What is time, how do you define the passing of time?

Time flies, it is often said. To keep track of it, let’s refer to clocks and calendars. It is usually represented by changes, such as the movement of a planet around its host star. But describing the true nature of time is difficult.

Even scientists don’t know what really happens over time. In fact, there are several possible definitions of this concept. Science, philosophy, religion and art have their own descriptions of time. According to the theory of relativity, the universe was formed during the Big Bang about 13.7 billion years ago. Previously, all of the material was compressed to an extremely small point.

“In the theory of relativity, the concept of time begins with the Big Bang, just as the latitudes begin at the North Pole. It doesn’t get any further north than the North Pole, ”Kari Enqvist, professor of cosmology at the Institute of Physical Sciences at the University of Helsinki, told Science Daily.

The irreversibility of time

So before this great boom that allowed the birth of stars and planets, there was neither space nor time. According to Einstein, gravity affects them. The stronger the gravity, the more it bends in space-time and the slower time is. In nature, time has a direction. It flows from the past to the future and never the other way around. This is known as the “arrow of time”.

The question of the irreversibility of time is a puzzle that physicists have not yet solved. The reason for this is that nature follows the principles of thermodynamics. According to the second law of thermodynamics, entropy in a closed system remains constant or increases. Since the universe is viewed as a closed system, it cannot return to the exact same state it was in before.

Absolute or Relative?

In classical mechanics, the time is the same everywhere. When two clocks are calibrated to show the same time, the time will stay the same regardless of how far apart they are. However, general relativity says that time is relative. Speed ​​can expand it. For this reason, too, it passes faster at high altitudes. Mobile clocks run slower than stationary clocks.

The relativity of time! Photo credit: Shutterstock / tadamichi

The time dilation increases as the clock approaches the speed of light. The idea of ​​time travel has fascinated physicists for ages. Specifically, this means the ability to move forwards or backwards at different times. However, this concept poses a problem. As the website Thoughtco.com points out, traveling back in time can lead to a temporal paradox.

A subjective idea

Time is also a subjective term. Our brains perceive it differently depending on the situations we are going through or our concentration. For example, when our neurons are aroused by external factors, including chemicals, we may feel like time is passing faster. In times of danger or emergency, time seems to slow down. According to experts, these impressions are due to the fact that the amygdala becomes more or less active.

What about the end of time?

As mentioned above, time began with the birth of the universe, during the Big Bang more than 13 billion years ago. On the other hand, nobody knows if it will one day end. If a new big bang happened our timeline would end and a new one would begin. According to Einstein, the development of space can lead to the collapse of the universe.

“However, the latest observations do not support the idea of ​​a collapse, but intergalactic distances are increasing rapidly,” said Professor Engvist, according to the website Antonfoek.com. In short, only time will tell if the universe, and with it time, will come to an end.

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