Can Time Be Saved From Physics?

Craig Callender remembers the moment that really got him hooked on the study of time. He was in grad school at Rutgers University, in New Brunswick, New Jersey, studying philosophy, when he attended a lecture about quantum physics by David Mermin, a physicist at Cornell University. There he learned about a theorem, developed by Irish physicist John Bell, that said that two quantum particles can communicate information with each other instantaneously, no matter how far apart they are separated. The claim suggests that quantum particles have a "spooky" connection that may be in tension with Einstein’s theory of relativity, which says that nothing—not even information—can travel faster than the speed of light. This seemed so bizarre that Callender tracked down the theorem and studied it in depth. "I was just so floored by this," recalls Callender. "It just seemed so rock solid and such a striking departure from the way I figured things had to be."

It inspired Callender, now a philosopher at the University of California, San Diego, to switch his focus to studying physics and metaphysics, in an effort to get to bottom of what he regards as the last great mystery: the nature of time. In May 2018, Callender used an FQXi grant of over $36,000 to organise a conference at UC San Diego, inviting many specialists in multiple fields to try to solve the problem. It is often said that according to relativity, time’s flow is not fundamentally real. Callender’s own view, outlined in his Lakatos award-winning book, What Makes Time Special?, is that time is not an illusion—as modern physics may suggest—or just an intuition, but arises from the interaction between our senses and external stimuli.

Augustine’s Confessions

The slipperiness of subjective time puzzled philosophers long before physicists entered the debate. As the fourth century philosopher St. Augustine famously wrote in his Confessions: "What, then, is time? If no one ask of me, I know; if I wish to explain to him who asks, I know not." For theological reasons, Augustine felt compelled to place God and his existence, completely outside time. And this is a notion, as Callender explains, that persists with some theist philosophers and scientists to this day.

It’s tempting to think Augustine might have agreed with the definition of what Callender calls, "manifest time": our subjective sense of living in the present, which includes having a sense that time flows in only one direction, and with a clear demarcation between the irretrievable past and the future that is yet to come. "In philosophy there’s always the danger that you’re trapped in some kind of word game, or puzzle with words," says Callender. "But you know there is time, or something that goes by that description."

While we may all feel the passage of time, there is a major problem when you try to square that everyday experience with the laws of physics. Ever since Einstein, and the advent of relativity, it has seemed as though there is an unbridgeable gap between the subjective sense of time all humans share and the notion of time as it is understood and used in science.

Einstein in the end resigned himself to the notion that the difference between the past and the future was but an illusion. The only real time, as far as he could determine, is that of science, where, as in his theories of relativity, time is an axis on the four-dimensional spacetime grid that determines the change in ’position’ in both space and time of all things. There is no special "now" that can be uniquely marked out on this grid, separating the set past from the open future; instead, all stand on an equal footing.

More recently, physicists, such as Julian Barbour, of Oxford University, UK, have gone Einstein one better and argued that time does not exist at all. In his book, The End of Time, Barbour worked out a model of physics in which time can be dispensed with. In contrast, there are other physicists who would rescue the reality of time, such as Lee Smolin, of the Perimeter Institute in Waterloo, Ontario, and George Ellis, at the University of Cape Town, in South Africa. They have independently developed models in which time is preserved and a bridge can be built from the scientific time used in physics equations to the human understanding of manifest time, to borrow Callender’s lingo.

Callender believes these attempts to save time are too limited because physics can rarely account for human experience. He argues that a real reconciliation of manifest time with the time of science must be achieved from the other direction—starting from the human understanding of time, and utilizing all the sciences, including biology, neuroscience, psychology, and anthropology to create a more comprehensive model.

Information Gatherers

In this view, which Callender outlines at length in his book, What Makes Times Special?, time is more than just an intuitive sense. It is built by our continuous acquisition and assessment of feedback and data from multiple sources, most especially our senses: from what we see, what we hear, what we can touch, and what we can move through. In his view, not just humans, but animals have a sense of time that is built out of their interactions with their environments. Callender refers to these organisms—human or animal—as "information gathering and utilizing systems." The information about the environment thus built and processed by creatures becomes the network or platform that undergirds a robust definition of manifest time that can be correlated with the time of physics.

Callender hopes that children and animals will become a key source of information about how a sense of time initially evolved. Very small children, he notes, do not articulate their sense of time—and yet if you watch them in action, they act as what he refers to as ’updaters,’ living only for the moment. Their minds acquire and ’update’ information about their environments, and Callender believes that further study will show how manifest time grew out of this basic behavior.

As Callender’s meeting on time highlighted, there are strides being made in understanding how the brain perceives time through experiment. One of the presenters, Virginie van Wassenhove, a neuroscientist at Paris-Sud University in France, discussed how our brains position events in time when trying to imagine a different temporal viewpoint. For example, "thinking about yourself ten years ago: was the election of President Obama before or after where you mentally stand?" van Wassenhove asks. There is empirical data suggesting that time and space are treated differently by the human brain, when considering a change in temporal viewpoint compared with a change in spatial viewpoint, she explains.

Her own investigations use magneto-encephalograms to monitor how the brain distinguishes between sense of space and sense of time. For example, when subjects are shown movies with the audio tracks out of sync with the characters’ lips, the subjects very quickly (within a few seconds) adapt and can follow the storyline in spite of the ongoing discontinuity. Van Wassenhove describes this as the brain adapting to the phase of the rhythmic cerebral response, and this response is under the brain’s control. It’s not unlike the way the brain is believed by some researchers to process language; spoken language is continuous but the brain distinguishes language in discrete segments in order to analyze it and represent information in the nervous system. It’s possible, van Wassenhove says, that these cerebral rhythms give the brain time constraints that are relevant for the coding of information and language comprehension. "Psychological time and neural time need to be fundamentally understood if we wish to understand the brain and higher order functions of the human brain such as consciousness, language, music, foresight, and decision-making," she says.

While there remain many different, sometimes contrasting views on the origins of both subjective psychological time and the time of physics, many participants welcomed the interdisciplinary mix at the meeting. "The psychologists were especially interesting to me, as I don’t get to hear from them often," notes Caltech physicist Sean Carroll. "Questions like the development of language or metaphorical representations of time were fascinating."

Carroll himself has thought about whether time in physics is fundamental or a property that emerges from some deeper aspects of reality. This can be thought of in the same way that temperature emerges from the motion of multiple particles collected together. The faster that particles in a gas move on average, the hotter the temperature of the gas will be; however, it does not make sense to talk about the temperature of a single particle. Temperature is an emergent phenomenon in physics, and time may be too.

Columbia University philosopher Jenann Ismael notes that timing—excuse the pun—played a role in the meeting’s success. "I think many of us had been coming to the same ideas from different directions, and—with Craig’s book just out for a while, and Carlo Rovelli’s The Order of Time released the first day of the conference—it felt like kind of a moment," she says. Ismael notes that while participants at the meeting were able to learn from others from different disciplines, there are still huge points of contention between the different academic cultures. Physicists in general, are "more inclined to dismiss passage, flow and the sense of openness of the future as illusions," she says.

Accepting the view of many scientists that time is ultimately an illusion, is not an option for Callender, however. As he wrote at the close of his book, in some very loose and coarse-grained sense, manifest time might indeed be called an illusion without any harm done. "However, for many of its aspects, it’s a bit like calling our impression of a shape an illusion," says Callender, "and that seems wrong."

Watch Craig Callender’s classic talk at FQXi’s 2010 “Setting Time Aright” conference: