World Lines As A Tool To Describe Events
A one-dimensional line or curve can be represented by the coordinates as a function of one parameter. Each value of the parameter corresponds to a point in spacetime and varying the parameter traces out a line. So in mathematical terms a curve is defined by four coordinate functions (where usually denotes the time coordinate) depending on one parameter . A coordinate grid in spacetime is the set of curves one obtains if three out of four coordinate functions are set to a constant.
Sometimes, the term world line is loosely used for any curve in spacetime. This terminology causes confusions. More properly, a world line is a curve in spacetime which traces out the (time) history of a particle, observer or small object. One usually takes the proper time of an object or an observer as the curve parameter along the world line.
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Famous quotes containing the words world, lines, tool, describe and/or events:
“I did not live until this time
Crown’d my felicity,
When I could say without a crime,
I am not thine, but Thee.
This carcase breath’d, and walkt, and slept,
So that the World believ’d
There was a soul the motions kept;
But they were all deceiv’d.”
—Katherine Philips (1631–1664)
“His more memorable passages are as naturally bright as gleams of sunshine in misty weather. Nature furnishes him not only with words, but with stereotyped lines and sentences from her mint.”
—Henry David Thoreau (1817–1862)
“A broken altar, Lord, thy servant rears,
Made of a heart, and cemented with tears:
Whose parts are as thy hand did frame;
No workman’s tool hath touched the same.”
—George Herbert (1593–1633)
“To describe drunkenness for the colorful vocabulary is rather cynical. There is nothing easier than to capitalize on drunkards.”
—Anton Pavlovich Chekhov (1860–1904)
“It is clear to everyone that astronomy at all events compels the soul to look upwards, and draws it from the things of this world to the other.”
—Plato (c. 427–347 B.C.)