Myths
Absolute Space
Points of View
Twin Paradox
Einstein's Train
Andromeda Paradox
Time in Spacetime
Clocks & Time
Velocity of Light
Time in Spacetime
There is a myth that time in spacetime is just another dimension, i.e. it is equivalent to a spatial dimension. This has a very significant impact on the philosophic interpretation of spacetime.
However, it is very easily shown to be false, because time has a distinctly different impact on "distances" in spacetime from the spatial dimensions. Spatial distances in spacetime add according to the Pythagorean theorem, just as in Euclidean space. So:
d2 = x2 + y2 + z2
Where x, y and z are distances, in metres, measured against the 3 dimensional axes. However, the resulting distance (d) is subtracted from the time interval. So:
s2 = (ct)2 - d2
Where s is the spacetime interval. Note: In this case, we are measuring the spacetime interval in metres, so t (the time interval), is multiplied by c (the velocity of light) to convert seconds to the distance in metres that light travels in that number of seconds (so that all the units match).
Hence the time interval has the opposite effect on the spacetime interval from the spatial distance. This is explained in more detail under the heading of Spacetime Mechanics in the section on Spacetime.
