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Mathematics for Physics

200 Relativity Principle

The postulate that all physical laws look the same to every inertial observer, so absolute uniform motion cannot be detected.

The first postulate of special relativity. The laws of physics take the same mathematical form for every inertial observer. A law of physics is a relation that holds for nature. This principle is used to rule out a preferred absolute rest.

The equivalence of inertial observers. Each of two observers in uniform relative motion takes themselves as at rest. Uniform relative motion is motion at constant velocity of one observer with respect to the other. This principle is used to treat only relative velocity as physically measurable.

The extension of relativity to electromagnetism. The requirement covers mechanics, electromagnetism, and optics together. Optics is the physics of light. This principle is used to demand the same form of Maxwell’s equations in every inertial frame.

Note: Also called the principle of relativity. See Principle of Relativity.

200.1 References

  1. Knight, R. D. Physics for Scientists and Engineers: A Strategic Approach with Modern Physics. Pearson, 2023. — source for the heading explanation.
  2. Griffiths, D. J. Introduction to Electrodynamics. Cambridge University Press, 2024. — same form of the laws in every inertial frame.
  3. Shankar, R. Fundamentals of Physics I. Yale University Press, 2019. — equivalent observers in uniform relative motion.