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Truth Classification

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Capsule of the Day

DebunkedThe PolygraphThe instrument popularly called a lie detector, which records breathing, blood pressure, pulse and skin conductance dur…

New in the Library

  • FactTardigrade
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The library

Capsules

1,028 capsules, each one classified by the strength of its evidence.

All1,028Fact599Proven130Theory89Hypothesis71Contested90Debunked48
geography236biology88physics67history54medicine45astronomy33psychology26mathematics26chemistry20engineering20astrophysics19neuroscience19anthropology18art18

Trending now

Most recent activity

Factmedia studies

Radio

Communication using electromagnetic waves without a conductor between sender and receiver. It was the first medium to reach a mass audience simultaneously, and it remains the…

by Capsule · Aug 5, 2026
Factgeography

Selkirk

Selkirk is a city on the Red River about twenty-two kilometres northeast of Winnipeg, with 10,504 residents at the 2021 census. It came close to being the site of the…

by Capsule · Aug 7, 2026
Factbiology

Monarch Butterfly

The monarch, Danaus plexippus, is a large orange and black butterfly of the Americas, and the migratory population of eastern North America performs a journey no individual…

by Capsule · Aug 7, 2026
Fact

Browse all

Showing 321 to 340 of 1,028

NewestMost votedA to Z
neuroscience
Hypothesis

The Free Energy Principle

Karl Friston's proposal that everything a brain does, and arguably everything any self-organising system does, can be described as minimising a…

byCapsule
economics

Accounting

The systematic recording and reporting of financial activity. Double-entry bookkeeping is among the more consequential inventions in the history of commerce, and the reason is…

by Capsule · Aug 5, 2026
Facteducation

Libraries

Organised collections of recorded knowledge, held for use. Libraries are older than most of the writing systems that survive, their defining problem has always been finding rather…

by Capsule · Aug 5, 2026
Factnutrition

Salt

Sodium chloride. It is physiologically essential, it was the only reliable food preservative for most of history, and its scarcity relative to demand made it a strategic commodity…

by Capsule · Aug 5, 2026
Fact· Empirical

Selkirk

Selkirk is a city on the Red River about twenty-two kilometres northeast of Winnipeg, with 10,504 residents at the 2021 census. It came close to…

byCapsule0 votes0 reviewsAug 7, 2026
Fact· Empirical

Monarch Butterfly

The monarch, Danaus plexippus, is a large orange and black butterfly of the Americas, and the migratory population of eastern North America performs…

byCapsule0 votes0 reviewsAug 7, 2026

Also new

More from the last few days

agriculture
Fact

Livestock

Domesticated animals kept for food, fibre, labour and other products. Livestock made agriculture viable on land that grows no crops, and they are now…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Winnipeg

Winnipeg is the capital and largest city of the Canadian province of Manitoba, built where the Red and Assiniboine rivers meet near the longitudinal…

byCapsule0 votes0 reviews
epidemiology
Fact

Sanitation

The safe management of human waste. It has saved more lives than any medical treatment, it is the least discussed of the major public health…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Seahorse

Seahorses are small marine fish of the genus Hippocampus, around fifty species, distinguished by an upright posture, a prehensile tail, a tubular…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Common Raven

The common raven, Corvus corax, is the largest songbird in the world and among the most widely distributed birds on Earth, occupying the whole…

byCapsule0 votes0 reviews
medicine
Fact

Surgery

Treatment by physical intervention in the body. Surgery was limited for millennia not by knowledge of anatomy but by three specific obstacles, and…

byCapsule0 votes0 reviews
agriculture
Fact

Fishing

Catching aquatic animals for food. It is the last major food source still taken from the wild at scale, which is precisely why it is the one where…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Flin Flon

Flin Flon is a mining city on the Manitoba and Saskatchewan boundary, about 630 kilometres northwest of Winnipeg, built directly on the rock of the…

byCapsule0 votes0 reviews

On this day

A birth or event with an anniversary today

history
Fact· Empirical

Statue of Liberty

The Statue of Liberty is a colossal copper statue on an island in New York Harbor, one of the most famous monuments in the United States and a…

byCapsule0 votes0 reviews

Settled science

Verified facts and proven results

See all
astronomy
Fact· Empirical

The Solar System

The Solar System is the Sun and everything bound to it by gravity: eight planets, several dwarf planets, scores of moons, and countless smaller…

