In 2011, I wrote a little poem called the “Past”, which went like this:
The past, some say, is crystallized future that has been cast in the foundry of the present; forever, imprisoned in stasis what could have been, now lost forever In that transition, does the moment despair at its loss of choices? What could have been! Or is there a sense of loss of the present? And is this why the past is cast in pathos?.
Being a thinking person, I have spent much effort understanding the mystery of time. Recently, I came across a beautiful exposition, almost poetic, “The Order of Time”, by Carlo Rovelli, who takes us through the evolution of our understanding of time. Rovelli is a physicist working at the Centre de Physique Theorique de Luminy in Marseilles. He says on page 7: “The nature of time is perhaps the greatest remaining mystery. Curious threads connect it to those other great open mysteries: the nature of mind, the origin of the Universe, the fate of black holes, the very functioning of life on Earth. Something essential continues to draw us back to the nature of time.”
Earlier, in an idea called Presentism, only the present is real. There are no events in the past and future. This idea, however, runs into some severe problems when you start taking into account relativity, as many thought experiments do. Special relativity concludes that frames of reference may not agree on the order of events; in essence, there is no simultaneity. Thus, what we call the “present” is subjective.
In an alternate idea of how to think of time, instead of thinking of reality as three-dimensional, we can add time as the fourth dimension. In four-dimensional space, there is no issue with simultaneity. Rather than solely measuring the time between events, observers on spacetime would measure the spacetime between events, which should be the same for all observers.
In the four-dimensional world, events exist both in the past and future. Due to this, present no longer is unique”. Everything, from objects to events, exists. Our definition of “now” does not have a meaning in this concept. This idea is called ‘Eternalism’. Rovelli argues that we cannot put all the events on one timeline. Instead, events must have both time and space tags. Events are happening, but what is defined as the present may be different for spatial locations. We experience becoming in the local sense. There is no global becoming. We can be aware of things happening near us, but not at places far away in the Universe.
Rovelli proposes that events (a term for a given time and spatial location) are the primary constituents of the world, not particles or fields. The role of physics is to describe the relationships between those events. As Rovelli notes (Order of Time p65), “A storm is not a thing, it’s a collection of occurrences.” Events are the interaction of particles at a particular location and time. Time and space manifest from these interactions and the web of causality between them.
In Einstein’s theory of relativity, time is woven together with the three dimensions of space, forming a four-dimensional spacetime continuum. This “block universe” encompasses the past, present and future in their entirety. “The distinction between past, present and future is only a stubbornly persistent illusion” is a statement attributed to Einstein. Rovelli continues to explore how it is possible for our perception of time to emerge from this world without time. The surprise has been that we have played a role in the emergence of familiar aspects of time. From our perspective, we see that world flowing in time. However, our interaction with the world is partial, making us see it in a blurred way. Quantum indeterminacy adds to this blurring. The lack of information ignorance that follows from this determines the existence of entropy.
Rovelli tries to explain our sense of time (p117). The entropy of the world increases with our thermal time. We see things happening, ordered in this variable, which we call “time,” and the growth of entropy distinguishes the past from the future. It determines the existence of all indications and memories of the past. Human beings themselves are an effect of this marvellous history of entropy increase, held together by the memory enabled by these traces. Each of us is a unified being because we reflect the world. We have formed an idea of a unified being by interacting with our kind. The idea of the “flowing” of time emerges from this.
He concludes (p117): “In the end, therefore, instead of many possible times, we can speak only of a single time: the time of our experience — uniform, universal, and ordered. This is the approximation of an approximation of an approximation of a description of the world made from our particular perspective as human beings who are dependent on the growth of entropy, anchored to the flowing of time. This is time for us: a multilayered, complex concept with multiple, distinct properties deriving from various different approximations.”