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The Order of Time by Carlo Rovelli

December 28, 2018


This book is about time. Rovelli can take complex scientific concepts and wrap them in simple, understandable prose. The Order of Time is part science, part history, part philosophy, part poetry. Rovelli infuses the science of time with the wonder it deserves—wonder that often gets stripped out when the concepts are translated to formulas and taught in physics class.

He sets some basic premises about the nature of time, most of which are already mind-benders. Such as: Time is not universal. It passes at different speeds depending on where you are in space. This is described by Einstein’s General Theory of Relativity, but it’s something we mostly take for granted. With our synchronized clocks, we create the illusion that we are a “platoon advancing at the pace of a single commander.” But in reality, we experience different “times” based on our position in space and the speed at which we’re moving. It’s a concept that comes up mostly in science fiction, where extremes (like traveling at the speed of light) can nearly pause the passage of time, but it’s not fiction.

Another mind-bender is his walkthrough of the question: What makes the past different from the future? It turns out, not much.

By most fundamental laws of physics, there is no difference between the past and future.

The only fundamental physical equation that seems to be linked to a directional sense of time is the transfer of heat (the second principle of thermodynamics). Heat can only go one direction, toward greater entropy. Therefore, at a molecular level, the direction of time is indicated by a move toward disorder (most people would probably agree the same is true of life in general).

However, our description of the level of entropy is a somewhat flawed, using a statistically arbitrary “ordered” starting point (e.g. a new pack of cards, in order). But any two states of a deck of cards—perfectly “ordered” or what we’d consider a completely random sequence—has the same mathematical chance of existing. Molecules arranged in the form of a specific tree are equally as likely as molecules arranged in the form of a different specific tree, or in the form of a specific non-tree. Therefore, entropy—the one equation that seemed to define the flow of time—does not hold as a descriptor of time.

There is no difference between the past and future. In the “elementary grammar of things, there is no distinction between cause and effect.” If this concept doesn’t shake your idea about how things work, I’m not sure anything will.

This book is full of challenging concepts about time. I could hang with the first two sections, but by the third section, I was feeling a little lost. It reminded me of Michio Kaku’s Hyperspace, which tackles some of the same issues by describing the ten-dimensional model of our universe. Rovelli’s is a more poetic take and more focused on time alone. It avoids scientific jargon, and if any of the concepts are difficult to grasp, it’s not because of the language. It’s because they’re counter to some of our most fundamental concepts about how our world works.


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