The Heat Death of the Universe
Credit to The Conversation
Many theories about the end of the universe have been explored, but one theory—the heat death of the universe—is believed to be true by many experts and is particularly interesting.
To begin with, the second law of thermodynamics states that entropy, or the measure of disorder, will always increase when given an isolated system. In other words, the mechanical energy that performs the work producing heat is more ordered than the heat energy it produces. This means that all forms of energy are being converted into a more disordered state.
The interesting thing is that entropy isn’t as involved in laws of chemistry or physics as it is probability. The reason disorder continues to increase in the universe is because it is simply more likely for an ordered system to become disordered, than a disordered system to become ordered. To put this idea in an empirical example, think about a folder with a dozen numbered documents that you have organized in numerical order. Let's say that over time, these documents get jumbled up inside the folder in randomness. What is the probability that the documents will randomly be organized in perfect numerical order? Close to nothing. And the greater the number of documents in the folder, the slimmer the probability of perfect organization.
In a more specific example, take a heated cup of coffee. There is a chance that the coffee will instantly turn cold at any given moment while it cools, but this chance is so low that statistically, there isn’t enough time in the expected time of existence of the universe that such an event will take place. The number of particles in the coffee as well as the probability of instantaneous cooling are both unfathomable, which is why the conversion of energy into a more disordered state is considered irreversible.
Why is this important? Well, in simple terms, energy needs to be ordered for it to be able to be used. But as the world slowly reaches maximum entropy, we will reach a state of no free thermodynamic energy. Since heat is defined as a transfer of energy, a state of no transfer of energy, or thermal equilibrium, will result in a loss of heat. There will be no temperature difference to fuel thermodynamic processes, erasing the ability for biological life to continue to exist. Some believe that the universe will asymptotically approach a temperature near absolute zero (giving it its alternate name, the Big Freeze), while others think that there will be no temperature change. But one thing is for sure: nothing will change, and nothing will happen. We will lose the perception of time.
Some scientists remain skeptical of the heat death. They say that we shouldn’t assume that the laws of physics that support the theory cannot be applied to the entirety of the universe without doubt, given the amount of unknown aspects of space. This brings about the question of whether or not the universe should be considered a closed thermodynamic system, as well as how exactly the gravity of individual systems affects entropy. For this reason, a collection of theories, including the Big Crunch and Big Rip, exist to attempt to predict the end of the universe.