The Unreality of Time



For what is time? Who can easily and briefly explain it? Who can even
comprehend it in thought or put the answer into words? Yet is it not
true that in conversation we refer to nothing more familiarly or
knowingly than time? And surely we understand it when we speak of it;
we understand it also when we hear another speak of it.

What, then, is time? If no one asks me, I know what it is. If I wish to
explain it to him who asks me, I do not know. Yet I say with confidence
that I know that if nothing passed away, there would be no past time;
and if nothing were still coming, there would be no future time; and if
there were nothing at all, there would be no present time.

But, then, how is it that there are the two times, past and future,
when even the past is now no longer and the future is now not yet? But
if the present were always present, and did not pass into past time, it
obviously would not be time but eternity. If, then, time present--if it
be time--comes into existence only because it passes into time past,
how can we say that even this is, since the cause of its being is that
it will cease to be? Thus, can we not truly say that time is only as it
tends toward nonbeing?
Augustinus, Confessions, Book 11, chap. 14



2005-08-21

Assume that somebody has indeed found a Theory Of Everything and, furthermore, assume
that we know the exact initial state of the universe (either from observation or from some first
principles). Even then the simple question "What time is it?" could only be answered by looking
at a clock.
                                                                               
Of course, physics never asks or answers the philosophical questions about time, instead it uses
the 'definition' that time is what one reads from a clock. Both general relativity and quantum theory
assume the existence of localized, classical clocks of arbitrary precision.
                                                                               
Following the analysis of Salecker and Wigner, the mass of a clock needs to increase (and its
effective size needs to decrease) if one wants higher precision and the limit of Planck length and
Planck time would be reached when the clock begins to form a black hole; Thus our 'definition'
of time breaks down for quantum gravity. The 'problem of time' appears also as a direct consequence
of the Wheeler-deWitt equation, H|psi> = 0, of quantum gravity; It is formally a stationary Schroedinger
equation for only one eigenvalue E = 0.

Assuming that replacing elementary particles with superstrings does not help one with this 'problem
of time', one may want to look at the work of Julian Barbour instead, who proposes to eliminate time
from physics. While his book The End of Time and his more technical papers [1,2] are very interesting
indeed, one needs to realize that concepts such as 'prediction' and 'probability' (and thus physics as we
know it) would disappear with the concept of time. These issues, raised by Fay Dowker in an email
discussion printed at the end of the book, require good answers in my opinion.


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