VI. How do we understand the time?
We adopt the concept of time intuitively and consciously. A problem arises when we want to formulate a precise definition of it. We are in a similar situation to St. Augustine, when asked about what time is, he answered:, “If no one asks of me, I know what it is. If I wish to explain it to anybody who asks, I do not know”. The concept of time is so unclear and it is difficult to define. For example, Julian Barbour, a British physicist believes that it should be utterly eliminated from the science. Science is not science when it is based on an unclear concept of time, time which has not been seen by anybody and nobody knows precisely what time is. Barbour makes attempts to restructure the entire physics in a such manner to exclude the existence of time.
The truth is that time cannot be observed directly. However, we can observe changes in the surrounding environment and use some processes as a time meter. In practice, we can use various periodic processes, such as, rotation of the Earth or movement of a pendulum. Theoretical analysis can be based on the employment of a light clock, which consists of two mirrors and a phantom reflected between them. The problem is that the cyclic process does not measure time, that is, the flow of time. It does not ensure at all that time flows forward. On the contrary, the cyclic processes may suggest that time can flow in cycles and can return to the previous state.
There are also linear processes which can be used to measure time. For example, a lit candle or isotope decay. These ones better refer to our subjective perception of time as something that flows in one direction from the past through the present time to the future. Is such understanding of time only our illusion, or the direction of time is something objective? We see how we get old and we imagine that it cannot be different. But in the micro world this is all the other way round! Some particles do not get old in the elementary way. Everything around us is in motion, only the motion itself does not give the possibility of estimating the direction of time. What we observe is not only the movement of objects which can be forwards and backwards, but also changes related to the increase in entropy, which are irreversible. Is there in the micro world anything that helps to determine the direction of time? It appears that yes. There are elementary particles (so-called kaons), for which the decay and creation is not symmetrical in time, which suggests that the time arrow occurs already at the level of elementary particles.
When a time flow is something objective, how then it is included in our models of reality?
In classical mechanics time does not flow. It is simply a numerical parameter which is included in an equation. There is no reason which would indicate that time flows. In equations the direction of time is not even distinguished.
When the direction of time and the division into past, present and future times is a relative property of our Universe then we need a model which includes the same somehow. One of the possibilities is to use an idea of Stephen Wolfram, a British physicist, who postulates modeling of the Universe as a cellular automation.