The future is not written

In several posts in this blog, I've discussed determinism, always from a critical perspective. For example, in a post entitled The debacle of determinism, I mentioned the three devastating attacks suffered by determinism during the 20th century: Heisenberg's uncertainty principle (although it would be better to use the name Heisenberg originally proposed: the indeterminacy principle); chaos theory; and the Copenhagen interpretation of quantum mechanics.

Chapter 7 of Kevin Mitchell's book Free Agents, titled, like this post, The future is not written, analyzes and refutes determinism. However, it doesn't discuss just one type of determinism, but three, refuting them one after another in successive chapters. What are these three types of determinism?

1.      Physical predeterminism: the idea that only one possible timeline exists. In other words, that the future is entirely determined by the past; that the entire history of the universe is predetermined from the beginning; that nothing that happens could have happened otherwise.

Travelling to the past?

S.Augustin, by Louis Comfort Tiffany
Lightner Museum

In his Confessions (Book XI, chapter 14), St. Augustine wrote these words, still valid today:

What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.

In the current situation of our scientific and philosophical knowledge, we still don’t know what time is.

·         For classical philosophy and Newton’s science, time is a property of the universe. Therefore, time would be absolute.

·         For Kant, time is an a priori form of human sensibility (i.e. a kind of mental container to which our sensory experiences adapt).

·         For Einstein, time is relative to the state of repose or movement of each physical object. There is, therefore, no absolute time.

·         For the standard cosmological theory, there is the possibility to define an absolute cosmic time for every physical object, measuring the time distance since the Big Bang to the present.

·         For the A theory of time (using J. McTaggart’s terminology) the flow of time is part of reality. The past no longer exists. The future does not yet exist. There is only the present. If the A theory is correct, travel to the past is impossible, because you cannot travel to what does not exist.

·         For the B theory of time, the flow of time is an illusion. Past, present and future exist simultaneously, but for each of us the past is no longer directly accessible, and the future is not yet accessible. Einstein adopted the B philosophy of time. In a condolence letter written to someone who had lost a beloved person, he wrote the following:

The distinction between past, present and future is only a stubbornly persistent illusion.

Irreversible time: illusion, or simplification?

Ilya Prigogine

We know Einstein believed that the passage of time is an illusion. In a letter of condolence he wrote in 1955 he said: ...the distinction between past, present and future is only a stubbornly persistent illusion. To assert this, he relied on the fact that Newton’s equations of gravitation, his own equations of General Relativity, Maxwell’s equations (which apply to electromagnetic waves) and Schrödinger’s equation (which gives the wave function of a particle in quantum mechanics) are all symmetric with respect to time.

How then can we explain the fact that it seems so obvious that time goes from the past to the future? Usually, physicists who believe that time is an illusion explain it by saying that, at the microscopic level, time is actually reversible, but when we move to the macroscopic level, new, emerging phenomena appear, one of which is the irreversibility of time. Let's give an example:

According to the usual theories, the movement of the molecules of a gas is perfectly reversible. If we reverse the direction of time, all the particles behave exactly the same and continue colliding with each other, only they would move in the opposite direction. However, when we consider all the trillions of particles that make up a gas, we see irreversible phenomena arising, such as the fact that the gas always tends to occupy as much space as possible, while its accumulation in a corner of the container is much less likely.

The problem is that our physical theories are based on approximations. Mathematics is a very important tool for physics, but in mathematics there are several kinds of very different problems, which differ in their difficulty to be solved. Let us look at a few:

Is time an illusion?

Albert Einstein

Physicists sometimes deny the reality of irreversible time and consider it an illusion, a psychological phenomenon. In a letter of condolence written in 1955, Einstein said this: ...the distinction between past, present and future is only an illusion, although persistent. A curious way to comfort those who have lost a beloved one. His reasons for saying this were the following:

·         In Newton equations of universal gravitation, if the sign of the variable representing time is changed, the equations don’t change. If we look at the film of a gravitational process, the theory predicts that we won’t be able to detect if the projection was made in the right sense or in reverse.

·         The same is true of Maxwell equations, which describe the behavior of electromagnetic waves.

·         The same is true of Einstein equations of General Relativity, which replace Newton equations to describe gravity.

·         The same happens with the Schrödinger equation, the basis of quantum mechanics.

But there is a problem: the equations mentioned do not make all of physics. The second principle of thermodynamics implies the existence of an arrow of time. In 1928, in a book titled The nature of the physical world, the inventor of this term (Arthur Eddington), said the following: if your theory [opposes] the second law of thermodynamics... [it will] collapse in deepest humiliation.

Every physical theory is a simplified abstraction where some parts of reality have been eliminated. If the irreversibility of time is one of those simplifications, it is not surprising that the final result is always reversible. In real events, however, there is no abstraction or simplification. All the physical theories, including the second law of thermodynamics, must be applied together. If this is done, the alleged temporal symmetry goes away.

·        

Newton and his apple

One of the first applications of Newton’s theory describes the fall of an apple. If a film being projected shows several pieces of an apple on the ground, which suddenly set in motion and gather in a single fruit, which then rises upwards until it gets attached to a tree, would we doubt that it has been projected in reverse? The fact that we don’t is a consequence of the second law of thermodynamics.

·         This also applies to the movements of celestial bodies. Imagine a recording of Mercury moving in its orbit, with the sun visible. By studying the solar sunspots we could deduce whether the film is projected correctly or in reverse. Sunspots are a consequence of thermodynamic phenomena.

·         Radioactive decay is another example of a theoretically reversible process that in practice is irreversible. In fact, the proportion of uranium-238 and lead-206 in a rock provides a reliable method to calculate its age. The chain of disintegrations from uranium to lead is far more likely than the reverse chain, although physical theories affirm that both things could happen in theory.

·         Whatever Schrödinger equation says, the Copenhagen interpretation of quantum mechanics requires an irreversible time. If a photon hits an electron with some energy, the electron is left in two overlapping spin states. If the spin is measured, the quantum superposition collapses into a positive or a negative value. This process involves a direction of time: first comes the impact of the photon, then the electron in two superimposed states, finally a measurement and a quantum collapse. The reverse process cannot happen.

In these examples, when all of physics is taken into account without excluding thermodynamics, the supposed reversibility of time disappears. Apparently physicists put their theories above reality, doing the opposite of what the scientific method demands. Not even great men like Einstein were exempt.

El mismo artículo en español
Thematic thread on Time: Next

Manuel Alfonseca

Time A or Time B?

J.M.E. McTaggart, who in 1908 coined
the terms "A and B-theories of time."

Human beings seem to have an innate tendency to think that what we do not like or cannot explain does not exist. Thus in Hinduism and Buddhism, reality itself is considered an illusion (maya), something that must be discarded to achieve liberation. According to this philosophy, since it is an inseparable part of physical reality, time should also be considered as an illusion. In the Hindu Brahman and the Buddhist Nirvana, time does not exist.

In Western philosophy and science, the idea of ​​time has traditionally been quite different. Until the eighteenth century, nobody put in question the reality of reality. As an inseparable part of reality, time was absolute. In Newtonian mechanics, time plays that role. According to his theory of gravitation, the course of time is independent of the motion of the observer. Hence one can deduce the principle of relativity of classical mechanics: when several bodies are subjected to uniform rectilinear motion (at constant speed) it is impossible to distinguish which one is at rest and which is moving.