[Physics] "True" time

[Ilja Schmelzer]

2016-10-29 14:29 GMT+02:00, Thomas Goodey <thomas at flyingkettle.com>:
> Common sense is not precise enough for modern physics.

For a "meaning" it is precise enough.  Because all what you need for
the mathematical apparatus of physics is that time is a real
parameter.

> Anyway, if "true" time cannot be measured, i.e. if
> intervals of it cannot be assigned numerical values by the
> use of some apparatus, it is not a physical quantity.
> Perhaps it is a feeling... like when you get hungry? or
> cold?

No.  A parameter is a physical parameter if it is used in physical equations.

A nice example is quantum theory.  You have a wave function, psi(q,t),
 which depends on the (classical) configuration and the time.  And you
have the Schroedinger equation, which is an evolution equation in t.

Observables in quantum theory are self-adjoint operators.  There are
theorems that there is no such self-adjoint operator for time
measurement.  And even that every clock will, with some non-zero
probability, go even backward in time.

Nonetheless, without this time you cannot even write down the
Schroedinger equation.

And your argument should be simply rejected as positivistic.

> I do not know what the above means; it seems to be complete
> nonsense; but anyway, it is not physics.

Ok, another try.

Alice and Bob come sometimes to some place X.  If they meet each
other, that means, they have been there at the same time.  If they
have never meet there, they have never been there at the same time.
Above statements are clear and simple common sense statements, and
tautologically true.

If they meet each other or not is a simple physical fact.  This makes
statements of type "been there at the same time" physical statements
too.

With clock time instead of true time, above statements make no sense.
Except if one uses clock time as an approximation of true time. Else,
one would have to specify the clock time of which clock one has in
mind.

This is clearly not the only type of a physical, physically meaningful
statement involving true time. Another important class is related with
causality:  If event A has causally influenced event B, then when A
has happened before B has happened. Which is another physical
statement about the relation between the true times of the events A
and B.  Which is in no way a claim about their clock times.