“The Theory of Everything” – By Stephen Hawking: It would be very difficult to form a complete unified theory of everything at once. So instead we(Stephen Hawking and his Colleagues) have progressed by finding partial theories. These describe a limited range of events and ignore other effects or estimate them by some number.
For example, in chemistry, we can calculate the interactions of atoms without knowing the internal structure of an atom’s nucleus. Ultimately, however, one would expect to find a complete, coherent, unified theory that would include all of these partial theories as approximations.
The discovery of such a principle is known as the “integration of physics”. Einstein spent most of his later years unsuccessfully searching for a unified theory, but the time was not ripe: little was known about the nuclear forces. Furthermore, Einstein refused to believe in the reality of quantum mechanics, despite the fact that he had been instrumental in its development.
Yet it seems that the uncertainty principle is a fundamental feature of the universe in which we live. Therefore a successful integrative theory must incorporate this principle.
The chances of finding such a theory seem much better now because we know so much more about the universe. But we must beware of overconfidence. We have seen false mornings before. For example, at the beginning of this century, it was thought that everything could be explained in terms of properties of constant matter, such as elasticity and heat conduction.
The discovery of the atomic structure and the uncertainty principle put an end to it. Again, in 1928, Max Born told a group of visitors to the University of Göttingen, “Physics, as we know it, will be over in six months.
His belief was based on Dirac‘s recent discovery of the equation controlling the electron. It was thought that a similar equation would govern the proton, which was the only other particle known at the time, and this would be the end of theoretical physics.
However, the discovery of neutrons and nuclear forces also turned him on the head. Having said that, I still believe that there are grounds for cautious optimism that we may now be nearing the end of discovering the ultimate laws of nature.
At the moment, we have several partial theories. We have general relativity, a partial theory of gravity, and a partial theory that governs the weak, strong, and electromagnetic forces. The last three can be combined into the so-called grand unified principles.
These are not very satisfactory as they do not involve gravity. The main difficulty in finding a theory that integrates gravity with other forces is that general relativity is a classical theory. That is, it does not include the uncertainty principle of quantum mechanics.
On the other hand, other partial theories necessarily rely on quantum mechanics. Therefore, a necessary first step is to combine general relativity with the uncertainty principle. As we’ve seen, this can produce some remarkable results, such as black holes becoming non-black, and the universe is completely self-contained and without limits.
The trouble is that the uncertainty principle means that even empty space is filled with pairs of virtual particles and antiparticles. There will be an infinite amount of energy in these pairs. This means that their gravitational attraction will bend the universe into an infinitely small size.
Rather similar, seemingly absurd infinitesimals occur in other quantum theories. However, in these other theories, infinities can be canceled out by a process called renormalization. This involves adjusting the mass of the particles and the strength of the forces in theory to an infinite amount.
Although this technique is mathematically questionable, it appears to work in practice. It has been used to make predictions that agree with observations with exceptional accuracy. However, renormalization has a serious drawback from the point of view of trying to find a complete theory.
When you subtract infinity from infinity, the answer can be whatever you want. This means that the true values of the masses and the strength of the forces cannot be predicted by theory.
Instead, they have to be chosen to fit into the comments. In the case of general relativity, there are only two quantities that can be adjusted: the force of gravity and the value of the cosmological constant. But adjusting these is not enough to remove all infinity.
Therefore, one has a theory that seems to predict that some quantities, such as the curvature of space-time, are in fact infinite, yet these quantities can be observed and measured to be completely finite.
In an attempt to address this problem, a theory called “supergravity” was suggested in 1976. This theory was actually general relativity with some additional particles.
In general relativity, the force of gravity can be carried by a particle of spin 2 called the graviton. The idea was to add some other new particles of spin 3/2, 1, 1/2, and 0. In a sense, all of these particles can be thought of as different aspects of the same “superparticle”. Virtual particle/antiparticle pairs of spins 1/2 and 3/2 will have negative energy.
