Explore Paradoxes

If you replace all parts of a ship, is it still the same ship?

When does a heap of sand stop being a heap?

Does a green apple prove that all ravens are black?

Should you sacrifice one to save five?

Can an omnipotent being create a stone it cannot lift?

Where is everybody?

Why is the night sky dark?

Is the cat dead and alive at the same time?

What if you killed your grandfather before he met your grandmother?

Spooky action at a distance?

The set of all sets that don't contain themselves

This statement is false

You can decompose a ball into two identical balls

A fully booked infinite hotel can still accommodate new guests

Motion is impossible because you must cross infinite points

The barber shaves all who don't shave themselves

Individual rationality leads to collective irrationality

Should you take one box or two when a predictor knows your choice?

Seeking pleasure directly often prevents you from attaining it

More choices lead to less satisfaction

A judge says you'll be hanged on a day you don't expect

Increased efficiency leads to increased consumption

Unlimited tolerance must lead to the disappearance of tolerance

Individual rational behavior depletes shared resources

No perfect voting system exists

Adding roads can increase traffic

Collective preferences can be circular even when individual preferences are rational

Information or objects exist without ever being created

Are we living in a computer simulation?

Statistical reasoning suggests humanity will end sooner than we think

There are as many perfect squares as there are natural numbers

If this sentence is true, then Santa Claus exists

A donkey starves between two identical bales of hay

A microscopic being that violates the second law of thermodynamics

How many hairs must you lose to be bald?

What happens when an unstoppable force meets an immovable object?

The universe appears fine-tuned for our existence

No local hidden variable theory can reproduce quantum mechanics

Is the word 'heterological' heterological?

If the universe is deterministic, the future is knowable

Should you always switch envelopes?

Should you switch doors?

A family has two children, one is a boy. What's the probability the other is a boy?

What credence should you give to a coin flip when awakened?

What's the probability a random chord is longer than the triangle side?

23 people have a 50% chance of sharing a birthday

A trend appears in groups but reverses when combined

Selection bias creates spurious negative correlations

A highly accurate test can still be wrong most of the time

Moving items between groups can raise both averages

The length of a coastline depends on how you measure it

An infinite surface area can enclose a finite volume

100 kg of potatoes at 99% water becomes 50 kg at 98% water

Three guests pay $30, but the math doesn't add up

If a number is uninteresting, that makes it interesting

The smallest number not definable in under eleven words

Defining a number using a definition that should include itself

Some infinities are bigger than others

You can turn a sphere inside out

A surface with no inside or outside

A surface with only one side and one edge

Your friends have more friends than you do

You're rewarded for intending to drink poison but you shouldn't actually drink it

Can you intend to do something you know is irrational?

Why do we have emotional responses to things we know aren't real?

Why do we enjoy experiencing negative emotions through art?

Why do we enjoy being scared by horror fiction?

It's raining but I don't believe it

Authors believe their book contains errors, yet believe each claim

You believe each ticket will lose, but one must win

If all truths are knowable, then all truths are known

All emeralds observed before 2050 are 'grue' (green before 2050, blue after)

Justified true belief is not sufficient for knowledge

Is something good because God commands it, or does God command it because it's good?

How can an all-powerful, all-good God allow evil?

What happens to information that falls into a black hole?

A traveling twin ages slower than their Earth-bound sibling

Does a thread break between two accelerating spaceships?

A long pole fits inside a shorter barn due to length contraction

Frequent observation prevents quantum systems from changing

Hot water can freeze faster than cold water

A water droplet lasts longer on a hotter surface

Hard problems for humans are easy for computers, and vice versa

Can a system that appears to understand actually lack understanding?

Can imitation of intelligence be equated with actual intelligence?

Can there be beings behaviorally identical to humans but without consciousness?

Why does physical processing give rise to subjective experience?

We overestimate success by focusing on survivors

A game with infinite expected value that no one would pay much to play

People violate expected utility theory in predictable ways

People prefer known probabilities over unknown ones

Demand increases when price increases

Luxury goods become more desirable when expensive

If everyone saves more, total savings may decrease

Rising income doesn't increase happiness beyond a point

Computers are everywhere except in productivity statistics

Water is essential but cheap; diamonds are useless but expensive

Enriching an ecosystem can destabilize it

Complex organisms don't have more genes

A self-referential paradox without direct self-reference

A Cretan says 'All Cretans are liars'

'Yields falsehood when preceded by its quotation' yields falsehood when preceded by its quotation

A card with text on both sides creates a paradox

Set theory proves uncountable sets exist, yet has a countable model

Adding and removing from an infinite set yields unclear results

A sphere can be decomposed into more spheres

A lamp switched infinitely many times - on or off?

A rotating disk appears to contract, creating geometric contradictions

Future measurements seem to affect past results

Mixing identical gases seems to change entropy

How does irreversible thermodynamics arise from reversible mechanics?

Relativistic quantum particles can tunnel through any barrier

Water pressure depends only on depth, not container shape

Ideal fluid flow predicts zero drag on objects

Ultra-high-energy cosmic rays exist beyond theoretical limits

Early Earth should have been frozen but wasn't

Proteins fold too quickly to try all conformations

Can an omniscient being know what it's like not to know something?

How can analysis be informative if correct?

How can you search for what you don't know?

Does complete physical knowledge include experiential knowledge?

How can we have free will in a deterministic or random universe?

Does nihilism self-destruct as a position?

Trying to hide information makes it more public

Solutions make problems worse

Luxury cosmetics sales increase during economic downturns

Good complaint resolution creates more loyal customers than no problems

Groups make decisions no individual member wants

Cohesive groups make worse decisions

Incompetent people overestimate their ability

Competent people feel like frauds

Everyone is above average

We adapt to positive changes and return to baseline happiness

The more similar two options, the more time spent deciding between them

Familiarity breeds liking, not contempt

Intense suffering is overcome faster than mild suffering

Groups can be smarter or dumber than individuals

We consistently underestimate how long tasks will take

People are terrible judges of their own abilities