Science

At its core, science is a method more than a body of facts. It roughly goes: observe something curious → propose an explanation (hypothesis) → predict what would happen if the hypothesis is true → test the prediction with an experiment or new observation → revise or discard the hypothesis based on the result → share your work so others can check it.

Two features make it powerful. First, hypotheses must be falsifiable — they must forbid something. 'God loves us' is unfalsifiable (and belongs to theology, not science). 'Objects fall at 9.8 m/s²' is falsifiable — one measurement could refute it.

Second, science is public. Peer review, reproducibility, and open data are what turn one person's guess into shared knowledge.

Classical physics (Newton, 17th c.) explained motion and gravity with beautiful equations: F = ma, and the inverse-square law of gravity.

In the early 20th century, two revolutions overturned it. Einstein's relativity showed that space and time bend around mass and energy: E = mc². Quantum mechanics (Planck, Bohr, Heisenberg, Schrödinger) showed that at atomic scales the world behaves probabilistically — a particle can be in multiple states until observed.

The Standard Model of particle physics now catalogues the fundamental particles (quarks, leptons, bosons) and three of the four fundamental forces. Gravity still resists unification with quantum theory — the great unfinished problem.

Chemistry studies how atoms combine into molecules. The periodic table (Mendeleev, 1869) organises the 118 known elements. Almost everything you touch is made of at most a few dozen of them.

Biology is the study of life. Cells (Robert Hooke, 1665) are life's building blocks. DNA (Watson, Crick, Franklin, 1953) is the code inside every cell. Evolution by natural selection (Darwin, 1859) explains the diversity of every species — including us — from a common ancestor.

In the 21st century, genomics, CRISPR gene editing, and mRNA vaccines have opened powerful and ethically complex frontiers.

The observable universe is ~13.8 billion years old and ~93 billion light-years across. It began in a hot dense state — the Big Bang — and has been expanding ever since (Hubble, 1929).

Stars are nuclear furnaces that fuse hydrogen into heavier elements. The carbon in your bones and the iron in your blood were forged inside a star that died before our sun was born. As Carl Sagan said, we are made of star-stuff.

Atoms are the smallest units of an element that keep its properties. Each atom has a nucleus of protons (positive) and neutrons (neutral), orbited by electrons (negative). The number of protons is the atomic number and defines the element: hydrogen has one, oxygen has eight, iron has twenty-six.

Atoms bond by sharing (covalent), transferring (ionic), or pooling (metallic) electrons. Water is H₂O — two hydrogens covalently bonded to one oxygen. Table salt is Na⁺Cl⁻ — an ionic lattice.

Reactions rearrange bonds. The three great families are: acid–base (proton exchange), oxidation–reduction (electron exchange, which includes fire, rust, and respiration), and precipitation. Life itself is a controlled series of oxidation reactions powered by sunlight (photosynthesis) or by consuming photosynthesisers.

A cell is a bag of salt water wrapped in a membrane, running on molecular machines. Prokaryotes (bacteria, archaea) are one-celled and have no nucleus. Eukaryotes (plants, animals, fungi, protists) have organelles — mitochondria (energy), chloroplasts (photosynthesis in plants), nucleus (DNA), ribosomes (protein synthesis).

DNA is a four-letter code (A, T, G, C) written in a double helix. Three-letter 'codons' spell twenty amino acids that fold into proteins — the workhorses of the cell. The human genome is about 3.2 billion letters long, but only ~2% codes for proteins.

Evolution: heritable variation + differential survival + time = new species. Fossils, comparative anatomy, embryology, and genomes all confirm it. Humans share ~98.8% of our DNA with chimpanzees and 99.9% with each other. Race, biologically, is not a category.

Ecology studies how living things interact. A single hectare of rainforest holds more species than all of Europe. We are living through the sixth mass extinction — the first caused by a single species.

Everything that happens in the universe is one of four interactions. Gravity — the weakest force but with unlimited range — holds galaxies together. Electromagnetism (light, chemistry, electricity, magnetism) governs almost all of daily life. The strong nuclear force glues quarks into protons and neutrons and those into atomic nuclei. The weak nuclear force governs radioactive decay and lets stars burn.

Einstein's general relativity describes gravity as the curvature of spacetime — a heavy object 'dents' space; smaller objects fall along the slope. GPS satellites must correct for this curvature or they would drift kilometres in a day.

Quantum mechanics describes the other three forces and everything at atomic scales. It is bizarre — particles behave as waves, positions are probabilistic, entangled particles influence each other instantaneously — and it is the best-tested theory in the history of science.

You are ~37 trillion cells organised into ~200 cell types, ~78 organs, and 11 organ systems. Blood makes a full circuit through your body every minute; the heart beats ~100,000 times a day. The brain — 86 billion neurons and ~100 trillion synapses — runs on about 20 watts, less than a light bulb, yet outperforms any supercomputer for most real-world tasks.

The immune system distinguishes self from not-self and remembers infections for years. Sleep consolidates memory and clears metabolic waste from the brain. Chronic stress silently damages every system.

The observable universe is ~13.8 billion years old and ~93 billion light-years across. It began in a hot dense state — the Big Bang — and has been expanding ever since (Hubble, 1929). We can still detect the leftover heat as the cosmic microwave background.

Stars are nuclear furnaces that fuse hydrogen into heavier elements. Small stars die quietly as white dwarfs; large ones die as supernovae that seed galaxies with the elements essential for life. The carbon in your bones and the iron in your blood were forged inside a star that died before our sun was born. As Carl Sagan said, we are made of star-stuff.

About 68% of the universe is 'dark energy' driving accelerating expansion, and ~27% is 'dark matter' whose gravity we detect but whose nature we do not yet know. Only ~5% is the ordinary matter of stars, planets, and people.