Chapter 1: Understanding the Present in Physics

The saying "there's no time like the present" is widely known, typically interpreted as an encouragement to act without delay. This perspective resonates psychologically, as humans uniquely experience the flow of time. The present moment feels distinct, unlike the past or future, which we can only reflect upon or anticipate. However, does modern physics support this adage?

General relativity, our most comprehensive theory of space and time, suggests otherwise. Before Einstein's groundbreaking ideas over a century ago, time was viewed as an independent entity, unaffected by the universe. The ongoing philosophical debate surrounding whether time is genuinely experienced or merely an illusion predates Einstein and remains unresolved. What we now understand is that time isn't a universal constant; rather, it is an integral part of a physical system, intertwined with three spatial dimensions to form what we call "spacetime." This interconnection is influenced by factors such as speed and gravity, leading to the conclusion that time intervals are not fixed but elastic.

As a consequence, the idea of a universal present moment is misleading. What feels present to one observer might be perceived as a future event by another, or even as a past occurrence. Consider a scenario where your partner is on a business trip across the globe. At the moment you feel a pang of longing, she might be sending you an email expressing her own feelings of missing you. While these events seem simultaneous to you, an observer traveling at high speed might perceive them differently—either your thought precedes her email or vice versa. Thus, relativity teaches us that the present moment is not unique; there are countless "nows" experienced by different observers.

Chapter 2: The Complexity of Time in Modern Physics

Despite the success of general relativity, it does not encapsulate the entirety of our universe. It fails to integrate insights from quantum mechanics, the other great pillar of 20th-century physics, and the two remain incompatible in their current forms. When dealing with phenomena like black holes or the universe's origins, scientists must reconcile the theories that describe massive objects with those that govern the behavior of tiny particles. This challenge signals a potential paradigm shift in physics, possibly leading to a new understanding of gravity in quantum terms.

One intriguing approach to this challenge is shape dynamics, which eliminates time as a consideration altogether. Instead, it focuses on the evolution of spatial configurations, each representing a different narrative of the universe's development. This theory suggests that there are innumerable present moments—akin to snapshots in an album—chronicling our journey through time.

Proponents of shape dynamics refer to these instantaneous "nows" as "time capsules," arguing that our perception of time is an illusion created by the brain's ability to stitch these snapshots together. For instance, when watching a cat leap, we perceive the motion through a series of still images that our brain melds into a continuous flow. In a similar way, shape dynamics posits that our experience of time is constructed from these discrete moments.

In light of this, the traditional saying about the present loses its validity. If shape dynamics holds true, the universe is filled with countless simultaneous presents, and the continuous flow of time is merely an illusion.

Moreover, shape dynamics is not the only perspective on time within quantum gravity. String theory, for instance, also challenges the notion of a singular present. This theory suggests that the fundamental particles of nature are better understood as one-dimensional strings rather than point-like entities. It introduces additional spatial dimensions that we do not perceive in our three-dimensional reality, much like how a garden hose appears one-dimensional from afar but reveals more complexity upon closer inspection.

In this framework, time may emerge from a timeless aspect of the theory, challenging our conventional understanding of its significance. Thus, saying there’s no time like the present becomes irrelevant—time, as we know it, may not even exist in a fundamental sense.

As I wrap up this exploration, I realize there’s much to be done. And while I may feel the urgency of now, it’s important to remember that time is more complex than it seems.

Mark Shumelda is a Ph.D. candidate in the philosophy of physics at the University of Toronto, with extensive teaching experience in both the sciences and humanities in Canada’s North.