What exactly is time?

 What exactly is time?

  If there is one thing in the universe that is constantly increasing, it is time. That is why it is said that time does not stop for anyone. And no one can stop time. A person can stop himself, he can stop his watch. But you can never stop time even if you want to. That is why it is said that time is precious.

If you study time carefully, you will see a mystery in it. It looks different from all the objects in the universe. It has no physical form like matter, energy and space. But time is more real than anything else. Even if you are the only one in the universe, you will be with time. But time has become so normal that we never think about it.

Today, in this article, we are going to discuss time from the point of view of science. When someone asks you what time it is, you immediately look at the clock and say that it has been so many minutes. Someone asked how long the movie was and he said it was so long. The ticking sound of the clock makes us feel the time. That's why we consider those hours as time. But these watches did not exist before. It was definitely time. The rising/setting sun, the changing shape of the moon, the changing seasons.

Our ancient ancestors used these things to measure time. Nowadays, due to technology, the way of measuring time has changed. Now, electric clocks to automatic clocks are being used to measure time. But all of these are time scales. Not time. If we look a little deeper into the universe, we see something moving. We see the change. Change never stops. Change is irreversible. That is, the events that have happened cannot be changed.

If I hadn't made that decision, we would have been able to correct the decision by going back to the past. But everyone knows, we cannot do that. That is not possible. From this point of view, time is a continuous stream. This makes clear to us the characteristic that time always moves forward. Which we all believe to be true. It is called "arrow of time" in the language of physics. Because time increases from the past to the future. Therefore something becomes new first and then old.

It never happens that first the old and now the new. An egg that is cracked before is never whole again. Milk, sugar and tea leaves never return to their former state after coming out of tea. Because the fundamental property of the universe cannot be like that. "Disorder" is always increasing in the universe.

Because the characteristic of the universe is to go from 'order' to 'disorder'. If we draw an arrow between 'order' and 'disorder', it always returns from 'order' to 'disorder'. That is, first there is 'order' and then only 'disorder'. In the language of science, it is known as entropy. This characteristic of the universe defines time and the direction of time.

That is why some people think of time as a feeling that entropy gives us. But is it just an experience or perception? Does it exist? Is time real or an illusion? It raises questions like

Humans tend to consider only what their senses can assess as real. But in science there is a different way of considering something as real. Only scientific theories that correctly explain a natural phenomenon are considered real in science. Like: Subatomic particles like quarks that cannot be seen with the naked eye, we consider real.

Because quarks have been confirmed by physics. That's why it is real even if you don't see it with open eyes. Albert Einstein explained time in his theory of relativity (General relativity). Time is an important element for that theory. But his theory does not explain any phenomenon in the universe correctly. Like; What happens at the singularity of a black hole (singularity - a point in space that contains mass with infinite density)? His theory does not say that.

Also, his theory is not compatible with quantum theory. In quantum theory, the direction of the arrow of time is not fixed. According to this theory, it can be assumed that the arrow of time can go forward or backward. But it doesn't make a big difference. Perhaps this is the biggest obstacle in the disagreement between relativity and quantum theory. Because according to the theory of relativity, time is a dimension. But quantum theory does not say anything about the arrow of time.

The block universe, based on the four-dimensional universe, explains that space is three-dimensional and time is one-dimensional. A block universe is a theory of time that states that all moments in time occur simultaneously. That is, it explains that the past, present and future all exist in the same way. Time is a subjective concept. The experience varies from person to person. So is time an illusion? The answer is definitely no.

Some scientists also believe that time can be an emergent property. Let's understand it with an example: From the atomic theory, we can know about the characteristics of water molecules in the sea. What element is that water molecule made up of? What kind of chemical bond is there between them? Their chemical characteristics What are they?

