This disorder is described by the second law of thermodynamics, which is called entropy, and it is not as easy to understand as the disorder at home in the children’s room.
A physicist describes entropy as an expression of how evenly energy is distributed in a closed system between individual particles.
If a closed system – for example a gold bar – is in energy equilibrium, then the individual particles in the system have the same average energy. But since molecules always transfer energy, it is unlikely that they will have exactly the same energy at any given moment. It is also not likely that a single molecule can have all the energy.
Particles prefer chaos
If we imagine that the gold bar consists of three particles and only three energy units, then the particles may contain one unit, and one molecule may contain all three, and so on. In total, this example has ten possible combinations.
In a real nugget of gold, there are billions of molecules and trillions of combination possibilities, and it is statistically unlikely that all units of energy could come together into a single molecule.
In the real world, the energy would automatically be spread evenly over all the particles – the entropy would be as high as possible.
In a cold gold alloy, the particles vibrate only slightly. Then they have little ability to exchange energy, and the entropy is relatively low.
Now we take a glowing gold bar where the molecules vibrate and the entropy is high, and we put it on a cold bar. Quite automatically, the entropy will increase. The upper band sends heat to the lower band so that they are in temperature balance.
In this process, the entropy decreases slightly in the hot alloy, but at the same time the entropy increases in the one that was cold, as the molecules are now vibrating more.
In general, energy can now be distributed in many ways, so the entropy has increased. The process follows the second law of thermodynamics to the letter.
Development can never go the other way. If we placed an icy gold bar on top of the other two, the temperature in them would drop and the entropy would drop, but the cold gold bar led to more mayhem elsewhere: the freezer cooling the gold bar released heat into the air around the freezer, where the entropy increased.
Since entropy cannot decrease, all molecules in the universe will eventually swim in a great frosty misery. Fortunately, that won’t happen anytime soon. Calculations show that entropy doomsday will only come in 1026 year.
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