The passage of time has always been a question that has excited the imagination of scientists and artists. “There is something that has always interested me and even terrified me since I was a child. That something is the problem of time, the perplexity of time, the infinite whirlpool of time,” said Jorge Luis Borges, interested in physics and mathematics, thus answering a question about literatureIn recent decades, the development of neuroscience has driven numerous investigations into how different human experiences perceive the sweet or rushed passing of time.
“A first philosophical question that I always ask myself is whether time really exists or is it an invention of the brain. Physicists will say that it does exist, that it is just another dimension. The problem is that biologists and neuroscientists are absolutely convinced that everything we know passes through the filter of the human mind. So what is time? Defining it is a murky, slippery issue,” says Ignacio Morgado, emeritus professor of psychobiology at the Institute of Neuroscience and the Faculty of Psychology of the Autonomous University of Barcelona. It is a July morning when the voices of children, in their eternal childhood summer, filter through the window, at the same time as a huge chestnut tree begins to shed brown leaves onto the sidewalk.
Morgado distinguishes between objective time, which is measured by the obedient ticking of clocks, and mental time, which is what our brain considers to have elapsed. It would be as if the brain projected a sequence of images, reflections of the world, which feed the senses and are closely linked to memory, so that the sequence creates an idea of the past, present and future. “If we did not have this combination of time and memory, I have the impression that we would be in a kind of eternal present like the one probably experienced by some people with neurological diseases such as Alzheimer’s,” explains this neuroscientist.
This mental time, which is subjective, is also different from that measured by the circadian clock—located in a group of a few thousand neurons in the hypothalamus—which regulates the production of hormones and the states of sleep and wakefulness in cycles of about 24 hours. How does the brain create this idea that a certain amount of time has passed since it began to read, that yesterday was yesterday and that childhood is now a long way away?
Space and time
John Wearden, emeritus professor of psychology at Keele University, UK, has been researching time perception for almost forty years, first in animals and then in humans. From Slovenia, where he spends his summer hours, he talks about some timing experiments that he does in his laboratory to find out which parts of the brain are involved in inferring the time that has passed, which he calls retrospective timing: they apply a stimulus and the participants have to estimate its duration while the scientists record their brain activity.
“For example, we give them two short sounds, A and B, and we ask them if they were the same length. It sounds very simple, but if you think about it, it’s quite complex. You have to have some way of timing A and B, that’s obvious. But there’s also a memory process. And then you have to determine whether they’re equal or not – you need a decision process. Which parts of the brain activation are from the timing process, which are from the memory process, and which are from the decision process?” Wearden asks.
Although these underlying issues are still unclear, there are many common experiences that humans seem to agree on: it runs slowly in boredom and illness, fast in fun, calm in childhood, and runs wild in old age before the proximity of death: Wearden remembers that his mother felt that the days passed very slowly; but the months, very quickly.
The myth that time is accelerating
Scientists have also studied some of these beliefs about the duration of time. One consistent finding is that sounds last longer than visual stimuli, such as a light bulb being turned on. Recently, a lot of attention is being attracted—too much, according to Wearden—to the role of emotions: Angry faces seem to last longer than neutral ones, but happy ones do not. The phenomenon that time passes quickly when you are having fun is, in the opinion of this psychologist, something completely different, caused by the diversion of attention while you are doing something exciting.” Recently, studies have been carried out on the meditation and the mindfulness and small effects have been observed. Time of day affects duration judgments, probably due to changes in body temperature, which in turn alter time perception if induced experimentally. The list is very long,” explains Wearden.
One area where many of these beliefs reside is age. Psychologist Jean Piaget He conducted several experiments on children aged five or six. And, in general, he found that more intensity or size equals more time; that is, if a stimulus was brighter or larger, children judged it as lasting longer and were unable to extract time from other aspects of the situation. At the other end of the lifespan, there doesn’t seem to be much of an effect of age on time estimation until age 70 or 80, and the effect here is generally just an increase in variability.
The exception are tasks where in addition to timing, People also have to do something else“We do see deficits in older people there, but presumably due to general information processing problems, not timing per se. The idea that ‘time seems to pass faster as you get older’ has proven difficult to support in systematic studies, although people often believe this to be true. It’s not clear why data from actual studies don’t support this idea. Perhaps it’s just a popular myth, but maybe it’s true and we just haven’t found the right way to measure it yet,” Wearden concludes.
Time and relativity
Although we may say that clock time is objective, in contrast to the
subjective time that passes in the brain, this is not entirely true. The formulation of the Theory of Relativity at the beginning of the 20th century turned physics upside down and one of its most counterintuitive consequences deals with time and is as blunt as this: universal time does not exist. “That is to say, time exists, but it does not pass in a monotonous and equal way for all physical systems: if you move at a certain speed, time passes more slowly than for another person who is at rest, and it also depends on the gravitational field,” explains Alberto Casas, researcher at the UAM/CSIC Institute of Theoretical Physics.
This has been proven in many experiments. In 1971, physicist Joseph C. Hafele and astronomer Richard E. Keating They mounted four atomic clocks on board commercial aircraft. They circled the globe twice, first eastwards and then westwards, and compared them to the stationary clocks at the US Naval Observatory. Once put together, the three sets of clocks did not agree with each other, exactly by the amounts predicted by relativity. “And this is at, let’s say, home speeds, but if we approach the speed of light, these changes are enormous. For example, a muon is a particle that decays in two millionths of a second, very quickly. If muons are accelerated in a particle accelerator – at speeds close to that of light – they take 30 times longer to decay. It’s not as if time slows down, it’s that time slows down,” explains Casas.
Moreover, the stronger the gravitational field, the slower time passes under it. “If you put a clock on a table and then under it, the clock goes slower when it is down, it has slowed down again. And the effect has been observed even at distances of up to a millimetre: if you put a coin on the table, time passes faster on the upward side than on the side that touches the table,” explains the physicist.
Given the profound complexity of time, Ignacio Morgado recommends not living too dependent on it and, above all, managing it as best as possible. “If we do not have the feeling that we control our time, stress takes over. Controlling it is one of the main elements of mental health.”
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