In 1814, Laplace described an entity that would be able to calculate any future event if it knew the precise location and speed of every atom in the Universe, based on the principle of cause and effect. This will be known as Laplace's Demon. At that time, scientists believed that they could solve all the mysteries of the Universe. Decades later, with Heisenberg's uncertainty principle and other advances, that dream became to an end.

The Dead of Laplace's Demon

Causal determinism is a philosophical theory that defends that events are bound by causality, which is generally known as cause and effect. Laplace's Demon is described as an intellect that would be able to know all past and future events if it knew the positions and velocities of all atoms in the Universe. The Demon would be able to embrace in a single formula the movement of the greatest bodies and those of the tiniest atom. For the Demon, nothing would be undetermined.

Laplace's Demon was a symbol of the ultimate goal of science, the pursuit of truth. And at that time, scientists were confident that humanity will unveil all the secrets of the Universe, it was just a matter of time.

The last years of the nineteenth century put an end to this confidence. The second law of thermodynamics states that all natural processes are irreversible, in other words, the Universe tends to automatically degenerate into a more disordered state.

$$dS \gt \frac{\partial Q}{T}$$

This formula was the first blow to Laplace's Demon, since it was based on the premise of reversibility in classical mechanics. But very soon another blow was presented by Heisenberg in 1927.

$$\sigma_x \sigma_p \ge \frac{\hslash}{2}$$

The Uncertainty Principle states that is not possible to measure the position of an atom and its velocity with infinite precision. In other words, if we want to measure the position of an atom with high precision, we will have a high error in measuring its velocity. This simple formula might be the saddest achievement of the human thought. In 1927, the humanity realized that we will never be able to know all the truth, the Universe has an intrinsic limitation to what we can observe.

Not only that, Einstein's Relativity Theory discovered that time and space were not absolute, as it was believed since Aristotle. This contributed to a higher disbelief in science that still persist in our days. For some people, time and space being relative means that everything is relative, therefore there is no truth but views or opinions, each of them as valid as the others.

The Pursuit of Truth

It is paradoxical that the second law of thermodynamics, the uncertainty principle and the relativity theory created such a social disbelief in science. The truth nowadays is either unattainable or unreal. Some politicians and journalists took advantage of this situation, if everybody has their own truth then it is easier to lie and manipulate people. Fake news or alternative truths are something that we see everyday in our society.

The pursuit of truth based on evidence is the ultimate goal of science. It is an innate desire of the human being to understand why events happen. From ancient Greeks until the modern era, human knowledge has grown to limits never imagined before. But how was this possible? The answer is the scientific method.

The Scientific Method

The scientific method is the methodology science uses to distinguish between what is true and what is not. A scientist proposes a theory with evidence that supports it. In a different lab, a rival scientist replicates the experiment, and the theory is verified based on independent calculations. This process is replicated across different labs and countries, until the scientific community accepts the theory. That is how science can grow strong:

"If I have seen further than others, it is by standing on the shoulders of giants". Isaac Newton

In the scientific method it is extremely difficult to accept a theory, it takes a tedious process of replication and verification, whereas it is extremely easy to refute. A single contradictory proof will dismantle the theory. If there is a single thing that the scientific method excels at, it is at disproving hypothesis.

A great example is the theory of evolution that states that monkeys and humans have a common ancestor (which is not the same as saying that my great-great-great...grandfather was a monkey). The first evidence was the fossil record. The body and skeleton structures point to common ancestors. But maybe the fact that removed all reasonable doubt was genetics.

Unlike other animals, humans are not able to synthesize vitamin C. This was discovered during the long sea voyages when sailors contracted scurvy, while horses, dogs or mice didn't. When scientist compared the genetic code of humans and other animals, they realized that there was a gene that prevented the production of vitamin C. This gene was found as well in other primates. The best explanation is that a mutation has occurred in a common ancestor of these species, and so all descendants are unable to synthesize the vitamin.

Moreover, scientists identified that guinea pigs and fruit bats didn't synthesize vitamin C. These animals are from a complete different family tree, and when their the genetic code were examined, scientists found that the mutations were different. This provided another evidence of the evolution theory, because it would be highly unlikely that the same mutation would occur twice.

To date, no single proof denying evolution has been found, while there are plenty of evidence that supports it. A single proof, independently evaluated, will make all scientists in the world deny evolution. That is how the scientific method works.

Laplace's Demon is dead, since it has been proven that science will never know all the secrets of the Universe. However, the scientific method is a strong methodology that allows us to distinguish between truth and falsehood and push the human knowledge forward.

This video of Neil deGrasse Tyson talks about the importance of the scientific thought.