Tag Archives: light cone

April 10, 2015

SR #18: Light Cones

sr18-0a Last time I focused on how it was possible for Al to see — even enclose in a tunnel — a train that appears shorter to him due to its motion. It turns out that the train Al sees is a stack of time slices of the train at different moments. As we’ve seen, lots of things look different in a moving frame.

Today I want to say a little about Em’s point of view, run some numbers, and take you through a little math (just one equation, I promise). Then, because it’s Friday (when I try to write about light), I’ll introduce you to light cones.

They’re not actually necessary, but they’re kinda cool.

4 Comments | tags: 2D, 3D, gamma factor, gamma term, light, light cone, light speed, line of simultaneity, plane of simultaneity, simultaneity, simultaneous events, space-time, Special Relativity, surface of simultaneity, time-space diagram | posted in Physics

April 3, 2015

SR #13: Coordinate Systems

By Wyrd Smythe

The main topic this week was how simultaneity is relative to your frame of reference. How there are (virtual) lines of simultaneity where all points on some line — at all distances from you — share the same moment in time. For any instant you pick, that instant — that snapshot — includes all points in your space.

A line of simultaneity freezes the relative positions of objects at a given moment — which enables distance measurements. Simple example: When their watches both read 12 noon, Al and Em were 30 miles apart. A more mathematical example uses x, y, & z (& t), but it amounts to the same thing: a coordinate system.

The gotcha is that simultaneity and coordinate systems are relative when motion is involved!

5 Comments | tags: 1D, 2D, 3D, Albert Einstein, Emmy Noether, frame of reference, Galilean invariance, light, light clock, light cone, light speed, line of simultaneity, simultaneity, simultaneous events, space-time, Special Relativity, surface of simultaneity, time-space | posted in Physics