Physics · University
Special relativity and invariant intervals · revision notes
Special relativity describes inertial-frame transformations with invariant vacuum light speed. It replaces Galilean transformations when relativistic effects matter.
Key ideas and conditions
Postulates
Special relativity describes inertial-frame transformations with invariant vacuum light speed. It replaces Galilean transformations when relativistic effects matter.
Proper time
Proper time is measured by a clock along its own worldline. For uniform inertial relative speed, a coordinate interval satisfies Δt=γΔτ.
Interval
Using the +−−− convention, s²=c²Δt²−Δx²−Δy²−Δz². The sign distinguishes timelike, null and spacelike separations.
Simultaneity
Spatially separated simultaneous events in one inertial frame need not be simultaneous in another. Time dilation must not be used without identifying the clock and events.
Explain without looking
- In an inertial frame, a massive free particle's speed is constrained how?
- Why must one identify event pairs before applying a time-dilation formula?
Further reading and review references
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