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Physics (from Ancient Greek: φυσική (ἐπιστήμη)  “knowledge of nature”, from φύσις phúsis "nature") is the natural science that involves the study of matter and its motion often in the form of waves through space and time, along with related concepts such as energy and force. 

More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.

Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.

A laser set up with an optics table is a typical physics investigation. image: wikipedia/NASA

An oscilloscope screen is the basis of early televisions. image: wikipedia/Oliver Kurmis

Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches of mathematics, and biology, but during the Scientific Revolution in the 17th century, the natural sciences emerged as unique research programs in their own right.

Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry,  often making the boundaries of physics  not rigidly defined. 

New ideas in physics often explain the fundamental mechanisms of other sciences while opening new avenues of research in areas such as mathematics and philosophy.

Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs.

 For example, advances in the understanding of  electricity or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons. 

Advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.

Physics is often explained in terms of its history beginning with astronomy.

Ancient astronomy

Astronomy is the oldest of the natural sciences. The earliest civilizations dating back to beyond 3000 BCE, such as the Sumerians, Ancient Egyptians, and the Indus Valley Civilization, all had a predictive knowledge and a basic understanding of the motions of the Sun, Moon, and stars. 

The stars and planets were often a target of worship, believed to represent their gods. While the explanations for these phenomena were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy. 

Nebra sky disc from 1700-1500 BCE, These symbols are interpreted generally as the Sun or full moon, a lunar crescent, and stars (including a cluster of seven stars interpreted as the Pleiades)

According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. 

Egyptian astronomers left monuments showing knowledge of the constellations and the motions of the celestial bodies, while Greek poet Homer wrote of various celestial objects in his Iliad and Odyssey; later Greek astronomers provided names, which are still used today, for most constellations visible from the northern hemisphere.

Natural philosophy

Natural philosophy has its origins in Greece during the Archaic period, (650 BCE – 480 BCE), when Pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause.  

They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment;  for example, atomism was found to be correct approximately 2000 years after it was first proposed by Leucippus and his pupil Democritus. 

Classical physics

Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics.

A replica of Galileo's  workshop in the Deutsches Museum. image: R.Conan-Davies

Major developments in this period include:

      The replacement of the geocentric model of the solar system with the Sun-centric Copernican model. 

     ▪ The laws governing the motion of planetary bodies determined by Johannes Kepler between 1609 and 1619, 

     ▪ pioneering work on telescopes and observational astronomy by Galileo Galilei in the 16th and 17th Centuries, and 

     Isaac Newton's discovery and unification of the laws of motion and universal gravitation that would come to bear his name. Newton also developed calculus, the mathematical study of change, which provided new mathematical methods for solving physical problems.


The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased. Comment: Inventors like James Watt were important contributors to improving efficient in steam engines. 

 The laws comprising classical mechanics remain very widely used for objects on everyday scales travelling at speeds not close to that of light, provided a very close approximation in such situations.

It was observed that inaccuracies start to creep into classical mechanics for very small objects and very high velocities leading to the development of modern physics in the 20th century.

Modern physics -The development of special relativity and history of quantum mechanics

Modern physics began in the early 20th century with the work of Max Planck in quantum theory and Albert Einstein's theory of relativity

These theories came about due to inaccuracies in classical mechanics in certain situations. Classical mechanics predicted a varying speed of light, which could not be resolved with the constant speed predicted by Maxwell's equations of electromagnetism; this discrepancy was corrected by Einstein's theory of special relativity, which replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light. 

Black body radiation provided another problem for classical physics, which was corrected when Planck proposed that light comes in individual packets known as photons; this, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to the theory of quantum mechanics taking over from classical physics at very small scales.

A comparison of classical and modern physics. image: wikipedia

Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger and Paul Dirac. From this early work, and work in related fields, the Standard Model of particle physics was derived which explains the fundamental forces

Following the discovery of a particle with properties consistent with the Higgs boson at CERN in 2012, all fundamental particles predicted by the standard model, and no others, appear to exist; however physics beyond the Standard Model, with theories such as supersymmetry, is an active area of research.


Other resources: College Physics textbook from Open StaxCollege