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The following is my response to a 6th grade student's questions
about Schrödinger's cat. It involves a limited discussion of some of the issues
in quantum mechanics, which led to Schrödinger's famous cat.
There are partial answers to your questions based on the
Copenhagen Interpretation of quantum mechanics. Schrödinger was referring to
this interpretation in his description of the cat experiment. There are
currently no scientific answers to your questions. The Copenhagen
Interpretation is not a scientific theory and is not universally, or even
widely, accepted by scientists.
First, if a person was in the box, then he or she would observe
their own demise or continued existence. This would be the same as looking in
the box. You second question is similar to the first. If any person looks in
the box and sees what happened to the cat, then it has happened, and everyone
else will see the same thing. I suspect your friend, that talked about people
in different realities, has heard about the Many Worlds Interpretation of
quantum mechanics. This is an interpretation that competes with the Copenhagen
Interpretation, and did not exist at the time that Schrödinger described the
cat experiment.
Schrödinger invented this fiendish experiment, not to explain what
happens to the cat, but to show that the existing theory had confusing aspects
to it. Scientists understand a great deal, but the more they learn the more new
unanswered questions occur to them. Although the cat example is over 70 years
old, it is left for future generations, perhaps for you and your friends, to
figure out a good answer to your questions.
I do not usually have time to answer questions like yours, but I
thought it might be useful and fun to write an simple explanation of
Schrödinger's cat and post it on my web site.
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 time traveled multiplied by 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 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.
Quantum mechanics only describes how probabilities change with
time. For example, if the particle in the cat example has a 50% probability of
decaying in one hour, then in one minute it will have only a slight chance of
having decayed. After 10 hours it will have a probability very close to one of
having decayed. Quantum mechanics gives an exact model of how that probability
changes over time. It says nothing at all about the state of
the cat as these probabilities change. Science tells us what the probabilities
are, but is completely silent on what (if anything) happens between
observations. That is why there is no scientific answer to your questions.
There is not even a scientific definition of what an observation is.
In the quantum mechanical model nothing ever happens! The particle
never has to decay. The probability just keeps getting closer and closer to
one. There is nothing to force a real event to happen. This is very confusing,
because what we observe is always real events. We see the particle decay at
some particular time.
Niels Bohr proposed a solution to create the events we all
observe. He assumed that conscious observation caused events. He thought there
was an aspect of the world described by the evolution of probabilities in
quantum mechanics, and an aspect of the world that we observe. Whenever we look
in the box or make a measurement, we get some definite result and not just a probability.
But quantum mechanics never models these events. If we do not look, there are
no events. There are just probabilities changing.
Bohr's idea is called the Copenhagen Interpretation of quantum
mechanics. It is not science. For something to be part of science, you must be
able to test it experimentally. Interpretations do not make predictions that
differ from the probability evolution described by quantum mechanics. They are
an attempt to give a philosophical explanation of how specific measurements come
about. Because one cannot test them experimentally, physicists cannot reach
agreement about them. Thus there are several different interpretations, and
there is no way to know if any of them are correct.
If you are confused by this you are not alone. I do not think
anyone has a good understanding of what is going on here although many
physicists are firmly convinced of the correctness of the interpretation they
favor. My own inclination is to think that Einstein was correct, and we need a
deeper theory to explain events, like the decay of a particle, that will
dispatch Schrödinger's poor cat.
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