The Winged
Chariot of Time
The Winged
Chariot of Time |
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The Direction of Time
Quite a strange title, it seems. The direction of time?? But time only goes in one direction! If it didn’t I’d have ample time to finish preparing for my SATs! These are thoughts that often cross one’s mind when one reads about it. But the fact remains that time has a definite direction, which depends on the state of the universe, and changes according to the state of the universe. Now we know of only one state. We think that the universe could never be any different. But we do not realize how minute and insignificant we are in the bigger picture. Indeed, the time that we have so far taken up on the universe is just a fraction of a second when compared to the time the universe has been in existence, and the time it will continue to be in existence long after the extinction of the human race.
The direction of time as we perceive it depends on what is known as the second law of thermodynamics, which states that the total disorder, or ‘entropy,’ always increases with time. A glass on the table always shatters when it hits the floor, but it does not reform and jump back onto the table. Therefore, the state of disorder increases as the glass breaks. Also, before it falls, we only remember the glass being on the table, but not when it is broken, for that is something which, as far as we are concerned, has not yet occurred. The fact is that there are three different directional ‘arrows’ of time. There is the thermodynamic arrow, the direction of time in which disorder increases, the psychological arrow of time, the direction in which we feel time passing, and the cosmological arrow of time, the direction of time in which the universe is expanding. We will first consider the thermodynamic arrow. In any system, there are always more disordered states than ordered states, e.g. the glass on the floor is whole in only one configuration of the pieces that make it up, but it can be broken in many ways. So if it starts out in an ordered state (whole), then it is almost definite that in time it will end up broken, and then the pieces broken further. In other words, it is extremely unlikely that if one were to pick up the pieces and place them in a box and shake the box, that the glass would end up as it started out. Now we know that the universe started out in a disordered state, so we know also that the probability is that disorder will increase as the universe continues to exist, i.e. disorder will increase with time. But if disorder were to decrease with time, then the people would have a backward psychological arrow of time. The cup on the table would reform and jump back onto the table. But they would remember things in their future, i.e. they would remember the cup being on the table, but not on the floor, even though that was in their past. But we see that the psychological arrow must always follow the thermodynamic arrow. We will examine a simplified example of the human brain. Say that one was studying for one’s finals. By the end, when there was about an hour left for it to start, one had learned all the formulae required. So one’s mind was in a state of order, greater order than when one started out, like storing files onto a computer. But in achieving this state of order, one needs to expend energy, and this energy used up by the brain to perform the task of ‘remembering’ is dissipated as heat. The energy is obtained from food. So in other words, the ordered energy contained within food is converted to disordered energy in the form of heat lost to the surrounding air. As a result, the total disorder in the universe increases, because it can be mathematically proven that the disorder is always greater than the order created. So we see that psychologically we measure time in the direction in which disorder increases, and consequently the psychological and thermodynamic arrows of time always point in the same direction. Now we come to the cosmological arrow of time. We know now, after a number of conflicting theories, that the universe began in a disordered state, and that it will take so long before it re-collapses that all the stars will have burned out and the protons and neutrons decayed into light particles and radiation. This implies that at the Big Crunch there will be a state of complete disorder, in which disorder can longer increase. At some undefined date in the future, nothing will be hotter or cooler than anything else. The slowest radioactive elements will have decayed into stability. The stars will have radiated away their furious energy, warming the frigid dust of interstellar space to a fraction of a fraction of a degree. Earth and its sister planets, their rotation slowed by friction with cosmic dust and gases, will have fallen out of orbit into the sun. Man himself will be long extinct. In this burned-out universe, there will be no change by which time can be observed or measured. In some abstract, metaphysical sense, time may still exist, but scientifically speaking, it will have ended. As a result, there will be no distinct thermodynamic arrow of time in the contracting phase of the universe. But without the cosmological arrow intelligent beings cannot exist, since to live we must convert food into heat, as explained earlier. So it is that the cosmological and thermodynamic arrows as we observe them always point in the same ‘forward’ direction, simply because if they didn’t then conditions would not be suitable for us to exist to observe them in the first place. In a nutshell, the end of the universe will be a situation of maximum chaos, and we cant live without increasing chaos in the process.
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Since the theory of relativity was first introduced and came to be widely
accepted, man has discovered many remarkable things about the universe. The
significant discovery was that the universe is expanding. It is finite in space,
and is expanding at a rate which is decreasing. Now the reader must be careful
not to become confused between contraction and reduced expansion. To clarify it,
let us say that at the start of the universe, it was expanding, at an
exponential rate. Since then, the rate at which it is expanding
has decreased. It is still expanding, but not as fast as it once was. It follows
then that there must come a time when it is not expanding, and then begin to
contract. We needn’t worry, because this will be long after we cease to exist,
but from a theoretical aspect, the widely accepted view is that the universe had
a beginning (the Big Bang, see picture on left) and will have an end (the Big
Crunch, see picture on right). So time, too,
should have a beginning and an end, although this is still a subject of some
debate. But more importantly, how does this affect the direction of time, and
why is it that we remember the past and not the future.
Why time goes forward is shown by an experiment which
illustrates the relation of time flow to changes in the universe's energy
distribution. The experiment requires 3 jars, 40 numbered slips of paper
and 40 numbered balls representing energy. At the start, all the slips are
in Jar 1, all the balls are in Jar 2 and nothing is in Jar 3. A slip is
drawn at random and the ball having the same number is transferred to Jar
3. The paper is replaced and the process is repeated, each time a ball is
moved either from Jar 2 to Jar 3 or vice versa. After about 25 moves, the
jars hold equal quantities of balls. This results from mathematical laws
of chance, which govern:
