Time, it seems so simple, but it is so complicated.
If you ask the people around you: What exactly is time? It is likely that you will get a variety of answers, but no one will be able to give time an accurate and convincing answer.
Because until now, scientists have not defined "what exactly is time".
The nature of time is like the ultimate question, and people may never find the answer. There are many similar ultimate questions in the universe, like "does the universe have no boundaries?" If any question is asked continuously, the "ultimate problem" will eventually arise.
But that doesn't stop people from thinking about exploring the answers to the ultimate question.
The general perception of time is that it is related to movement or vibration. For example, we usually say that a day is closely related to the earth's rise and fall, and the year we say is related to the earth's orbit around the sun.
In ancient times, when there was no watch, people could also use the movement of the sun or the moon to measure time, relying on the periodic movement of the sun and moon.
In fact, modern human timing methods are also inseparable from periodic movement, watches use this way, periodic vibrations, including the most accurate cesium atomic clock of human beings is also the use of periodic movement. If human beings travel in space in the future, it is most likely inseparable from periodic movements to time and use the periodic movements of pulsars.
Having said all that, is the essence of time movement? Does time really exist?
If the essence of time is motion, then when all matter in the universe is stationary, does that mean that time does not exist? If this is the case, it can only show that motion is the essence, and time is only the appearance, the appearance of movement.
According to the interpretation of the universe's "heat silence theory", our universe will really come to an end on a distant day, there will be no movement, no information transmission, the universe is in a completely static state, and the universe is dead! Then time doesn't exist.
The above view is only a guess by scientists, and it is difficult to confirm it at present.
Then again, if time is the embodiment of motion, there should be no fixed direction, but in reality we find that the arrow of time has only one direction, that is, it is constantly moving forward.
In this way, the movement should also have a direction. Scientists have found through research that indeed, movement will only develop in the direction of "entropy increase", that is, the so-called "entropy increase principle", everything in the universe will move inexorably in a disordered direction, and finally the entropy value will reach the highest, and the universe will become completely disordered.
As for the nature of time, Einstein put forward a view that completely subverts our traditional cognition, arguing that the so-called time does not exist in isolation, time and space are one and inseparable, and the two must exist at the same time, otherwise there is no meaning. Together, time and space make up the four-dimensional space-time in which we live.
Einstein's view of space-time gives us the implication that it is meaningless for us to discuss time alone at any time and anywhere, and that time and space must be discussed together to make sense.
Since time and space are relative, this means that everyone's feelings about time and space are actually different. When we say, "It's 7 o'clock in the morning," it doesn't make sense technically. Because what you call "7 o'clock in the morning" defaults to this: time in your own perception in your space.
It's just that we don't say what we default to, otherwise it will seem redundant. Just like when we say "the speed of the car is 100 kilometers per hour", we certainly do not say "the speed of the car is 100 kilometers per hour using the ground as a reference".
At the same time, since we live in a low-speed, low-gravitational world, which means that everyone feels almost no difference in time and space, we will default to time and space as absolute.