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Discussion 3 to Meditation 8
The second law of thermodynamics

Mark Rotchell

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Ah, the second law of thermodynamics. Quite possibly the most misunderstood and misused physical law by the lay man.

It is a problem of language really. Physics is best described using the language of mathematics. Once it gets expressed in English or any other spoken language it unfortunately becomes open to interpretation, which the laws of physics, generally, are not.

The second law of thermodynamics is a statement about the allowed direction of natural processes. It allows certain processes and disallows others. A process can only happen if it's result is to increase the entropy of the universe rather than decrease it. A process is not spurred into action because it will increase the entropy of the universe, it is merely allowed.

Let me give you an example that may explain this:

When a space shuttle flies into orbit it ejects lots of hot gases out it's rear end. Fuel is taken from the simple homogenous "ordered" state it has in tanks, gets burned and thrown out of the back as a mass of rushing, energetic, swirling, "disordered" gas. Entropy increases in this process, however it is not spurred into action because the universe wants more entropy. The shuttle is launched by pressing a button, not by the universe seeing the opportunity for entropy and taking it.

The opposite direction, i.e. all these gases spontaneously coming together from the air, separating themselves into fuel and oxygen and ramming themselves into fuel tanks, obviously doesn't happen.[1] This is because it would be a significant drop in entropy. The second law of thermodynamics is merely a statement about which of these two processes is allowed if one of them is to take place. It does not say that the process will take place, simply which direction it will go in if it does.

The big bang[2] is allowed by the second law of thermodynamics, however it is not the cause of it.

Sorry to rain on your parade.

Footnotes:

  1. It can be forced to happen in the lab, though other processes must occur simultaneously so that the net entropy change is positive, such as the burning of fuel at the power stat ion that provides all the electricity needed. It is possible for a certain processes to be forced to take an entropy decrease however the entropy of the universe as a whole must go up overall as that small part of it goes down. "Entropy decrease" processes do not happen spontaneously, they require forcing, and the process of forcing creates a bigger increase of entropy than the drop in entropy achieved.
  2. The "Big Bang" is perhaps the best example of why language and science don't match. The big bang wasn't very big, it was in fact the smallest explosion ever. Neither did it go "bang", the matter at the start of the universe was so dense and hot that a sound, or pressure, wave wouldn't have been able to form.