A Non-Linear Reality

Time, as we experience it in our everyday lives, feels like a constant flow—seconds, minutes, and hours ticking forward in unison. We set our clocks, follow schedules, and live in the expectation that time is universal and absolute. Yet, modern physics, particularly through the lens of Carlo Rovelli and his work in quantum gravity, has shown that this familiar perception of time is a facade. In reality, time is far more complex and elusive.

In The Order of Time, Rovelli challenges the notion of a single, uniform time that applies everywhere in the universe. Instead, time behaves differently depending on where and how you observe it. At first, this might seem counterintuitive, but it’s a natural consequence of how the universe works on both cosmic and quantum scales. Let’s unpack this strange and captivating perspective on time.

Time Isn’t Uniform

According to general relativity, the theory formulated by Einstein, time is relative. This means that the rate at which time passes is not the same for everyone, everywhere. The famous example is that of two clocks, one placed on the surface of the Earth and another placed on a satellite orbiting the planet. These clocks, which are supposed to tick uniformly, will actually diverge slightly over time, with the one in orbit running faster. Why? Because time is affected by both velocity and gravity—two factors that alter how quickly or slowly time flows.

This phenomenon is known as time dilation, and it highlights the fact that time isn’t the steady, universal flow we might imagine. Near a massive object, such as a planet or a black hole, time runs slower because the gravitational field is stronger. Conversely, as you move faster—closer to the speed of light—time slows down for you relative to someone who is stationary. This is why astronauts, who travel at incredibly high speeds in space, experience time slightly differently than those of us on Earth.

In essence, time is local, not universal. Different regions of space experience time in different ways. What we once assumed to be a single, omnipresent clock ticking through the cosmos is, instead, a complex web of times—interwoven, overlapping, and diverse.

The Direction of Time

Another peculiar feature of time that Rovelli explores is its apparent directionality. We experience time as an irreversible arrow that points forward—from past to future. We remember the past but not the future, and events seem to unfold in one direction. This, however, is not a fundamental feature of the universe but rather a product of entropy.

In simple terms, entropy refers to the measure of disorder in a system. According to the second law of thermodynamics, in any closed system, entropy tends to increase over time. This is why a hot cup of coffee cools down but never heats up on its own. The process of heat exchange is irreversible—heat always flows from a hotter body to a colder one. The increase of entropy is what gives time its direction.

Without entropy, the distinction between past and future would vanish. Rovelli suggests that time’s arrow, its forward motion, is an emergent property of thermal processes. In regions or moments where entropy doesn’t play a role, time as we experience it becomes almost meaningless.

At the microscopic level, most physical laws are time-reversible. If you filmed the motion of particles or the behavior of fundamental forces and played it backward, there would be no violation of physical laws. Both directions of time would seem equally valid. It’s only when we introduce thermodynamics and the increase of entropy that time appears to “move” forward.

Time and the Quantum World

Rovelli’s research in quantum gravity adds even more complexity to the nature of time. In quantum mechanics, time becomes even more ambiguous. Events do not happen in a smooth, continuous flow, but in discrete, probabilistic jumps. At the quantum level, particles exist in a state of superposition, meaning they can be in multiple states or locations simultaneously, and it’s only when we observe them that they “collapse” into a specific state.

In this quantum realm, time seems to lose its traditional meaning entirely. Rovelli points out that in quantum gravity, time is not a fundamental component of the equations describing the universe. In fact, the universe may function perfectly well without time as a fundamental entity—suggesting that our experience of time may be an illusion created by our limited understanding of reality at larger scales.

The Illusion of Time

So, what is time? From Rovelli’s perspective, time is not a fixed, external entity but a manifestation of our interactions with the world. The passage of time, the ticking of the clock, and the direction of past to future are not universal truths but emergent properties arising from the particular conditions of our universe—especially from thermal phenomena and our subjective perception.

Rovelli encourages us to rethink time not as an objective reality but as a complex relationship between events. The true nature of time lies in the connections between things, how they change and interact, not in an independent, overarching flow. Time, in this sense, is not the fabric of the universe but a human interpretation of the changes we observe.

The next time you glance at your watch or mark an appointment on your calendar, remember that the clock you’re following is but one of many clocks ticking at different speeds and directions in a vast, intricate cosmos. Time, as Rovelli sees it, is far more mysterious than it first appears—a fluid, ever-changing concept that shapes our experience yet may be more illusion than reality.