Proper time, time dilation and length contraction
Along a timelike worldline in an inertial coordinate frame, dτ=dt√(1−u²/c²), and elapsed proper time is its integral.
Key knowledge
Along a timelike worldline in an inertial coordinate frame, dτ=dt√(1−u²/c²), and elapsed proper time is its integral. A rod's rest length L₀ is measured as L=L₀/γ along its motion when its endpoints are simultaneous in the measuring frame.
Values and equations
Δτ=∫dt√(1−u(t)²/c²); L=L₀√(1−v²/c²)
- τ,t
- Proper and coordinate time s
- u,v,c
- Particle/frame/light speeds m s⁻¹
- L,L₀
- Moving/rest lengths m
Conditions and scope
- Flat spacetime, massive timelike motion u<c; the local proper-time relation also applies along an accelerated worldline.
- Length contraction assumes a rod with a defined inertial rest frame and simultaneous endpoint observations; it is not an arbitrary photographic length.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Electromagnetism (2014): Proper time: Equations 1714–1717 and final length-contraction discussion; interval-sign convention not copied.
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Entry details
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- physics-proper-time-length
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- university-core.1
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- University core expansion