in DNA is given roughly by the number of nucleic acids in the molecule. Each bit of information can be thought of as the answer to a yes no question. 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 no significant change in human DNA in the last ten thousand years. But it is likely that we will be able to completely redesign it in the next thousand. Of course many people will say that genetic engineering on humans should be banned. But I rather doubt if they will be able to prevent it. Genetic engineering on plants and animals will be allowed for economic reasons and someone is bound to try it on humans. Unless we have a totalitarian world order, someone will design improved humans somewhere.
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. This is why I don't believe science fiction like Star Trek where people are essentially the same four hundred years in the future. I think the human race, and
its DNA, will increase its complexity quite rapidly.
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. And it also needs to increase its complexity if biological systems are to keep ahead of electronic ones. At the moment computers have an advantage of speed, but they show no sign of intelligence. This is not surprising because our present computers are less complex than the brain of an earthworm, a species not noted for their intellectual powers. But computers obey Moore's Law put forward by Gordon Moore of Intel. This says that their speed and complexity double every 18 months. It is one of these exponential growths which clearly can not continue indefinitely. However it will probably continue until computers have a similar complexity to the human brain. 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.
This is why I don't believe the science fiction picture of an advanced but constant future. Instead, I expect complexity to increase at a rapid rate, both in the biological and electronic spheres. Not much of this will happen in the next hundred years, which is all we can reliably predict. But by the end of the next millennium, if we get there, the change will be fundamental.
Lincoln Steffens once said, "I have seen the future and it works." He was actually talking about the Soviet Union, which we now know didn't work very well. Nevertheless, I think the present world order has a future, but it will be very different.