What is time? It is constantly around us, and every day we are faced with this phenomenon. Time progresses and is being translated into our experience: the future becomes the present and the present becomes the past. Speaking of an event, it is normal to ask: when did it happen? Why can a person "feel" the time? From the point of view of classical physics, time always goes at the same pace, but when it comes to its perception, everything becomes much more complicated. The problem of time is one of the central in physics, philosophy, psychology and biology.

How to wind the "internal clock"?

All life on Earth obeys biological rhythms: plants bloom and animals migrate according to the season; a person goes to bed at a certain time of the day. Physiological state of brain activity and even mood depend on time. Biorhythms affect the heart rate, breathing, growth and fall of body temperature, blood pressure, as well as many processes in the cells (for example, clearing of the debris). Like a conductor controls an orchestra, biorhythms control an entire internal system.

Chronobiology is the science that studies biological rhythms, and many discoveries have been made related to the description of the process of human exposure to diurnal cycles. Some defining concepts were formulated in the second half of the XX century, and in 2017 American scientists were awarded with the Nobel prize "for the discovery of molecular mechanisms that control the circadian rhythm", the circadian internal clock that adjusts the life of all organisms to the change of day and night.

Illumination, in particular the rotation of the Earth around its axis, determines the circadian oscillations of the organism. These biological rhythms are "invented" by nature in order to adapt the body to the perception of dark and light time of day. Information about the ambient light comes from the retina of the eye in a special area of the brain, suprachiasmatic nucleus, and from there commands to other brain areas are sent to produce certain hormones and neuropeptides (proteins of the nervous system). So, through the eye we receive a signal that it's time to go to bed or that it's time to get up.

It may seem that in complete darkness a person will cease to navigate in time, but he doesn’t. Even in the absence of information about the light day, the circadian period will still be stable, only its duration will change — it will become longer. To prove this, German physician and biologist Jurgen Aschoff conducted an experiment: he put the volunteers in a completely dark room for a few days. It turned out that the sleep — wake cycle in this room stretched for half an hour. Sleep in complete darkness was not perceived as a complete shutdown, but mainly took place in the slow-wave phase, became superficial and fragmentary. Similar studies by other scientists have led to similar results. 

Most of the animals strictly obey the biorhythms. However, for some of them evolution has found a way to turn off the "internal clock"! For example, reindeer do not express the key genes responsible for circadian rhythms, so they focus only on the actual duration of the day and do not lose touch with astronomical time. In other animals, the circadian rhythm coincides with the periods of daylight.

In modern man, living at a pace 24/7, biorhythms can be disturbed that leads to "circadian stress", which in turn contribute to the development of many diseases. There is also such a thing as seasonal depression — a negative reaction of the body to reducing of the daylight lenght. Cortisol blood level increases with this disease. This change is able to inhibit the immune system. Often in the Nordic countries, short daylight hours are the cause of spikes in morbidity and increasing suicide rates.

All internal organ systems, as well as cells have their circadian activity. The field of study of this issue is only developing, but there are already interesting data. For example, scientists from Cambridge University observed how fibroblasts (skin cells) react to the change of time of day. They found that cells regenerate more slowly at night than in the daytime. In addition, analysis of the database of human burns also showed that wounds received during the day are healed faster than at night.

Although man can be considered highly adapted to the environment, yet he has the most difficult. It is very difficult to resist circadian stresses. It is important to remember the main rule - enough is as good as a feast. If a person has cases of lack of sleep, it will be a serious mistake to build them into a habit. In addition, frequent movements to other time zones will affect the "mode of operation" of the body. Experts are convinced that even a seemingly simple switch to daylight saving time increases the risk of fatal accidents and the number of heart attacks. You need to listen to your body and comply with its conditions: do not sit late at work, do not eat at night, minimize physical activity in the evening, turn off the lights at night, as well as computers and televisions for half an hour before the bedtime. Artificial light coming at night from various gadgets, as scientists have proved, worsen the physiological and cognitive functions of human.

Psychology of time perception

Although from the physical point of view time is absolute and unchangeable, everyone perceives it subjectively. We have some experience, sensation, or sense of time. This is directly related to biorhythms, which control the basic life processes taking place in the body. And yet the perception of time is conditioned not only by them, but also by the content that fills and breaks it into pieces: time and events that take place in reality are inseparable from each other. 

Psychologists have found that estimating small time intervals, people tend to either underestimate or overestimate them. The past seems longer if it is full of bright and rich events, and shorter if there is nothing special about it. The opposite is true of the present tense: the poorer and more monotonous its flow, the slower it flows, the more substantial its filling, the more imperceptible it seems.

