The fact that time is a perception was proved by the greatest physicist of the 20th century, Albert Einstein, in his "General Theory of Relativity". In his book, The Universe and Dr. Einstein, Lincoln Barnett says this:
Along with absolute space, Einstein discarded the concept of absolute time - of a steady, unvarying inexorable universal time flow, streaming from the infinite past to the infinite future. Much of the obscurity that has surrounded the Theory of Relativity stems from man's reluctance to recognize that sense of time, like sense of colour, is a form of perception. Just as space is simply a possible order of material objects, so time is simply a possible order of events. The subjectivity of time is best explained in Einstein's own words. "The experiences of an individual" he says, "appear to us arranged in a series of events; in this series the single events which we remember appear to be ordered according to the criterion of 'earlier' and 'later'. There exists, therefore, for the individual, an I-time, or subjective time. This in itself is not measurable. I can, indeed, associate numbers with the events, in such a way that a greater number is associated with the later event than with an earlier one.
From these words of Einstein, we can understand that the idea that time moves forward is totally a conditioned response.
Einstein himself pointed out, as quoted in Barnett's book: "Space and time are forms of intuition, which can no more be divorced from consciousness than can our concepts of colour, shape, or size."
According to the "General Theory of Relativity", time is not absolute; apart from the series of events according to which we measure it, it has no independent existence.
Our dreams are very important in understanding the relativity of time. In our sleep we experience events that we believe go on for days but actually, we are having a dream which lasts for only a few minutes or even a few seconds.
In order to make this clearer, let us think of an example. Let us think of a specially designed room with one window and that we spend a certain amount of time in it. In the room there is a clock by which we will be able to see the passage of time. Through the window we can see the sun coming up and going down at regular intervals. After a few days we are asked how long we have stayed in the room. Our answer will be calculated by information we have received based on looking at the clock from time to time and on how many times the sun rose and set. For example, we calculate that we have spent three days in the room. But if the person who put us in the room comes and says that we were actually in the room for two days, that the sun we saw in the window was actually artificially produced, and that the clock in the room was fast, then our calculations would make no sense.
This example shows that our knowledge about the rate at which time passes depends on references which change according to the person who is perceiving it.
One twin sister takes a space trip at a speed close to the speed of light. When she returns thirty years later, the sister who stayed on the earth will be much older compared to the sister who went into space.
This is an example of how under different circumstances a person perceives the same amount of time as longer or shorter. Here is another example. For a person who is waiting for his brother to come out of an operation, one hour seems like several. But if the same person is doing something he really enjoys, he cannot understand how the hour passed so quickly.
Einstein scientifically established the following fact in his "General Theory of Relativity": The rate at which time passes changes according to the speed of a body and its distance from the center of gravity. If the speed increases, time decreases, contracts, moves slower and seems that the point of inertia approaches.
Let us explain this with one of Einstein's thought experiments. Suppose that there are two twin brothers. One of them stays in this world, the other goes on a space journey during which he travels almost at the speed of light. When he returns from space, he will find that his twin brother is much older than he is. The reason for this is that the time passed much more slowly for the brother who went on the space trip. The same example can be thought of in relation to a father who went on a space trip in a rocket traveling at nearly 99 percent of the speed of time and his son who remained on this earth. According to Einstein, if the father was 27 years old and his son was three, 30 earth-years later when the father returned to earth, the son would be 33 and the father would be 30 years old.
The relativity of time is not something that is relative to the speeding up or slowing down of the clock; it comes from the fact that every material system, to the particles at the subatomic level, works at different rates of speed. In an environment where time was slowed down, a person's heartbeat, rate of cell division and brain activity would happen more slowly. In this situation, a person would go about his daily business unaware that time had slowed down.
