Three Roads To Quantum Gravity

24 THREE ROADS TO QUANTUM GRAVITY
is not the same as
FIGURE 4
In a non-relational theory it matters also where the ®eld lines are in absolute
space.
have a meaning and existence that transcends any particular
process of change in the universe.
In the twentieth century we learned that this view of time is
as incorrect as Newton's view of absolute space. We now
know that time also has no absolute meaning. There is no time
apart from change. There is no such thing as a clock outside
the network of changing relationships. So one cannot ask a
question such as how fast, in an absolute sense, something is
changing: one can only compare how fast one thing is happening
with the rate of some other process. Time is described
only in terms of change in the network of relationships that
describes space.
This means that it is absurd in general relativity to speak of
a universe in which nothing happens. Time is nothing but a
measure of change ± it has no other meaning. Neither space
nor time has any existence outside the system of evolving
relationships that comprises the universe. Physicists refer to
this feature of general relativity as background independence.