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Why do we perceive time marching in one direction? Combining physics, evolutionary biology and cognitive science could close the gap between the symmetrical notion of time in fundamental science and our everyday experience.
CRAIG CALLENDER University of California, San Diego
"The distinction between past, present and future is only a stubbornly persistent illusion." It was none other than Einstein who uttered these words. He was speaking about how our perception of time differs from the fundamental nature of time in physics.
Take our perceptions first: We have a clear sense of the present moment, what came before, and what might come after. Unfortunately, physics treats time rather differently. Einsteinís theory of special relativity presents us with a four-dimensional spacetime, in which the past, present and future are already mapped out. There is no special "now," just as thereís no special "here." And just like spacetime does not have a fundamental direction—forcing us to move inexorably from east to west, say—time does not flow.
"You have this big gap between the time of fundamental science and the time we experience," says Craig Callender, a philosopher at the University of California, San Diego. Itís this gap that he has set out to narrow, using ideas from physics, evolutionary theory and cognitive science.
The question of why time marches in one direction is tough to answer, says Callender, not least because if you want to talk about an arrow of time, you have to be specific about exactly which arrow you mean. While Einsteinís naked spacetime—without any fields and particles—may not differentiate between the past and the future, Callender notes that physical processes have directionality. That brings us to the first arrow: thermodynamic systems become more disordered, moving towards greater and greater entropy. There is also a second arrow: the causal arrow of time, which we take for granted in everyday life. "Actions I do now can change where Iíll die, but nothing I can do will change where I was born," says Callender.
Slicing Up Spacetime
These arrows and our commonsense notions treat time as very different than space. Is there some connection between these different ways of treating time? To find out, Callender has been slicing up Einsteinís spacetime, as though it were a 4-dimensional loaf of bread. You can imagine taking a 3-dimensional slice of spacetime along the time axis and another 3-dimensional slice along, say, the east-west axis. The idea is to evolve each slice along its respective axis and get to the next slice. In the first case, you are varying time and, in the second, you are varying time and space.
THE HISTORY OF THE UNIVERSE Could the story of the cosmos have been told sideways rather than from past to future? Credit: NASA/WMAP
The slicing allows Callender to investigate if can we tell the story of the universe sideways, from east to west, rather than from past to future. Given that Einsteinís picture puts time and space on an equal footing, with time having no special properties, we might expect the answer to be yes. "Well, the answer is no, surprisingly, for some specified class of equations," Callender says.
Intriguingly, these equations, which suggest that time and space are different on a fundamental level, tend to be the ones that physicists use most often to describe nature. Callender wants to see whether this holds generally across physics because it might provide a link between the thermodynamic and causal arrows of time.
Callender described the problem of time, and his way of slicing up the universe, in a talk at FQXi’s Setting Time Aright meeting:
If physics can explain how a causal arrow of time emerges, then biology will do the rest, says Callender. Evolution, he argues, selects for creatures that care more about the future than about the past. "Because of a causal arrow, a creature canít do anything about the past to increase its fitness, but can towards the future," he explains.
If physics can explain how a causal arrow of time emerges then biology will do the rest.
- Craig Callender
We would have developed the perception that now is distinct from the past and future in order to communicate and survive in the world. Our brains gather information, via the eyes, ears and other senses, and integrate them to create an impression of an event thatís occurring now. Itís necessary to, say, figure out that a tiger is about to attack you now, and you have to run. Or if two people are communicating, there is an implicit understanding that whatís being said is being said now (contrast this with exchanging letters, which have to dated). The brain automatically timestamps anything thatís being said as being said now.
Research in cognitive science backs Callenderís claim that caring more about the future than the past is important. Eugene Caruso a behavioral scientist at the University of Chicago in Illinois, and colleagues asked 121 volunteers at Harvard University to imagine working for five hours entering data into a computer and to think of a fair payment for the job. Some volunteers were asked to imagine that they had already completed the work a month ago, while others were asked to think about it as work to be done in a monthís time. The result: the volunteers felt they deserved about 101 per cent more for future work than for past work.
Thereís another interesting twist to this notion of "value asymmetry": If you are asked to value some future action that you would undertake versus the value of the same action done by someone else, relative to the same action done in the past, youíll tend to ask for more money for yourself, while estimating someone elseís past and future actions as having equal value.
Caruso and colleagues have shown that there are two main factors that contribute to this value asymmetry: the desire to reduce uncertainty and the ability to exert control over oneís life. Our emotions play a key role accounting for value asymmetry. "Emotions tend to be aroused most effectively by events that actions can meaningfully influence," says Caruso.
Callender will use part of his $102,263 FQXi grant to test whether this value asymmetry extends to kinship. He plans to set up a study in which people will be asked to compare the value of past versus future actions, not just for themselves and unrelated individuals, but also for people who are emotionally close to them, such as their spouses and kids. Such an experiment would specifically test whether evolution has selected for such emotions to increase our future fitness, says Callender, and Caruso agrees.
But donít be mistaken into thinking that these ideas about an asymmetric overvaluation of the future are anything new. Humans have always been doing it, prompting Seneca the Younger, the Roman philosopher, to rather bluntly warn over 2000 years ago: "All the future is uncertain, and more certain to be worse than otherwise."
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OMAR MASARWEH wrote on April 16, 2013 Prof. Callender is my Prof at UCSD and he does an outstanding job teaching the philosophy of physics, hes so great!!!
ANONYMOUS wrote on October 19, 2012 The evolutionary and psychological aspects of this are largely about avoiding the physics issues, as they have not been solved. So instead of admitting that the problems have not been solved, and tackling them head on, people try to explain them away by resorting to other areas, and areas that are conveniently blurred, and can't lead to anything solid. The funding sometimes goes to projects that make us feel better about the problems in physics, rather than projects that might actually lead to...
STEVE DUFOURNY wrote on February 1, 2012 JCN Smith,you are right.
The administration seems bizare. A lot of publicity and bizare marketing. It is sad, I beleived that FQXi was more rational and universal.
Mr Aguire and Tegmark. What do you do ?
A real sorting is necessary in your administrations and responsabilities. What is all this circus ?
You have a responsability !And the business and the monney has nothing to do with the sciences.