**Is Time ‘Real’ or an Illusion?**

In our everyday experience, we normally take it completely for granted that time ‘exists’ and that it passes at a uniform rate. In the everyday sense, a unit of time, such as one hour is a measurable quantity that does not seem to change from one day to the next. However, we can legitimately ask what is the quantity that a clock can be said to measure? Is time dimensional?

In contrast to the everyday concept of the passage of time, there have been unusual claims about the nature of time resulting from modern mathematical physics. Some of these claims arise from general relativity rather than quantum mechanics and are very well accepted. This includes the relativistic axiom which declares that the rate at which time passes varies between observers travelling at different velocities within a frame of reference.

However, we are now being asked to believe in a book and also in a very stimulating public lecture by Carlo Rovelli, who was one of the originators of loop quantum gravity theory, that time itself is an illusion and is not needed in his quantum mathematical re-formulations of gravitational theory. In other words, the *passage or existence* of time, as we commonly think of it, is no longer such an axiomatically primitive notion within the axioms of physics.

Worse still he expects us to believe that we are merely emotionally wedded to the idea of time. Time, we are told, does not ‘really’ exist in the sense that we commonly accept. This is despite the very obvious claim that time is a crucial *explanatory* ‘primitive’ in every *event* *or process* that has happened in your life and every scientific observation that has been made related to the history of the universe since the Big Bang, the formation of heavy atoms in cycles of star formation, the existence of chemical reactions, the second law of thermodynamics, radio-nucleotide half-life, and all of biology and evolutionary theory. Any understanding of ourselves or the universe requires us to understand macroscopic* processes*, which by definition occur in time, and require entirely different levels of explanation that can *never* meaningfully incorporate quantum states.

I believe we should be extremely sceptical of all claims that seek to undermine extremely well-established and pragmatically valuable concepts. Rovelli is, without doubt, fully aware that axioms are simply declared. He would presumably reply that individual axioms can be dropped or modified when they are inconvenient or appear to be not mathematically required.

So how do we choose axioms? One unsatisfactory alternative is that we do not make a choice and instead behave like the logician and admit the possibility of different systems that are conceptually useful in distinct ways. However for reasons of coherence that is not desirable. Fortunately, in an award-winning paper entitled, ‘The Universe as a Process of Unique Events‘ by Marina Cortˆes and Lee Smollin have possibly come to our rescue with a more philosophically well-embedded view of time. (Smolin was one of the originators and collaborators of Rovelli in the development of loop quantum gravity and describes him as a friend of Rovelli). Cortˆes and Smollin have provided a highly mathematical case (that is unintelligible to me) in support of the idea that we should regard time as progressive or flowing between events and a necessary ‘primitive’ (or axiomatic) concept. What a surprise! Whether or not the new way of looking at things it will be accepted in the long run is largely dependent on the potential of the theory to generate observationally or experimentally testable predictions.

Lee Smolin even managed to inject a degree of sanity into an otherwise highly speculative BBC Horizon science fantasy documentary on the (im)possibility of time travel. He says ” … (mathematics) is very powerful, but it is so powerful that we begin to make a mistake and imagine that nature* is* mathematics and then because something is true in mathematics it is always true. There is a sense in which mathematics is timeless .. is time free. So we begin to unconsciously import the timeless of mathematics into our conceptions of nature.” As argued above, mathematical descriptions (or laws) in science emerge from the axioms, not the other way round.

In the first part of the interview above Marina Cortˆes describes the problems with the block universe and how mathematical physicists have created, from my perspective, obvious philosophical problems with the logical implications of their mathematical approach. In the next part, she talks about how these problems can be relieved by accepting the axiom that time is a fundamental primitive and that the flow of time in a particular technical sense is also axiomatic. In the very last section of the video, she acknowledges the social dimension of scientific collaboration.

In a very short philosophical lecture by Lee Smolin about his popular book ‘Time Reborn‘, he makes a very sound case for favouring the axiom that time exists over the timelessness of ‘mathematical objects’. Do you agree that AC Grayling, who is one of the panel commenting on the talk, makes a category error when he refers to time and timelessness?

A much longer philosophical public lecture by Lee Smolin on the same subject that contains many interesting additional points. He points out, for example, that in science one of the most important aspects of research is deciding what questions to ask. For me, the other great personal discipline in science is learning to question our most basic axiomatic assumptions and data interpretations.

Steve Campbell

Glasgow, Scotland

2017, 2019

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