byCapsule0 votes0 reviews
history
Fact· Empirical

The Colosseum

The Colosseum is a giant amphitheatre in the centre of Rome, the largest ever built and one of the most recognisable monuments of the ancient world.…

byCapsule0 votes0 reviews
physics
Fact

Gravity

Gravity is the universal attractive interaction between masses, described at low energy by Newton's law of universal gravitation and at all energies…

byCapsule0 votes0 reviews
agriculture
Fact

Traditional Yoruba Agricultural Practices in Southwestern Nigeria

The Yoruba people of southwestern Nigeria developed sophisticated agricultural systems over centuries that integrated intercropping, seasonal…

byCapsule0 votes0 reviews
astronomy
Fact· Empirical

The Moon

The Moon is Earth's only natural satellite and the brightest object in our night sky. Large in proportion to its planet and close enough to study…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Amazon Rainforest

The Amazon Rainforest is the largest tropical rainforest on Earth, a vast sea of green covering some 5.5 million square kilometres across nine South…

byCapsule0 votes0 reviews
history
Fact· Empirical

Great Wall of China

The Great Wall of China is not a single wall but a vast, discontinuous system of fortifications, walls, watchtowers, garrisons, and beacon towers,…

byCapsule0 votes0 reviews
astronomy
Fact· Empirical

Black Hole

A black hole is a region of space where gravity is so intense that nothing, not even light, can escape once it passes a certain boundary. They are…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Grand Canyon

The Grand Canyon is one of the most spectacular landscapes on Earth: an immense gorge carved by the Colorado River through the high plateau of…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Domestic Cat

The domestic cat, Felis catus, is the most numerous small carnivore on Earth, with something over six hundred million individuals. It is also barely…

byCapsule0 votes0 reviews
agriculture
Fact

Nitrogen Cycling in Prairie Soils of the Canadian Prairies

Nitrogen cycling in Prairie soils is a well-documented biological and chemical process that determines agricultural productivity across Manitoba,…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Canada

Canada is a country in North America, the second-largest in the world by total area, stretching from the Atlantic Ocean in the east to the Pacific in…

byCapsule0 votes0 reviews

Open questions

Hypotheses under investigation and ideas still debated

See all
astronomy
Hypothesis

Planet Nine

Planet Nine is a hypothetical large planet proposed to exist in the far outer reaches of our Solar System, well beyond Neptune and Pluto. It has…

byCapsule0 votes0 reviews
astrophysics
Contested

Dark Energy

Dark energy is the name given to an unknown influence that appears to be driving the expansion of the universe to speed up over time. It is thought…

byCapsule0 votes0 reviews
psychology
Contested

Nature versus Nurture

The nature versus nurture debate asks how much of who we are, our intelligence, personality, talents, and behavior, comes from our genes, and how…

byCapsule0 votes0 reviews
physics
Contested

The Multiverse

The multiverse is the hypothesis that our universe is only one of many, perhaps even infinitely many, other universes. It is taken seriously by many…

byCapsule0 votes0 reviews
astronomy
Contested

The Fermi Paradox

The Fermi paradox is the puzzling contrast between the high apparent likelihood that alien civilizations exist somewhere in our vast galaxy and the…

byCapsule0 votes0 reviews
mathematics
Hypothesis

Goldbach's Conjecture

Goldbach's conjecture is one of the oldest and simplest sounding unsolved problems in mathematics. It states that every even whole number greater…

byCapsule0 votes0 reviews
astrophysics
Contested

How the Universe Will End

The ultimate fate of the universe is one of the deepest questions in science. Cosmologists have proposed several very different endings, and which…

byCapsule0 votes0 reviews
neuroscience
Contested

The Hard Problem of Consciousness

The hard problem of consciousness is the question of why and how physical processes in the brain give rise to subjective experience, the felt quality…

byCapsule0 votes0 reviews
earth science
Contested

What Causes the Ice Ages

Throughout its history, the Earth has repeatedly cooled into ice ages, when vast sheets of ice spread across the continents, and warmed again between…

byCapsule0 votes0 reviews
philosophy
Hypothesis

The Simulation Hypothesis

The simulation hypothesis is the proposal that the reality we experience might actually be an artificial simulation, such as an immensely…

byCapsule0 votes0 reviews
psychology
Contested

The Origin of Language

How human language first arose is one of the hardest questions in science. That we alone among animals possess full language is clear; when, how, and…

byCapsule0 votes0 reviews
earth science
Contested

What Killed the Dinosaurs

Around sixty six million years ago, the dinosaurs and many other forms of life suddenly vanished in one of the great mass extinctions in Earth's…

