Within the field of physics, experimental physics is the category of disciplines and sub-disciplines concerned with the observation of physical phenomena in order to gather data about the universe. Methods vary from discipline to discipline, from simple experiments and observations, such as the Cavendish experiment, to more complicated ones, such as those going on at the LHC.
Experimental physics regroup all the disciplines of physics that are concerned with data-acquisition, data-acquisition methods, and the detailed conceptualization (beyond simple thought experiments) and realization of laboratory experiments . It is often put in contrast with theoretical physics, which is more concerned with predicting and explaining the physical behaviour of nature than the acquisition of knowledge about it.
Although experimental and theoretical physics are concerned with different aspects of nature, they both share the same goal of understanding it and have a symbiotic relation. The former provides data about the universe, which can then be analyzed in order to be understood, while the latter provides explanations for the data and thus offers insight on how to better acquire data and on how to built experiment. Theoretical physics can also offer insight on what data is needed in order to gain a better understanding of the universe, and on what experiments to build in order to obtain it.
Experimental physics had its roots in the Middle Ages, particularly in Iraq and Egypt, in the work of the Muslim physicist, Ibn al-Haytham (965-1039), known in the West as Alhazen, who is considered the "father of modern optics" and one of the most important physicists of the Middle Ages, for having developed the earliest experimental scientific method in his Book of Optics (1021). Some of his most famous experiments include his development and use of the camera obscura and pinhole camera to prove that light travels in straight lines. Matthias Schramm wrote in his Ibn al-Haythams Weg zur Physik:
“Through a closer examination of Ibn al-Haytham's conceptions of mathematical models and of the role they play in his theory of sense perception, it becomes evident that he was the true founder of physics in the modern sense of the word; in fact he anticipated by six centuries the fertile ideas that were to mark the beginning of this new branch of science.”
Another medieval Muslim physicist who contributed towards experimental physics was Abū Rayhān al-Bīrūnī (973-1048), who developed the earliest experimental method for mechanics. Al-Biruni and Al-Khazini (fl. 1115-1130) also unified statics and dynamics into the science of mechanics, and combined hydrostatics with dynamics to create the field of hydrodynamics.
After the Latin translations of the 12th century, when the Book of Optics became available in Latin, the scientific method was adopted and further developed by Robert Grosseteste, who emphasized mathematics as a way to understand nature, and by Roger Bacon who emphasized an empirical approach. Bacon conducted further experiments into optics, improving on the work of his predecessor, Alhazen. Bacon also recorded the manner in which he conducted his experiments in precise detail so that others could reproduce and independently test his results, a cornerstone of the scientific method, and a continuation of the work of researchers like Alhazen and Albatenius.
As a distinct field, experimental physics was established in early modern Europe, during what is known as the Scientific Revolution, by physicists such as Galileo Galilei, Christiaan Huygens, Johannes Kepler, Blaise Pascal and Sir Isaac Newton. In the early 17th century, Galileo made extensive use of experimentation to validate physical theories, which is the key idea in the modern scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the law of inertia, which later became the first law in Newton's laws of motion. In Galileo's Two New Sciences, a dialogue between the characters Simplicio and Salviati discuss the motion of a ship (as a moving frame) and how that ship's cargo is indifferent to its motion. Huygens used the motion of a boat along a Dutch canal to illustrate an early form of the conservation of momentum.
Experimental physics is considered to have culminated with the publication of the Philosophiae Naturalis Principia Mathematica in 1687 by Sir Isaac Newton (1643-1727). In 1687, Newton published the Principia, detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's law of universal gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The Principia also included several theories in fluid dynamics.
From the late 17th century onward, thermodynamics was developed by physicist and chemist Boyle, Young, and many others. In 1733, Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. In 1798, Thompson demonstrated the conversion of mechanical work into heat, and in 1847 Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the nineteenth century, is responsible for the modern form of statistical mechanics. Classical mechanics was re-formulated and extended by Leonhard Euler, French mathematician Joseph-Louis Comte de Lagrange, Irish mathematical physicist William Rowan Hamilton, and others, who produced new results in mathematical physics. The law of universal gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories. Newton's Law of gravitation also helped put celestial mechanics on proper scientific and mathematical footing.
After Newton defined classical mechanics, the next great field of inquiry within physics was the nature of electricity. Observations in the seventeenth and eighteenth century by scientists such as Robert Boyle, Stephen Gray, and Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and current. By 1808 John Dalton had discovered that atoms of different elements have different weights and proposed the modern theory of the atom.
