What is Physics ?

Human beings have always been curious about the world they live in — the regular rising and setting of celestial objects, the change of seasons, eclipses, tides, volcanoes and rainbows have all provoked wonder since ancient times. One enduring response to this wonder has been to observe nature carefully, look for patterns and regularities, and build tools to interact with it. That response, over centuries, grew into modern science and technology.

The word science comes from the Latin scientia, "to know" (the Sanskrit Vijnan and Arabic Ilm carry the same sense). Every early civilisation — Egypt, India, China, Greece, Mesopotamia — contributed to it, and from the sixteenth century onward Europe accelerated its growth into the truly international enterprise it is today.

Science is best understood as a systematic attempt to understand natural phenomena in depth, and to use that understanding to predict, modify and control them. The scientific method is not a single fixed recipe, but a set of interconnected steps: careful observation, controlled experiment, qualitative and quantitative reasoning, mathematical modelling, and the testing of predictions against further observation. Speculation has its place, but a theory earns acceptance only when it survives contact with experiment or observation.

Science is never "finished". As observations sharpen or experiments turn up new results, theories must adapt — sometimes with a modest tweak, sometimes with an upheaval. When Kepler examined Tycho Brahe's precise planetary data, Copernicus's neat circular orbits had to give way to ellipses. When early-twentieth-century experiments exposed the limits of Newtonian mechanics at the atomic scale, and the classical wave picture of light failed to explain the photoelectric effect, an entirely new framework — quantum mechanics — had to be built. The traffic runs both ways: Rutherford's 1911 alpha-scattering experiment forced a new (nuclear) model of the atom, which Bohr then used in 1913 to build the quantum theory of the hydrogen atom; conversely, Dirac's 1930 theoretical prediction of the antiparticle was confirmed only two years later by Anderson's experimental discovery of the positron.

Physics is one of the natural sciences, alongside chemistry and biology. The word itself comes from a Greek term for "nature" (Sanskrit: Bhautiki). A tight one-line definition is neither possible nor useful — but physics can broadly be described as the study of the basic laws of nature and how they show up in the phenomena around us. Two threads run through the whole subject: unification, the attempt to explain a huge range of phenomena using a small number of concepts and laws (the same law of gravitation that pulls an apple to the ground also governs the Moon's orbit and the planets' motion; the same set of Maxwell's equations covers every electric and magnetic effect); and reduction, the attempt to explain the properties of a large, complex system from the properties of its simpler constituent parts (thermodynamics describes a gas through bulk quantities like temperature and entropy, but kinetic theory later showed that temperature is really just the average kinetic energy of the gas's molecules).