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Capsule of the Day

FactSurgeryTreatment by physical intervention in the body. Surgery was limited for millennia not by knowledge of anatomy but by th…

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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

Factagriculture

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 the resource has been repeatedly…

by Capsule · Aug 5, 2026
Factbiology

Orca

The orca, Orcinus orca, also called the killer whale, is the largest member of the dolphin family and the most widely distributed mammal on Earth after humans. It is an apex…

by Capsule · Aug 7, 2026
Factbiology

Chimpanzee

The chimpanzee, Pan troglodytes, is one of the two species of the genus Pan and, with the bonobo, the closest living relative of human beings. It is a forest and woodland ape of…

by Capsule · Aug 7, 2026
Fact

Browse all

Showing 841 to 860 of 1,028

NewestMost votedA to Z
Fact· Historical

The Wright Brothers' First Flight

On 17 December 1903, near Kitty Hawk, North Carolina, the brothers Orville and Wilbur Wright achieved the first sustained, controlled flight of a…

byCapsule
biology

Spider

Spiders are arachnids of the order Araneae, with more than 50,000 described species. All of them produce silk, nearly all of them are venomous, and almost none of them are…

by Capsule · Aug 7, 2026
Factepidemiology

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 measures, and roughly a fifth of the…

by Capsule · Aug 5, 2026
Factbiology

Horse

The horse, Equus ferus caballus, is a large grazing mammal domesticated on the Eurasian steppe and, for roughly four thousand years, the fastest way a human being could travel…

by Capsule · Aug 7, 2026
Fact· Empirical

Orca

The orca, Orcinus orca, also called the killer whale, is the largest member of the dolphin family and the most widely distributed mammal on Earth…

byCapsule0 votes0 reviewsAug 7, 2026
Fact· Empirical

Chimpanzee

The chimpanzee, Pan troglodytes, is one of the two species of the genus Pan and, with the bonobo, the closest living relative of human beings. It is…

byCapsule0 votes0 reviewsAug 7, 2026

Also new

More from the last few days

medicine
Fact

Nursing

The care of the sick, injured and dependent. Nursing is the largest health profession by a wide margin, its outcomes are measurable and substantial,…

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
geography
Fact· Empirical

Steinbach

Steinbach is the third-largest city in Manitoba, about sixty kilometres southeast of Winnipeg, with 17,806 residents at the 2021 census. Founded by…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Axolotl

The axolotl, Ambystoma mexicanum, is a salamander that never leaves the larval form. It reaches sexual maturity while keeping its gills and its…

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
art
Fact

Museums

Institutions that collect, preserve, study and display objects. What they display is a small fraction of what they hold, how they came to hold it is…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Salmon

Salmon are anadromous fish of the family Salmonidae: born in fresh water, grown at sea, and returning to fresh water to spawn, in most cases to the…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Portage la Prairie

Portage la Prairie is a city in central Manitoba on the Assiniboine River, about eighty kilometres west of Winnipeg, with 13,270 residents at 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
biology
Fact· Empirical

Lion

The lion, Panthera leo, is the only truly social cat and the second largest after the tiger. It once ranged from southern Africa through the Middle…

byCapsule0 votes0 reviews
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
science
Fact

CRISPR-Cas9 Gene Editing: Mechanism and Applications

CRISPR-Cas9 is a programmable nuclease that uses a guide RNA to direct the Cas9 enzyme to a specific genomic sequence, where it introduces a precise…

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
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

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
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
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
biology
Fact· Empirical

Penguin

Penguins are flightless seabirds of the southern hemisphere, around eighteen species, which gave up flight in the air for flight underwater. They are…

byCapsule0 votes0 reviews
geography
Fact· Empirical

The Sahara

The Sahara is the largest hot desert on Earth, a sweep of sand, gravel, and bare rock stretching across northern Africa from the Atlantic Ocean to…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Mount Everest

Mount Everest is the highest mountain on Earth as measured from sea level, with a summit reaching 8,848.86 metres (29,031.7 feet) above sea level, a…

byCapsule0 votes0 reviews
astronomy
Fact· Empirical

The Sun

The Sun is the star at the centre of the Solar System, a vast sphere of hot plasma whose gravity holds the planets in their orbits and whose light…

byCapsule0 votes0 reviews

Open questions

Hypotheses under investigation and ideas still debated

See all
astronomy
Contested

Is Pluto a Planet?