This spin will cancel out the positive energy of the virtual pairs of particles 0, 1, and 2. In this way, many possible infinities would cancel out, but it was suspected that some infinite might still remain.
However, the calculations required to find whether any infinities were non-stop were so long and difficult that no one was willing to perform them. Even with a computer, it was believed that it would take at least four years.
Chances were high that someone would make at least one mistake, and probably more. So one would know that one had the correct answer if someone else repeated the calculation and got the same answer, and it was very unlikely. Because of this problem, opinion changed in favor of what is called string theories.
In these theories, the original objects are not particles that occupy a point in space. Rather, they are things that have length but no other dimensions, such as an infinitely thin loop of string. A particle occupies a point space at each instant. Thus, its history can be represented by a line in space-time called the “world-line”.
On the other hand, a wire encircles a line in space at each instant of time. So its history in space-time is a two-dimensional surface called a “world-sheet”. Any point on such a world-sheet can be described by two numbers, one specifying the time and the other specifying the point’s position on the string.
The worldsheet of a string is a cylinder or tube. A piece through the tube is a circle, representing the position of the string at a particular time. Two pieces of string can be joined together to form a string. It’s like joining two legs on a pair of trousers.
Similarly, a piece of string can be split into two strings. In string theories, what was formerly regarded as particles, is now characterized as waves moving down the string, such as waves on a washing line. The emission or absorption of one particle by another corresponds to the splitting or joining of stars.
For example, the gravitational force of the Sun on Earth corresponds to that of an H-shaped tube or pipe. String theory is like plumbing in a way. The waves on the two vertical sides of H correspond to the particles in the Sun and the Earth, and the waves on the horizontal crossbar correspond to the force of gravity traveling between them.
String theory has a curious history. It was originally invented in the late 1960s in an attempt to find a theory to describe the strong force. The idea was that particles such as protons and neutrons could be thought of like waves on a string.
The strong forces between the particles would correspond to pieces of string that go between other bits of string, as in a spider’s web. For this theory to give the observed value of the strong force between the particles, the strings must be like a rubber band with a stretch of about ten tons.
In 1974 Joel Scherk and John Schwarz published a paper in which they showed that string theory could describe the force of gravity, but only if the tension in the string was very high – about 1039 tons.
String theory’s predictions would be very similar to those of general relativity on the general length scale, but they would differ over much smaller distances—less than 10-33 centimeters. However, his work did not receive much attention, because, around the same time, most people had abandoned the basic string theory of the strong force.
Scherk died under tragic circumstances. He was suffering from diabetes and went into a coma when no one was there to give him an injection of insulin. So Schwarz was left alone as almost the only proponent of string theory, but now with a much higher proposed value of string tension.
It appears that there were two reasons for the sudden resurgence of interest in strings in 1984. One was that people weren’t really making much progress toward showing that supergravity was limited or that what kinds of particles we could observe.
The second was the publication of a paper by John Schwarz and Mike Green, which showed that string theory may be able to explain the existence of particles that have inherent left-handedness in some of the particles we observe.
Whatever the reason, a large number of people soon began working on string theory. A new variant, the so-called heterotic string, was developed. It looked like it might be able to explain the types of particles we see.
String theories also lead to infinity, but it is believed that they all cancel in heterotic string-like versions. However, string theories have a major problem. They seem to be compatible only if space-time has ten or twenty-six dimensions instead of the usual four.
Of course, the extra space-time dimension is a common feature of science fiction; In fact, they are almost a necessity. Otherwise, the fact that relativity implies that one cannot travel faster than light means it would take much longer to cross our own galaxy, let alone travel to other galaxies. The idea of science-fiction is that one can take a shortcut through a higher dimension. It can be depicted as follows.
