Paradoxes have amazed us for centuries. Paradoxes have enticed our hopes of exploring the unexplored, keeping our hopes alive by letting us know that there is more to this mundane, random world than meets the eye. Many are unsolved to this day. Paradoxes have been a central part of philosophy for centuries, and are always ready to challenge our interpretation of otherwise simple situations, turning what we might think to be true on its head and presenting us with probably plausible situations that are in fact just as probably impossible. Read on to find out some amazing paradoxes that have been nothing short of mysteries.

The Bootstrap Paradox

The Bootstrap Paradox is a paradox of time travel that questions how something that is taken from the future and placed in the past could ever come into being in the first place. Imagine that a time traveller buys a copy of Hamlet from a bookstore, travels back in time to Elizabethan London, and hands the book to Shakespeare, who then copies it out and claims it as his own work. Over the centuries that follow, Hamlet is reprinted and reproduced countless times until finally a copy of it ends up back in the same original bookstore, where the time traveller finds it, buys it, and takes it back to Shakespeare. Who, then, wrote Hamlet?

The Predestination Paradox

A Predestination Paradox occurs when the actions of a person traveling back in time become a part of past events, and may ultimately cause the event he/she is trying to prevent, to take place. This results in a ‘temporal causality loop’ in which Event 1 in the past influences Event 2 in the future (time travel to the past) which then causes Event 1 to occur, with this circular loop of events ensuring that history is not altered by the time traveller, and that any attempts to stop something from happening in the past will simply lead to the cause itself, instead of stopping it. This paradox suggests that things are always destined to turn out the same way, and that whatever has to happen will happen. This concept has been wonderfully demonstrated in one of the most bone chilling sci-fi movies of all time “Predestination”. 

The Grandfather Paradox

If you travelled to the past and killed your grandfather, you would never have been born and would not have been able to travel to the past – a paradox. Let’s say you did decide to kill your grandfather because he created a dynasty that ruined the world. You figure if you knock him off before he meets your grandmother then the whole family line (including you) will vanish and the world will be a better place. According to theoretical physicists, the situation could play out as follows:

You pop back in time, walk up to him, and point a revolver at his head. You pull the trigger and Boom! The deed is done. You return to the “present” but you never existed here. Everything about you has been erased, including your family, friends, home, possessions, bank account, and history. You’ve entered a timeline where you never existed. Scientists entertain the possibility that you have now created an alternate timeline or entered a parallel universe.

The black hole information Paradox

Quantum mechanics states that information cannot be destroyed. But what happens to the particles that go inside the black hole? Things such as the mass and spin of a particle, the structure of atoms that make up a molecule, can never be destroyed according to the “Principle of conservation of mass and energy”. But what happens to the particles inside a Black hole? Black holes suck things up and then, over a very, very, very long time, radiate that stuff out in the form of Hawking radiation. Unfortunately, Hawking radiation contains no information about where it came from: all Hawking radiation is the same, which implies that black holes destroy information about the universe. If this is the case then we need to seriously rethink much of modern physics!

The catch-22 Paradox

In a novel, written by Joseph Heller, a World War II pilot named Yossarian is trying to get out of military duty by requesting psychiatric evaluation, hoping to be declared insane and therefore unfit to fly. His doctor, however, informs him that anybody trying to get out flying in combat cannot possibly be insane; the insane thing to do would be wanting to fly into combat.

That’s the catch-22: a situation that somebody cannot escape because of paradoxical rules. If Yossarian wants to be considered insane, he has to fly in combat. If he flies in combat, then being labelled as insane doesn’t do him any good. It’s like how young college graduates need experience to get a job but can’t get a job without experience.

The Fermi Paradox

The Fermi paradox is the contradiction between how likely alien life is in the universe and its apparent absence. Considering the billions of stars in the galaxy like the sun, the many Earth-like planets that must be orbiting some of those stars, the likelihood that some of those planets developed life, the likelihood that some of that life is as intelligent or more intelligent than humanity, the galaxy should be teeming with alien civilizations. But instead, we haven’t encountered any alien life till now. This paradox has kept the best physicists of our time, puzzled, for a long time.

The paradox of intolerance

The paradox of tolerance is the idea that a society that is entirely tolerant of all things will also be tolerant of intolerance. Eventually, the tolerated intolerant elements of a society will seize control, rendering that society a fundamentally intolerant one. Therefore, in order to remain a tolerant society, intolerance cannot be tolerated.

The Observer’s Paradox

The observer’s paradox is that, when observing a given phenomenon, merely observing it changes the phenomenon itself. If a researcher wants to observe casual communication in a population, those being observed will speak more formally since they know their speech will be involved in academic research.

Polchinski’s Paradox

Theoretical physicist Joseph Polchinski posed a puzzle to other physicists in a letter: consider a billiard ball tossed through a wormhole at a certain angle. The billiard ball is then sent back in time through the wormhole and, because of its trajectory, strikes its past self, knocking the ball off course before it can enter the wormhole, travel back in time, and strike itself. 

Peto’s paradox

Biologist Richard Peto noticed in the 1970s that mice had a much higher rate of cancer than humans do, which doesn’t make any sense. Humans have over 1000 times as many cells as mice, and cancer is simply a rogue cell that goes on multiplying out of control. One would expect humans to be more likely to get cancer than smaller creatures such as mice. This paradox occurs across other species too: Blue whales are much less likely to get cancer than humans, even though they have far more cells in their bodies.