Science

• 1. Introduction

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  Science is a systematic discipline that builds and organises knowledge as testable hypotheses and predictions about the universe. The earliest identifiable predecessors to it date to the Bronze Age, in Egypt and Mesopotamia, roughly 3000 to 1200 BCE. From there the thread runs through Greek natural philosophy, medieval scholarship, and a Scientific Revolution that began in the 16th century. Yet for most of that span, the word itself meant something else. There was no scientist. There was a natural philosopher, or a man of science. So how did a synonym for plain knowledge become a method that reshaped how humans understand reality? Who decided what counted as proof? And why do some people, even now, refuse to believe what science finds? The answers run from a Sumerian medical prescription to the first image of a black hole.

• 2. What Counts As Science

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  Natural science, social science, and formal science are the three major branches into which modern science is commonly divided. Natural science studies the physical world, splitting into life science and physical science, with physics, chemistry, astronomy, and earth science among its specialisms. Social science studies human behaviour and societies, spanning anthropology, economics, history, human geography, political science, psychology, and sociology. Formal science generates knowledge using formal systems, the abstract structures that infer theorems from axioms by fixed rules. Logic, mathematics, and theoretical computer science sit here, and they are treated as separate. They rely on deductive reasoning rather than the scientific method, which is why there is disagreement about whether they constitute science at all. Both natural and social sciences are empirical. Their knowledge rests on observations that other researchers can test under the same conditions. The formal sciences are a priori, needing no empirical evidence to verify their abstract concepts. Then there are the applied sciences, which use scientific knowledge for practical goals. Engineering invents, designs, and builds machines, structures, and technologies. Medicine maintains and restores health through prevention, diagnosis, and treatment. Calculus shows how the boundaries blur. It was first invented to understand motion in physics.

• 3. Before The Word

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  Women likely played a central role in prehistoric science, as did religious rituals. Science has no single origin. Scientific thinking emerged gradually over tens of thousands of years, taking different forms around the world, and few details survive about the earliest developments. Some scholars use the term protoscience for past activities that resemble modern science in some features but not all. That label has been criticised as denigrating, or too suggestive of presentism, judging the past only against modern categories. From the 3rd millennium BCE, the ancient Egyptians developed a non-positional decimal numbering system, solved practical problems with geometry, and built a calendar. Their healing therapies mixed drug treatments with the supernatural, including prayers, incantations, and rituals. Ancient Nubians pioneered early antibiotics and used a trigonometric methodology comparable to their Egyptian counterparts. The ancient Mesopotamians knew the properties of natural chemicals well enough to manufacture pottery, faience, glass, soap, metals, lime plaster, and waterproofing. They studied animal physiology, anatomy, and behaviour, and they read astrology for divinatory purposes. The earliest known medical prescriptions appeared in Sumerian during the Third Dynasty of Ur. These people studied subjects with practical or religious uses, and showed little interest in satisfying mere curiosity.

• 4. The Greek Turn

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  Thales of Miletus founded the Milesian school, and with his successors Anaximander and Anaximenes, was among the first to explain natural phenomena without relying on the supernatural. Before that, the same words described the natural way a plant grows and the way a tribe worships a god. Distinguishing nature from convention is part of why these men are called the first philosophers in the strict sense. Leucippus and his student Democritus developed the theory of atoms, indivisible particles, and Epicurus later built a full cosmology on atomism with a canon of physical standards for scientific truth. The Greek doctor Hippocrates founded the tradition of systematic medical science, earning the name The Father of Medicine. Socrates applied philosophy to human matters, including human nature, political communities, and knowledge itself. The Socratic method, documented in Plato's dialogues, is a dialectic of hypothesis elimination. Better hypotheses survive as those leading to contradictions are steadily removed. In the 3rd century BCE, the astronomer Aristarchus of Samos became the first to propose a heliocentric model, the Sun at the centre with the planets orbiting it. His model was widely rejected as a violation of the laws of physics. Ptolemy's Almagest, with its geocentric Solar System, was accepted instead, and it held through the early Renaissance.

• 5. Keeping The Flame

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  John Philoponus, a Byzantine scholar in the 6th century, began questioning Aristotle's physics and introduced the theory of impetus. Galileo Galilei would cite his works extensively ten centuries later. The collapse of the Western Roman Empire brought an intellectual decline in the 5th century, with Latin encyclopaedists such as Isidore of Seville preserving most general ancient knowledge as Greek conceptions faded in Western Europe. The Byzantine Empire, resisting its invaders, preserved and improved earlier learning, and Arabic translations of Greek texts were made by Christians, mainly Nestorians and Miaphysites. By the 6th and 7th centuries, the Sasanian Empire's medical Academy of Gondishapur was regarded by Greek, Syriac, and Persian physicians as the most important medical hub of the ancient world. The House of Wisdom in the Abbasid capital of Baghdad became a centre of Aristotelian study until the Mongol invasions of the 13th century. Ibn al-Haytham, known as Alhazen, used controlled experiments in his study of optics. Avicenna compiled The Canon of Medicine, used until the 18th century. In 1088, the University of Bologna emerged as the first university in Europe, and in the 13th century its medical teachers and students began opening human bodies, producing the first anatomy textbook based on human dissection by Mondino de Luzzi.

