Thursday, February 25, 2016

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.

From the eighteenth century, philosophers began to distinguish between reality and the idea we have of reality. Since we just have access to the second, through our senses and their amplification by our instruments, reality itself would be unknowable. Thus was raised the question on whether space and time (which seem to us two essential components of reality) really exist or are simply modes of perception. Thus, Kant described space and time as a priori forms of human sensibility. He left open the possibility that both would be illusions, rather than reality.
Diagram of the Michelson-Morley experiment 
In 1883, the Michelson-Morley experiment showed that light is not carried away by the movement of the Earth around the sun, which disproved in that case the law of composition of velocities based on the principle of relativity of classical mechanics. The explanation was provided by Einstein’s special relativity, which saved this principle at the expense of postulating that the speed of light must be independent of the coordinate system. As a result, absolute time was abolished, because the course of time depends on the speed of movement. Anyway, the principle of causality (the cause always comes before the effect) remains in force.
By then, the philosophical ideas about time had been expressed in two different incompatible theories:
         A-theory of time: our common idea of time. The flow of time is a part of reality. The past no longer exists. The future does not yet exist. There is only the present.
         B-theory of time: the universe is an unchanging block. The flow of time is an illusion. Past, present and future exist simultaneously, only the past is no longer directly accessible for us, and the future is not yet accessible.
Einstein happily adopted the B-philosophy of time. In a letter of condolence (!) he wrote this, to comfort his interlocutor for the loss of a beloved person: The distinction between past, present and future is only an illusion, albeit persistent.
And yet, it was Einstein himself, with the general theory of relativity, who reintroduced in the world of science the idea of ​​absolute time, for his theory led directly to the definition of cosmological time, the time elapsed since the Big Bang, which is the same for the whole universe.
Many modern scientists, not realizing they are doing philosophy rather than science, are determined to consider as illusion things such as the pass of time, or human consciousness, because they cannot find convincing scientific explanations for them. Yet these same scientists would protest vociferously if someone dared to suggest that the cosmic background radiation, to give just one example, is an illusion generated by our instruments, because the existence of this radiation they believe can be explained. Thus their eagerness to consider time and consciousness as illusions could be (in addition to an ideological trend) a simple confession of ignorance.

Thematic thread on Time: Preceding Next
Manuel Alfonseca


  1. Not absolute surely since time since big bang still depends on frame of reference. Fast moving body will have experienced less time since big bang.

    1. When you say "fast moving body" you are in the frame of special relativity. In general relativity, there is a cosmological equation that applies to the universe as a whole, not to any one of the moving bodies in it. In this equation, one term is a time derivative. The time in question is universal time, the time since the Big Bang, which we can compute by analyzing the redshift of the oldest photons we can receive, those in the cosmic microwave background radiation. In fact, this universal time since the Big Bang has been computed as 13,800 million years. This is what I meant with the allusion in my post.