Can we get warm by snuggling up to an icicle? Can water ever become steam at zero degree or ice at 100 degrees Celsius? In a coin flip, is it possible to get 100 heads in a row? In a poker game, can you expect to be dealt a royal flush _ ace, king, queen, jack and 10 of the same suit _ ten consecutive times? You are probably saying: “That’s absurd! Things don’t happen that way”.
Yes, they don’t. But why? The answer is entropy _ from the Greek word entropia meaning transformation. The concept of entropy, introduced in 1865 by German physicist Rudolf Clausius, is a quantitative measure of chaos or disorder. The less ordered a system is, the greater is its entropy.
British astrophysicist Arthur Eddington in his book, ‘The Nature of the Physical World’, discusses with delightful humor ordered and disordered states. He considers the process of shuffling a deck of cards, and points out that there is only a ghost of a chance that a thoroughly shuffled deck can be reshuffled back to the original order.
Whenever an event occurs that cannot be undone, like the shuffled deck of cards, it is called an “irreversible process.” Once an irreversible operation has been performed, “total” entropy, i.e. entropy of the system and its surroundings, irremediably increases.
Since entropy quantifies disorder, this means that the decrease of disorder in one region of the Universe is always accompanied by increasing disorder somewhere else. Consequently, any changes that occur in nature will invariably drive up the total entropy until it can go no higher. This is the essence of the second law of thermodynamics, an inviolable pillar of physics. In its widest sense, the law says that an ordered system will always tend to become more disordered because disorder is a far more likely outcome.
Since it requires more energy to create an ordered system than a disordered one, increased entropy corresponds to a loss of energy that cannot be recovered. In other words, natural processes come with a penalty of the permanent loss of energy. It tends to transform into high entropy, disordered energy of heat. Once entropy becomes maximum, there will be no further change and the system will have reached a state of thermal equilibrium.
Now back to ice, water and steam. If water becomes steam at zero degree or freeze at 100 degrees Celsius, then the total entropy will decrease which is a violation of the second law. Does this mean we cannot make ice without violating the second law? No, it doesn’t. To see this, we have to look at the broader picture. We extract heat from water to make ice, but at the expense of releasing larger amount of heat into the air. Similarly, a refrigerator won’t work without producing a lot of hot air. The refrigerator lowers the entropy inside but raises the entropy of the outside air by a much larger amount. For the same reason, air conditioners need an exhaust, but space heaters don’t. Indeed in all these processes, total entropy increases.
Regarding the coin flip, you would have to toss it for eons before you would get the low entropy ordered state of 100 heads in a row, while it would take only a few minutes to get the high entropy disordered state of 50 heads and 50 tails.
In a poker game, out of 2.6 million possible five-card hands from a thoroughly shuffled deck of cards, there are only four royal flushes. However, there are over a million worthless five card combination. Obviously, the chance of getting a high entropy worthless hand is immeasurably higher than the chance of getting a low entropy royal flush.
The concept of entropy is not confined to physics, engineering, coin tosses or card games only. In the social sciences, it carries the connotation of disorganization, anarchy and dystopia. Since entropy is a measure of the universal tendency of order to degenerate into disorder, we can use it to understand the degree of satisfaction and/or dissatisfaction in the human society. It can also be used to determine whether a society will eventually decompose into a state of total disorder or anarchy as its complexity, and hence the entropy, increases with time.
In data communications, entropy refers to the relative degree of randomness. The higher the entropy, the more frequent are signaling errors. Entropy also refers to disorder deliberately added to data in certain encryption processes.
The laws of nature, except the second law of thermodynamics, are symmetric in time. Putting it differently, it means that the physical laws governing a dynamical system would be equally descriptive and valid if time is reversed. The second law is the only principle of physics that distinguishes between forward and backward direction of time. This led Eddington to coin the term “Arrow of Time,” an abstract entity that depends on the thermodynamic asymmetry, always pointing in the direction of higher entropy. Simply stated, the Arrow of Time dictates that things change as entropy increases and once these changes happen, they are never undone.
If it weren’t for the second law, everything could just as well run backward in time. That is to say, after “Humpty Dumpty had a great fall, all the king’s horses and all the king’s men” could have “put Humpty together again.” Or like Charles Dickens’ Ebenezer Scrooge, we could travel back in time. But they couldn’t and we can’t because the past lies behind us. It is fixed and immutable with access prohibited by entropy.
When entropy will reach its maximum value and becomes steady, time’s arrow won’t know which way to point. Time will still be there and retain its ordinary properties, but its arrow will be lost.
The irreversible increase of entropy does not bode well for the future of the Universe. When the estimated one billion trillion stars in the observable Universe convert hydrogen to helium, there is a direct translation of order into disorder in the form of radiation or heat energy that extends through space. The associated increase in entropy will gradually but inexorably push the Universe towards a state of maximum disorder. In the words of novelist John Updike, when this will happen, “The stars long since will have burnt their hydrogen and turned to iron. Even the black holes will have decayed. Entropy! Thou seal on extinction, Thou curse on Creation.”
In the language of physics, there won’t be any “free energy” available to sustain motion or life and the Universe will die, wallowing, as it were, in its own entropy. It will be a vast, empty, frozen Universe. This gloomy state of affairs is referred to as the “heat death” of the Universe.
The writer is Professor of Physics at Fordham University, New York.
Photos: Google Image
Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.
Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.
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