Physics

Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. It is one of the most fundamental scientific disciplines, and a scientist who specializes in this field is called a physicist.

Physics is one of the oldest academic disciplines. Over the past two millennia, it was part of natural philosophy, along with chemistry, biology, and certain branches of mathematics. During the Scientific Revolution in the 17th century, these areas branched into separate fields of study.

Advances in physics often lead to new technologies. For example, understanding electromagnetism, solid-state physics, and nuclear physics helped create televisions, computers, domestic appliances, and nuclear weapons. Progress in thermodynamics made industrialization possible, and advances in mechanics inspired the development of calculus. Physics continues to intersect with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and its ideas often open new paths for other sciences and academic fields.

History

Main article: History of physics

The word physics comes from the Latin physica ('study of nature'), which itself is a borrowing of the Greek φυσική (phusikḗ 'natural science'), a term derived from φύσις (phúsis 'origin, nature, property').

Ancient astronomy

Main article: History of astronomy

Astronomy is one of the oldest natural sciences. Early civilizations dating before 3000 BCE, such as the Sumerians, ancient Egyptians, and the Indus Valley Civilization, had a predictive knowledge and a basic awareness of the motions of the Sun, Moon, and stars. The stars and planets, believed to represent gods, were often worshipped. While the explanations for the observed positions of the stars were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy, as the stars were found to traverse great circles across the sky, which could not explain the positions of the planets.

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

Main article: 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 proposed by Leucippus and his pupil Democritus.

Aristotle and Hellenistic physics

During the classical period in Greece (6th, 5th and 4th centuries BCE) and in Hellenistic times, natural philosophy developed along many lines of inquiry. Aristotle (Greek: Ἀριστοτέλης, Aristotélēs) (384–322 BCE), a student of Plato, wrote on many subjects, including a substantial treatise on "Physics" – in the 4th century BC. Aristotelian physics was influential for about two millennia. His approach mixed some limited observation with logical deductive arguments, but did not rely on experimental verification of deduced statements. Aristotle's foundational work in Physics, though very imperfect, formed a framework against which later thinkers further developed the field.

Medieval European and Islamic

The Western Roman Empire fell to invaders and internal decay in the fifth century, resulting in a decline in intellectual pursuits in western Europe. By contrast, the Eastern Roman Empire (usually known as the Byzantine Empire) resisted the attacks from invaders and continued to advance various fields of learning, including physics. In the sixth century, John Philoponus challenged the dominant Aristotelian approach to science although much of his work was focused on Christian theology.

In the sixth century, Isidore of Miletus created an important compilation of Archimedes' works that are copied in the Archimedes Palimpsest. Islamic scholarship inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further.

The most notable innovations under Islamic scholarship were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. In his Book of Optics (also known as Kitāb al-Manāẓir) Ibn al-Haytham presented the idea of light rays as an alternative to the ancient Greek idea about visual rays. Like Ptolemy, Ibn al-Haytham applied controlled experiments, verifying the laws of refraction and reflection with the new concept of light rays, but still lacking the concept of image formation.

Scientific Revolution

Further information: History of physics § Scientific Revolution

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. Major developments in this period include the replacement of the geocentric model of the Solar System with the heliocentric Copernican model, the laws governing the motion of planetary bodies (determined by Johannes Kepler between 1609 and 1619), Galileo's pioneering work on telescopes and observational astronomy 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, and separately Gottfried Wilhelm Leibniz, developed calculus, the mathematical study of continuous change, and Newton applied it to solve physical problems.

• Galileo Galilei (1564–1642) related mathematics, theoretical physics, and experimental physics
• explained planetary motions, formulating the first "natural laws" in the modern sense
• Johannes Kepler (1571–1630) explained planetary motions, formulating the first "natural laws" in the modern sense
• Isaac Newton discovered the laws of motion and universal gravitation

19th century

Further information: History of physics § 19th century

The discovery of laws in thermodynamics, chemistry, and electromagnetics resulted from research efforts during the Industrial Revolution as energy needs increased. By the end of the 19th century, theories of thermodynamics, mechanics, and electromagnetics matched a wide variety of observations. Taken together these theories became the basis for what would later be called classical physics.

A few experimental results remained inexplicable. Classical electromagnetism presumed a medium, an luminiferous aether to support the propagation of waves, but this medium could not be detected. The intensity of light from hot glowing blackbody objects did not match the predictions of thermodynamics and electromagnetism. The character of electron emission of illuminated metals differed from predictions.

20th century

See also: History of special relativity and History of quantum mechanics

Further information: History of physics § 20th century: birth of modern physics

Modern physics began in the early 20th century with the work of Max Planck in quantum theory and Albert Einstein's theory of relativity. Both of these theories came about due to inaccuracies in classical mechanics in certain situations. Classical mechanics predicted that the speed of light depends on the motion of the observer, 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 the excitation of material oscillators is possible only in discrete steps proportional to their frequency. This, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to the theory of quantum mechanics improving on classical physics at very small scales.

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. 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. Areas of mathematics in general are important to this field, such as the study of probabilities and groups.

Core theories

Further information: Outline of physics

Physics studies how things move, how energy works, and what matter is made of. Physicists use a few main ideas to understand the world, no matter what they specialize in. These ideas have been tested many times and help scientists explore new topics.

There are two big groups of physics ideas: classical physics and modern physics. Classical physics talks about things we see every day, like how objects move when pushed or how heat works. Modern physics looks at very tiny things, like atoms, and very fast things, close to the speed of light. These ideas help us understand the universe in ways that classical physics cannot explain.

Research

Physicists use a special way of studying called the scientific method to check if their ideas about how nature works are correct. They do experiments and make observations to see if their ideas match what really happens.

Physics tries to explain many different things in nature, from tiny particles to huge groups of galaxies. It aims to describe these things using simpler ideas. For example, scientists discovered that electricity and magnetism are really two parts of the same force, called electromagnetism. Physics continues to search for even deeper explanations about how nature works. Today, physicists are studying many exciting questions, like how certain materials can conduct electricity without any loss, and what makes up mysterious things called dark matter and dark energy.

Branches and fields

Physics has many different areas of study, called fields. These fields can be divided into groups like nuclear and particle physics, condensed matter physics, atomic, molecular, and optical physics, and astrophysics.

Particle physics looks at the tiniest pieces of matter and energy and how they interact. It also designs special tools for this research. Nuclear physics studies the parts of atoms called nuclei and has uses in power and medicine. Atomic, molecular, and optical physics studies single atoms and molecules and how they interact with light. Condensed matter physics looks at the big properties of matter, like solids and liquids. Astrophysics uses physics to study stars, the universe, and how they form and change.

Other aspects

Main article: Philosophy of physics

Physics relies on the scientific method to learn about the world. This method uses careful observation and testing to check ideas. Physicists also think deeply about their work, exploring big questions like the nature of space and time and what really makes things happen.

Physics uses mathematics to describe patterns in nature. Math helps physicists make exact predictions and understand experiments. While math deals with abstract ideas, physics always connects back to the real world. This makes physics a special mix of math and real-life science.