Observables, Measurables, and Detectors

From: Lee Corbin <lcorbin.domain.name.hidden>
Date: Wed, 25 May 2005 02:27:06 -0700

Patrick Leahy wrote

> To answer [the] initial question: interference effects are not branches.
> Actually they imply the absence of effective branching.
>
> You don't get branching in time because time is a parameter, not an
> observable: this means that there is no quantum uncertainty about what the
> time is. (At least in the non-relativistic theory. Frankly, I don't know
> how to handle the relativistic case).
>
> You might say: we don't know what time the particle will be detected. Yes,
> but the theory doesn't consider the detection event as *one thing* with an
> uncertain time. In the MWI there are many (a continuum) of detection
> events, each of which happens at a well defined time and each of which
> starts off its own branch. And the act of detection changes the detector
> physically, which is to say that its particles are re-arranged. Hence the
> slogan "every measurement is a position measurement". Of course they are
> all momentum measurements as well, etc.

It looks as though you advocate a role for each of these:

   observables
   measurements
   detectors

and for all I know

   observers

It seemed to me that MWI allowed me to get away with a considerable
simplification. Gone were observers and even observations. Even
measurements, I discard. (After all, who can say that a measurement
occurs in the middle of a star? And yet things do go on there, all
the time.)

Now *some* of that language perhaps returns when decoherence is
discussed. I mean, I'll grant that *something* significant starts
off a new branch, and so it's okay for it to have a name. :-)

But here is what I'd like to be able to say:

A new branch starts, or decoherence obtains, or an irreversible
transformation occurs, or a record is made. They all seem the
same to me. Why not?

My main motivation is to get as far away from Copenhagen as possible,
and so thereby get free of observers and observations, and anything
else that seems to afford some pieces of matter a privileged status.
Do you think that such simplified language leaves out anything important?

Thanks,
Lee
Received on Wed May 25 2005 - 05:31:07 PDT