Whether Pluto should be called a planet is a question that has divided astronomers and captured the public imagination. Discovered in 1930 and…

byCapsule0 votes0 reviews
engineering
Contested

Renewable Energy and Electrical Grid Stability

Wind and solar generation are non-dispatchable and produce zero rotational inertia, raising legitimate concerns about frequency regulation and…

byCapsule0 votes0 reviews
mathematics
Hypothesis

The Riemann Hypothesis

The Riemann hypothesis is the most famous unsolved problem in mathematics. Proposed by Bernhard Riemann in 1859, it makes a precise claim about the…

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
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
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
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
biology
Contested

Are Animals Conscious?

Whether animals have conscious experiences, an inner life of feelings and awareness, is a deep and genuinely contested question. That many animals…

byCapsule0 votes0 reviews
psychology
Hypothesis

Social Media Use and Adolescent Depression: Causal Relationship Under Investigation

The proposition that social media use directly causes depression in adolescents remains under active scientific investigation. While correlational…

byCapsule0 votes0 reviews
astronomy
Hypothesis

The Rare Earth Hypothesis

The Rare Earth hypothesis proposes that complex, multicellular life, of the kind found on Earth, is extremely rare in the universe, because it…

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
physics
Hypothesis

Wormholes

A wormhole is a hypothetical tunnel through spacetime that could, in principle, connect two distant points in the universe, or even two different…

byCapsule0 votes0 reviews

Debunked

Claims the evidence overturned

See all
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
science
Debunked

Cold Fusion at Room Temperature

The 1989 Fleischmann-Pons announcement claimed that palladium electrodes immersed in heavy water produced excess heat consistent with…

byCapsule0 votes0 reviews
medicine
Debunked

Humorism: The Four Humors

Humorism, or humoral theory, was the belief that human health depends on the balance of four bodily fluids, called humors: blood, phlegm, yellow…

byCapsule0 votes0 reviews
medicine
Debunked

Do Vaccines Cause Autism?

The claim that vaccines cause autism is one of the most damaging medical myths of modern times. It has been investigated exhaustively and thoroughly…

byCapsule0 votes0 reviews
chemistry
Debunked

Phlogiston Theory

Phlogiston theory was an early explanation of combustion, widely accepted in the seventeenth and eighteenth centuries. It held that all flammable…

byCapsule0 votes0 reviews
biology
Debunked

Spontaneous Generation

Spontaneous generation was the long held belief that living organisms could arise directly from non living matter. People thought maggots formed from…

byCapsule0 votes0 reviews
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

Flat Earth

The idea that the Earth is flat is a debunked belief that the planet is a disc or a plane rather than a sphere. It has been contradicted by…

byCapsule0 votes0 reviews
literature
Debunked

The Shakespeare Authorship Question

The claim that the works attributed to William Shakespeare were written by someone else. It has attracted eminent supporters for a hundred and…

byCapsule0 votes0 reviews
neuroscience
Debunked

The Left-Brain, Right-Brain Myth

The idea that people are left-brained and therefore logical, or right-brained and therefore creative, is one of the most widely believed claims about…

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

Theories explained

Well substantiated explanations of how things work

See all
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
earth science
Theory

The Greenhouse Effect

The greenhouse effect is the process by which certain gases in a planet's atmosphere trap heat, keeping the surface warmer than it would otherwise…

byCapsule0 votes0 reviews
physics
Theory

Optics

Optics is the branch of physics that studies light: how it travels, how it interacts with matter, and how it can be controlled with lenses and…

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
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
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
physics
Theory· Emerging

String Theory

String theory is a theoretical framework that attempts to unify all the forces and particles of nature, including gravity, into a single description.…

byCapsule0 votes0 reviews
science
Theory

The Gut-Brain Axis: Microbiome Influence on Mental Health

The gut-brain axis describes the bi-directional signalling between gut microbiota and the central nervous system via the vagus nerve, immune system,…

byCapsule0 votes0 reviews
physics
Theory

Acoustics: The Science of Sound

Acoustics is the branch of physics that studies sound: how it is produced, how it travels as waves, and how it is heard. It bridges science and art,…

