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@ Ariane.

You said you're interested in quantum mechanics, so it might interest you to read a small explantion of, what the principle of Schrödinger's cat is, I wrote some time ago and posted over at the Seti boards, as people there asked me about the quote I had then and also have here now "Some days I feel like Schrödinger's cat!"

I was asked if Schrödinger's cat actually is a cat, but it isn't! It's a quantum cat! So here is goes:

No, Schrödinger used the cat as an example to explain the principles of uncertainty in quantum mechanics, which says that the photons can exist both as a particle and as a wave. Schrödingers cat has the destiny to be both alive and partly alive at the same time and suffers from a certain quantum-identity crisis.

So he puts the cat in a cage with opaque walls, so nobody can see the cat until the story is over. Then he puts a small amount of radioactive material in the cage, which has the, for the clarity of it, the probability of 50% to send radiation upwards and the probability of 50% to send radiation downwards. If the radiation goes upwards it will hit a particledetector which turns on a switch, which lets a lethal dose of poison drop down in the foodbowl, and if the radiation goes downwards, it turns on a switch, which drops food down in the bowl, and the cat will survive until the next experiment.

These possibilities, upwards, the cat dies, downwards, the cat lives, are what we usually expect in our daily world, but things are not so simple for the quantum cat, as it, according to the prevalent quantum theory, both is dead and alive. The cat in in the same condition as the electrons, which can be both waves and particles at the same time.

So the best thing we can do for this poor cat is to descibe it with all its possibilities with a Schrödinger wave-function, an equation, which describes all its possibilities. (And don't ask me about this equation!)

In this example the possibilities tells us that the cat has eaten the poison and is dead (1. possibility) and that the cat has eaten the food and is alive (2. possibility). First when this wavefunction collaps, when all possibilities solidify, we can approach a real cat which we either can pet or burry. A such collaps must happen at a certain time, because when we, as the story goes, open the cage and see the cat, it's dead. The question is then: What killed the cat?

This question, which isn't only relevant to our quantum cat, but to all of us and all what we see around us, goes directly to the question of, why there exists a reality, and this creates a paradox because the world is full of ordinary cats which are either dead or alive, and on the other side the physics that says that this is impossible. The math behind Schrödingers equation says that nothing can decide the destiny of the cat, that nothing can make its wavefunction collaps. Even if we place a camera inside the cage to monitor if it's dead or alive, the camera will be so "overwhelmed" by all the possibilities, so it will assume the classic quantum mechanic behaviour and show everything to everybody.

So, despite of what we say, the quantum theory says that the cat is - and must always be, both dead and alive. And this paradox is called the observationproblem, as it contradicts our usually observations and because it focus on the role of the observervation and thereby the observer in creation of reality.

I hope you understand it. :-)

I change my quotes frequently, so now I have a German quote over at Seti:

"Ich hab' gesucht ganz allein meine Sterne,

die Träume verflucht und mit keinem geteilt."

which is from a song:

Gefährten des Sturmwinds
Komposition: Ulrich Swillms / Text: Norbert Kaiser, Herbert Dreilich

Jeden Tag neu
wird der Sturmwind gebor'n.
Er fliegt um die Welt,
und er kennt keine Spur.
Und jeden Tag
sucht er neue Gefährten.
Er klopft an mein Herz,
und er sucht eine Tür.

Einsam und wild
war mein Hunger nach Freiheit.
Ich habe geliebt,
was der Zufall mir gab.
Ich hab' gesucht
ganz allein meine Sterne,
die Träume verflucht
und mit keinem geteilt.

Auch wenn der Sturm
dein Dach zerbricht,
und wenn er dich
bis zur Erde biegt,
steh wieder auf,
biet ihm die Stirn,
denn er trägt dich weit,
wenn du mit ihm fliegst.

Jeden Tag neu
wechseln Lichter und Schatten.
Ich zieh' meine Bahn
wie ein Treibholz im Fluß.
Und manche Nacht
träume ich von den Fluten.
Ich geh' mit dem Sturm,
und er wartet auf mich.

Denn hundertmal
bin ich ihm schon begegnet,
und jeden Tag neu
schau' ich ihm ins Gesicht.