How Well Do You Know The World's Most Famous Paradoxes?

Isadora Teich

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About This Quiz

Paradoxes contradict themselves with possible outcomes and shatter expectations. Test your knowledge of all things paradoxical with this HowStuffWorksQuiz.

In which paradox is a cat alive and dead at the same time?

This famous thought experiment was an invention of Austrian physicist Erwin Schrödinger to criticize the Copenhagen interpretation of quantum mechanics. In the thought experiment, a cat may be both alive and dead as long as it is unobserved.

__________ asks if after flicking a lamp on and off infinitely, the lamp is on or off?

This philosophical puzzle was thought up by philosopher James F. Thomson and is seemingly impossible to solve. Considering a lamp cannot be turned off unless it is already on, this is a contradiction.

Which paradox involves a card with two contradictory statements on each side?

This paradox was created by Philip Jourdain. To create it the front of a card could say "The sentence on the other side of this card is true." and the back of a card could say "The sentence on the other side of this card is false." In this case, trying to prove either true ends in paradox.

Which paradox occurs when a liar says that they are lying?

This is a classic paradox in both logic and philosophy. It has been discussed and explored around the world for centuries.

A situation which a person can't escape due to contradictory rules or conditions is described by this paradox:

The term Catch-22 was coined by Joseph Heller in his 1961 novel Catch-22. An example of a Catch-22 would be getting turned down for jobs which require experience, making a person unable to get the experience they need to get hired.

____________ states that a hotel with infinite rooms can always take in more guests, even if it's full.

This thought experiment explores the idea of infinite sets. It was introduced by mathematician David Hilbert.

Which paradox states that the position and velocity of an object can never both be measured exactly?

This paradox was introduced by German physicist Werner Heisenberg. It is a principle of quantum mechanics.

According to classical logic, inconsistent premises suggest that any argument is logically sound.

This paradox exists because the language of classical logic is different than that of everyday language, and how validity is defined is different. In the statement "It's night and it's day, therefore, clouds are made of bubblegum," there is no possible situation where the premises could be true, so any conclusion is possible.

The __________ is a logical paradox in which a crocodile, having stolen a child, tells the parents that they will return it if the parents guess correctly what they will do with the child. If the parents correctly guess that the crocodile will not return the child, what should the crocodile do?

This dilemma is a logic paradox. If the crocodile does not return the child, the parents' guess was proven correct, which means they have to return the child. If they do return the child, the parents' guess is proven wrong, which means they get to keep the child.

Declaring that it is Opposite Day, and thereby negating Opposite Day, is described by which paradox?

Opposite Day is a children's game. When it's declared, everything said means the opposite of what it usually does. However, since Opposite Day means that everything means the opposite, by declaring Opposite Day kids actually just announce a normal day.

Which paradox asks "Where is everybody?" as there is no evidence of life in the universe beyond earth.

This cosmological paradox is the high probability of there being life in the universe other than ours, but no evidence. It is named after physicist Enrico Fermi.

The statement "I know that I know nothing," is known as the:

This saying comes from Plato's account of the philosopher Socrates, though the exact phrase does not appear anywhere in Plato's writings. It refers to Socrates' methods of teaching and learning, which begin with admitting what you don't know and exploring it.

___________ asks if an object that has had all of its parts replaced is still the same object?

This paradox asks if a ship that has had all of its parts replaced over time remains the same ship at the end. There are a few variants of this, including the Grandfather's Ax Paradox, which asks if an ax that has both the head and handle replaced is still the same ax?

Which paradox asks whether or not a single grain of sand makes a difference between a heap and non-heap of sand?

The Paradox of the Heap is also known as Sorites Paradox. If you take one grain of sand from a heap, you still have a heap, but if you remove grains one by one, eventually the heap will vanish. Does one grain of sand make the difference between a heap and not a heap?

Which paradox states that most people have a lower number of friends than their friends have?

This appears to be a statistical paradox but is a real phenomenon. Sociologist Scott L. Feld first noticed this phenomenon.

___________ relates to the paradox of black holes being able to possibly destroy information.

This paradox violates the tenet of science that energy cannot be destroyed. Calculations suggest that physical information can permanently vanish within a black hole.

Which paradox asks "If a male barber shaves only men who don't shave themselves, does he shave his own face?"

This is not exactly a true paradox, but has been considered and criticized throughout history and literature. It is a puzzle derived from Russell's paradox.

Which paradox involves putting in and removing an infinite number of balls from a vase?

In this hypothetical abstract mathematics problem, out of an infinite number of balls, 10 are added to a vase and 1 is removed repeatedly. It then asks how many balls are in the vase when the task is finished.

