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What is time?

by Jan T. Trembley, BMC '75

This article first appeared in the Bryn Mawr Alumnae Bulletin, Fall 2003. It gives an overview of the series of four talks/ discussions held in the Time Symposium sponsored by the Center for Science in Society the previous academic year.
o A flower begins to unfurl before sunrise in order to absorb as much light as possible; the internal clock present in all living organisms, as far as we know, anticipates something that is going to happen.

o Most of our basic theories of physics (Newtonian, electromagnetism, relativity, quantum mechanics), which deal with a few particles at a time, don't care which way time goes. According to the Second Law of Thermodynamics, however, some energy is transformed as heat into a less usable form in an irreversible process, and the system becomes increasingly disordered. But is this sufficient to explain aging, or for that matter, does not evolution contradict it?

o Are we all playing out roles in a pre-determined universe or in some way authors of the tragicomedy in which we participate?

When people from different academic disciplines gather to talk about time, they need a lot of space. At a five-part symposium held this spring, Bryn Mawr philosophers, physicists and biologists summarized theories about the function of time in society, science and the universe. Spirited discussions after each presentation with audience members conjured up a modern version of a parable: blindfolded scholars feeling different parts of an elephant-by turns intrigued, cautious and puzzled.

Organized by Marion Reilly Professor of Physics Alfonso Albano and sponsored by the Center for Science in Society, "A Matter of Time" was loosely based on the September 2002 issue of Scientific American. "My hope was that the lectures would inspire greater discussion and exploration of the role and pertinence of time, both on campus and beyond," Albano said.

What made the gatherings so invigorating was a mix of participants-faculty, students and staff-willing to think out loud; to say, "I don't understand what you mean;" to explain patiently; or to analyze fallacious reasoning and press for more rigorous definitions of terms.

Flow or frozen dimensions?

Post-doctoral fellow in philosophy Cheryl Chen outlined philosophical debates behind two opposing views of time: the conventional view that only "now" is real, flowing steadily forward, and the "block universe" model preferred by some physicists, a four-dimensional, frozen timescape in which past, present and future are equally real. The latter is the model of a deterministic universe, because we can calculate backwards or forwards from any given point in the system.

Chen, whose area of specialization is epistemology and philosophy of mind, commented afterwards in the online discussion forum for the symposium: "If the passage of time is an illusion, it is interestingly different from some of the other things we call illusions. Scientists tell us that objects only seem to look colored because of the way light reflects off their surfaces. …

"We can easily imagine having other kinds of experiences without experiencing color, however, or even vision.… The passage of time, on the other hand, is a much more pervasive feature of our experience. It's unfathomable how we could have experiences in which time did not pass. … I'm wondering now if this is why many of us [at our first session] were trying to find a way to reconcile the conventional and the block views."

Can we measure it and how?

Hourglass, sundial, water drops-in a presentation on measuring time, Assistant Professor of Physics Michael Noel asked the audience for examples of clocks and pointed out that all were types of oscillators. "It's important to start from the baseline that we're not measuring time with something that's sitting still but that's in action," he said. "We have developed more sophisticated mechanical oscillators; the state of the art is to use atoms, which have characteristic frequencies."

Noel said time can be measured to a precision 1000 times that of any other fundamental constant: "The meter, lumen and ampere are now defined in terms of the second; the kilogram, mole and Kelvin may soon follow." The development of clocks that measure time with increasingly smaller intervals will improve the accuracy of Global Positioning Systems, make possible interplanetary space flights, and help measure the effects of an expanding universe.

"Planck length" is the smallest measurement of length with any ascribable meaning in physics, roughly 10-20 times the size of a photon. "Planck time" is smallest division of time with any meaning, the amount it would take a photon traveling at the speed of light to cross a distance equal to the Planck length. Physicists call time and distances smaller than Planck scales "fuzzy"-if it were ever to turn out that interpretation of smaller measurements is impossible, there would be an opening for the argument that time does in fact flow!

Interpreting physics

Physicist Tony Rothman, author of Doubt and Uncertainty and A Physicist on Madison Avenue, among other books, reviewed the so-called seven "arrows of time," ways in which nature tells us that time goes in one direction. These include the fact that human memory works only backwards, that the universe is expanding rather than contracting, and that entropy increases. According to the second law of thermodynamics, entropy is a measure of increasing disorder in a system; physicists have tried to derive this from Newtonian mechanics-which, like other basic laws of physics, is time symmetric-by defining it in terms of the probability of numbers of molecules moving from one arrangement to another.

