Time is like air. We live in it and do not even think about what it is and how to use it. However, it is a very complex thing that underlies everything. No wonder there is a phrase "space and time". With space everything is clear - here it is. 10 kilometers to work by car, and 300 meters to the store on foot. But the time along this path will be very relative. But what is this in general, and is it fair to say that time is infinite and it has always been? Can you touch the time? Maybe it can be stopped or reversed? People often ask all these questions to each other and to themselves. Let's try to answer at least some of them.
What is time?
Usually, by time we mean what is counted by the hands of the clock and what we always lack. At the same time, it is believed that time is divided into past, present and future. With the first and the last it is clear, but does the present exist?
Any microscopic fraction of time that we try to describe as the present will already be the past. It turns out that the present, as such, does not exist. It is only what we used to call that, that is, a very broad concept in the spirit of "our days". It can include periods from several months to several years and even thousands of years, if we are talking, for example, about the existence of the universe or the formation of our planet.
One of the definitions of time says that this is what makes all events happen at the same time.
At the same time, many scientists still perceive time as a progression in which the future becomes the present, and the present becomes the past, and this process is continuous. Even if our Sun explodes, time will not stop anyway and will continue to exist. It's just not for us anymore.
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What gives understanding of time
And also time is fundamental for understanding what dynamics is. Only having an idea of time can we talk about events that develop at a certain speed. After all, it is considered completely normal to ask when something happened and how long this or that phenomenon lasted. It turns out that time is like space - these are coordinates, but not points on the map of when it was. There is only one difference. You can walk anywhere on the map, but only in one direction in time. It is this property of time that is the main mystery over which scientists fight and build their hypotheses of science fiction writers.
People perceive time more or less the same, since the clock we are used to is ticking at the same speed. However, this is only true for classical physics. Quantum physics asserts the opposite and says that the system becomes active only at the moment when it is observed. That is, in a way, it is quantum physics that does not exclude the possibility of the movement of time backward.
Albert Einstein's theory of relativity
At one time, Albert Einstein revealed to the world the theory of relativity, which you have probably heard about. It completely changes the typical idea of time and the way it looks. According to this theory, the progression of time is not universal. Quite simply, according to this theory, the watch runs at different speeds depending on whose wrist it is worn.
If the owner of the watch finds himself in an unusual situation for him, for example, moves at the speed of light or finds himself near a strong source of gravitational waves - for example, next to a black hole - time will go differently for him. In some situations, it may even stop or even reverse itself.
Simply put, in such a situation, the perception of habitual physical processes changes and a person who finds himself in such a place can not only observe time, but also move along it as in ordinary space - left, right, forward, backward, and so on. That is, relativity equalizes time and space, endowing them with the same properties.
Is time travel possible
There is also the concept of T-symmetry, when the phenomena and the quantities by which they are represented do not depend on the coordinate scale, and when a positive value changes to a negative one, the curve on the graph becomes mirror-like. In the theory of relativity, despite such a difference from the usual world, this rule also holds.
Interestingly, thermodynamics intervenes in the debate about the possibility of time travel in the opposite direction, which says that all processes in the world tend from an ordered system to chaos, that is, an increase in entropy. This process cannot be reversed. That is, exploded stars cannot be "glued" back together, and a rotted sheet of iron cannot be turned into a new one. Simply put, "minced meat cannot be turned back and you cannot recover meat from it."
As a result, roughly we can say that time for us is the time that is on Earth. If we start traveling in space beyond the nearest planets, we will have to understand what time is and how it changes. Although, formally, there are deviations on the Earth for insignificant fractions of a second. This is even taken into account when creating some ultra-precise systems and atomic clocks.
Do we understand the time
In general, humanity still poorly understands what time really is, and everything that has been said is only theories and hypotheses. We have not yet been able to reach the sources of gravitational waves, although we were able to record them.
So far, we only know about time that it is a geometric parameter that characterizes the duration of processes. It is part of the space-time continuum and the fourth axis of the familiar three-dimensional world. Oh yeah … Another thing is that it's a damn interesting and incomprehensible thing. As we say, nothing is clear, but very interesting.
