Defining time contest replies

Subject: defining time replies
From: Doug Sweetser <sweetser@alum.mit.edu>
Date: 1996/04/25
Message-Id: <DqFs13.5qq@murdoch.acc.Virginia.EDU>
Newsgroups: sci.physics.research
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Last month, I posted the following message about defining time:

>Please e-mail me (sweetser@alum.mit.edu) your favorite definition
>of time. There are two constraints: it must be based on mathematics
>or physics - not philosophy - and it must be two sentences or less.

The most popular submission, attributed to John A. Wheeler, was:
"Time is Natures way of keeping everything from happening at once."


More technical responses follow:
I have two (serious) definitions of time. One technical, and the
second in plain words, with (as much as possible) the same content:
1. Time is the parameter of the Tomita group of automorphisms of the
observables algebra, generated by the statistical state
in which the Universe around us happens to be.
2. Time is an illusionary side product of our ignorance of the precise
state of the Universe: ignorance implies statistical predictions only,
these imply increase in entropy, entropy increase gives us the
illusion of time.
Carlo Rovelli <rovelli+@pitt.edu>


The observable difference between a pair of events in 4 dimensional
spacetime defines a quaternion - a member of a skew field - whose
scalar component is the wristwatch time difference between the events
as measured by the observer and the vector component is the locally
measured distances, which can also be written as the following matrix:
| t -x -y -z |
| x t -z y | = q(t,x,y,z)
| y z t -x |
| z -y x t |
The interval between these two events is
Interval(q) = scalar(q . q)^.5
and for a particular q, there exists a set of quaternions {L} which
performs an affine transformation L . q = q' to a different frame of
reference such that
Interval(q) = scalar(q . q)^.5 = scalar(L . q . L . q)^.5
the set {L} serving a function similar to the Lorentz group in the
neighborhood of the interval, for example
L = (vector[q . q] - scalar[q . q])/norm[q]
preserves the interval but L . q = q' reverses the time.
Doug Sweetser <sweetser@alum.mit.edu>


Nature's monotonic count in the process of creating an
objective reality where the interval between the ticks
is dilated by curvature.
Myke Stanbridge <mykestan@cleo.murdoch.edu.au>


I think it is essential for quantum gravity to distinguish different
notions of time:
1. Time measurement by clocks (GR time).
2. Time as the thing which defines present, future and past (QM time).
The idea behind is that these different notions have not to be unified
in quantum gravity, but are different.
Ilja Schmelzer <schmelze@wias-berlin.de>


t=<T>=tr((rho- adjoint)T(rho))
Prigogine,"From Being to Becoming",p.204.
Ross Powell via DGedye@netlink.co.nz


I have two definitions:
Time is what prevents all things from happening simultaneously.
Time is what separates two different events at the same place.
Sven Nielsen <snil@daimi.aau.dk>


The distance between two separate events occurring at the same
location.
Keith <F.MALFANTI@kcl.ac.uk>


An editorial comment: I think it is vital that the community of
physicists settle on a precise technical definition of time that is
explicit instead of the implicit definitions of time found in the
working equations of physics.

Hope you find this interesting,
Doug Sweetser <sweetser@alum.mit.edu>