In the present time, a person often sets an attitude for the future, on which the duration of the experience depends. Often you can feel that in front of the desired event time is painfully slow, but before the junk — treacherously quickly. "Sad hours are long," said Romeo in Shakespeare's tragedy. Psychologists call this phenomenon the law of emotionally determined estimation of time. 

Perception of reality is also conditioned by the degree of concentration. This is similar to the situation with the kettle, which still can not boil — it seems that the event on which the attention is focused, lasts longer than usual. When, on the contrary, a person is busy with several things at once, it seems that time runs faster.

Can it stop? In human perception, it certainly can. This phenomenon is called chronostasis, which is literally translated from the Greek language like "stop time." Focusing on a particular subject, the brain makes a "freeze frame" for a person and gives him the opportunity to consider it, and then returns to normal perception. To see this effect in action, the researchers conducted an experiment with an alien image. With a certain frequency for the same period of time the subjects were shown an image of an apple. And suddenly, among the pictures there was a picture of a shoe, which was being shown for exactly the same time as the apple. People had a feeling that the shoe was shown longer. So, the brain, perceiving information, creates illusion.

It is believed that in a critical, dangerous situation, time also tends to be distorted, or rather to slow down. A similar example is the time-lapse movie: when a shell explodes in front of a soldier or a scene of a car accident unfolds in front of the victim. To test this hypothesis, American neurophysiologists set up an experiment. They rented a tower with a height of 31 meters and hung a safety net under it. The fact that it was possible to fall from the tower, had to cause fear in volunteers, and then, perhaps, the effect necessary for scientists. However, the hypothesis was not confirmed, most likely due to the fact that the subjects did not experience the desired level of stress, as they knew that life was not in danger. But no one dared to send people towards real danger for experiment purpose.

The sense of time is distorted with age. People over 60 years of age say that events begin to go faster than in youth. Scientists believe that the brain of older people is worse at processing the received visual and audio information, so you can see how they can lose the thread of conversation during a dialogue, have difficulty driving a car or poorly maintain the balance of their own body while walking. The brain simply does not have time to "add up" all the pictures in a single sequence.

Perception can also be impaired due to various diseases. Diseases such as autism, attention deficit hyperactivity disorder, and age-related Alzheimer's and Parkinson's are often accompanied by an inability to determine time. 

Is it possible to slow down the ever-accelerating time, and at the same time the flow of life? Experts say that it is possible. Developing cognitive abilities, you can adjust your "internal clock" with the help of training attention, reaction and memory. Meditation aimed at developing mindfulness and concentration could also be useful. All this can help to perceive life slowly, measured, in all its splendor.

Physics of time

There is no doubt among most physicists that time does exist. It is a measurable observable phenomenon that is defined as a development of events. In the natural world it has one direction, called the arrow of time. This phenomenon was described more than two and a half thousand years ago by the ancient philosopher Zeno of Elea and consists in the fact that no object can be in two places at the same time, and the arrow at every moment should occupy only one place in space, and from such elusive positions its trajectory is formed. Thus, movement is a sequence of individual events, and time flows from the past to the future, not back. In fact, if the system does not change, it is timeless. It is something we cannot see, touch, or taste, but we can measure it.   

The direction we observe in the macroscopic world is very real: cups break, but do not stick back together, eggs can become an omelet, but not vice versa. One explanation is that the natural world follows the laws of thermodynamics. Another law states that within a closed system, entropy (the degree of disorder) remains constant or increases. That is, the Universe cannot return to exactly the same state in which it was at an earlier point. Time cannot move backwards. However, it also cannot stand still. 

Albert Einstein showed that the passage of time depends on both speed and gravity, but he could not explain the meaning of "now". For us, the present moment separates the past from the future. Some scientists have stopped trying to understand the passage of time and what the present moment is, because they call it an illusion, but the outstanding American physicist and Professor at the University of California at Berkeley, Richard A. Muller protested. 

In his opinion, "now" is a single point on the time axis, as if the future already exists, just not yet experienced. This is the only moment when we can have some impact on the world around us, direct the growth of entropy and thus influence what is happening and what will happen. For example, we can break a cup or make a new one, but we cannot change what has already happened. And the continuous addition of such new moments of the present moment gives us the impression that time is moving forward. 

British physicist Roger Penrose believes that it flows for us only because we have consciousness. In General relativity, time is just one of the coordinates used to describe the position of a particular event in a four-dimensional world. It is static and not able to "flow" as well as space. Why do we seem to sense its course? At any moment we have the feeling that the past has already happened and the future does not yet exist, and that everything is changing. All we are ever aware of is our perception of the world at any given moment, which adds up to an experience. The reason there seems to be a past is because the brain contains memories of that experience. Due to the peculiarities of our perception, the brain registers changes in the world, which we interpret as the passage of time. According to Penrose, the only thing we really perceive is the present moment. 

