One thing we all know is that time moves in one direction. But have you ever wondered what the reason is? Scientists have already asked this question, and found the answer in a steam engine.
Like length, height and width, time is a dimension. But while we can move in any direction in the other three options, we can only move in one direction in time: forward and on and on. Because?
Why can't we go back?
For a long time, scientists could not find a convincing explanation.
One of the complications was that the laws of physics worked well, whether going backwards or forwards in time.
Finally, the answer came from an unexpected place: the steam engines.
At the beginning of the Industrial Revolution, engineers were trying to understand how to make steam engines more efficient.
By examining how all this heat and energy moved in an engine, they developed a whole new field of science that they aptly called thermodynamics.
The force of heat
It turns out that thermodynamics can explain much more than the behavior of steam engines.
In particular, the second law of thermodynamics helped to understand why things happen in a particular order.
Such a law points out that an isolated system can either remain closed or evolve into a more chaotic state, but never into a more orderly one.
A cup falls to the floor, for example, and all its contents are scattered.
Intuitively, we know that the process is irreversible.
Things have a way of being disorganized, but some of them may come back to order, and the second law of thermodynamics says why.
Another way to prove this is in terms of clutter.
A cup is in order and, as it breaks, clutters, becomes messy.
The word in physics for this is …
The more entropy there is in a place, the more cluttered, messy and useless it is.
Thus establishes the second law of thermodynamics.
The "S" represents entropy and the "d" is a mathematical way of representing change. Therefore, "dS" is equivalent to a change in entropy.
Now, looking at this equation from left to right, what it says is that the entropy of a system always has to increase.
When a cup shatters, or when milk mixes with coffee, it is also in accordance with the second law of thermodynamics because the entropy of these things increases.
But if the cup is expected to be reconstituted, or the milk and coffee to separate, that would mean a drop in entropy. And therefore would violate the second law.
The second law of thermodynamics indicates in what order things can happen in the universe. It gives us a clear direction of how the flow we call time moves forward.
Time simply cannot flow differently because it would decrease entropy and consequently violate the second law.
But where does the relentless march of time lead us?
The entropy of the universe? ie the clutter? It is always increasing. Ever.
This means that at some point in the distant future, our universe will come to a state of total disorder, of maximum entropy.
Scientists call this "thermal death".
Despite its name, death by heat will not be a fiery hell in which everyone will be reduced to ashes.
It will be worse.
What will happen, according to this prediction coming from physics, is that all the thermal differences will disappear, causing everything to have the same temperature and no more life.
All stars will die, almost all matter will decompose, leaving only an amalgam of particles and radiation.
Over time, this energy will also disappear, due to the expansion of the universe, which will eventually become cold, dead and empty.
This is what is called the "Big Freeze": the Great Freeze.
This will end our universe.
But don't worry, billions and billions of years will be before this dark destiny arrives, and by then there will be no humans to witness how time and entropy have devastated our universe.