Ever since the beginning of human kind, humans were fascinated by the concept of time.
It’s probably mostly due to the fact, that time was always a very important thing. Even prehistoric people had their system of measuring time, which was basically watching the stars, the sun and the moon. Later civilizations discovered various clocks, starting with simple sand or sun clocks, ending with complex water clocks. In Middle Ages mechanical clocks were discovered.
As we can see, civilizations throughout the history believed in two different time models. The first one and possibly the earliest was cyclic time model. Most of the ancient civilizations measured time by observing the sun, the moon and the change of the seasons, which naturally led them to think that time runs in cycles. For example in ancient
years were named and once the 60 names are finished, the next year starts with the first name again. Ancient Aztecs also had special calendars divided in cycles. After every cycle, they believed, a new similar cycle starts once again. It’s interesting to notice that the famous Mayan calendar also measured time in cycles. So it’s not true that it ends in 2012, actually only one of the cycles will end at 2012 and then a new cycle will begin. India
Another way of thinking about the run of time was linear time model. It’s the most familiar model to us. Perhaps, the best comparison about time was given by Einstein, who said that time is like a river. This river, by the way, can fork, have whirlpools and run in very interesting ways.
The biggest question, when talking about time, is, of course, what exactly time is. What is that magical river, which brings us to the future? It seems that this question is harder to answer than you might think. Let’s see how people throughout various periods of history answered this question.
Many ancient civilizations believed that time, like all the nature, is controlled by the gods. The Vedas, the earliest texts on Indian philosophy and Hindu philosophy dating back to the late 2nd millennium BC, describe ancient Hindu cosmology, in which the universe goes through repeated cycles of creation, destruction and rebirth, with each cycle lasting 4,320,000 years. Ancient Greeks believed that that time, as well as their destiny was controlled by divine deities for the Mount of Olympus. However, ancient Greek philosophers had more sophisticated ideas. Some of them believed that time is infinite – the universe, as well as time had no begging, nor will it have an end. However, there were philosophers, like Zeno, who didn’t believe in any kind of change. Zeno, in his famous paradox (Zeno’s paradox) argued that any kind of change or movement is impossible. This lead to the conclusion, that time is only an illusion.
Philosopher and theologians argued that both universe and time had a beginning, and will have an end. They believed, that time started at the beginning of the universe.
Immanuel Kant, a famous Prussian philosopher, had his own ideas. He believed that time was only an idea like numbers, or dimensions. Kant thought of time as a fundamental part of an abstract conceptual framework, together with space and number, within which we sequence events, quantify their duration, and compare the motions of objects.
Isaac Newton shared similar ideas. He believed that time is like an arrow, which always goes only one way. He believed that time was universal – it was running at the same rate for all observers.
All of these ideas caused two distinct viewpoints of time among philosophers and scientists. One view is that time is a fundamental part of the structure of the universe. It’s like another dimension, in which events occur like in normal special dimensions. Other point of view is that time is not a part of the structure of the universe. Time, according to this point of view, is not an event, nor a dimension or a thing.
The big breakthrough in understanding the nature of time came in the beginning of the XX century. Einstein, with his famous theories (Special and General Theories of relativity) showed that time is not universal. The rate of the clock depends how fast you are moving. Simply speaking, time flow depends on various conditions, which include the velocity of the body. Later in his General Relativity Theory Einstein showed that time also slows down in a gravitational field. These two very important conclusions lead scientists to believing that time actually is a part of the fundamental structure of the universe. Also when Einstein showed that time travel (at least to the future is possible) it became clear that the old view of time as nor a dimension or a thing was wrong.
Now, a century later, we know many wonderful things about time. We know that time is highly connected with the form of Space Time continuum. For instance, if you would spend some time orbiting a huge star, the gravitational field of which is very strong, you would age slower than let us say your twin brother who is spending his days on Earth. We also know that the speed of time flow is connected to the velocity of the body. Another great discovery is the so called arrow of time. It’s clear that time goes from the pas to the future. This makes time a unique dimension. We can freely movie in any of the three special dimensions, but when it comes to time we are prisoners. Scientists believe that the entropy of the universe is the so called arrow of time. In this case entropy can be viewed as a measure of disorder. According to thermodynamics, the entropy of a closed system tends to increase. And since universe is a closed system, entropy in the universe increases steadily. Thus, for instance, a broken cup of coffee, newer comes back to the table and fixes itself as it was traveling back in time.
Only one thing is really certain – time is connected to the geometrical properties of the space-time continuum. The newest discoveries of astrophysics gave us many mysteries. Mysterious Dark Matter and Dark Energy are great examples, that we still don’t know many secrets of the Universe and time itself. For instance some scientists believe that time is highly connected to the accelerating expansion of the Universe, which is supposed to be caused by the Dark Energy. This Dark Energy, according to scientists, is constantly changing the form of the Space-time continuum. This means that in order to understand more about the Space-time continuum, the Universe and the time itself we need to understand what Dark Energy is. Even at this moment, due to the Dark Energy, the time itself can be speeding up. All in all, the mysteries of the Dark Energy and Dark Matter hold many secrets of time.
Our generation is a really lucky generation, because we know more about Universe and time than any other generation throughout the history. So let’s hope we will find out the secrets of the universe sooner or later. After all, who wouldn’t like to find out what exactly is the magical river of time.