We often use "inseparable" to describe the close relationship between people and shadows. In fact, there is another thing that is closer to us than shadows, and it is time.
Time is everywhere around us, filling every corner of our lives, and we can feel the existence and passage of time at every moment.
So what is the time? Does it really exist?
In the thousands of years before Einstein proposed the theory of relativity, people realized that time was inherent and absolutely unchanged. Like space, they exist objectively and have nothing to do with changes in the surrounding environment.
But people do not think that time is a physical matter, but it has practical significance, and is even an existence independent of the universe.
However, this view has actually fallen into some kind of idealistic idea: since you think that time is nothing, you also think that time does exist!
Many people think that time is just a feeling of people, or that it is an illusion of people that they do not exist.
By the end of the 19th century and the beginning of the 20th century, Einstein's emergence completely broke people's traditional view of time and space, proposed a completely subversive concept of time and space, and for the first time linked time and space with material movement .
Einstein regards time as a special dimension, and together with three-dimensional space, form , four-dimensional space-time . More importantly, Einstein believed that time and space are organic wholes, and the two are inseparable, and any act of dividing time and space has no meaning.
It's like when we date, we have to clarify the time and space location at the same time. If there is only space (location) and no time, your date will make no sense. For example, if you meet at a certain place tomorrow afternoon, such a date is meaningless because you didn’t say when to meet!
The world is moving, moving never stops, and this ever-changing movement changes manifests time, and space is the same.
Since the essence of time is movement and change, the movement of objects will of course affect time, which is also the basis for the establishment of the "clock slow effect".
The "clock slow effect" in , that is, the "time expansion effect", fully illustrates the existence of time.
clock slow effect, to put it bluntly, it is the observer effect . The time elapsed speed felt under different reference systems is different. The time each observer feels under his own reference system will not be different. This is also called "inherent time". In layman's terms, it is the time that everyone feels subjectively.
But sometimes the feelings are not the same for observers under different reference systems. For example, if you are still on the ground and I am flying at a high speed in a spacecraft. In your opinion, my inherent time is different from what you see me. You will find that my inherent time has slowed down, but I myself do not feel slowed down.
In fact, this is the core of the "twin paradox". The brother left the earth on a sub-light speed spacecraft, and the younger brother stayed on the earth. When the brother left and returned to the earth, he accelerated and slowed down, and actually changed the time and space. When the brother returned to the earth, he became younger than the younger brother. Compared to the younger brother, the brother's time slowed down.
Use general relativity to explain the twin paradox is simpler, and special relativity can also be explained, but it is somewhat complicated. And using " world line " to explain is easy to understand.
world line, to put it bluntly, it is " Minkovsky four-dimensional space-time interval". Note that this is not the time or space interval, but the time-space interval.
The world line in any reference frame is the same at the same time, so if you discuss the twin paradox under any reference frame, the result will be the same. The picture below shows the world line between the elder brother and the younger brother.
It can be seen that the brother's world line is longer and the younger brother's world line is shorter. Does it mean that the brother has a longer time and the younger brother has a shorter time?
is not! In fact, it's the opposite.You may question: It’s obvious that the brother in the picture has been longer. It's true, but that's in European geometry. And in Minkovsky's time and space, the length of the brother's world line is shorter than the length of the younger brother's world line! So my brother’s time is slower than my brother!
summary is that time is also an objective reality, which does exist. Like the measurements of the color, shape, weight, etc., it exists objectively. Although it is not a physical object, it can be felt by us that it is a form of existence of physical matter!
