Physics

Physics is the study of matter. It looks at how things move and act in space and time. It also studies energy and force. People who study physics are called physicists.

Physics is one of the oldest subjects to learn about. For a long time, it was part of natural philosophy. This also included biology and mathematics. In the 17th century, during the Scientific Revolution, these areas became separate subjects.

When we learn more about physics, it helps us make new things. For example, learning about electromagnetism and solid-state physics helped us make televisions and computers. Progress in thermodynamics helped create factories. Physics also connects with other areas of study, like biophysics and quantum chemistry. It helps other sciences grow, too.

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 basic awareness of the motions of the Sun, Moon, and stars. The stars and planets were often seen as gods. While their explanations for the positions of the stars were not scientific, these early observations helped later astronomy, as the stars moved in great circles across the sky, which did 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 began in Greece during the Archaic period (650 BCE – 480 BCE), when pre-Socratic philosophers like Thales rejected non-natural explanations for natural events and said that every event had a natural cause. They proposed ideas verified by reason and observation, and many of their ideas were later proven correct; for example, atomism was found to be correct about 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 in many ways. 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 observation with logical arguments, but did not rely on testing ideas. Aristotle's work in Physics, though imperfect, formed a base for later thinkers.

Medieval European and Islamic

The Western Roman Empire fell to invaders and internal problems in the fifth century, leading to a decline in learning in western Europe. By contrast, the Eastern Roman Empire (usually known as the Byzantine Empire) resisted attacks and continued to advance 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 experiments and math to discover what are now called 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 math study of continuous change, and Newton applied it to solve physical problems.

• Galileo Galilei (1564–1642) linked math, theory, and experiments
• explained planetary motions, creating the first "natural laws" in the modern sense
• Johannes Kepler (1571–1630) explained planetary motions, creating 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 during the Industrial Revolution as energy needs grew. By the end of the 19th century, theories of thermodynamics, mechanics, and electromagnetics matched many observations. Together these theories became the basis for what would later be called classical physics.

Some experimental results remained unexplained. 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 problems in classical mechanics. Classical mechanics said that the speed of light depends on the motion of the observer, but this did not match the constant speed predicted by Maxwell's equations of electromagnetism. This 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 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. These ideas have been tested many times and help scientists learn new things.

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 watch what happens to see if their ideas match reality.

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 deeper explanations about how nature works. Today, physicists are studying 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 grouped into types like particle physics, condensed matter physics, atomic, molecular, and optical physics, and astrophysics.

Particle physics studies the smallest pieces of matter and energy and how they work together. It also makes special tools for this research. Nuclear physics looks at the parts inside atoms called nuclei and helps with power and medicine. Atomic, molecular, and optical physics studies single atoms and molecules and how they react with light. Condensed matter physics looks at big properties of matter, like solids and liquids. Astrophysics uses physics to study stars, the universe, and how they change.

Other aspects

Main article: Philosophy of physics

Physics uses the scientific method to learn about our world. This means looking closely and testing ideas to see if they are true. Physicists also think about big questions, like what space and time really are and what makes things happen.

Physics uses math to describe what we see in nature. Math helps physicists make good guesses and understand tests. Even though math can be abstract, physics always ties back to the real world. This makes physics a mix of math and real-life science.