Who the hell farted?
It starts slow, finding its way through the room. The reactions mostly ranging towards the disgusting side, with one person cursing so loudly. It acts as a warning sign to the rest. Then it saturates the room, and disgust is on the face of everyone who smelt the fart. The Farter (hehe, sounds like father) stares at everyone; grinning that his work is complete, and he can go back to concocting another horrendous fart.
But why do farts spread like so? And can they flow in reverse? What laws govern this? Why is it important? Well, let us find out.
The mid to late 19th century was a time of great discovery in the field of thermodynamics, with guys like Sadi Carnot, Mayer, Thompson, Maxwell, and Clausius bringing in breakthroughs in the field. The Carnot engine worked on finding something that was conserved whenever an engine worked. And though he died young, his work was profound.
William Thompson (Lord Kelvin) and Robert Mayer then worked out that energy can neither be created nor destroyed, but it changes from one form to another (first law of thermodynamics). This is a fundamental law in nature that has withstood the test of time. It is the reason why we cannot have perpetual motion machines, or rather, machines that give free energy. In short, you can never get something for nothing.
Then came Rudolf Clausius with the second law of thermodynamics, defining Entropy, and stating that it always tends to a maximum. However, we will focus on entropy and statistical Thermodynamics (sounds hard but it is actually very simple.)
What is Entropy?
Entropy is the tendency of a system to move towards disorder. It is the reason why things rot, decay,
disorganize, etc. Entropy is the reason you cannot unfry an egg (looking at those who wanted to
make omelets and ended up with scrambled eggs), unbake a cake, or basically uncook food.
The law of the universe states that all systems tend towards disorder while trying to attain thermal equilibrium (unless in special cases such as lasers). But why is this important? Well, it determines the useful amount of energy in a system. It determines how much of heat produced by wood can actually be converted into mechanical energy in a steam engine, or the efficiency of the fuel you use in your vehicle since some part of it is always lost.
In short, the second law of thermodynamics tells us that there is nothing perfect in the universe (not even your partner).
It is the reason the typical efficiency of most energy generators that use heat rarely surpass 50% (nuclear at 35% and thermal at 42% give or take). This makes it important in the planning of power stations, the amount of fuel to be used, and the conditions that allow for maximum utilization of energy to get the maximum energy efficiency.
Entropy is also the reason why it takes more energy to cool something than heat it up.
However, this theory needed further explanation, and Clausius formulated a formula to work out the speeds of individual molecules, making the point that they averaged a certain speed (the hotter molecules are, the faster they move).
James Clerk Maxwell (yes, the electromagnetism guy) later came up with a better way of explaining, saying that not all molecules had the same speed at a given temperature, but that the speeds were distributed, with some above the average speed, and some below. This statistical explanation seemed to have solved some fundamental problems and lay the groundwork for Ludwig Boltzmann.
Ludwig Boltzmann, an Austrian Mathematician, and physicist later came up and perfected the work of Maxwell. He clarified Maxwell's formula and tried to streamline the process. He explained why
Maxwell’s distribution was right and reconciled the process with Newtonian mechanics. However, since Newtonian mechanics worked as well when time-reversed, he had to explain why the case was not the same with thermodynamics.
Now, why is it that a fart or perfume spreads out fast, and does not concentrate in one confined area?
Well, Boltzmann explained that there are multiple ways in which the smell could spread keeping in mind the nature of the room at thermal equilibrium
The perfume could, for example, decide not to spread, and remain on your body, but there are more ways for it to exist in a spread-out form than in a concentrated form. In short, this is the same reason it is easier for your room to be untidy than neat. Reason being that there are more ways for your room to be untidy than neat. For neatness, everything should be in the right place, but for the condition of untidy, one or two things in the wrong place can be considered untidy.
So next time your mum asks why your room is untidy, tell them it is because of entropy, and that it is the most probable state of your room. The same goes for perfumes. Perfume is more likely to spread because there are more states in which it can exist while spread.
Boltzmann’s work was met with a lot of criticism due to the fact that molecules and atoms had not been observed. It wasn’t until later when a patent clerk in Bern (Albert Einstein) would write a paper proving their existence. Boltzmann took his life in 1906, after a severe depression bout (he was bipolar).
Entropy is so ingrained into life and the universe, that it is sometimes referred to as time’s arrow, that is, if a system’s entropy is increasing, then time is moving forward in that system.
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