Long read: Does Anybody Really Know What Time Is?

Dean Buonomano, a neuroscientist, is the author of ‘Your Brain is a Time Machine: The Neuroscience and Physics of Time’. In this interview, he explains four different facets of how the human brain comprehends time. He begins with basic concepts and then gradually takes us towards the frontiers of science.

Firstly, we need to understand that the brain has multiple clocks (and thus multiple perceptions of time) on the go all at once: “The brain has fundamentally different mechanisms to tell time on different timescales. You have a circadian clock; that’s what guides you when you’re hungry, tells you when you go to bed, when to get up. But that clock doesn’t have a second hand; it cannot “tell time.” It’s not going to help you determine the tempo of a song that you’re listening to. So that clock is independent of the other clocks. We also have other clocks, other timers, that guide our ability to have this conversation.

We know that many of these forms of timing rely on what’s called a “neural population clock”—that’s a circuit of neurons where one neuron can contact and excite another neuron, and another, and another. You can imagine them as falling dominoes. If you have a long line of dominoes, you could use that as a clock, because you could mark time based on which domino is currently falling. So that’s how the brain tells time on the scale of milliseconds, using what we call “neural dynamics.” Neurons make up a dynamical system, and they create spatio-temporal patterns of activity, and we use those spatio-temporal patterns of activity to tell time…

… your whole brain is a timer. You don’t have one little clock; you have your entire brain. You don’t have a centralized timer. All neurons, in effect, can contribute to timing on an as-needed basis.”

Secondly, we learn that ‘mental time travel’ is something that only humans are capable of: “Mental time travel refers to the ability to relive things that have happened in the past and to simulate or imagine different future scenarios. Mental time travel is one of the most fundamental or defining cognitive abilities that humans developed. It’s what really allowed us to get where we are. You think of something as simple as agriculture—one of the most important technological advances we ever had. It’s a simple idea, right? Planting a seed and then reaping the benefits of that in terms of assuring the presence of food in the future. But that simple idea really eluded all other animals, and eluded early humans for millions of years. And why is that? I think it’s because it involves mental time travel. Without that ability, it’s hard to say, “Well, I’m going to plant this seed today in order to reap the benefits months or years into the future.” So, this connecting the causal dots between cause and effect over long periods of time is something most animals are largely incapable of….

…Now, other animals do future-oriented actions; a squirrel will store food, a beaver will build a dam, and birds will build nests. But by most accounts, those are innate behaviors. Animals don’t seem to be aware of why they’re doing it. That’s how evolution works; it creates innate behaviors so that you can do future-oriented things without having to understand why you’re doing them.”

Thirdly, we learn that mental time travel and the development of languages is closely linked: “…mental time travel and language have to be intertwined. To prepare for the future, we need linguistic abilities and language and symbols to plan ahead and to quantify time as it passes. I think those things co-evolved.

It’s also interesting that when we talk about time, in many cultures, we use spatial metaphors. People have argued that we had [neural] circuits in place to deal with space—left, right, north, south—essential for tracking animals as they migrate over long distances. And then those circuits for space were co-opted or transformed, and allowed us to mentally travel through time. We have the past, we have the present, we have the future. And when you and I talk about time, we often use spatial metaphors. We say, “it was a long day,” or “I’m looking forward to seeing you,” or “In hindsight, that was not my best idea.” So, that’s one of the tools we use to engage in mental time travel, and it goes precisely toward your point of the relationship between mental time travel and language.”

And then we enter the realm of the unknown as Dean Buonomano tells us about the unsolved mysteries linked to time:

“Time sits at the center of a perfect storm of unsolved scientific mysteries involving free will, consciousness, and the unification of relativity and quantum mechanics. There’s two views.

One is called presentism; that’s the intuitive view—the view that only the present is real, and the past is no longer real and the future is not yet real. And that we can take actions in the present and modify or change or shape the future. That’s certainly been the dominant view throughout history. Now in modern physics, going back to Einstein, that view began to change.

Now there’s a tension between neuroscience and physics, with many physicists and philosophers saying that the laws of physics suggest that the presentist view is wrong, and that the correct view is eternalism, also called the “block universe” view. In that view, “now” is to time as “here” is to space. We have no problem saying we both exist in space, even though we’re far apart; you’re in Toronto and I’m in LA. Under eternalism, the same thing is true of time. There would be other “versions” of you in the past or in the future that all coexist.

I think the most intuitive way for people to understand this notion—that all of time is laid out in this way—is through the concept of time travel, that is, the Hollywood version of time travel. Under presentism, time travel is 100 percent impossible, because you cannot travel to moments that don’t exist. So all our favorite time travel movies, whether it’s The Terminator or Predestination, are non-starters.

… under eternalism…since time isn’t flowing in the normal sense [in the physical world], then it must be an illusion imposed by the brain. And this is what causes this tension between neuroscience and physics…

The laws of physics don’t tell us that there’s anything special about the present moment. Also, the laws of physics are generally time-reversible. You can run Newton’s laws or Einstein’s laws forward or backward, to predict the future or retrodict the past. And then, with relativity theory, we’ve proven that there is no absolute “now.” If I was traveling in a different reference frame at a very high speed, it doesn’t make sense for me to ask, “What is Dan doing now?” because our clocks are ticking at different rates. Some people have taken that to say, well, maybe there is no now; maybe all moments are already “out there.””

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