A visiting member of Bryn Mawr's physics department, Rothman "created some heat" during the symposium with his position that probability arguments cannot prove increases in entropy go only forward in time, not backward. "The whole topic of entropy is confusing to most people and has been ever since it's been introduced," he said. "To date there is no satisfactory explanation in physics for the direction of time."

Some physicists also find problems with the use of probability in conventional interpretations of quantum theory to calculate alternative possible states. A subatomic object can be measured as a particle or a wave, but not both. This is "wildly successful"at the quantum level, said Associate Professor of Physics Elizabeth McCormack, but produces "nonsensical results" in the world of larger objects.

Einstein objected to the phenomenon of two seemingly unconnected, disparate objects exerting influence on each other as "spooky actions at a distance." Although the laws of physics are not concerned with consciousness, mystical literature has invoked quantum theory as a scientific foundation for belief in paranormal phenomena, for example that individuals can receive information from the past, future, or others in the present at a distance.


Associate Professor of Biology Peter Brodfuehrer began his session with questions about the "clocks" that time living organisms. "I asked my physiology class what the notion of biological clocks meant to them," he said. "Of 33 students, probably 30 said it suggested to them that their biological clocks were ticking away and would they be able to have kids at the right time in their lives?"

"We could talk at length about how biological organisms track time, but the more interesting route for us might be to ask 'What is the function of biological systems that they can count time?'," Brodfuehrer said.

"Organisms in the natural world have to anticipate when to mate, when food will be available, so they need very accurate mechanisms to measure the lapse of time. Circadian rhythms are molecular-based timing systems that run approximately 24 hours; they can reset through feedback cues from the environment such as light, temperature, or the cries made by birds or primates. … What is the effect on our physiological processes when we work night shifts or fly across time zones? Our bodies are out of sync with the signals we're getting from the surrounding environment."

"The fact that an endogenous clock is present in all living organisms is in some sense very strong evidence that, despite physicists, there must actually be a direction of time in the universe - because if there wasn't, it's very unlikely that organisms would have evolved a way to keep track of it," said neurobiologist Paul Grobstein, who led a session on the implications of timing for thinking and the implications of thinking for time. Eleanor A. Bliss Professor of Biology and director of the Center for Science and Society, Grobstein co-taught an undergraduate seminar this spring with Milton C. Nahm Professor of Philosophy Michael Krausz on the aims of scientific explanation (Philosophy 310).

Making up stories

"I'm skeptical about time reversal, except in the brain, where the problem of simultaneity gets even worse," said Grobstein. "Temporal order plays a very strong role in our conceptions of causality, but in the brain, causality is bidirectional." He cited experiments published in the late 1970s by Berkeley physiologist Benjamin Libet, who found that it took about a half second before human subjects were aware of stimuli applied to their skin, although it had only taken 20 milliseconds for nerve traffic to reach the somatosory cortex of the cerebrum. When Libet stimulated that part of the brain and then the skin, however, patients thought the latter had occurred first.

The automated skills of gifted athletes or chess players can not make up for the time lag; some researchers have suggested that their reaction times may appear to be so rapid because they are able to anticipate or subconsciously imagine a set of possibilities.

"Libet's findings suggest that our sense of reality may include an unconscious presumption of the future being available to and affecting the present but that is, in his terms, an artifact of how the brain creates consciousness," Grobstein said. "Is it perhaps this ability to backdate that give rise to the 'block model' of time? … What's nice, of course, is that if the block model of time is in fact a 'story' made up by the brain, then there's still room for brains (and selves) to create change by their own actions, and so be meaningful contributors to both change and the stories we tell to make sense of it."

In the beginning, or is it the end…

During the final session, discussions about measurement returned inexorably to the way we think about time under careful questioning from Michael Krausz. Can physics say that time exists independently of its measurement? When we define time we ask how far a pointer on a clock travels. In turn, we define space in terms of time. "In the statement, 'time is that which is measured,' the phrase 'that which' is ambiguous because it allows for two possibilities: 1) that there is an objective fact of the matter which is independent of measurement, or 2) that the phenomenon is posited in virtue of measurements," Krausz said.

"We've come face to face with the idea that in order to make any sense of measurements, we need a theoretical context," Albano said. Participants finally declared they had reached the end of the usefulness of "time" as a term that stands alone and were ready for a new symposium on "the hyphenated matrix of space-time."

"The real mystery is the speed of light," trumped McCormack.

"Or maybe it's ... 'Which way does the story goes next?' " Grobstein said. "Everyone is invited to help move it along in their own way by contributing to an on-line forum at http://serendipstudio.org/forum/newforum/time-read.html." For notes and further references, see http://serendipstudio.org/ local/scisoc/time/. The Spring 2003 issue of Daedalus, Journal of the American Academy of Arts and Sciences, also was devoted to essays on time.

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