Have you heard of paradoxes?

These are little stories or problems that either appear to produce two completely contradictory (but still possible) outcomes, or provide proof for something that is totally against what we intuitively expect.

How can that be, we are totally rational, right? Well, the fact is that we are not. Paradoxes played a central role in phylosophers's work, but they are still popular nowadays.

Here is a selection of my favourites:

The Barber Shop Paradox

As most of the paradoxes posted here, this one also has a lot of versions. The oldest of all these is originated from mathematician, philosopher and conscientious objector Bertrand Russell, who lived at the beginning of the twentieth century. You can learn more about his original version here.

I prefer this version, which was derived from his work:

In a small town there is only one barber shop with one local barber shaving customers. Half of the men living in the town shave themselves and the other half make themselves shaved by the barber.

The question is, which group does the barber belong to?

Time travel paradox

This is a topic that appears in sci-fi books and movies quite often. (For example the movies, Predestination or Back To the Future). Maybe the most frequent version is dealing with the "time-loops", or the origin of things/people taken from the future and sent back to the past - how can these people/things could come into being at all?

But my favourite of this type is coming from the book of David Toomey, The New Time Travellers:

Let's imagine that a someone buys a copy of Hamlet from a bookstore, travels back in time to 1601 and gives the book to Shakespeare, who then copies it nicely and claims he made it up. Later, for centuries the book is reprinted and reproduced countless times until finally a copy ends up in the same bookstore, where our hero finds it.

The question is who wrote then Hamlet?

Omnipotence paradox

This paradox deals with the fact that someone has no limits, therefore he/she is capable of anything.

My favourite of such paradoxes is only one question:

Can God create a rock so huge and heavy that even He cannot lift it?

Liar paradox

This one comes from Ancient Greeks (as many others) and it is a paradox in logics. Here is one version of it:

A crocodile steals your child and promises to return him/her only if you can correctly guess what the crocodile will do with your child. You have two options to choose from: the crocodile gives the child back or the crocodile would not return the child.

Well, here the question is: assuming the crocodile keeps its word, what would happen if you guessed that he wouldn't return your child?

Obviously there are hundreds of similar ones. Even in everyday life, we can find many paradoxes such as these:

If you have a good paradox to share I would appreciate it if you could post it as a reply. Thanks a lot!

Sources of pictures:

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