Measurement in QM FAQ question

From: DDEckerslyke (spambin_at_tiscali.co.uk)
Date: 07/20/04 

Date: 20 Jul 2004 02:41:04 -0700

OK i've read the FAQ here
http://www.mtnmath.com/faq/meas-qm.html
wherein lies the link to Schrodinger's Cat for a 6th grader
http://www.mtnmath.com/cat.html
from which this is taken

"To understand Schrödinger's cat one must understand what a strange
theory quantum mechanics is. In all other scientific theories we have
models of how we think things work. For example we know that distance
traveled equals speed times velocity. If you travel for two hours at
50 miles an hour you will go one hundred miles. We can measure the
time with a clock and the distance with the odometer on your car.
Quantum mechanics is not like that. What we measure in experiments is
not described by quantum mechanics. Instead quantum mechanics gives
the probability that we will make a given measurement.

"Probabilities occur all the time in science because we almost never
know everything we need to make a completely accurate prediction. For
example if you really want to make a trip of a hundred miles you can
not know ahead of time exactly how long it will take. You might run
into a traffic jam. You can only give an estimated time. In quantum
mechanics probabilities are different. They are not considered to
result from our limited understanding of the universe but to be
fundamental. Of course Einstein thought this was mistaken but most
physicists do not agree with him."

Continuiung the analogy of the car journey: Observing whether you have
arrived at your destination does not determine your arrival it just
confirms it, or otherwise, in the mind of the observer. Similarly with
Schrodinger's Cat. It's either alive or dead but the observer doesn't
know till they look. Or am I missing the point? Did Scrodinger use the
example of the cat to highlight the apparent absurdities of the
participant observer?

ISTM making the observation does not determine/decide the state of the
system it just means the observer now knows what the state of the
system is. Now AIUI this is exactly the cherished notion of an
objective universe 'out there' that QM undermines but I'm not clear
how exactly it is undermined. Help?

I've Gooooogled on this but no luck yet.

cheers

dd

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