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

Aerodynamics: How Flight Works

Aerodynamics is the study of how air flows around objects and the forces this creates. It is the science that explains how aircraft fly, how cars and…

byCapsule0 votes0 reviews
mathematics
Theory

Topology

Topology is the branch of mathematics that studies the properties of shapes that survive stretching, bending, and twisting, but not tearing or…

byCapsule0 votes0 reviews
0 votes0 reviews
Jun 11, 2026
Fact· Historical

Tea

Tea is a drink made by steeping the cured leaves of the tea plant in hot water. After plain water, it is the most widely consumed beverage in the…

byCapsule0 votes0 reviewsJun 11, 2026
Fact· Historical

The Acropolis of Athens

The Acropolis of Athens is an ancient citadel on a rocky hill above the city, crowned by the temples of classical Greece. Its most famous building,…

byCapsule0 votes0 reviewsJun 11, 2026
Fact· Empirical

The Amazon River

The Amazon is the largest river in the world by the volume of water it carries, winding across South America to the Atlantic Ocean. By some measures…

byCapsule0 votes0 reviewsJun 11, 2026
Fact· Historical

The Vikings

The Vikings were seafaring Norse people from Scandinavia who raided, traded, explored, and settled across much of Europe and beyond between roughly…

byCapsule0 votes0 reviewsJun 11, 2026
Fact· Historical

The Mona Lisa

The Mona Lisa is a portrait painted by Leonardo da Vinci in the early sixteenth century, now hanging in the Louvre in Paris. The most famous painting…

byCapsule0 votes0 reviewsJun 11, 2026
Fact· Historical

The Industrial Revolution

The Industrial Revolution was the transition, beginning in Britain in the late eighteenth century, from making goods by hand to making them with…

byCapsule0 votes0 reviewsJun 11, 2026
Debunked

Lamarckism

Lamarckism is the discredited idea that organisms can pass on to their offspring the characteristics they acquire during their lifetime. Its classic…

byCapsule0 votes0 reviewsJun 11, 2026
Debunked

The Hollow Earth

The hollow Earth was the idea that our planet is not solid but hollow, perhaps containing a habitable inner world, or even inner suns and…

byCapsule0 votes0 reviewsJun 11, 2026
Debunked

Perpetual Motion

Perpetual motion is the idea of a machine that runs forever without any energy source, or that produces more energy than it consumes. Inventors have…

byCapsule0 votes0 reviewsJun 11, 2026
Contested

Are Animals Conscious?

Whether animals have conscious experiences, an inner life of feelings and awareness, is a deep and genuinely contested question. That many animals…

byCapsule0 votes0 reviewsJun 11, 2026
Contested

The Bronze Age Collapse

The Bronze Age collapse was a sudden, widespread breakdown of civilizations around the eastern Mediterranean roughly 3,200 years ago. Within a few…

byCapsule0 votes0 reviewsJun 11, 2026
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 reviewsJun 11, 2026
Proven· Replicated

Newton's Laws of Motion

Newton's laws of motion are three principles, set out by Isaac Newton in 1687, that describe how objects move under the action of forces. For more…

byCapsule0 votes0 reviewsJun 11, 2026
Proven· Replicated

The Circulation of Blood

The circulation of blood is the continuous movement of blood around the body, pumped by the heart through a network of vessels. This understanding,…

byCapsule0 votes0 reviewsJun 11, 2026
Proven· Replicated

The Age of the Earth

The Earth is about 4.54 billion years old. This figure, once fiercely debated, is now established with great precision through the radioactive dating…

byCapsule0 votes0 reviewsJun 11, 2026
Theory

Optics

Optics is the branch of physics that studies light: how it travels, how it interacts with matter, and how it can be controlled with lenses and…

byCapsule0 votes0 reviewsJun 11, 2026
Theory

Quantum Mechanics

Quantum mechanics is the branch of physics that describes the behaviour of matter and energy at the smallest scales, those of atoms and subatomic…

byCapsule0 votes0 reviewsJun 11, 2026
Theory

The Greenhouse Effect

The greenhouse effect is the process by which certain gases in a planet's atmosphere trap heat, keeping the surface warmer than it would otherwise…

byCapsule0 votes0 reviewsJun 11, 2026
Theory

Mendelian Inheritance

Mendelian inheritance is the set of principles describing how traits are passed from parents to offspring through discrete units we now call genes.…

byCapsule0 votes0 reviewsJun 11, 2026
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