“Time is money”, “time heals”, “time drags on” – our whole life is subordinated to the running hand on the clock, but humanity still knows very little about what time is
What is time – in simple words
For the vast majority of people, time is an intuitively understandable quantity that characterizes the past, present, and future. There is no single definition of time in the scientific space yet. Moreover, representatives of different branches of science have almost opposite opinions on this matter.
For example, in classical physics, time is an absolute and unchanging value based on a certain sequence of events that occur at equal intervals. It is on this principle of periodicity that clocks are based. At the same time, Einstein’s theory of relativity says the opposite: time can change depending on the observer and the coordinate system. In this context, we can talk about the expansion and even slowing down of time.
In philosophy, time is the universal form of being and the flow of all mechanical, organic and mental processes. Time is a condition for movement, change and development, and only in one direction – forward.
Some scientists argue that the way we perceive time is just an illusion, an artifact of our consciousness. According to American physicist Sean Carroll, what we experience as the flow of time is a by-product of our brains as we process sensory information from our environment.
Aristotle pondered over what time is almost two and a half millennia ago. “Time is the most unknown of all unknown things,” said the Greek philosopher. Little has changed since then; scientists continue to conduct experiments and make calculations to catch time by the tail, subjecting it to rational explanation.
How the flow of time works
The physical equations of classical mechanics work equally well whether time moves into the future or into the past. However, in reality, seconds only go in one direction, determined by the thermodynamic arrow of time, and this arrow leads exclusively forward. Let’s figure out why it is impossible to turn back time and what can still be done to change the flow of time.
Linearity of time
The reason for the irreversibility of time is that the natural world obeys the laws of thermodynamics, according to which all processes in the world tend from an ordered system to chaos, that is, to an increase in entropy. In other words, a fallen leaf will never grow back to a branch, dust will not gather into paper, and the Universe can never return to exactly the same state it was in at the previous moment.
Einstein’s Theory of Relativity
In classical mechanics, time is absolute, uniform, and unchanging, and all synchronous clocks tick at the same rate. However, we know from Einstein’s theory of relativity that time depends on the position of the observer – in other words, clocks tick at different rates depending on who is wearing them. For example, if the observer experiences a large acceleration or is near a black hole with strong gravitational forces, time can change, slow down, stop, and even reverse. But there is also more tangible evidence that time can be made to tick slightly slower
Is it possible to slow down time?
In 1971, two scientists, physicist Joseph Hafeli and astronomer Richard Keating, measured the time difference between a super-precise cesium atomic clock that flew around the world on a jet plane and another clock that remained on the surface of the earth. It turned out that the clock on the flying plane ran slower than the one at rest below. Twenty-five years later, the experiment was repeated with even more precise equipment and Einstein’s theory of relativity was once again proven.
If one of the twins went on a journey in a spaceship and traveled for several years at a speed close to the speed of light, then upon returning to Earth he would be younger than his brother on Earth. Thus, NASA astronaut Scott Kelly actually lived a few milliseconds less than his twin Mark, thanks to the fact that he spent more time in space, traveling at a speed of about 28.1 thousand km/h.
Is time travel possible?
Time travel is not only a figment of the imagination of sci-fi fans, but also a real object of scientific research. However, scientists understand a time machine not exactly as we saw in the films Back to the Future or Star Trek. The closest to scientific ideas were the creators of the film Interstellar, describing movement through black holes. Einstein claimed that supermassive objects such as black holes really do bend time around themselves. Therefore, near a hole, time moves more slowly, or even stops altogether.
There is a hypothesis that it is possible to travel through time through “wormholes” or “wormholes” of space-time. They are similar to tunnels, through which a person can get into another dimension. However, such “wormholes” instantly collapse, and it is assumed that only ultra-small particles can pass through them.
Another time travel hypothesis is the “infinite Tipler cylinder.” Astronomer Frank Tipler proposed a mechanism in which matter equal to ten solar masses, rolled into an infinitely long and very dense cylinder, rotates at a speed of 1 billion revolutions per minute. A spacecraft, having passed through a spiral, would enter the cylinder and end up in a “closed timelike curve” – a world line where everything returns to its original point in space-time.
All these hypotheses are doomed to exist only in theory, since a person can neither approach a black hole, nor reach the speed of light, nor acquire supermass. In addition, time travel can lead to major problems – from the release of radiation, fatal to all living things, to the “paradox of the murdered grandfather.” Its essence is that a time traveler returns to the past, kills his grandfather in his youth and as a result disappears – because he was never born. However, this theory has opponents. They argue that it is possible to travel to the past only along a closed curve, inside which all events are looped with each other and one cannot interfere with the other.
How Living Organisms Perceive Time
The human brain has learned to track time itself, adjusting its biological rhythms to the time of day. The perception of time is affected by the level of dopamine in the body. This hormone-neurotransmitter is responsible for a good mood and is produced when a person anticipates something pleasant. The higher the level of dopamine, the slower time flows for a person. People with some mental disorders have a disturbed sense of time: for the especially impulsive, time goes too quickly, and in schizophrenia, it slows down significantly.
As we age, dopamine production declines and the brain becomes less responsive to stimuli. This may explain why older people complain about time passing too quickly.
Animals also perceive time differently. Scientists from the National University of Ireland in Galway compared how quickly animals of more than 100 species react to changes occurring around them and process the information received. It turned out that blowflies and dragonflies perceived time the fastest. Their vision allows them to process changes at a frequency of 300 Hz, that is, to record 300 times per second. Humans, by comparison, perceive the world at a frequency of only 65 Hz, dogs – 75 Hz, and the “slowest” eyes belong to starfish – only 0.7 Hz.
Does time have a beginning and an end?
The beginning of everything, including time, is considered to be the Big Bang: 13.8 billion years ago, the observable Universe began to expand and continues to grow with constant acceleration – no one knows when it will reach its limit. If the Universe expands forever, then time will continue along with it. But if a new Big Bang or another doomsday scenario occurs, our timeline will end and a new one will begin.
