Conversations With Einstein

by Carlos Calle

  The equivalence between gravity and acceleration can take you to it. Returning to the laboratory aboard the accelerating spaceship, one can see that if the scientists examine the path of a ray of light coming horizontally through a small hole on one side of the ship, they see a curved path. I’ll sketch it for you on the back of this envelope:

  It might help you visualize it if you think of a small meteorite that penetrates the accelerating ship. When the meteorite first enters through the hole A, the ship is at a certain position. An instant later, when the meteorite has moved a small distance to B, the ship has accelerated away from this location but the meteorite continues moving along its original path. From the perspective of the meteorite, the ship accelerates in its direction and the floor of the laboratory moves to meet it. From the perspective of the scientists standing on that floor, the path of the meteorite bends and hits the floor here at point F. The same is true for a ray of light: the scientists will see the path of the light ray bending and striking the floor. Since acceleration is the same as gravity, we conclude that a gravitational field also curves the path of a ray of light. That result was of great importance because it could be compared with reality.

  Your sketch does help me to understand it. So the bending-of-light prediction was confirmed?

  Yes, that prediction was confirmed by the British astronomical expedition of 1919. This measurement isn’t easy to make, since the curvature of space close to the gravitational field of the Earth is extremely small. But the Sun’s gravitational field causes a curvature that, in principle, could be measured. I’d calculated the small deviation of light rays from a star passing the Sun at a grazing angle. The star’s light could be seen during a solar eclipse and that’s why Arthur Eddington travelled to West Africa to measure it during the solar eclipse of 1919. He obtained exactly the amount I’d calculated.

  Your discovery showed how the laws of nature are designed. What would you have said if the results had been different and the theory proven wrong?

  Then, I would have been sorry for the dear Lord. The theory is correct.

  QUANTUM THEORY AND REALITY

  Einstein’s first paper of his year of wonders marks the beginning of the long road towards the full development of quantum theory completed by Niels Bohr (1885–1962), Werner Heisenberg (1901–1976), Erwin Schrödinger (1887–1961), and Paul Dirac (1902–1984) in the early 1920s. Einstein never fully accepted quantum physics, because it is a theory of probabilities, not certainties, and he felt it would one day be superseded. Today, several experiments have shown that quantum theory does describe correctly the way nature is. However, there are problems integrating quantum physics with general relativity; and either theory, or both, may one day be supplanted by a more complete theory that integrates them.

  Professor Einstein, you said earlier that your first paper of 1905 provided the foundation for quantum physics. What is quantum physics?

  Quantum physics governs the behaviour of atoms, molecules, subatomic particles and light. It’s the physics of the very small. In contrast, general relativity is the physics of the very large, from rocks to planets and galaxies. Quantum physics was developed out of the need to explain several important observations of the behaviour of matter and radiation that couldn’t be explained with Newtonian physics. The fundamental reason for the failure of Newtonian mechanics in the realm of the atom is that the world turned out to be grainy, not continuous. When you consider radiation, for example, you find that it is made up of very small packets or quanta of energy which are indivisible. It’s similar for matter: when atoms or molecules interact and absorb or give off energy, they do so by means of quanta of energy. An atom can’t absorb half a quantum of energy, since such a thing doesn’t exist. Newtonian physics expects the world to be continuous and that’s why it fails at the atomic level.

  So, both quantum physics and relativity showed Newtonian physics to be incorrect.

  No. Newtonian physics was shown to be incomplete, not incorrect. It is still correct for objects much larger than atoms moving at speeds not close to the speed of light. In fact, both quantum physics and relativity become Newtonian physics for those sizes and velocities. However, no theory is ever proven to be completely correct. It is entirely possible that general relativity could one day be shown to be incomplete – the theory that may replace it should encompass it and expand it, keeping the same approach. However, I think that quantum physics, in spite of its success, isn’t the right approach.

  If quantum physics is not the right approach, is there a theory that can replace it?

  There isn’t any other theory now that can replace it, and I believe it will take a long time to develop one. I must tell you that I’m in the minority in regarding quantum physics to be incomplete. Great physicists like Bohr, Heisenberg, Dirac, Born and many others disagreed with me on this. When pressed, Bohr would say that even if quantum physics were one day replaced by a more comprehensive theory, this new theory would still have the probabilistic properties of quantum physics. I disagree.

  If I follow what you’re saying, it’s the probabilistic properties of quantum physics that you object to. What are those properties specifically?

  Quantum physics does not provide a mathematical representation of the atom or its structure, or of any other physical entity that exists in space and time. What quantum physics does is to determine the probability of finding these particles at a specific location, or in a specific state of motion, when a measurement is performed. I have no objections to the logical construct of the theory and I recognize its important successes. However, the theory forbids one from knowing at once everything one wants to know about an object. One may not ask both where an electron is and how fast it’s moving at a given time. One can’t even ask what an electron is. In quantum physics, those questions have no meaning. But one can calculate the probability of finding the electron at a given location if one attempts to measure it. If quantum physics is correct, one can never know for certain the past or present, much less calculate the future of anything in the universe. I cannot accept that. The theory gives us much, but I don’t think that it really uncovers God’s secrets. I, at any rate, am convinced that God is not playing dice. I believe that quantum physics provides only a temporary interpretation of the world. I think that one day a model of reality will be developed that will represent the objects themselves and not the probability of their existence.

