History of Relativity

Special Relativity (1905)

Einstein's Special Theory of Relativity revolutionized our understanding of space and time, introducing concepts that showed these were not absolute but relative to the observer's motion.

Key Principles

  • Speed of light is constant in all reference frames
  • Laws of physics are the same for all inertial observers

Major Equations

Mass-Energy Equivalence:

E=mc2E = mc^2

Time Dilation:

t=t01−v2c2t = \frac{t_0}{\sqrt{1-\frac{v^2}{c^2}}}

Length Contraction:

L=L01−v2c2L = L_0\sqrt{1-\frac{v^2}{c^2}}

General Relativity (1915)

General Relativity extended Special Relativity to include gravity, describing it as a curvature of spacetime caused by massive objects.

Key Concepts

  • Gravity is a manifestation of curved spacetime
  • Mass tells spacetime how to curve; spacetime tells mass how to move
  • Light follows curved paths in curved spacetime

Einstein Field Equations

Gμν+Λgμν=8πGc4TμνG_{\mu\nu} + \Lambda g_{\mu\nu} = \frac{8\pi G}{c^4}T_{\mu\nu}

Modern Applications

  • GPS Satellite Systems
  • Gravitational Lensing
  • Black Hole Physics
  • Gravitational Waves (LIGO)

Experimental Confirmations

  • Eddington's Solar Eclipse Expedition (1919)
  • Pound-Rebka Experiment (1959)
  • Hafele-Keating Experiment (1971)
  • Gravity Probe B (2004-2011)
  • LIGO Gravitational Wave Detection (2015)