What is science?
Science is a way of understanding the natural world by asking questions and answering them with evidence. Evidence means observations and measurements that other people can check and repeat.
- Science studies things that can be observed or measured, directly or with instruments.
- It looks for natural causes, not magic or luck.
- Its answers can change when better evidence arrives.
Each branch has its own focus. Physics looks for the basic rules of matter, energy and motion that every other science uses. Biology studies living things. Geology studies the Earth and its history. Together they build one connected scientific world view.
Observation and inference
An observation is what you notice with your senses or instruments: "the leaf is yellow". An inference is an explanation you reason from observations: "the plant needs more nitrogen". Inferences must be tested.
Evidence-based thinking
Good scientific claims are built on evidence, not on who says them.
- Empirical: based on observation and experiment.
- Reproducible: someone else, using the same method, should get similar results.
- Controlled: change one variable at a time, compare with a control group.
- Correlation is not causation: two things rising together (ice-cream sales and drowning in summer) does not mean one causes the other; heat causes both.
Reasoning
Inductive reasoning goes from many examples to a general rule ("every metal I heated expanded, so metals expand when heated"). Deductive reasoning goes from a rule to a prediction ("copper is a metal, so it will expand"). Science uses both.
Peer review and community
Before results are published, other experts check the method and data (peer review). Mistakes and fraud are found when others try to repeat the work. Science is a team effort across countries and centuries.
Hypothesis, law, theory and model
| Word | Meaning | Example |
|---|---|---|
| Hypothesis | A testable, possible explanation or prediction | "Seeds need light to sprout" |
| Law | Describes WHAT always happens, often as an equation | Newton's law of gravitation, Ohm's law |
| Theory | A well-tested explanation of WHY, linking many facts | Atomic theory, theory of evolution, plate tectonics |
| Model | A simplified picture, drawing, equation or computer program of something real | Ball-and-stick molecule, climate model |
In everyday speech "just a theory" means a guess. In science, a theory is the strongest kind of knowledge we have. A theory does not become a law when it is "proved": a law and a theory answer different questions.
Big fundamental theories include the atomic theory of matter, cell theory, evolution by natural selection, the theory of gravity and relativity, quantum theory, and plate tectonics.
Tentative knowledge, falsifiability and paradigm shifts
A scientific claim must be falsifiable: it must be possible to imagine a result that would show it is wrong. "It will rain tomorrow in Pune" is testable; "invisible spirits move the clouds in ways no one can detect" is not.
Scientific knowledge is tentative: strong, but open to change. Most change is small and steady. Sometimes the whole framework changes. The historian Thomas Kuhn called this a paradigm shift.
Examples from history
- Astronomy: from an Earth-centred universe to Copernicus's Sun-centred model, supported by Galileo's telescope and Kepler's orbits. Aryabhata in India had already argued that the Earth spins on its axis.
- Geology: James Hutton showed the Earth is very old (deep time). Alfred Wegener's idea of drifting continents was rejected for decades, then accepted as plate tectonics once sea-floor evidence arrived in the 1960s.
- Medicine: "bad air" (miasma) was replaced by germ theory after the work of Pasteur and Koch.
- Physics: Newton's mechanics still works for everyday speeds, but relativity and quantum theory replaced it for very fast and very small things.
Science, other disciplines and society
Science answers questions about how nature works. Other subjects ask different questions: ethics asks what we should do, art and literature express experience, history studies human events. Science can tell us how to edit a gene; ethics and law help decide whether we should.
Science and pseudoscience
Pseudoscience looks scientific but is not: claims that cannot be tested, rely only on stories (anecdotes) or authority, ignore evidence against them, or never change. Examples: astrology predicting personality, "miracle" cures with no trials.
Science and civilisation
Science grew in many cultures: Babylonian astronomy, Greek geometry, Indian mathematics (place value and zero), Chinese inventions, and the Islamic world's optics and chemistry. Today science, technology and society shape each other.
Try it at home
Pick a claim from an advert ("this drink makes you run faster"). Ask: What is the evidence? Was there a control group? Could the result have been chance? Who checked it?
Key formulas and definitions
- Observation = what you sense or measure; Inference = what you conclude from it
- Hypothesis = testable idea; Law = what happens; Theory = why it happens (well tested)
- Model = simplified representation (drawing, equation, computer program)
- Falsifiable = a possible result could show the claim is wrong
- Tentative = reliable now, but open to change with new evidence
- Peer review = experts check work before publication
- Paradigm shift = a change of the whole framework of a science
Worked examples
1. Sort these into observation or inference: (a) the road is wet, (b) it rained last night, (c) the thermometer reads 31 °C.
(a) observation, (c) observation: both are seen or measured. (b) inference: it explains the wet road, but a water tanker could also have done it.
2. A student says "Evolution is only a theory, so it is just a guess." What is wrong?
In science a theory is a well-tested explanation supported by many lines of evidence (fossils, DNA, observed changes in bacteria). It is not a guess. A guess would be a hypothesis before testing.
3. Is "All metals expand when heated" a law or a theory? Can it be falsified?
It describes what happens, so it is a law-like statement. It is falsifiable: one metal that shrinks when heated would show it wrong. (Some special alloys barely change, which shows why laws have stated conditions.)
4. Why was continental drift rejected at first, then accepted later?
Wegener had evidence (matching coastlines, fossils, rocks) but no believable mechanism, so many geologists rejected it. In the 1950s–60s, sea-floor spreading and magnetic stripes gave a mechanism. The idea was then accepted as plate tectonics: evidence changed minds.
5. A study finds that children who own more books score higher in tests. Can we say books cause higher scores?
No. This is a correlation. Other factors (family income, reading time, school) could cause both. A controlled experiment or careful study of other variables is needed.
6. Give two signs that a claim is pseudoscience.
It cannot be tested or proved wrong, and it ignores evidence against it. Other signs: it relies only on personal stories, uses scientific-sounding words without data, and never changes.
Common mistakes
- Thinking a theory becomes a law when it is proved. They are different kinds of statements.
- Treating an inference as if it were an observation.
- Believing science "proves" things for ever. It supports them strongly, but stays open to new evidence.
- Confusing correlation with cause.