  THE EQUATION

  Einstein discovered his famous E=mc2 equation a few months after completing his paper on the special theory of relativity. In a magnificent three-page paper – the last paper of his year of wonders – he showed how the equations of relativity implied that energy has mass. Some time later, he was also able to show that mass has energy. “This result is of extraordinary importance,” he wrote then. But was the equation correct? Einstein had some doubts, and a few weeks after publication he wrote in a letter to his close friend Conrad Habicht: “the line of thought is amusing and fascinating, but I cannot know whether the dear Lord doesn’t laugh about this and has played a trick on me.”

  Professor, I’d like to turn now to your famous E=mc2 equation. You said earlier that the equation states that energy and mass are equivalent and that one can change into the other. Could you give an example of this?

  The equation says that the mass of an object is a form of energy and that energy is a form of mass. A pair of common magnets can easily illustrate this. If, while holding the magnets, you allow them to come together with the north pole of one magnet facing the south pole of the other, the magnets will pull your hands together. The energy required to pull your hands comes from the conversion of part of the mass of the two magnets into energy. If you had an exceptionally precise scale, you’d find that the two magnets weigh slightly less when they are together than when they are apart. The actual value can be calculated with the E=mc2 equation. The energy E given off, which is contained in the magnets, is equal to the decrease in mass (m) times the speed of l
ight (c) squared. Since the speed of light is such a large number, about 300,000 kilometres per second, the minuscule mass loss of the magnets yields a sizable amount of energy.

  If matter contains so much energy, why did this phenomenon remain unnoticed?

  The mechanisms needed to release large energies, like the ones seen in nuclear reactions, hadn’t been discovered. Unless sufficient energy is given off, it can’t be measured. It’s like the case of a very wealthy man who never spends much of his fortune – no one would know he was wealthy. The equation had to be deduced theoretically using the theory of relativity.

  In what way did your E=mc2 equation make the atom bomb possible?

  The equation was one of many theoretical and experimental discoveries made in our search for the nature of the universe that were used in the construction of the bomb. During radioactive disintegration, when an atom splits into two atoms, a relatively large amount of energy is released. The equation itself says nothing about how to bring about such a split. To illustrate the radioactive disintegration process, we can use the example of our wealthy man again. The original atom that splits into two fragments is like the rich man who has a large amount of money hidden away. When he dies, he leaves all his money to his two children under the condition that they donate a small fraction of their inheritance to the community. The children together end up with less money than their father had, but the man was so wealthy that this small donated fraction is still a large amount of money that destabilizes the local economy.

  Without the equation, the bomb wouldn’t have been possible.

  Yes, but you also need quantum mechanics and nuclear physics, which were developed after the equation.

  Professor, does the equation have other applications?

  The discoveries in nuclear medicine are a direct application. The equation also explains how the millions of tons of hydrogen that are squeezed together in the core of the Sun each second convert some of their mass into the energy that makes life on Earth possible.

  THE BOMB

  “Sir: Some recent work … leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future.” These were the opening words of a letter that Einstein sent to President Roosevelt in 1939 urging him to develop a nuclear bomb ahead of Nazi Germany. Although ultimately other political events led to the start of the Manhattan Project to develop the first nuclear weapon, Einstein deeply regretted the letter. He was a pacifist before the Nazi threat, but became a “militant pacifist” during World War II, serving as a consultant for the US navy on a variety of issues related to weapon design and explosive capabilities. He returned to his stronger pacifist views after the war.

  Professor Einstein, if you’d known how the atomic bomb would be used, would you still have written that now-famous letter to President Roosevelt?

  That is a painful question for me. I now believe that I made a great mistake in writing that letter. There was, of course, justification for writing it: the fear that the Nazis would develop the bomb first. The threat of Hitler was so horrifying that I abandoned my absolute pacifism.

  When and how was the letter written?

  In July of 1939, the physicist Leo Szilárd came to my house in Princeton with the alarming news of Germany’s imminent invasion of Belgium, a country with a large stockpile of uranium. We knew by then that uranium was fissionable and that, given time and funding, a powerful nuclear bomb could be made. Originally, Szilárd had wanted me to write to my friend Queen Elizabeth of Belgium. Knowing of the grave danger, I agreed straight away and in a few days I gave a draft of this letter to Szilárd. He came back later with the physicist Edward Teller and gave me a new draft that he’d written, now addressed to President Roosevelt. I didn’t like Szilárd’s draft and decided to dictate another draft to Teller. Szilárd later wrote two versions of this letter and sent them to me for approval. I signed them both. The longer version was delivered to the President in October.

  You weren’t part of the Manhattan Project that built the bomb. Were you asked to participate?

