[Physics] "Real" time

[Thomas Goodey]

On 30 Oct 2016 at 12:00, physics-request at tuks.nl wrote:

> 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. 

The above statements are not expressed in space-time terms. 
More properly, if Alice and Bob have met, then their 
meeting has been a real space-time event (call it E), which 
in various reference frames may be referred to by a variety 
of coordinates, such as (x1, y1, z1, t1) or (x2, y2, z2, 
t2) or the like. If they have never met, then no such event 
has ever existed.

> 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 the meaning described above, yes.

> 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.

The above does not refer to the time on clocks that Alice 
and Bob are carrying with them. It refers to the clock in 
any inertial frame: the event E has coordinates in that 
frame, including a time coordinate tN.

> 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.

This statement is also subject to the same clarification as 
I have given above.

Thomas Goodey
****************** 

But remember, please, the rules by 
which we live. 
We are not built to comprehend a 
lie. 
We can neither love, nor pity, nor 
forgive. 
If you make a slip in handling us you 
die.  

Rudyard Kipling, 'Secret of the 
Machines'