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Entropy

 

By John Dobson
Published 2004-10-22 13:25:46
From 1995

 

It's easier to scramble an egg than to unscramble it. Entropy is a measure of the scrambledness of the energy, and because there are more ways to be scrambled than to be unscrambled, the scrambledness of the energy tends to increase. The entropy tends to go up.
 
Energy is simply the nature of the underlying existence showing through in space and time, and its amount remains constant. It is only the quality of the energy, its usableness, that gets degraded. And entropy is a measure of this degradation."Die Energie der Welt bleibt konstant; die Entropie strebt\einem Maximum zu." (The energy of the world remains constant the entropy strives to a maximum.) -- Rudolf Clausius (1822-1888). This is a statement of the first and second laws of thermodynamics. And the term laws doesn't mean edicts, but ally statements about how matter behaves. Physics is about how matter behaves, and these are statements about that. This is simply a statement that although the energy in the Universe remains constant, the entropy tends to go up.

 

Negative entropy is a measure of the usableness of the energy. Gravitational energy and the kinetic energy of large moving objects is completely usable. Heat energy is not, because the directions of the motions of the particles have been scrambled. That's what we call heat. And temperature is a measure of the mean kinetic energy of the molecules. When you panic stop on the freeway, the kinetic energy of your large moving vehicle gets scrambled to heat by friction in the brake drums and the brake shoes, the tire and the road. If you could unscramble it, it would once again be the kinetic energy of your large moving vehicle. Now if, instead of being scrambled by friction in the brakes, the energy had been run into a flywheel (which is a large moving object), you could have used it to restart your car. That's how they restart the mail trucks and the milk trucks in Europe.

 

Since all living organisms must find and use a source of energy less scrambled at the start, life is impossible except in a world that is going from bad to worse. All living organisms live in this cascade of increasing entropy by directing streams of the increase through their forms. For all living organisms, negative entropy is food. When you eat it, it's cake; when you're through with it, you push the plunger.

 

In the last century, and in the early days of this century, it was usually taken for granted that the mix of the chemical elements in the Universe was given at the time of creation, if there was a creation, or had been around forever, if there was a forever. (It was not known than that the other chemical elements are fashioned from hydrogen in the bellies of the stars.) And it was thought that if you just shuffled the mix long enough, it might come out in the present configuration again. But there was the problem of entropy. It was already known that entropy tends to a maximum and would surely go up. (In those days the expansion of the Universe had not been noted, nor its extent.) Then, considering the consequences of the continuously increasing entropy, it was thought that the Universe would eventually reach a "heat death." It was thought that eventually every chemical reaction that could have taken place would have taken place, and that everything that could have fallen would have fallen. And it was thought that when all these other energies had gone to heat, the Universe would be just a little warmer and life would be muffed out.

 

Now it turns out that, like life, the formation of galaxies and stars would also be impossible except in this cascade of increasing entropy. A galaxy could not be formed by stars falling together because the stars would be too lonely to collide. The entropy would not go up because the stars would not collide and therefore the energy of falling would not be scrambled to heat. Galaxies are formed when clouds of hydrogen fall together because the clouds are big enough to collide. The clouds, unlike the stars, are large with respect to the spaces between them. So the particles of each cloud collide with the particles of the other cloud and thus scramble their motions to heat. (Stars like the Sun have a density of more than a pound per pint, whereas the density of the interstellar clouds is closer to a pound per billion cubic miles.) It is because of their large sizes that the clouds collide, and the energy of falling is transformed to heat. We say that the entropy has gone up.

 

Similarly, stars are formed when clouds of gas and dust collide because the entropy goes up as the energy of falling is transformed to heat. (Stars are not hot because of nuclear fusion at the core. They are hot because the energy of falling has been transformed to heat. The heat released by fusion simply keeps them from collapsing farther and thus getting too hot. But it's only temporary.)

 

Locally, within the Universe, the entropy goes up. However, for the Universe as a whole, the entropy may not go up. The observable Universe has a border, some fifteen billion light years distant in all directions, imposed on us by what is called "the expansion." It is imposed on the observer by the fact that all the distant objects appear to be moving away. At some fifteen billion light years from us (at the present apparent rate of expansion), they are estimated to be receding at the speed of light. It is this apparent" expansion" that imposes a border to the observable Universe because things receding faster than the speed of light are not observable. And if the rate of expansion were increased, the border would of course be closer.

 

Now, when we consider matter near the border, its radiation, as seen by us, would be red-shifted (lowered in frequency) much as the pitch of the fire engine's bell is lowered where the fire engine has passed us and is going away. But if the energy of the radiation of the distant particles is lowered, so too is the energy of the panicles themselves, and therefore also their mass. (We know from Einstein's 1905 equations that what we see as matter is just potential energy. Swami Vivekananda had suggested this to Nikola Tesla some ten years earlier. But Tesla had failed to show it.) Now there are two very interesting consequences of this apparent lowering of the mass. First, radiation running through a field of low-mass particles would be so often picked up and reradiated that it would be thermalized to 3° Kelvin and would appear as the background radiation discovered by Penzias and Wilson in 1965. Second, if the mass of the particles approaches zero, their momentum must also approach zero (because the momentum is the mass times the velocity, and the velocity approaches a constant). But if the momentum approaches zero, so does our uncertainty in that momentum. Then, by Heisenberg's uncertainty principle, our uncertainty in where they are must approach totality. (According to Heisenberg's uncertainty principle, if we can know where a particle is, we cannot know its momentum. Likewise, if we can know its momentum, we cannot know where it is. So if we can know the momentum of a particle at the border, we cannot know that it's at the border. We cannot know both its momentum and its position.) Now if the particles thus recycle by "tunneling" back into the observable Universe as hydrogen (with its gravitational energy thus restored) then the entropy of the whole Universe might not increase.