Before Einstein — Classical Physics
Newton dominates: time and space are absolute, the same for all observers.
Problem: Maxwell's equations (light/electromagnetism) did not fit with Newtonian mechanics.
1905 — Special Relativity
Einstein publishes his theory for moving bodies without gravity.
Consequences: time dilation, length contraction, universal speed limit (c), and E = mc².
1915 — General Relativity
Extends the theory by including gravity and non-inertial systems.
Gravity is not a force, but the curvature of spacetime caused by mass.
1919 — First Public Verification
During a solar eclipse, it is observed that light bends when passing near the Sun.
Einstein was right: mass curves space and deflects even light.
Today — Real-world Applications
Satellite GPS, nuclear energy, cosmology, and models of the universe's origin.
Without relativistic correction, GPS would accumulate kilometers of error per day.
Core Idea
The Observer Matters
The location in space and time of a phenomenon depends on the observer's speed. What was once thought absolute (time, space) actually varies. Two observers moving at different speeds can measure different times and distances for the same event.