Relativity
Definition
The idea that measurements of space and time depend on how the observer is moving. There is no single universal clock or ruler — your motion changes what you measure, while the laws of physics stay the same for everyone.
Symbol: ·
Technical definition
Einstein's framework describing physics in different frames of reference. Special relativity (1905) shows the speed of light is constant for all observers, forcing time dilation and length contraction at high speeds; general relativity (1915) describes gravity as the curvature of spacetime by mass and energy.
Example
GPS satellites move fast and sit far from Earth's gravity, so their clocks tick at a different rate than ground clocks — about 38 microseconds per day. Without relativity corrections, GPS positions would drift by kilometers within a single day.
Relativity does not mean 'everything is relative and there are no rules.' The point is the opposite: the laws of physics and the speed of light are absolute for every observer — only measurements of space and time shift between frames.