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

by Dean Buonomano

Saint Augustine: “What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.”

Clock time is a local measure of change, neither absolute nor universal.

There is even a name for the phenomenon of hearing multiple interpretations of a song: a mondegreen.

Neurocomputational models have shown that simple circuits composed of excitatory and inhibitory neurons that exhibit short-term synaptic plasticity can respond selectively to a range of different temporal intervals—for example, to a 100 ms interval, but not a 50 or 200 ms interval.7 Such interval-tuned neurons could potentially be used to detect the voice-onset time of phonemes, the interval between Morse code symbols, or between musical notes.

there is increasing experimental support for the notion that many of the computations the brain performs, particularly those that are temporal in nature, rely on the brain’s ability to generate complex, time-varying neural trajectories that can be used to produce the spatiotemporal patterns that underlie our ability to reach out and flip the page of a book or play the piano.20

Coordinating time was not an esoteric academic matter, but one driven by the railroads, telegraphs, and financial businesses. And as with most practical matters, inventors sought to patent their inventions. Because Switzerland was a hub for time technology, many such patents were submitted to the patent office of Bern. There, from 1902 to 1909, a reportedly diligent patent officer reviewed all sorts of patents, including some relating to the electrocoordination of clocks. In 1905 the patent officer, Albert Einstein, published the paper On the Electrodynamics of Moving Bodies, which, in addition to abolishing the notion of absolute time, briefly describes a way to synchronize distant clocks.11

a meter is defined as the distance light travels in 1/299,792,458th of a second.

according to presentism only the present is real: all that exists exists in the perpetual present (in my use of the term, presentism does not imply that time is absolute). The past refers to a configuration of the universe that no longer exists, whereas the future represents a yet-to-be-determined configuration. Under eternalism, time has been spatialized into a full-blown dimension in which the past, present, and future are equally real. The universe becomes a four-dimensional “block” with one temporal and three spatial dimensions—the so-called block universe.

in practice, clock time is always measured by change. No matter how accurate or inaccurate, clocks are always quantifying change of some physical phenomenon.

Simultaneity, and indeed the order in which two events occur, can be relative.

The linguist and ex-missionary Daniel Everett believes the Pirahãs are grounded in the present: “Pirahãs don’t store food, they don’t plan more than one day at a time, they don’t talk about the distant future or the distant past—they seem to focus primarily on the now.”12 Everett originally set out to learn their language, translate the Bible into Pirahã, and convert them to Christianity. He became fluent in their language, but failed epically in his missionary aspirations as the Pirahãs eventually led him to atheism. He thinks part of the failure was due to their lack of interest, and skepticism, toward events that they did not directly experience, or at least have secondhand knowledge of: they had little interest in stories of Jesus once they realized Everett had never actually met Jesus. Similarly, they seemed not to be preoccupied with the future, or what, if anything, happens after they die. Everett does not believe that the restricted temporal outlook of the Pirahãs reflects any sort of inherited neurological deficit, as they are intelligent and exquisitely skilled at surviving in the jungle: “They can walk into the jungle naked with no tools or weapons, and walk out three days later with baskets of fruit, nuts, and small game.”13 Rather, he thinks, the Pirahãs’ present-based existence is a signature of their culture. Such moment-by-moment existence is certainly enabled by their environment and the more or less continuous availability of food. Their indifference towa...

According to one estimate, between saccades and blinks, a full hour of visual information is lost throughout the course of a day, without any perceived blanks in our visual stream of consciousness.

“Not only do we consciously perceive only a very small proportion of the sensory signals that bombard us, but when we do, it is with a time lag of at least one-third of a second. . . . the information that we attribute to the conscious ‘present’ is outdated by at least one-third of a second. The duration of this blind period may even exceed half a second when the input is so faint that it calls for a slow accumulation of evidence before crossing the threshold for conscious perception.”

neuroscientist Read Montague has put it, “Free will is the close cousin to the idea of the soul—the concept that ‘you,’ your thoughts and feelings, derive from an entity that is separate and distinct from the physical mechanisms that make up your body.”14

Stephen Hawking states, “The reason we say that humans have free will is because we can’t predict what they will do.”15 Similarly, for Roger Penrose, “The issue of free will is discussed in relation to determinism.”16 In other words, if the laws of physics establish that it is possible to predict the state of any system at time t, including the human brain, from previous moments in time, then free will does not exist. As explained by the philosopher Michael Lockwood: “Universal determinism is so widely held to be incompatible with the existence of free will. For universal determinism is the thesis that the universe is subject to a set of rigid laws that, in conjunction with the state of the universe at any given time, prescribe precisely what state the universe will be in at any subsequent time. If the universe really is deterministic in this sense, it follows, . . . that all future outcomes—including, therefore, all our own future choices and actions—are already fixed.”

In this context, quantum mechanics is a thorny theory because, unlike the rest of physics that deals in certainties, quantum mechanics deals in probabilities. We know that at some level quantum events must affect the state of the brain—after all, every photon detected (or not) by your retina is playing by the probabilistic rules of quantum mechanics. So even in theory it is probably impossible to predict human behavior with 100 percent accuracy. Nevertheless, quantum mechanics provides a form of probabilistic determinism: it establishes a domain of options and their respective probabilities, leaving in the eyes of many philosophers little room for free will.

But for those who believe we live in a 4D block universe, the issue of whether the laws of physics are deterministic or not is rather secondary, as the block universe itself leaves no room for free will. If the past, present, and future all coexist within the block universe, all choices to be made have “already” been made.

perhaps we should define free will as exactly that: a feeling. As the psychologist Daniel Wegner defined it in the early aughts, free will “is merely a feeling that occurs to a person. It is to action as the experience of pain is to the bodily changes that result from painful stimulation.”19 Defining free will as the flavor of consciousness associated with the neural processes responsible for making decisions is not a new idea. Almost three hundred years ago the philosopher David Hume stated that “by the will, I mean nothing but the internal impression we feel and are conscious of, when we knowingly give rise to any new motion of our body, or new perception of our mind.”20 Thomas Huxley also argued that “the feeling we call volition is not the cause of a voluntary act, but the symbol of that state of the brain which is the immediate cause of that act. We are conscious automata, endowed with free will in the only intelligible sense of that much-abused term.”21

Evolutionarily speaking, subjective experiences and free will may be primarily future-oriented phenomena. For example, perhaps it is the feeling of free will that provides the conviction that we are in control of our destiny, and thus the impetus to take charge and make the long-term, future-oriented, actions necessary for survival.