All these things are explained by the atomic theory. But the atomic theory does not tell about the waves coming in the sea. Waves in the ocean are the 'emergent property' of water molecules. That wave comes after trillions of molecules come together. In the same way, time is also an emergent property of this universe. Which is produced due to the activities in the universe. Just as the waves of the sea are real, time is also real. So real that without the idea of time the scientific theory that explains nature, the mathematical equations based on it, do not work.

In Einstein's famous theory 'Theory of General and Spatial Relativity', time is shown as four dimensions in three dimensional space. This theory answers some of the questions raised by recent research. Like: How is the speed of light the same in all conditions? How is the speed of light coming from the same source the same for a dynamic or stationary observer?

Now let's look at this matter with an example. Imagine, a car is moving at a speed of 100 km per hour on the highway. A police car is on the side of the road. They also have speedguns there. From that they measure the speed of the car. Speedgun shows the speed of the car at 100 km per hour. Now imagine that the police car is moving in the direction of the car at a speed of 40 km per hour.

At that time, looking at the speed of the car with a speed gun shows a different result. Because the police car is moving in the direction of that car at a certain speed. In this case, the speed of the police car decreases with the speed of that car. That is, now the speedgun shows the speed of the car at 60 km per hour. Which is the 'relative speed' of both vehicles. But if the police car is coming from the opposite direction, the speed of both will be added.

At that time, the speedometer shows the speed of the car at 140 kilometers per hour. Now let's put the light in place of the car. What happens when we measure the speed of light in both the above cases? In general, the result should be similar to the above event. That is, the speed should be lower when going in the direction of the light and the speed should be higher when going in the opposite direction of the light. But otherwise the speed of light is the same in both cases. This is not a theoretical matter. This has been proven by testing. But how is this possible? The answer was given by Albert Einstein. According to him, to keep the speed of light the same, time slows down and space is also narrow.

Let's understand this also in a simple way. According to Einstein, time is not the same everywhere. Time moves slower for a moving observer than for a stationary observer. So there is no difference in the speed of light. Let's understand it like this. To measure the speed of any object, distance must be divided by time. In the scientific world, it is said that light travels a distance of 300,000 kilometers in one second. Now imagine two observers, one in motion and one not, trying to measure the speed of light.

In this case, the time of the observer who is not in motion is slower than that of the observer who is in motion. That is, 1 second of the first observer is slightly more than 1 second of the second observer. Due to the long duration of seconds, light easily travels a distance of 300,000 km without any obstacles. The greater the speed of any object, the slower its time will be in proportion. Therefore, the speed of light is the same in every situation. This means that according to the location of the universe, time also varies. Einstein said that not only the movement of objects but also the force of gravity affects it.

This means that the time of a large object like a star or a black hole is slower than that of a small object like the Earth. For the same reason, large objects shrink space time. That's why time moves slowly there. Einstein named this phenomenon 'time dilation'. This idea given by him was so strange and amazing that many people found it difficult to believe.

We used to think that time is the same for everyone till then. But that's not the case anymore. According to this theory, a person on earth ages faster than a person traveling at high speed in space. Because his time runs relatively fast. In theory it is also said that if someone travels at the speed of light, time stops for him. That is, for a person sitting in a spaceship with the speed of light, not even a second has passed after thousands of years have passed on earth.

However, this is practically impossible. Because the laws of the universe prevent us from doing so. If we try to move a spacecraft to the speed of light, its mass will increase rapidly. Which is infinite at the speed of light. And infinite mass requires infinite power to fly. Therefore, it is impossible for a massive object to attain the speed of light.

Only weightless objects like photons and gravitons can travel at the speed of light. This is a matter of principle. But in 1971, a time dilation test called the Hafele-Keating Experiment was conducted in America. Three synchronized atomic clocks were used in that test. One of them was flown to the east and the other to the west by placing it in an airplane to make two circles around the earth. One was placed on the ground.

Later on comparing them, there was a difference in the time of all the three clocks. Which was consistent with Einstein's theory. Then the proof that 'time dilation' really happened.