byCapsule0 votes0 reviews

Debunked

Claims the evidence overturned

See all
neuroscience
Debunked

Phrenology

Phrenology was a popular nineteenth century practice that claimed a person's character and mental abilities could be read from the shape and bumps of…

byCapsule0 votes0 reviews
geology
Debunked

The Expanding Earth

The expanding Earth was a hypothesis, taken seriously by some scientists into the twentieth century, which claimed that the planet is steadily…

byCapsule0 votes0 reviews
astronomy
Debunked

The Martian Canals

The Martian canals were a network of fine, straight lines that some astronomers in the late nineteenth and early twentieth centuries believed they…

byCapsule0 votes0 reviews
history
Debunked

Piltdown Man

Piltdown Man was a supposed "missing link" between apes and humans, announced in 1912 from fossil fragments found in England. For decades it misled…

byCapsule0 votes0 reviews
nutrition
Debunked

Breakfast as the Most Important Meal

The claim that eating breakfast is necessary for health and weight control, and that skipping it causes weight gain. The phrase was popularised by…

byCapsule0 votes0 reviews
medicine
Debunked

Bloodletting

Bloodletting was the practice of deliberately draining blood from a patient to cure or prevent illness. For more than two thousand years it was one…

byCapsule0 votes0 reviews
medicine
Debunked

Miasma Theory

Miasma theory was the belief that diseases such as cholera and the plague were caused by "bad air," a poisonous vapor thought to rise from rotting…

byCapsule0 votes0 reviews
history
Debunked

Astrology

Astrology is the belief that the positions of the Sun, Moon, planets, and stars influence human affairs and personalities, and that they can be used…

byCapsule0 votes0 reviews
history
Debunked

Alchemy

Alchemy was an ancient and medieval practice that sought to transform base metals such as lead into gold, to discover a universal cure for disease,…

byCapsule0 votes0 reviews
astronomy
Debunked

The Geocentric Model

The geocentric model was the ancient belief that the Earth sits motionless at the center of the universe, with the Sun, Moon, planets, and stars all…

byCapsule0 votes0 reviews
biology
Debunked

Vitalism

Vitalism was the long held belief that living things contain a special, non physical "vital force" or "life energy" that animates them and that…

byCapsule0 votes0 reviews
music
Debunked

The Mozart Effect

The claim that listening to Mozart makes people, and especially babies, more intelligent. It came from one small study whose actual finding was far…

byCapsule0 votes0 reviews

Theories explained

Well substantiated explanations of how things work

See all
medicine
Theory· Scientific

Germ Theory of Disease

The germ theory of disease is the scientific theory that many illnesses are caused by microorganisms, living agents too small to see, that invade the…

byCapsule0 votes0 reviews
mathematics
Theory

Graph Theory

Graph theory is the branch of mathematics that studies networks of connected objects. A graph is simply a collection of points, called vertices,…

byCapsule0 votes0 reviews
geology
Theory

Uniformitarianism

Uniformitarianism is the foundational principle of geology: that the same natural processes we observe today, such as erosion, sedimentation, and…

byCapsule0 votes0 reviews
physics
Theory

Thermodynamics

Thermodynamics is the branch of physics concerned with heat, energy, and work, and how they transform from one form to another. Its laws are among…

byCapsule0 votes0 reviews
biology
Theory· Scientific

Evolution by Natural Selection

Evolution by natural selection is the scientific theory that explains how the diversity of life arose and continues to change. It holds that…

byCapsule0 votes0 reviews
mathematics
Theory

Set Theory

Set theory is the branch of mathematics that studies collections of objects, called sets. Though it begins with an idea as simple as grouping things…

byCapsule0 votes0 reviews
astrophysics
Theory

Stellar Evolution

Stellar evolution is the scientific account of how stars are born, live, and die over millions or billions of years. Though no one can watch a single…

byCapsule0 votes0 reviews
earth science
Theory· Scientific

Plate Tectonics

Plate tectonics is the scientific theory that Earth's outer shell is broken into a set of large, rigid plates that drift slowly over the hotter,…

byCapsule0 votes0 reviews
mathematics
Theory· Mathematical

Game Theory

Game theory is the mathematical study of strategic decision making, where the outcome for each participant depends not only on their own choice but…

byCapsule0 votes0 reviews
physics
Theory

Electromagnetism

Electromagnetism is the branch of physics that describes the forces between electric charges and the deep connection between electricity and…

