Special Relativity & the Speed of Light: Observation, Measurement & Evidence

Events are described in spacetime rather than separate absolute space and time. Different inertial observers can disagree on elapsed time, spatial separation, and simultaneity while agreeing on the spacetime interval and causal order of timelike-related events.

Particle lifetimes increase at high speed, accelerator measurements obey relativistic energy-momentum relations, atomic clocks on aircraft and satellites show predicted timing shifts, and astronomical jets display relativistic beaming and apparent superluminal motion without transmitting information faster than light.

Lorentz transformations replace Galilean transformations when relative speeds become comparable to light speed. The geometry of spacetime requires moving clocks to accumulate different proper times and prevents material objects with nonzero rest mass from being accelerated through the speed of light.

Muon lifetimes, particle accelerators, atomic clocks, binary timing, and relativistic jets all confirm special-relativistic predictions. Apparent superluminal motion in jets is a projection/light-travel effect rather than faster-than-light information transfer.