What is Time in Physics?

Time is one of the most complex concepts to understand, explain and define!

Physicists define time as the progression of the future from the past to the present; In the three-dimensional space we live in, it is considered to be the fourth and abstract dimension of reality used to describe events. Basically, if there is no change in a system, it does not exist in time, it is timeless. Time is not something we can see, touch or taste, but we can measure its flow by developing various systems. Time is one of the most precisely measurable quantities in physics.

Philosophy, religion, and the literary sciences have given different definitions of time throughout history, but the system of measurement is relatively consistent. This measurement is based on the system of seconds, minutes and hours. The basis of these units of measurement, whose origins date back to the Sumerians, has varied throughout history. Today, the international unit of time, the second, is defined by the vibrational frequency of the cesium atom.

Physics is the only science that explicitly studies time. Understanding time is one of the most difficult phenomena in the universe for physicists to understand. Time may be the most modern and complex physical model in the universe. So what exactly is time?

In physics, time is a dimension within the boundaries of this universe and in which all living and non-living matter is contained. Everything that happens in space is in time. Time is subjective, meaning it's not the same for everyone. Physicists define time as the progression of the future from the past to the present. Time is a continuum that has no spatial dimension, it does not depend on anything. In other sciences, it is defined as elapsed time or one hour.

The importance of the concept of time in modern physics begins with Albert Einstein.

Newtonian physics, which was valid until the Einstein period, deals with space-time separately, time; accepting absolute for every point of the universe, he says that time is independent of all reference systems. Einstein predicted that this concept could be wrong even back then. He thinks that there may be a breaking point between the speed of light and time. He tries to support this idea with examples.

Thinking that he is near a clock tower, Einstein assumes that the tower shows 12. The clock showing exactly 12 means that the rays of light are reflected first on the clock tower and then on Einstein's eyes. But he realizes that the light rays carry the same information throughout the entire time interval (the information that it is 12 o'clock) while they are in the clock tower and coming to Einstein's eyes. From this point, he concludes that time has stopped for light rays. In this thought of Einstein, who thought "How would I see the world if I had traveled on that light beam", the infrastructure of the theory of relativity, which he would find years later, began to form.

The time that human beings can observe consists of the speed of light, in other words, the speed of light is the point at which time stops. As we move, we slow down time. Albert Einstein said that the space-time-motion relationship is interdependent. This theory was studied in an experiment in 1971. According to this experiment, two atomic clocks were adjusted according to each other and one clock was kept fixed on the earth, and the other clock was put on an airplane and traveled around the world. The result of the experiment proved that Einstein was right. Because the clock that made the world tour showed a shorter time than the stopped clock.

In his theory of relativity, Einstein says that no accelerating object in the universe can reach the speed of light. Suppose you have a rocket of sufficient power. In line with the principle of relativity, when we insist on increasing the speed despite reaching speeds very close to the speed of light, the energy given turns into mass. In other words, nothing with mass can reach the speed of light. When we look at the particles that make up the light, namely photons, it is observed that they are massless. Also, the fact that photons travel at the speed of light means they don't have time, so they move in zero time.

With the theory of relativity, it turns out that time is a relative concept. Thus, the door of a brand new science was opened and modern physics was born.

The sunrise and sunset, that is, the day-night cycle, is a natural event that human beings have been familiar with and followed since time immemorial. He was placing many of the facts he used in his practical life and the works he carried out in this direction. It is like getting up in the morning with the light of the sun, hunting, grazing the sheep, going to sleep when it is dark.

It can be said that the day-night cycle is the basis of the concept of "time". Later on, mankind felt the need to explain the time in which he lived, what he had done before or what he would do later, within the concept of time. He realized that for this it was necessary to define a quantity that is constant for everyone as a measure of time.

When talking about an abstract concept such as time, it is necessary to specify a reference point in order to make it understandable and to avoid confusion. Until 1960, the average solar day was considered as the time standard. A second was calculated to be [(1⁄60)*(1/60)*(1/24)] one 86,400th of a solar day. But this definition gradually lost its sensitivity in the face of developing technology. Physicists created a new constant for the concept of time in 1967: the atomic clock. The time during which the cesium atom vibrated 9,192,631,770 times was called 1 second. This was because the cesium atom vibration was the most stable vibration. While the vibrations of other atoms deviate in shorter periods, cesium deviates for 1 second in 100 million years. is delayed. The precision of this definition, which seems to be very precise, has started to be difficult to meet the needs of developing nano technology in the present times.