Edaw asked:

If time has a beginning (when things started to change) does it have an end (when things stop
changing)?

How is it possible for the universe to stop changing?

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What is time? From the way you put your question, it seems to me that you think of time as
something independent, some entity or process that runs its course, irrespective of the entities or
processes comprising the universe. But this is not the case: time is dependenton entities and
processes being there; and it is altogether appropriate to look upon time as their periodicity.So, for
example, what we humans understand by the concept of "time" is tied to the physical processes
which control our lives, from the periodical rotations of the sun and moon, which strongly affect the
chemical processes of life on earth, to the small-scale (and sometimes imperceivably minute)
activities of subcellular and even submicroscopic events that occur in these realms and (as it were)
set the agenda for the larger-scale events which we call "living".

Even without going into the specialised meaning attached to the concept of time in physics, which is
however an altogether analogous meaning — i.e. tied to the large-scale rotations of cosmic events
controlled by gravitation etc. — it should be clear to you now that "time" is a human concept and has
no independent existence whatever. It is merely a wordwith a specific meaning to us humans. Time
itself is neither observable nor measurable; what we call the "measurement" of time is merely a
gauge we put on processes developing in a monodirectional way. If you really want to confuse
yourself, you might like to try this little logical exercise: we measure time today by the vibration rate of
the caesium atom. This atom flutters something like 900 billion times a second. What is a second?
Well, 900 billion vibrations of the caesium atom! There is merit, then, in the old wisecrack that God
invented time to prevent everything from happening at once.

The question of the universe stopping is a little more difficult to answer properly. It depends in large
measure on the theory of thermodynamics and the subsidiary question of whether that theory is
accurate. We believe it is, but there are no guarantees. We cannot observe the universe, only a very
small portion of it. So the current theory is that thermodynamic processes will "run down", that
ultimately the fuel which drives all the nuclear interactions we can detect out there will burn
themselves out. For example, an atom vibrates when it is active, and in doing so dissipates its mass.
This dissipation is what we mean by "burning out". Like striking a match and watching it turning to
ash. Ash is not renewable; so if the thermodynamic theory is correct, then at some time in perhaps
20-30 billion years, the presently known mass of the universe will have burnt itself out and everything
will come to a stand still.

However, there is a countervailing theory, which assumes a "residual electric potential", like an
"energy pump", which in fact continuously recycles these processes. You can understand this in
terms of such phenomena as superconductivity, a state of matter where (because of the coldness)
resistance to the dispersal of energy across the vast distances of an empty universe is practically nil;
and these energy fragments are bound, sooner or later, to collide and build up the dissipated
structures again. As they build up, heat is generated, resistance increases etc etc. Time resumes.

For the time being, these are the main theoretical alternatives. But which one you choose to believe is
entirely up to you.

Jürgen Lawrenz

Sydney