God does play
dice with
the universe

Michele DiEgo

Among the most influential personalities of the twentieth century, Albert Einstein is the man who embodies intelligence and curiosity more than any other genius of the collective imagination. Perhaps for this very reason it is interesting to explore the grey areas of his thoughts. And I am not only referring to aspects of his private life, such as his second marriage to his cousin or the intimidating letters sent to his first wife, listing the rules to which she should have been subjected to, (you will stop talking if I ask for it; you will renounce all personal relationships with me, unless they are strictly necessary for reasons of etiquette and social life; you will immediately leave my bedroom or my study, without any protest, when I ask for it; etc.). Not even his ethical evaluations about atomic energy, which led him to write to President Roosevelt in favour of nuclear projects that then materialized in the bombs dropped on Hiroshima and Nagasaki, about which the German physicist then said: “If I had known what they were going to do, I would have been a shoemaker”. I am referring to his real scientific beliefs.

Although he made history for what goes under the name of “Theory of Relativity” (a theory that concerns space-time and its connection to gravity), in 1921 Einstein received the Nobel Prize for his studies on the photoelectric effect, a fundamental element in the formulation of quantum mechanics. This effect allows light to extract electrons from a metallic material (as it happens in photovoltaic panels). In formulating his theory, Einstein described light not as a wave, but as a set of energy packets, quanta, particles (then called photons). It is the single photon to hit an electron inside the metal and transmit its energy to it. Then, if the transmitted energy is high enough, the electron can escape from the metal and be used as electric current.

The clash between Einstein‘s realistic conception, which sees a world in which an absolute and describable truth exists, and Bohr‘s conception that the scientific description of nature does not coincide with the very nature of reality.


Einstein’s interpretation of light, however, was not universally accepted for many years. Even Max Planck – another great physicist, although less recognized in popular culture – did not believe in the existence of quantum light. Yet it was Planck himself, even before Einstein, who hypothesized the existence of energy quanta to explain another and more complex phenomenon (the black body radiation), thus winning the Nobel Prize in 1918. Planck thought that quanta were nothing but a mathematical expedient, useful to realize the calculations, but not adherent to natural reality.
We are therefore faced with two undisputed geniuses of physics, both awarded the Nobel prize for theories underlying quantum mechanics, and both sceptical about the actual truthfulness of quantum physics. This distrust comes from the paradigm shift that quantum mechanics involves in the philosophical structure of science. It is a radical, Copernican revolution, in which many of the concepts on which physics was based in the nineteenth century collapse. New concepts, so counterintuitive that even today are considered completely unthinkable by anyone who has not specifically studied the subject.
Quantum theory no longer describes matter as a set of rigid particles, which occupy a certain volume and with well-defined characteristics (position, speed, extension, etc.). Matter becomes a wave of probability, so a particle no longer has a precise position, it has no univocal velocity, it does not have a well-defined energy; the particle can be anywhere. It has a position scattered throughout space, its energy can have many different values at the same time, it can have opposite and incompatible characteristics at the same time. When you make a measurement on the particle, for example you verify position, then these infinite possibilities converge into one; the particle “collapses” in only one point of space. Repeating the position measurement experiment several times, the particle will collapse once in one point, another time in another, according to a probability calculation. If the particle is a wave scattered all over space with equal probability, then when measuring its position, we may find that it is with equal probability in our hands, on the Sun, on Proxima Centauri, in another galaxy, or wherever we think.
What Einstein contested about quantum theory is precisely its intrinsically probabilistic and non-deterministic nature. Until then, in physics, probability was associated with an uncertainty due to ignorance, not to the very essence of nature. For example, if we throw a coin in the air, we have a 50% probability that heads comes out and 50% probability that tails comes out. But it is a probability due to ignorance that we have about the force applied during the toss, the speed of rotation of the coin, the air resistance, etc. If we could have access to all this information, we would be able to predict with certainty if the coin flip would be heads or tails.
In quantum mechanics the probability referred to is, on the contrary, intrinsic to nature itself: a particle is really in different positions at the same time and in no way it would be possible to predict with exact certainty where we would find it if we made the measurement of its position. Nature itself is uncertain and acts according to laws of probability. Einstein could not accept that uncertainty is congenital to the laws of the universe, and he summed up his scepticism in the famous phrase “God does not play dice with the world”.
Yet quantum mechanics is the physics theory that more than any other has been systematically confirmed by every experiment. It is physicist Niels Bohr who explained, better than any other, why Einstein’s perplexity is unfounded. According to Bohr, to observe the properties of nature means to conduct some kind of experiment, of measurement. As long as we do not conduct a measurement, it makes no sense to define how nature behaves. In practice it is useless to try to question the structure of the world when it is not measured by us. Any mathematical structure that predicts the correct values of an experiment is equally and perfectly valid.
There is therefore the clash between Einstein’s realistic conception, which sees a world in which an absolute and describable truth exists, and Bohr’s conception that the scientific description of nature does not coincide with the very nature of reality. And this difference in thought between Einstein and Bohr is perfectly shown in a paradigmatic example: the relationship of the two physicists with Eastern philosophy.
In 1930, a meeting between Einstein and Indian poet/philosopher Rabindranath Tagore (Nobel Prize for Literature in 1913) took place in Berlin. The discussion between the two was about the existence of an objective reality, independent of the mind that observes it. In a salient passage, Einstein states that, even if you do not observe a room, it is known what the behaviour of the table inside it is, which will continue to exist, as saying that “the table is there” is true regardless our personal beliefs. Tagore replies that no, the very idea that we have of the table is an appearance produced by our mind and therefore the table does not exist without our presence.
On the contrary, Bohr is so close to the Eastern doctrines of duality and complementarity of opposites, that when in 1947 he was awarded the most important knightly order of Danimarch, the order of the Elephant, he chose a coat of arms with the symbol of Yin and Yang on it, and on it he had the motto “Contraria sunt complementa” written.
Einstein and Bohr, two opposite approaches to the idea of science, a desire for scientific realism opposed to a more abstract interpretation of mathematical laws, the desire to impose on the world’s reality he thought of man and the acceptance that the ultimate truth remains unknowable.

And in this philosophical dispute, however, there is another interpretation of quantum mechanics, called “many worlds theory”. The “many worlds” interpretation is often criticized as experimentally unverifiable, but it is worth describing it because it is very evocative. It provides for each measurement made on a system, all the possible responses of the system occur simultaneously, each in a different universe. Let’s take the example of a quantum electron located at the same time in two separate points (points A and B). When we measure the position of the electron, two universes are generated, one in which the electron will collapse at point A and, another one in which it will collapse at point B. Depending on the universe we are in, we will find the electron at point A or point B.
Therefore, according to this interpretation, the universe in which we live does nothing but split into multiple universes whenever a quantum phenomenon is measured or observed. If then instead of taking a system with only two possibilities (A or B), we take one that has infinite possibilities (for example an electron located simultaneously throughout the universe), then from the measurement of its position infinite universes will arise. Since nature “measures” itself continuously, even without realizing it, in every moment infinite universes are separately born, following their own different realities, like a lottery where everyone wins, but each one in a different world.