• 6. Breaking With Tradition

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  Around 1440, a single print shop in Mainz, Germany began producing movable type. By the end of the 15th century the press had spread to roughly 270 cities across Central, Western, and Eastern Europe and had produced more than 20 million volumes. Printing ended the manuscript culture where facts were few and far between, replacing it with reliable, documented facts that proliferated as a foundation for knowledge. In the 16th century Nicolaus Copernicus placed the Sun near the centre of the Universe, motionless, with Earth and the planets orbiting in circular motions modified by epicycles. His model challenged Ptolemy's geocentric system but never displaced it. Ptolemy fell from favour 70 years later, after Galileo's telescopic observations of 1610. Tycho Brahe's unprecedentedly accurate observations in the late 16th century combined with Galileo's early 17th-century telescope to turn astronomy into the first modern science. Johannes Kepler used Brahe's data to find that planets move in elliptical, not circular, orbits, and he derived the laws of planetary motion. Because of Kepler, astronomical events came to be seen as governed by physical laws. The New Science that emerged by the end of the 17th century was more mechanistic, more integrated with mathematics, and obsessed with acquiring and interpreting new evidence.

• 7. A Century Of Names

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  Wilhelm Wundt founded the first laboratory for psychological research in 1879, splitting psychology from philosophy. The 19th century gave science many of its modern features. Precision instruments came into frequent use, terms such as biologist, physicist, and scientist emerged, and science journals appeared as those studying nature grew professionalised. Charles Darwin and Alfred Russel Wallace independently proposed the theory of evolution by natural selection in 1858, and Darwin set it out in detail in On the Origin of Species in 1859. In 1865, Gregor Mendel presented Experiments on Plant Hybridisation, outlining the principles of biological inheritance that became the basis for modern genetics. Early in the century John Dalton proposed modern atomic theory, returning to Democritus's idea of indivisible atoms. The steam engine and the Industrial Revolution revealed that not all energy converts equally to useful work, leading to the laws of thermodynamics and the rule that a closed universe's entropy increases over time. Electromagnetic theory was built by Hans Christian Orsted, Andre-Marie Ampere, Michael Faraday, James Clerk Maxwell, Oliver Heaviside, and Heinrich Hertz. The discovery of X-rays inspired Henri Becquerel and Marie Curie to discover radioactivity in 1896. Marie Curie then became the first person to win two Nobel Prizes. The next year brought the first subatomic particle, the electron.

• 8. How Knowledge Is Tested

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  An explanatory hypothesis is put forward using parsimony principles, and it is expected to seek consilience, fitting with other accepted facts. The scientific method seeks to explain nature objectively in a reproducible way. It rests on assumptions scientists take for granted. There is an objective reality shared by all rational observers, governed by natural laws, discovered through systematic observation and experimentation. A hypothesis is used to make falsifiable predictions, typically posted before being tested, and disproof of a prediction counts as evidence of progress. If a hypothesis survives testing it may be adopted into a scientific theory, which describes much broader sets of observations and can bind many hypotheses together. The Austrian-British philosopher Karl Popper proposed replacing verifiability with falsifiability as the landmark of scientific theories. He argued that observation is made in the light of theories, not the reverse. Thomas Kuhn argued that observation and evaluation take place within a paradigm, a logically consistent portrait of the world, and that revolutionary science occurs when one paradigm overtakes another in a paradigm shift. The replication crisis, named in the early 2010s, shows the stakes. A 2026 replication study found low replication rates across business, economics, education, political science, psychology, and sociology. The physicist Richard Feynman coined cargo cult science for work that looks like science but lacks the honesty to let its results be rigorously evaluated.

  39% of Americans held the notion that COVID-19 was not a major health threat to the US in August 2021. In late 2019 and early 2020-40% believed climate change was not a major threat. Psychologists point to several drivers of this rejection. Scientific authorities are sometimes seen as inexpert, untrustworthy, or biased. Some marginalised social groups hold anti-science attitudes partly because they have been exploited in unethical experiments. And scientific messages may contradict deeply held beliefs or morals. Fear of rejection within social groups often seems to be the cause. Climate change is perceived as a threat by only 22% of Americans on the political right, but by 85% on the left. Someone on the left who dismissed the threat might face contempt and rejection, so people may deny an accepted fact rather than jeopardise their social status. Politics shapes attitudes in other ways too. Governments, businesses, and advocacy groups have used legal and economic pressure on researchers, and politicisation often works by emphasising the uncertainty in scientific evidence. The same pattern of pressure surfaced in the global warming controversy and in disputes over the health effects of pesticides and tobacco. The replication crisis now feeds a field called metascience, which studies how to improve the quality and integrity of research itself.