  My involvement in making the bomb ended with the letter to the President. Instead of prompt action, my letter resulted in the formation of a committee to study the issue. I was asked by the President to serve on that committee but I declined. I was not asked to participate in the Manhattan Project when it was established right after Pearl Harbor. I would have refused that invitation, too, if it had come.

  You said earlier that you had to overcome your pacifist views because of the Nazi threat. Did you return to those views after War World II?

  Yes. My pacifist feeling wasn’t acquired intellectually but is instinctive and innate. I believe that the killing of human beings in a war is no better than common murder. Before War World II, I’d strongly stated my refusal to do war service in any form and said that I’d attempt to convince my friends to take the same position, regardless of the war. I believed then that if only 2 per cent of those called to war declared themselves conscientious objectors, and at the same time demanded that all conflicts be resolved peacefully, wars would end. That was, of course, years before Hitler appeared on the scene. If I’d known that the Nazis weren’t going to succeed in making the bomb, I would never have signed the letter to the President. After the war, I very soon returned to my pacifist views and have often spoken against the proliferation of nuclear weapons. I’m a dedicated but not an absolute pacifist – this means that I am opposed to the use of force under any circumstances except when confronted by an enemy who pursues the destruction of life as an end in itself.

  Once we learned to make nuclear weapons, there was no turning back – the genie was out of the bottle. How do we stop other countries from acquiring the bomb?

  That’s probably impossible. What must change are the policies of the powerful nations. We came out of a world war in which we were forced to endure the shameful low ethical practices of the enemy. The Nazis started the practice of bombing civilian centres and the Japanese then did the same. The Allies then had to respond in kind and even more effectively. However, after the war, instead of re-establishing the sanctity of human life and the safety of innocent civilians, we continue degrading to the same low standards in our present conflicts. This policy only creates antagonism and enhances the danger of war. I don’t know how the Third World War will be fought, but I can tell you what they will use in the Fourth – rocks!

  Is it justifiable for any country to possess nuclear weapons?

  The United States and the other industrialized nations that now possess the bomb have agreed to use it only as a deterrent. I believe that this is the correct policy. To possess the bomb without the promise of not using it unilaterally is a misuse of the bomb for political ends, with the sole purpose of creating fear in the enemy.

  Do you think that humanity will be able to survive this atomic age?

  The discovery of atomic power doesn’t have to bring about the destruction of the world any more than the discovery of fire. If we do everything in our power to prevent the misuse and proliferation of atomic weapons, humanity will survive. But if every effort fails and men end up destroying themselves, the universe will not shed a single tear for them.

  UNFINISHED BUSINESS

  “After an unremitting search during the past two years I now believe I have found the true solution,” wrote Einstein in 1925, referring to his new unified field theory, a single theory encompassing all the forces of nature. His enthusiastic statement turned out to be too optimistic and he would later admit that, on more careful consideration, the true solution was not at hand. Einstein spent the last 30 years of his life working relentlessly on this quest for unification. On Sunday 17 April 1955, feeling slightly better after having suffered an aneurysm the previous Wednesday, he asked for his notebook and continued with his calculations. He died a few hours later, at one o’clock on Monday morning.

  Professor Einstein, is there a discovery you would have liked to have made, a Grail that
slipped your grasp?

  My search for the unification of all fields, a single theory that could describe the nature of the universe, has been my lifelong goal. I’m convinced that this unification will be achieved one day because I cannot accept the idea that nature works through separate fields that have no connection with each other. Electromagnetism, gravity and matter should come naturally out of this unified field theory.

  I’m afraid I don’t fully understand the significance of this unification. Why would the fields need to be unified? Why couldn’t nature have different fields?

  Each individual field theory is incomplete by itself. Moreover, the individual theories of physics contain subtle inconsistencies. Historically, whenever separate theories have been brought together, the inconsistencies have been resolved. Reformulating Maxwell’s electromagnetism in the light of the principle of relativity removed the inconsistent view of absolute motion that it had with Newton’s mechanics. Quantum physics and general relativity offer inconsistent views on reality. Both cannot be correct, and a theory that unifies them should resolve the inconsistency. I believe that the distinct fields we have today are a manifestation of a single, consistent unified field that I’d like to discover.

  So then we’d know how everything in nature works.

  Not in every single detail, but in very general terms, yes. We’d know why gravity is what it is, we’d see where all the properties of the electron and the proton come from and why they attract or repel each other. We’d understand all the interactions in nature and see how they make possible all that we observe in the world.

  Could you give me an idea of your approach?

  My broad idea was to extend general relativity so that it would encompass all other fields, thus creating a theory of pure geometry that would include all matter. Material particles like electrons would be small distortions of space and time, much like wrinkles in a piece of fabric. The theory would solve the problem of understanding how an electron can be a point particle with no extension in space, as quantum theory requires. When I developed my first unified theory with this approach, I discovered that it had a feature that I’d failed to understand at the time: it predicted the existence of mirror-image particles to the electron and the proton. Dirac predicted these mirror-image particles a few years later using a different approach. They were discovered some time later and are known today as antimatter. Not understanding this feature in my theory was one of my great blunders.