Paradoxes

First of all, what is a paradox?

a fact or phrase is designated that seems to oppose the principles of logic. The word, as such, comes from the Latin paradox, plural of paradoxon, which means ‘the opposite of common opinion’; this in turn comes from the Greek παράδοξα (paradox), plural of παράδοξον (paradoxon), which could be translated as ‘unexpected’, ‘incredible’ or ‘singular’.

That said let's start

1. The paradox of Epimenides (or Cretan)

A highly known paradox is that of Epimenides, which exists since Ancient Greece and serves as a basis for similar ones based on the same principle. This paradox is based on logic and says the following.

Epimenides of Knossos is a Cretan man, who states that all Cretans are liars. If this statement is true, then Epimenides lies, so it is not true that all Cretans are liars. On the other hand, if it lies, it is not true that the Cretans are liars, so that their statement would be true, which in turn would mean that they were lying.

2. Scrödinger's cat

Probably one of the best known paradoxes is that of Scrödinger. This physicist from Austria tried with his paradox to explain the operation of quantum physics: the moment or wave function in a system. The paradox is as follows:In an opaque box we have a bottle with a poisonous gas and a small device with radioactive elements with a 50% probability of disintegrating in a certain time, and we put in it a cat. If the radioactive particle decays, the device will cause the poison to be released and the cat will die. Given the 50% probability of disintegration, once the time has passed, is the cat inside the box alive or dead?This system, from a logical vision, will make us think that the cat can indeed be alive or dead. However, if we act based on the perspective of quantum mechanics and value the system at the moment, the cat is dead and alive at the same time, since based on the function we would find two overlapping states in which we cannot predict the final result.

the past paradoxes were focused on a more realistic scientific or logical field let's get something fanciful.

3. The grandfather's paradox

Being attributed to the writer René Barjavel, the grandfather's paradox is an example of the application of this type of situation to the field of science fiction, specifically in relation to time travel. In fact, it has often been used as an argument for a possible impossibility of time travel.
This paradox states that if a person travels to the past and eliminates one of their grandparents before they conceive of one of their parents, the person itself could not be born.
However, that the subject was not born implies that he could not commit the murder, something that in turn would cause him to be born and could commit him. Something that would undoubtedly generate that he could not be born, and so on.

4. Russell's paradox (and the barber)

A paradox widely known in the field of mathematics is that proposed by Bertrand Russell, in relation to set theory (according to which every predicate defines a set) and the use of logic as the main element to which it can be reduced. Most of the math. There are numerous variants of Russell's paradox, but all of them are based on this author's discovery that "not belonging to himself" establishes a predicate that contradicts set theory. According to the paradox, the set of sets that are not part of themselves can only be part of themselves if not part of themselves. Although said that sounds strange, then we leave you with a less abstract and more easily understood example, known as the barber's paradox.

“A long time ago, in a distant kingdom, there was a shortage of people who were dedicated to being barbers. Faced with this problem, the king of the region ordered that the few barbers who had only and exclusively shave those people who cannot shave on their own. However, in a small town in the area there was only one barber, who was faced with a situation for which he could not find a solution: who would shave him? The problem is that if the barber only shaves everyone who cannot shave themselves, technically he could not shave himself just by being able to shave those who cannot. However, this automatically makes it impossible to shave, so it could shave itself. And that in turn would lead him to not be able to shave by not being unable to shave. And so on.In this way, the only way for the barber to be part of the people he should shave would be precisely that he should not be part of the people he should shave, which is why we find Russe's paradox