Theoretical physics
Theoretical physics is the branch of physics in which scientists try to work out the laws of nature by building mathematical models of physical systems and solving the equations behind those models, sometimes with the help of computers. It differs from experimental physics, in which scientists use tools and instruments to make measurements.[1]
Theory and experiment
Theoretical physicists use the language of mathematics to set up models and then work out what those models predict; powerful computers are often used for this work. Theory and experiment are closely linked and depend on one another.[2] Experiments are used both to test theoretical predictions and to find new laws and new questions.[3]
How theorists use models
Many models in science deliberately simplify the real world. Well-known examples from physics include frictionless planes, point masses and completely isolated systems.[4] In physics, general laws such as Newton's equation of motion lie at the heart of a theory, and they are applied to a particular system, such as a pendulum, to make a model of it.[5]
History
According to the historian Elizabeth Garber, by 1870 theory was an accepted research activity in physics, and its main mathematical language was calculus.[6] She argues, however, that theoretical physics did not become a separate, accepted subfield, with theorists forming their own community within physics, until the twentieth century.[7] To get there, theorists had to train students as theorists and win recognition from experimental physicists that their work was valuable; Garber places this process in the roughly forty years between 1870 and World War I.[8]
In Germany, the historians Christa Jungnickel and Russell McCormmach describe how, in the 1870s and 1880s, almost every university began leaving the teaching of mathematical, or theoretical, physics to a second, usually younger physicist.[9] They call Hermann von Helmholtz the most influential physicist for the growth of theoretical physics in Germany at that time; at Berlin he gave the first regular course in the subject there.[10] Gustav Kirchhoff was appointed to a new professorship at Berlin, and after his death in 1887 he was succeeded by Max Planck.[11]
References
- ↑ "$11 million gift establishes Mani L. Bhaumik Institute for Theoretical Physics at UCLA". UCLA Newsroom. 21 June 2016. Retrieved 20 October 2026.
Theoretical physicists attempt to determine the action of the laws of nature by constructing mathematical models of physical systems and solving the equations that underlie those models, sometimes aided by computers. This is in contrast to another primary branch of physics, experimental physics
- ↑ "Physics". Saarland University, Department of Physics. Retrieved 20 October 2026.
Theoretical physics establishes models formulated with the language of mathematics and examines them for their consequences and predictions. The most powerful computers available are often used for these investigations. Both subfields of physics are interconnected and depend on close cooperation.
- ↑ "Physics". Saarland University, Department of Physics. Retrieved 20 October 2026.
experiments, which serve to verify theoretical predictions on the one hand and to develop physical laws and new questions on the other
- ↑ "Models in Science". Stanford Encyclopedia of Philosophy. Retrieved 20 October 2026.
Frictionless planes, point masses, completely isolated systems, omniscient and fully rational agents, and markets in perfect equilibrium are well-known examples.
- ↑ "Models in Science". Stanford Encyclopedia of Philosophy. Retrieved 20 October 2026.
This is salient in physics, where general laws—such as Newton's equation of motion—lie at the heart of a theory. These laws are applied to a particular system—e.g., a pendulum
- ↑ Garber, Elizabeth (1999). "Epilogue: Forging New Relationships, 1870–1914". The Language of Physics. Birkhäuser. doi:10.1007/978-1-4612-1766-4_10. Retrieved 20 October 2026.
By 1870 both physics and mathematics had become distinct academic specialties within universities across Europe ... Theory was an accepted research activity and its language was the calculus
- ↑ Garber, Elizabeth (1999). "Epilogue: Forging New Relationships, 1870–1914". The Language of Physics. Birkhäuser. doi:10.1007/978-1-4612-1766-4_10. Retrieved 20 October 2026.
theoretical physics as an accepted subfield within physics, with theoreticians forming a distinct subcommunity within physics, did not coalesce until the twentieth century
- ↑ Garber, Elizabeth (1999). "Epilogue: Forging New Relationships, 1870–1914". The Language of Physics. Birkhäuser. doi:10.1007/978-1-4612-1766-4_10. Retrieved 20 October 2026.
They also had to replicate themselves by training students as theoreticians, rather than students merely taking courses in theory. Even if they did not develop their own specialist societies and journals, their work needed the recognition of experimentalists as valuable and complementary to their own research. These processes as well as the development of a sense of collective identity as theoreticians unfolded within physics during the forty odd years between 1870 and World War I.
- ↑ Jungnickel, Christa; McCormmach, Russell (2017). "Positions in Theoretical Physics". The Second Physicist. Springer. doi:10.1007/978-3-319-49565-1_11. Retrieved 20 October 2026.
the arrangement by which regular instruction in mathematical, or theoretical, physics was left to a second, usually younger physicist was introduced at almost every German university
- ↑ Jungnickel, Christa; McCormmach, Russell (2017). "Positions in Theoretical Physics". The Second Physicist. Springer. doi:10.1007/978-3-319-49565-1_11. Retrieved 20 October 2026.
Helmholtz was the most influential physicist for the development of theoretical physics in Germany in the 1870s and 1880s. At Berlin, in addition to teaching experimental physics, he gave a course on theoretical physics, the first regular teaching in the field there.
- ↑ Jungnickel, Christa; McCormmach, Russell (2017). "Positions in Theoretical Physics". The Second Physicist. Springer. doi:10.1007/978-3-319-49565-1_11. Retrieved 20 October 2026.
Kirchhoff was appointed to the new position at Berlin, and when he died in 1887, he was replaced by Max Planck.