It was Hans Christian Ørsted who first proposed the connection between electricity and magnetism after observing the deflection of a compass needle by a nearby electric current. By the early 1830s Michael Faraday had demonstrated that magnetic fields and electricity could generate each other. In 1864 James Clerk Maxwell presented to the Royal Society a set of equations that described this relationship between electricity and magnetism. Maxwell's equations also predicted correctly that light is an electromagnetic wave. Starting with astronomy, the principles of natural philosophy crystallized into fundamental laws of physics which were enunciated and improved in the succeeding centuries. By the 19th century, the sciences had segmented into multiple fields with specialized researchers and the field of physics, although logically pre-eminent, no longer could claim sole ownership of the entire field of scientific research.
Some examples of prominent experimental physics projects are:
- Relativistic Heavy Ion Collider which collides heavy ions such as gold ions (it is the first heavy ion collider) and protons, it is located at Brookhaven National Laboratory, on Long Island, USA.
- HERA, which collides electrons or positrons and protons, and is part of DESY, located in Hamburg, Germany.
- LHC, or the Large Hadron Collider, which is currently under construction. The LHC will is scheduled to begin operation in 2008 and will be the world's most energetic collider upon completion, it is located at CERN, on the French-Swiss border near Geneva.
- JWST, or the James Webb Space Telescope, is planned for launch in 2013. It will be the successor to the Hubble Space Telescope. It will survey the sky in the infrared region. The main goals of the JWST will be in order to understand the initial stages of the universe, galaxy formation as well as the formations of stars and planets, and the origins of life.
Experimental physics uses two main methods of experimental research, controlled experiments, and natural experiments. Controlled experiments are often used in laboratories as laboratories can offer a controlled environment. Natural experiments are used, for example, in astrophysics when observing celestial objects where control of the variables in effect is impossible.
Famous experiments include:
- 2-degree-Field Galaxy Redshift Survey
- 2-Micron All-Sky Survey (2MASS)
- Bell test experiments
- BOOMERanG experiment
- Camera obscura experiments
- Cavendish experiment
- Cosmic Background Explorer (COBE)
- Davisson-Germer experiment
- Double slit experiment
- Foucault pendulum
- Frank Hertz experiment
- Gravity Probe A
- Gravity Probe B
- Homestake experiment
- Oil-drop experiment
- Michelson-Morley experiment
- Neutrino experiment
- Rutherford experiment
- Sloan Digital Sky Survey
- Stern-Gerlach experiment
- Wilkinson Microwave Anisotropy Probe
Some well-known experimental techniques include:
- Faraday cage
- Raman spectroscopy
- Signal processing
- X-ray spectroscopy
Prominent experimental physicists
Famous experimental physicists include:
- Alhacen (965–1039)
- John Bardeen (1908–1991)
- Antoine Henri Becquerel (1852–1908)
- Abū Rayhān al-Bīrūnī (973–1043)
- Jagadish Chandra Bose (1858–1937)
- William Lawrence Bragg (1890–1971)
- Marie Curie (1867–1934)
- Michael Faraday (1791–1867)
- Enrico Fermi (1901–1954)
- Galileo Galilei (1564–1642)
- Al-Khazini (fl. 1115-1130)
- Max von Laue (1879–1960)
- Ernest Orlando Lawrence (1901–1958)
- Ernst Mach (1838–1916)
- Albert Abraham Michelson (1852–1931)
- Robert Andrews Millikan (1868–1953)
- Isaac Newton (1643–1727)
- Chandrasekhara Venkata Raman (1888–1970)
- John William Strutt (3rd Baron Rayleigh) (1842–1919)
- Wilhelm Conrad Röntgen (1845–1923)
- Ernest Rutherford (1871–1937)
- William Bradford Shockley (1910–1989)
- Joseph John Thomson (1856–1940)
See the timelines below for listings of physics experiments.
- Timeline of classical mechanics
- Timeline of electromagnetism and classical optics
- Timeline of gravitational physics and relativity
- Timeline of nuclear fusion
- Timeline of other background radiation fields
- Timeline of particle physics technology
- Timeline of quantum mechanics, molecular physics, atomic physics, nuclear physics, and particle physics
- Timeline of states of matter and phase transitions
- Timeline of thermodynamics, statistical mechanics, and random processes
- Timeline of particle discoveries