Book Review: Your Brain is a Time Machine: The Neuroscience and Physics of Time

On a recent family trip, I persuaded my dad to continue on from Grand Teton to Yellowstone National Park. Time was short before driving back to our lodging in Idaho. The main attraction in Yellowstone, of course, was Old Faithful. But just when would this famous geyser erupt? Was the eruption an event that had “already occurred” in the future, or a completely unrealized abstraction? How did my anticipation of the eruption alter my perception of time? Is anticipating the future a uniquely human activity?

If these questions interest you, so will Dean Buonomano’s Your Brain is a Time Machine: The Neuroscience and Physics of Time. Part I of the book explores how the brain tells time, while Part II addresses physical (and metaphysical) questions concerning the nature of time. Buonomano, Professor of Behavioral Neuroscience at UCLA, makes the case that the brain “is a machine that creates the sense of time.” Our sense of time is different from other senses, because the brain does not have a time-sensing organ in the same way that it has a light-sensing organ or an odor-sensing organ.

In fact, time measurement may be ubiquitous in the brain, like a cartoon watch salesman whose overcoat is brimming with watches. In Part I of the book, we learn that “asking which neurons or neural circuits within the brain tell time is a bit like asking which of the billion transistors in the CPU of your desktop are responsible for performing binary logic. They all are, that is their raison d’être.” But unlike the salesman caricature, the brain carefully uses different clocks in different contexts.

Yet there is much we don’t understand about these clocks. We all know that boring days feel long. Yet people who spend dreadfully boring months in caves with no day or night cues often underestimate the duration of their stay. Take French geologist Michel Siffre, described in the book’s third chapter. As a participant in a NASA research study, Siffre believed his 179-day stay in a Texas cave had lasted for only 151 days!

Our sense of time is also altered during scary events such as skydiving, in which time seems to slow. Is it really time that is slowing? Or are you speeding up, your internal clock ticking faster and faster with fewer external events occurring between each tick?

We know that time doesn’t really slow when the rollercoaster creaks forward from atop the track. (It does slow during a rocket voyage close to the speed of light, but more on that later). So how can neuroscience explain this strange illusion? One explanation is that the illusion is itself, well, an illusion. A metaillusion, to be precise. According to this view, described in the fourth chapter, the flow of time as experienced during a rollercoaster is just as “correct” as one’s normal perception of time. Because one’s sense of time is created in the brain, there is no correct perception. Time may not flow outside the skull.

Part II, my favorite half of the book, digs deeper into the question of whether time truly flows. The traditional view, presentism, holds that only the present moment is real—the past and the future only exist in our imagination. In this view, time does flow. Eternalism, on the other hand, is the view that the past and future are just as real as the present moment. In this view, time does not flow—only consciousness. (Somehow, the term eternalism never fails to conjure The Legend of Zelda’s “Song of Time” in my mind’s ear.)

Throughout history, our dominant view of time has shifted from presentism to eternalism. As Buonomano mentions early in the book, ancient myths make almost no mention of time travel—the concept is simply incoherent in the presentist framework. Time travel does not make a full cultural debut until H. G. Well’s 1895 novel The Time Machine. Soon after, Einstein’s theory of relativity enthroned eternalism by demonstrating that space and time are both part of a 4-dimensional continuum. Time is relative, slowing during a journey that approaches light speed. In fact, events that are simultaneous in the frame of reference of such a traveler may not be simultaneous at all as viewed from a stationary observer! (Note that these are objective, physical phenomena, not subjective, psychological phenomena). Einstein’s theories, widely accepted today, are best understood in the eternalist framework, forcing us to consider whether time truly flows outside of the mind. Buonomano writes, “Within the block universe of eternalism our feeling of the passage of time is more akin to the visions of a schizophrenic, something that only exists within.”

Your Brain is a Time Machine offers something for casual readers and experts alike. As a neuroscience graduate student, I enjoyed seeing familiar information about neuroscience connected to other ideas, such as Einstein’s special relativity and general relativity. If I could add anything to this book, I would like to learn about the brain’s slowest clock, the enigmatic oscillator that regulates mood in bipolar disorder. Unlike other brain oscillators, a typical cycle of this clock lasts not for milliseconds or even hours (as in the case of circadian rhythms discussed in Part I), but rather an astonishing period of weeks to months. The mystery of the bipolar mood cycle would surely be an important chapter in any follow up to Your Brain is a Time Machine.

So, is the brain really a time machine?

Passing through Yellowstone with my family, I imagined Old Faithful erupting as it certainly would in the next hour. I also imagined the long drive that awaited us returning to Idaho. Walking amongst the hot springs and sulfur pools, time slowed as I absorbed the novel sensations of a geothermal wonderland. Alas, we were out of time. Pulling out of the parking lot, I glimpsed a white fountain flaring up above the visitor center.

Is this past moment just as real as the present moment in which I write this sentence? A place in time that you or I could visit with sufficient technology?

Maybe. Maybe not. Either way, I revisit it with the time machine in my skull.