In virtue of the latter
property we speak of a " continuum," and owing to the fact that there
are three co-ordinates we speak of it as being " three-dimensional."
Similarly, the world of physical phenomena which was briefly called "
world " by Minkowski is naturally four dimensional in the space-time
sense. For it is composed of individual events, each of which is
described by four numbers, namely, three space co-ordinates x, y, z,
and a time co-ordinate, the time value t. The" world" is in this sense
also a continuum; for to every event there are as many "neighbouring"
events (realised or at least thinkable) as we care to choose, the
co-ordinates x[1], y[1], z[1], t[1] of which differ by an indefinitely
small amount from those of the event x, y, z, t originally considered.
That we have not been accustomed to regard the world in this sense as
a four-dimensional continuum is due to the fact that in physics,
before the advent of the theory of relativity, time played a different
and more independent role, as compared with the space coordinates. It
is for this reason that we have been in the habit of treating time as
an independent continuum. As a matter of fact, according to classical
mechanics, time is absolute, i.
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