sci.physics.research

In article , goatREMOVETHIS123
@ says...

> I am trying to find an objective definition of 'measurement', one that
> need not involve physicists, other humans, or cats. I want to be able
> say that this or that experimental setup constitutes a 'measurement'
> regardless of whether anybody looks at the results. It seems to me that
> the basic function of a measurement is to turn a small uncertainty into
> a large one. The questions I wonder are:
>
> How can we quantify the uncertainty?
> To what system does it apply?
>
> As an aside, if Schrodinger's cat is replaced by a physicists, who
> I guess we must deem able to make a measurement, then the
> situation gets even more weird. Presumably the physicist knows
> that he is alive (if that is the case) and the measurement is thus made.
> If on the other hand he is dead then he cannot make the measurement
> to that effect and he therefore must remain half-dead/ half-alive,
> except that we have just said that he is dead. Weird!

But the weirdness comes precisely from your insistence that there must
be an "objective" definition of measurement, or, put another way, that
state vector resolution is a physical process that occurs at a
particular point in spacetime!

[The necessity of placing it at a particular point in spacetime, in
fact, seems to be another problem with the concept of physical state
vector resolution that I haven't seen mentioned before. Since quantum
systems are often extended in spacetime, the process of state vector
resolution, however we understand it, must be extended also. And this
seems to fit very poorly with any simplistic approach to the issue.]

Personally I think that Schrodinger's Cat leads naturally to the concept
of decoherence. It can perhaps be seen better with another gedanken
which I will call the Simplified Schrodinger's Cat.

In the Simplified Schrodinger's Cat Experiment, we simply put a cat in a
box, close the lid for a period, and open it again. There are a large
variety of things we might now observe; the cat may be asleep or awake,
it may have scratched or otherwise left its mark in one or more places
inside the box. And it's obvious that no meaningful quantum
superpositions can be observed between any two distinct states of this
kind. The cat has apparently been generating entropy via interactions
with itself and anything else on the inside of the box - or at least the
portion of the wave function of the universe covering the region of
spacetime where the box was closed has evolved in such a way as to
produce an equivalent result.

Wherever we choose to define measurement - inside the box, or when it is
opened - it makes no difference to the physics. And thus, it would
appear, state vector resolution is not physical, unless it operates
according to some criterion we do not currently recognise.

- Gerry Quinn