Which paradox states that there is no true defined length of any coastline?

Length is based on the scale and units used, meaning that coastlines could have varied lengths depending on the measurement system used. This phenomenon was first observed by Lewis Fry Richardson.

___________ is illustrated with the use of a hypothetical donkey, who starves to death when he is placed an equal distance from both food and water while equally hungry and thirsty.

This paradox is named after 14th century French philosopher Jean Buridan. It deals with a person impossibly stuck between two equally sound outcomes, without any reason for preference.

Which paradox states that even choosing a method by which to solve a problem is a problem in itself?

As different decision-making methods yield different results, choosing the right one is in itself an issue. This paradox is a part of Decision Theory.

Which paradox describes the belief that people dislike Congress as a whole, but support their local congressman?

Fenno's Paradox describes a Decision Theory Paradox where US citizens distrust Congress but like their own congressman. It is named for political scientist Richard Fenno.

________ states that the more similar two choices are, the longer it will take a person to decide.

This idea was proposed by Edward Fredkin. It states that it is the hardest to choose between two equally attractive alternatives, which causes decision-makers to spend more time on less important decisions.

Which of these suggests that human intimacy cannot happen with mutual pain?

This paradox is a metaphor about the pitfalls and struggles of emotional connection. It involves a group of hedgehogs want to huddle for warmth in the cold, but can't do so without hurting each other with their pointy spines. While they want to be close to each other, this cannot happen without pain due to circumstances beyond their control.

_________ describes a fallacy in which two observations are used incorrectly to support an answer.

Morton's Fork is a false dilemma, which means that something is presented as an either/or situation when there is a reality of multiple options. It was originally used by 15th Century Archbishop of Canterbury John Morton to defend taxing both the poor and rich using illogical statements.

Which paradox asks: How do you play a game against an all-knowing opponent?

Newcomb's Paradox was devised by William Newcomb, and to this day it is highly debated within decision theory. It's a thought experiment in which one player plays a game against an all-knowing player.

Which paradox asks: Should intolerance be tolerated even if it destroys the possibility of tolerance?

This decision theory paradox was first described by Karl Popper. It states that a society that is completely tolerant will eventually be overtaken by intolerance. In order for any kind of tolerance to exist in a society, it must not tolerate intolerance.

___________ explores how two people might not work together, even if doing so would benefit both of them.

This dilemma has numerous examples throughout the human and natural world. One of the most common is in sports, where abstaining from steroids and other performance-enhancing drugs benefits everyone, but athletes have still taken them anyway. If steroids became the norm, all athletes would suffer the dangerous health consequences of taking them without actually gaining an edge.

Which paradox asks: What occurs when an unstoppable force hits an immovable object?

This paradox involves a pair of contradictory things which could not exist in the same universe. It is also known as the Shield and Spear Paradox.

Which paradox states that an archer must not aim straight at their target in order to hit it?

This phenomenon describes the bending of an arrow under pressure before it's shot. It was first used by E.J. REndtroff in 1913.

_________ describes the movement of tea leaves.

Albert Einstein actually solved the paradox and the forces behind what was considered a strange phenomenon until 1926. In it tea leaves in a stirred cup of tea gather in the center, even though the centrifugal force is expected to push them out.

Which paradox states that gravity should pull all matter into one point?

This paradox states that in a Newtonian Universe, gravitation should pull all matter into one point. This cosmological paradox was written in a letter from Isaac Newton to Cambridge Philosopher Richard Bentley, who attempted to solve the paradox by claiming that God was preventing the collapse of matter.

Which paradox involves a group of people coming to a decision which makes no one happy while trying to avoid upsetting anyone.

Abilene Paradox is part of decision theory. It describes a breakdown in group communication in which people ignore what they want to do in favor of appeasing a group, and end up, as a group, coming to a decision in which no one is satisfied.

_____________ suggests that policies to limit future CO2 emissions may lead to more emissions right now.

German economist Hans-Werner Sinn noticed this paradox. As policies slowly get greener over time, it inspires the owners of fossil fuel resources to extract and take advantage of all they can before their product becomes obsolete, which causes society's shift toward eco-friendliness to inspire fossil fuel owners to accelerate global warming.

__________ is a phenomenon where a trend that appears in different groups of data vanishes or switches when the groups are combined.

This is a paradox in both probability and statistics. An example is the Low birth-weight paradox, in which low birth weight babies born to mothers who smoke tobacco have a lower infant death rate than low birth-weight babies born to non-smoking mothers.

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