In physics, the principle of relativity is the idea that the laws of physics should remain consistent over time and from one place to another. Several principles of relativity have been successfully applied during the development of physics, implicitly in Newtonian mechanics and explicitly in Albert Einstein's special relativity and general relativity.

For example, in the framework of special relativity, the Maxwell equations have the same form in all inertial frames of reference. In the framework of general relativity, the Maxwell equations or the Einstein field equations have the same form in arbitrary frames of reference.

Basic concepts

A principle is an idea that is taken as fundamentally true. In the physical sciences, principles play somewhat the role of axioms in logic and mathematics, or more loosely, as foundations or guides on which to build theories. The Principle of Relativity in physics is the idea that laws should be universal, and the same for all observers. This then becomes a definition of what can be a physical law: anything that different observers see differently is not a physical law, but is incidental to the observer. Whatever remains constant for different observers is a candidate for a physical law. This principle is most useful in dynamics and kinematics, the descriptions of forces and the motion of bodies. The term "relative" in this context refers to the fact that measurements are always relative to an observer, and the "universal" suggests there may be rules relating the measurements of any observer to those of any other.

Theoretical physics attempts to describe observations as models. These are usually systems of equations that predict how the measured data will change from one instant to the next, depending on zero or more free parameters. A simple example of a model is Galileo's law of falling bodies. Measurements made by a single observer are relative to that observer, and use arbitrary coordinate systems selected by the observer.

The form the model takes depends strongly on the observer's coordinate system.

For example, if an observer uses Cartesian coordinates, the path of a falling body has a simple form; but if the observer is contrary and uses, say, time-varying ellipsoidal coordinates, measurements of the same path will be described by a much more complicated expression. Fortunately the mathematical rules for switching between coordinate systems are inherent in their definitions. This applies to all possible coordinates, including those in arbitrary relative motion.

But the idea that laws must look the same to all observers in any coordinate system imposes a symmetry on the laws. According to a mathematical result called Noether's theorem,[1][2] any continuous symmetry will also imply a corresponding conservation law.[3]

As an example, if a law is the same for observers at different times, energy must be conserved. In this light, relativity principles make testable predictions about how nature behaves.

History

The ideas behind the principle of relativity have been around since Galileo. By the mid nineteenth century, the idea was widespread, especially in the context of electromagnetism, but the term was only formalized in 1904 by Poincaré:

See also

Notes and references

  1. ↑ Courant, R.; Hilbert, D. (1965). Methods of Mathematical Physics. New York: Interscience Publishers. p. 262 ff.
  2. ↑ Schwarzbach, Bertram E.; Kosmann-Schwarzbach, Yvette (2010). The Noether Theorems: Invariance and Conservation Laws in the Twentieth Century. Springer. p. 174. ISBN 978-0-387-87868-3. Extract of page 174
  3. ↑ [1]
  4. ↑ Poincaré, H (1904). "L'état actuel et l'avenir de la Physique mathématique". Bulletin des sciences mathématiques. 28 (St Louis Conference): 302.
  5. ↑ "Apparently this impossibility of demonstrating absolute motion is a general law of nature; which I will call the principle of relativity."
  6. ↑ Einstein, A.; Lorentz, H. A.; Minkowski, H.; Weyl, H. (1952) [1923]. Arnold Sommerfeld (ed.). The Principle of Relativity: A Collection of Original Memoirs on the Special and General Theory of Relativity. Mineola, NY: Dover Publications. p. 111. ISBN 0-486-60081-5. {{cite book}}: ISBN / Date incompatibility (help)
  7. ↑ Weistein, Galina (2015). Einstein's Pathway to the Special Theory of Relativity. Cambridge Scholars Publishing. p. 272. ISBN 978-1-4438-7889-0. Extract of page 272
  8. ↑ Newton, I. (1726). Philosophiæ Naturalis Principia Mathematica (3 ed.). London.
  9. ↑ Everitt, C.W.F. "James Clerk Maxwell: a force for physics". Physics World. IOP Publishing. Retrieved 12 March 2026.
  10. ↑
    The principle of relativity, according to which the laws of physical phenomena should be the same, whether for an observer fixed, or for an observer carried along in a uniform movement of translation; so that we have not and could not have any means of discerning whether or not we are carried along in such a motion.

    — Henri Poincaré, 1904

    Poincaré, Henri (1904–1906). "The Principles of Mathematical Physics" . Congress of arts and science, universal exposition, St. Louis, 1904. Vol. 1. Boston and New York: Houghton, Mifflin and Company. pp. 604–622.
  11. ↑ C. Møller (1952). The Theory of Relativity (2nd ed.). Delhi: Oxford University Press. p. 220. ISBN 0-19-560539-X. {{cite book}}: ISBN / Date incompatibility (help)

Further reading

See the special relativity references and the general relativity references.

allikas: https://en.wikipedia.org/wiki/Principle_of_relativity