Imagine that the space we live in had only two dimensions and was curved like the surface of a donut or torus. If you happen to be on one side of the ring and you want to reach a point on the other side, you have to go around the ring. However, if you were able to travel in the third dimension, you could cut straight. Why don’t we pay attention to all these extra dimensions, if they really exist?
Why do we only see three spaces and a one-time dimension? The suggestion is that the other dimensions are curved into space of much smaller sizes, like one million million million millionth of an inch. It’s so small that we don’t notice it. We only see three dimensions of space and a time in which space-time is completely flat.
It’s like the surface of an orange: If you look at it up close, it’s all curved and wrinkled, but if you look at it from afar, you don’t see the bumps and it appears to be smooth. So it is with space-time. On a very small scale, it is ten-dimensional and highly curved. But on a large scale, you don’t see curvature or extra dimension.
If this picture is true, it’s bad news for astronauts. The additional dimensions would be too small to allow the spacecraft through. However, this raises another major problem. Why should some, but not all, dimensions be rolled into a small ball?
Presumably, in the very early universe, all dimensions would have been very curved. Why are the three space and one-time dimensions flattened, while the other dimensions are tightly twisted?
One possible answer is the anthropometric theory. Two space dimensions don’t seem like enough to allow the evolution of complex beings like us. For example, two-dimensional people living on a one-dimensional Earth would have to climb on top of each other to cross each other.
If a two-dimensional creature eats something that it cannot fully digest, it must bring up the remains as it ingested them, because if there was a passage through its body, it would cause the creature to be in two separate compartments. splits into separate parts. Our two-dimensional existence will fall apart.
Similarly, it is difficult to see how blood can be transmitted in a two-dimensional creature. There will also be problems with more than three space dimensions.
The gravitational force between two objects will decrease more rapidly with distance than in three dimensions. The significance of this is that the orbits of the planets around the Sun, like the Earth, would be unstable.
Minimal disturbances from a circular orbit, such as those caused by the gravitational attraction of other planets, will cause Earth to spiral away from the Sun or into the Sun. We either freeze or burn. In fact, the same behavior of gravity with distance would mean that the Sun would also be unstable.
It would either break apart or collapse to form a black hole. In any case, it would not be of much use as a source of heat and light for life on Earth. On a smaller scale, the electric forces causing electrons to orbit around the nucleus in an atom will behave similarly to gravitational forces.
Thus, the electrons will either escape the atom completely or it will spiral into the nucleus. In any case, no one could have had atoms as we know them.
- There really is a complete unified theory, which we will someday
discover if we are smart enough.
- There is no ultimate theory of the universe, just an infinite
sequence of theories that describe the universe more and more accurately.
- There is no theory of the universe. Events cannot be predicted
beyond a certain extent but occur in a random and arbitrary manner.
Some would argue for the third possibility on the grounds that if there were a complete set of laws that would infringe on God’s freedom to change his mind and intervene in the world.
It’s like some old paradox: Can God make a stone so heavy that he can’t lift it? But the idea that God wants to change His mind is an example of the fallacy, pointed out by St. Augustine, that God is to be imagined as an existence over time.
Time is only a property of the universe that God has created. Presumably, he knew what he intended when he installed it. With the advent of quantum mechanics, we have realized that events cannot be predicted with absolute accuracy, but there is always a degree of uncertainty.
If one prefers, this randomness can be attributed to God’s intervention. But that would be a very strange kind of interference. There is no evidence that it is directed towards any purpose. In fact, if that were the case, it wouldn’t have been random. In modern times, we have effectively removed the third possibility by redefining the goal of science.
Our aim is to formulate a set of laws that enable us to predict events to the extent determined by the uncertainty principle. The second possibility, that there is an infinite sequence of more and more sophisticated theories, is consistent with all our experience so far.
On several occasions, we have increased the sensitivity of our measurements or created a new class of observations simply to discover new phenomena that were not predicted by existing theory.
To account for these, we have to develop a more advanced theory. So it wouldn’t be too surprised if we find that our current grand unified theories break down when we test them at larger and more powerful particle accelerators.