One of the leading experts in the field of regenerative medicine, Professor Robert Lanza, supports the theory that the perception of time is only due to the presence of consciousness. According to his concept, which was called "biocentrism", time as such does not exist outside of our sensory perception, it is the result of understanding the changes taking place in the Universe around us. It "animates" fixed "frames" of space states before our eyes, turning them into events. The sensation of movement is formed in our minds when the mind combines these frames into a sequence. 

The perception of the velocity of time may not be the same for every object in the Universe. Einstein discovered that space and time are intertwined into a single continuum known as spacetime. Events that occur simultaneously for one observer may occur at a different time for the second. When he developed the equations for General relativity, he realized that distortions in space-time caused massive objects. This distortion was called gravity. It really interferes with the passage of time, which means that the more massive the object, the slower time flows near it. For example, compared to a clock in space, time on the surface of the Sun slows down by six billionths, and near the surface of a black hole, where gravity is enormous, time hardly moves.

However, it slows down not only in strong gravitational fields, but also at high speeds. This effect, called "relativistic time dilation", usually remains insignificant, but at sublight speeds it gives an amazing result. At 98% of the speed of light, time flows half as slowly as usual. When it reaches 99%, it slows down seven times. For example, in 1971, scientists Joseph Hafele and Richard Keating measured the deceleration of time in flight. As a reference system, the researchers used a conventional passenger jet. They found that at a speed of 900 km/h people live longer. Each day for 29 nanoseconds (billionths parts of a second) longer.

Time is linear and continuous in classical physics at macro scales. But there is a theory that it can also have a quantum nature. In this case, it will probably be at the level of Planck time (about 10-43 seconds), the shortest possible duration according to theoretical physics, and most likely we will never be able to measure it. 

Physicists have suggested that time actually occurs as a result of quantum entanglement, when two particles are connected to each other, even if they are separated by space, so that the state of each of them can only be described with respect to other entangled particles. When two particles interact, they can no longer be described as separate, independent "pure states." They become entangled components of a more complex probability distribution that describe two particles together. 

As objects interact with the environment — for example, as particles of cooling coffee come into contact with the air in a room — information about their properties is mixed with the environment. This loss leads to the fact that the state of the drink reaches thermal equilibrium and then remains unchanged. Thus, the cooled cup can not spontaneously heat up. Theoretically, coffee particles can suddenly return to their original state, but it would take billions of years to register such a rare event. You can imagine that you are in the park at the gate. Once you cross them, you get into a huge space and get lost in it. Most likely, you will never return to the gate. This improbability makes the arrow of time irreversible.

But in 2018, researchers at the Moscow Institute of physics and technology, along with colleagues from the US and Switzerland, managed to turn time for subatomic particles and return them to a fraction of a second in the past. How did scientists do the impossible? — They used a quantum computer to model a single particle, and the system was small enough, the process short and carefully controlled. In real life, the aging of even a single particle remains too complex for nature to reverse. After running the algorithm in a quantum computer, it was possible to return a simple system to its original state in 85% of cases. However, with increasing complexity, reduced the ability to control all aspects of the process and the success of the experiment reached only 50% of cases. Scientists believe that as technology advances and quantum computers improve, it will be possible to control increasingly complex systems for much longer.


Time cycles affect human physiology and psychology. As scientists have found, life expectancy and our health depend on the harmony of biological rhythms. Modern chronomedicine is engaged in the development of drugs and methods that regulate their work. This will allow to influence the causes of diseases at the earliest stages of development and reduce the time of recovery.

If biologists are already using their knowledge of the nature of time to influence the human body, physicists are left with more questions than answers.  Thanks to Einstein's special theory of relativity, scientists know that when traveling at high speed or near massive objects, time slows down, and when traveling at the speed of light, it stops altogether. However, physicists have calculated that life does not become longer, we will be younger relative to those who remained on Earth, but also live a shorter time period compared to them. 

With the advent of quantum mechanics, new unusual properties of matter were discovered. It became clear that it consists of elementary particles that behave in a certain way. Many hypotheses trying to explain the physics of space-time are based on this knowledge. For example, from the perspective of the theories of Penrose and Lanz, time is the product of consciousness, comprehending the changes that occur in the world. It is believed that the time axis and space itself appear as a result of decoherence of the quantum state of elementary particles. In other words, time is created by outside observers. If these hypotheses are confirmed, it is possible that in the distant future such observers will be able not only to set the direction, but also to influence the course of time itself.

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