ZapperZ said:
Just so you know, you both are replying to a thread that had its last post in 2004! The ship had long ago left the harbor.
Zz.
And now I'm responding 6 months later, because humans think alike in many ways and thus often arrive at the same question. My view on the question is as follows (and is most likely wrong, and hence why I came across this thread in search of an answer).
An observer always sees himself as being in the center of the universe, whether the universe is open, flat or closed. Thus the worldline of an observer appears as a straight line through time to the observer himself (the observer never appears to move relative to himself and everything else moves about him).
However, as one approaches the speed of light, space contracts in the direction of which you are traveling and when you actually attain the speed of light, space flattens into a 2-D plane perpendicular to your direction of travel (based on my current understanding).
Also, as an observer approaches the speed of light, the observer also perceives "time contraction." Thus events seem to occur faster to the observer than they do to observers at rest. When an observer attains the speed of light, all events occur in zero time. Since events cause other events, he observes all events in the history of the universe between the time he reached the speed of light and the time he slowed down from the speed of light occurring at the same time without any causality.
Hence, that when traveling at the speed of light, the worldlines of all particles contract to a 2-D line upon a 2-D plane perpendicular to the observer, including the observer's light cone, meaning the observer's light cone becomes a circle on the 2-D plane whose radius is determined by the "life" of of the photon (the time between emission and absorption).
Therefore a photon experiences a flat 2-D universe with no time, and thus every event in its light cone happens simultaneously with no causality, as the notion of causality is meaningless in a universe with no passage of time. All point particles would be observed as line particles in such a universe.