What is entropy? Also, can anyone explain how it relates to matter, gravity, time, other physics terms?
In: Physics
Imagine you have a pot of water at 0 energy units that you want to heat up to 10 energy units. You have a stove that can produce 8 energy units per minute. Theoretically, in a perfect system, it should take 1.25 minutes to heat the pot of water to your target energy level, right?
However, the pot itself is also at 0 energy units and wants to be the same as the water, so some of the energy produced by the stove will go into the pot, which means that the water takes longer than 1.25 minutes to reach the target energy level, the difference in time is measured and converted to energy “lost” to the pot. That “lost” energy is entropy.
Now we make it a little more complicated. Let’s say the air around the pot is also at 0 energy units. Although there is a finite amount of air, the difference between the amount of pot, water, and air is more-or-less infinite. The air also wants to be the same as the pot and the water, so a lot of the energy of the stove goes to the air, but no matter how much energy you pour into the air, it would take an infinite amount of time to make an infinite amount of “stuff” hold an infinite amount of energy (a heat sink). But the pot and the water still gain energy because they hold onto the energy better than the air does. The energy that goes into the air is also entropy.
Finally, to make things more interesting, the outlet in your house that the stove is plugged into is actually putting out 10 energy units per minute, but the wire connecting the outlet and the stove can’t transfer the energy perfectly, kind of like transferring water from a tap to a bucket through a cardboard tube: at first the tube holds up, but eventually the water seeps through the layers of paper and drips out along the way. So while every minute the stove is losing energy to the air and the pot, the energy from the outlet is lost through the wire. This is also entropy.
The important thing to remember is the First Law of Thermodynamics, energy can be neither created nor destroyed. So this energy still exists, somewhere, entropy is all relative to the boundary that you use to define your system. If your boundary is around the pot and the water, you’re gaining energy; if the boundary is expanded to include the stove, you’re losing energy.
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