1.Simultaneity 2.Time Dilation 3.Length Contraction SPECIAL RELATIVITY Space, time, motion, revisited

Special Relativity Postulates 1.The laws of physics are same for all observers in inertial reference frames (IRF) 2.The speed of light in vacuum is c, regardless of relative speed between source and observer. Rexamine basic concepts – space, time, speed,.. Demand operational definitions -> consensus based on observation

Simultaneity Is simultaneity absolute ? Operational def n Two clocks in different places strike Noon simultaneously if YOU, standing halfway between them, see them strike Noon at the same time. Moving Observer George is moving uniformly relative to YOU and the clocks In George’s IRF, the clocks do not strike Noon simultaneously Both YOU and George are correct Simultaneity is a relative conceptSimultaneity

Relativity of Time Two light clocks, synchronized at relative rest Tick-tock time is T for both YOU and George Now light clocks in relative motion George is moving relative to Your IRF…

You say light travels further in George’s clock, so his tick-tock lasts T G by Your clock, longer than T (2 nd Postulate). Conclude moving clock runs SLOWER NOTES: Dilation occurs for ALL clocks, not just light clocks Effect is tiny unless clocks move at nearly the speed of light George sees no change in his clock, tick-tock T (1 st Postulate)

Relativity of Length Put clocks at each end and You (halfway) on a train moving relative to George sitting on a tunnel. 1. Front clock strikes Noon as it exits tunnel 2. Back clock strikes Noon at it enters tunnel Suppose You see them strike Noon simultaneously you conclude train fits exactly in tunnel George sees back clock strike Noon first, front clock later concludes train is shorter than tunnel Moving objects are…