byCapsule0 votes0 reviews
astronomy
Theory· Scientific

The Big Bang

The Big Bang is the prevailing cosmological theory of how the universe began. It holds that the universe started about 13.8 billion years ago in an…

byCapsule0 votes0 reviews
physics
Theory· Scientific

General Relativity

General relativity is Albert Einstein's theory of gravity, published in 1915. It reimagines gravity not as a force pulling objects together but as…

byCapsule0 votes0 reviews
0 votes0 reviews
neuroscience
Hypothesis

The Glymphatic System

The proposal that the brain flushes waste through a network of fluid-filled channels, and that the flushing happens mainly during sleep. It was…

byCapsule0 votes0 reviews
earth science
Hypothesis

The Faint Young Sun Paradox

The Sun was about thirty percent dimmer when the Earth was young, which should have left the planet frozen solid. The geological record shows liquid…

byCapsule0 votes0 reviews
astronomy
Hypothesis

The Giant-Impact Hypothesis

The proposal that the Moon formed from debris thrown off when a Mars-sized body struck the early Earth. It is the standard account, it explains most…

byCapsule0 votes0 reviews
biology
Proven

Circadian Rhythms

Almost every organism runs an internal clock with a period of about a day, generated by a molecular feedback loop inside individual cells. It runs…

byCapsule0 votes0 reviews
biotechnology
Proven

The Polymerase Chain Reaction

A method for making billions of copies of a chosen stretch of DNA from a starting sample too small to work with. It made genetic testing, forensic…

byCapsule0 votes0 reviews
molecular biology
Proven

DNA Replication

Copying a genome of three billion letters, at a final error rate of about one in a billion, in a few hours, every time a cell divides. The mechanism…

byCapsule0 votes0 reviews
mathematics
Proven

Non-Euclidean Geometry

For two thousand years one of Euclid's assumptions looked like it should be provable from the others. It is not. Denying it produces consistent…

byCapsule0 votes0 reviews
mathematics
Proven

Bayes' Theorem

A rule for updating a belief when new evidence arrives. It is a short piece of algebra, it is not in any dispute, and misapplying it produces some of…

byCapsule0 votes0 reviews
mathematics
Proven

The Fourier Transform

Any signal can be decomposed into a sum of pure sine waves of different frequencies. The claim was disbelieved when made, it is one of the most…

byCapsule0 votes0 reviews
physics
Proven

The Hall Effect

Pass a current through a conductor in a magnetic field and a voltage appears across it, perpendicular to both. Discovered by a graduate student in…

byCapsule0 votes0 reviews
physics
Proven

The Ideal Gas Law

One equation relating the pressure, volume, temperature and quantity of a gas. It is an approximation that no real gas obeys exactly, it is accurate…

byCapsule0 votes0 reviews
microbiology
Proven

Pasteurisation

Heating a liquid to a controlled temperature for a controlled time kills enough pathogens to make it safe without destroying it. It is among the most…

byCapsule0 votes0 reviews
physics
Hypothesis

Loop Quantum Gravity

An attempt to make gravity quantum by quantising spacetime itself, producing a picture in which space is granular and area and volume come in…

byCapsule0 votes0 reviews
physics
Hypothesis

The Holographic Principle

The proposal that everything happening inside a region of space can be fully described by information stored on its boundary, so that a volume of…

byCapsule0 votes0 reviews
medicine
Hypothesis

The Cancer Stem Cell Hypothesis

The proposal that tumours are sustained by a small subpopulation of cells with stem-like properties, and that killing the bulk of a tumour without…

byCapsule0 votes0 reviews
medicine
Hypothesis

The Gut-Brain Axis

The proposal that gut microbes influence mood, behaviour and neurological disease, and that altering them could treat psychiatric and…

byCapsule0 votes0 reviews
medicine
Hypothesis

The Dopamine Hypothesis of Schizophrenia

The proposal that psychosis results from excess dopamine signalling. It has organised psychiatry for sixty years, it was inferred backwards from…

byCapsule0 votes0 reviews
anthropology
Hypothesis

The Cooking Hypothesis

Richard Wrangham's proposal that cooking made humans human: that controlling fire and processing food with it supplied the energy for a large brain,…

byCapsule0 votes0 reviews
biology
Hypothesis

Viral Eukaryogenesis

The proposal that the cell nucleus originated as a large DNA virus that took up permanent residence in an ancestral cell. It is a minority position…

byCapsule0 votes0 reviews
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