Duane is referring here to slide 11 of Dr. Matthew West's
presentation that we were going through just now. ref:
http://ontolog.cim3.net/cgibin/wiki.pl?ConferenceCall_2006_02_23#nidK49 (01)
=ppy
 (02)
Duane Nickull wrote Thu, 23 Feb 2006 09:17:32 0800:
> The light cone calculus is remarkably similar in theorem to Slide 11.
>
> "Null geodesics lie along a dualcone defined by the equation
>
> ds^2 = 0 = dx_1^2 + dx_2^2  c^2 dt^2
>
> or
>
> dx_1^2 + dx_2^2 = c^2 dt^2
>
> Which is the equation of a circle with r=c*dt. If we extend this to three
>spatial dimensions, the null geodesics are continuous concentric spheres, with
>radius = distance = c×(±time).
>
> ds^2 = 0 = dx_1^2 + dx_2^2 + dx_3^2  c^2 dt^2
>
> dx_1^2 + dx_2^2 + dx_3^2 = c^2 dt^2
>
> This null dualcone represents the "line of sight" of a point in space. That
>is, when we look at the stars and say "The light from that star which I am
>receiving is X years old.", we are looking down this line of sight: a null
>geodesic. We are looking at an event d = \sqrt{x_1^2+x_2^2+x_3^2} meters away
>and d/c seconds in the past. For this reason the null dual cone is also known
>as the 'light cone'. (The point in the lower left of the picture below
>represents the star, the origin represents the observer, and the line
>represents the null geodesic "line of sight".)
>
> The cone in the −t region is the information that the point is 'receiving',
>while the cone in the +t section is the information that the point is
>'sending'.
>
> The geometry of Minkowski space can be depicted using Minkowski diagrams,
>which are also useful in understanding many of the thoughtexperiments in
>special relativity."
>
> Great stuff!!!
>
> Duane
>
> *******************************
> Adobe Systems, Inc.  http://www.adobe.com
> Vice Chair  UN/CEFACT http://www.uncefact.org/
> Chair  OASIS SOA Reference Model Technical Committee
> Personal Blog  http://technoracle.blogspot.com/
> *******************************
>
>
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