In fact, if we don’t expect them to break down, it wouldn’t make sense to spend all that money on building more powerful machines. However, it seems that gravity may provide a limit to this sequence of “boxes within boxes”.
If one had the Planck energy, a particle with an energy greater than 1019 GeV, its mass would be so concentrated that it would cut itself off from the rest of the universe to form a tiny black hole.
Thus, it seems that there must be some limit to the sequence of more and more sophisticated theories as we move towards higher and higher energies. There must be some ultimate principle of the universe. Of course, the Planck energy is a long way from the energy of about one GeV, which is the most we can produce in the laboratory at the present time.
To bridge that gap would require a particle accelerator that is larger than the Solar System. Such an accelerator would be unlikely to be funded in the current economic climate. However, the very early stages of the universe are a region where such energies must have occurred.
I think there’s a good chance that the study of the early universe and the requirements for mathematical stability will lead us to a fully unified theory by the end of the century—always assuming we don’t blow ourselves up first. What would it mean if we actually discovered the ultimate principle of the universe?
This will end a long and glorious chapter in the history of our struggle to understand the universe. But it would also revolutionize the common man’s understanding of the laws that govern the universe.
In Newton’s time, it was possible for an educated person to have an understanding of all human knowledge, at least in outline. But since then the pace of development of science has made this impossible.
Theories were always being changed to account for new observations. They were never properly digested or simplified so that common people could understand them. You had to become an expert, and even then you could only hope for a proper understanding of a small portion of scientific principles.
Furthermore, the rate of progress was so fast that what was learned in school or university was always out of date. Only a few could keep pace with the rapidly expanding range of knowledge. And he had to devote his entire time to it and specialize in a small area.
The rest of the population had little idea of the progress being made or the enthusiasm they were generating. Seventy years ago, according to Eddington, only two people understood the general theory of relativity.
Today thousands of university graduates understand this, and millions are at least familiar with the idea. If a complete unified theory was discovered, it would only be a matter of time before it was digested and simplified in the same way.
Then it could be taught in schools, at least in outline. Then we will all be able to gain some understanding of the laws that govern the universe and are responsible for our existence.
Einstein once asked a question: “How much choice did God have in the creation of the universe?” If a boundary proposal is not true, he had no freedom at all to choose the initial conditions.
Of course, he still had the freedom to choose the rules that the universe obeyed. However, it really wouldn’t have been that much of an option. There can be only one or a lesser number of fully unified principles that are self-sufficient and which allow the existence of intelligent beings.
We can ask about the nature of God, even if there is only one possible unifying principle which is a set of rules and equations. What is it that ignites equations and creates a universe to describe them?
Science’s usual approach to building mathematical models cannot answer the question of why there must be a universe for the model to describe. Why does the universe go to all the trouble of the present?
Is the unified theory so compelling that it brings its own existence? Or does it require a creator, and, if so, does it have any effect on the universe other than being responsible for its existence? And who made it?
Until now, most scientists have been busy developing new theories that describe what the universe is, to asking the question why. On the other hand, people whose vocation is to ask why – philosophers – have not been able to keep up with the progress of scientific theories.
In the eighteenth century, philosophers considered all human knowledge, including science, as their field. They discussed questions such as: Did the universe begin?
However, in the nineteenth and twentieth centuries, science became too technical and mathematical for philosophers or anyone else, except for a few experts.
Philosophers narrowed the scope of their inquiry so much that Wittgenstein, the most famous philosopher of this century, said, “The only remaining work for philosophy is the analysis of language.” What was the decline of the great tradition of philosophy from Aristotle to Kant?
However, if we are to discover a complete theory, it must be understood in a comprehensive theory, not just for a few scientists, but for all. Then we will all be able to participate in the discussion of why the universe exists.
If we find the answer, it will be the ultimate victory of human intelligence. Till then we will know the mind of God.
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