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Author Topic: Schroedinger's Cat  (Read 4050 times)

JayzusB.Christ

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Schroedinger's Cat
« on: 28 May, 2008, 01:18:51 PM »
Continued from the 'Neither Embarrassed nor Ashamed' thread.

As I pointed out, i never understood this and i really want to. (Someday soon i might even work on getting a life, but first things first.) Feel free to ignore this thread, i wouldn't really blame you...

Andrew Goldsworthy says this in the other thread:
'So, Schrödinger has his hypothetical cat in sealed lead box with the vial of poison, the Geiger counter and a decaying isotope. Once the isotope decays enough so that the Geiger counter can detect it (a quantum event) the poison is released and the cat killed. All of which is unobserved. The condition of the cat is not known util the box is opened.'

So let me get it straight.  I don't really know what a decaying isotope is unfortunately, but here's what i gather:

1: Electrons act as waves until their position is measured, in which case they seem like particles. Therefore their position as particles can be said to be in loads of places simultaneously until they're observed by somebody, by which time they're only in one place. Which is incredibly weird but i suppose that's quantum physics. (For nonscientific dullards like me, Bill Bryson gave the easiest explanation.)

2: The particle having a single position is essential for the isotope to decay - i don't really understand how but it gives it a 50 / 50 chance that can't be measured until the box is opened.

3: Therefore we can't say that the cat is dead or alive until the box is opened. We have to say it's both. But the main point is that we can't say whether the isotope has decayed. We have to say it's both decayed and undecayed.

so am i right in saying it's not really the cat's state that we're checking when opening the box, but whether the quantum event has happened or not? And the cat's state is only a result of the quantum event?

I saw an explanation once that described the experiment as including a vial of poisonous gas that the cat has a 50 / 50 chance of STEPPING ON and breaking, without the isotope part. DOes this miss the point? Or is it right to say that because quantum events can't be said to have happened till they're observed, the same goes for any event in nature?

I do apologise. I wish i'd studied physics at school
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El Spurioso

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Re: Schroedinger's Cat
« Reply #1 on: 28 May, 2008, 01:31:49 PM »
Yeah, you've got it.  The continued survival or death of the cat is just a visible symptom of the quantum event having happened or not happened.

It's more of a thought excercise/paradox than anything else: a flashy way to demonstrate how bizarre quantum theory is compared to "standard" physics.  It seems ridiculous to most of us that the cat is both alive and dead at the same time, but nonetheless, because of the experiment's reliance on a quantum event, the simultaneous state of life *and* death is the only rational way of describing the cat.

Stranger still, you're simply not allowed to make excuses like "ahhh, but it's definitely one or the other -- you just can't tell until the box is open."  Because the act of observation is what defines the way we measure the quantum event, and therefore negates the entire thing.

Weird, but true.


pauljholden

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Re: Schroedinger's Cat
« Reply #2 on: 28 May, 2008, 01:36:52 PM »
I thought Shcoedinger's Cat was used, initially, at any rate, as a way of pointing out that Quantum Theory is ridiculous, because - there's no way for a cat to be both alive and dead, yet QT would suggest that is is both. The story has since moved on to be a way of explaining to people how QT works rather than being a proof against its absurdity.

Which, in itself is kind of interesting.

(A quick check of Wikipedia http://en.wikipedia.org/wiki/Schroedingers_cat suggests I might be right)

-pj
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Dark Jimbo

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Re: Schroedinger's Cat
« Reply #3 on: 28 May, 2008, 01:41:17 PM »
I always assumed the point was, essentially, that because there are only two possible outcomes, each of equal probability, then in theory you don't even need to open the box to see what's happened to the cat.

But I've probably missed the point.

Gavin_Leahy_Block

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Re: Schroedinger's Cat
« Reply #4 on: 28 May, 2008, 01:46:45 PM »
how i understand it is it is both dead and alive untel the box is opened then it will exist as a dead or alive cat rather then both.

Matt Timson

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Re: Schroedinger's Cat
« Reply #5 on: 28 May, 2008, 01:48:54 PM »
I used to buy lucky dips for the lottery and not look at what I'd got until after the draw- in the hope that once I knew what numbers I actually needed to win, they might be the ones observed on my ticket.

Crazy but true, folks!
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WoD

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Re: Schroedinger's Cat
« Reply #6 on: 28 May, 2008, 01:49:10 PM »
We covered this in Something Wicked...quite nicely too...go buy a copy!

Funt Solo

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Re: Schroedinger's Cat
« Reply #7 on: 28 May, 2008, 01:49:12 PM »
Aye, PJ's got it.  It was more acceptable for people to say "the weird QT thing is both on/off, there/not there, decayed/not decayed at the same time", but when presented with the idea of a dead/alive cat, common sense says "but it must be one or the other".

So, was Schroedinger wrong, then?  That is, despite the common sense aspect, the "cat" can actually be dead/alive?

I like when these physicists come on tele and go "listen, it melts our brains as well".
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pauljholden

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Re: Schroedinger's Cat
« Reply #8 on: 28 May, 2008, 02:02:11 PM »
Wouldn't the cat also be an observer and notice whether it was alive or dead? I know they're selfish animals and wouldn't notice, for example, if Schroedinger was alive or dead, but surely they'd notice if they were themselves? They'd stop being hungry for a start.

- pj
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Re: Schroedinger's Cat
« Reply #9 on: 28 May, 2008, 02:17:32 PM »
Id agree with PJ.  As a pseudo physicist, well Im a chemist by degree.  The cat analogy is meant to show that quantum mechanics is inherently flawed.  

Imagine an electron not being in a specific place around an atom as depicted by Rutherford et al.  But more like a smear of electrical charge surrounding atoms.  You can only find the probability of the electron existing in space around the atom at any time, not the actual electron itself as it may or may not exist in its classical form.  Of course using probability in this way means that the electron can then be any where and can "teleport" around the atom in an almost random fashion.

As I explained on the previous thread until Hugh Everett III came up with the idea of parallel universes or multiple dimensions (as in more than the 4 we exist in - length breadth height and time), the cat could essentially be dead and alive at the same time.  It is currently both in two different dimensions, currently they are looking at an 11 dimensional universe......

Unification theories attempt to merge, quantum mechanics and Einsteins relativity with varying degrees of success.  The most common form of unification theory is String theory which suggests  that every particle in the universe is a string or band of energy vibrating at a different frequency depending on what the particle is.  e.g. an electron has a different vibration to a proton.  

Tell you what Ive read about four books on the matter and just when I think I might know what Im talking about, I get confused.  

PS - Hugh Everett was actually an interesting chap, well worth a read if your interested.  His son, E, is THE member of the Eels (Rock Band)

worldshown

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Re: Schroedinger's Cat
« Reply #10 on: 28 May, 2008, 02:31:05 PM »
That takes us dangerously close to Wigner's Friend.

Please excuse the simplified space maths.

Wigner puts his friend in the box with the cat. To Wigner's friend, the cat will always be alive (cat = alive) as the same event that kills the cat also kills the friend. However, Wigner is in the same situation as Schrödinger (cat = (alive + dead)/2). Wigner's argument is how can the same experiment have two different equations.

Guess it couldn't have been any fun to be one of Wigner's friends.

Bongo Jack

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Re: Schroedinger's Cat
« Reply #11 on: 28 May, 2008, 03:33:46 PM »
Poor pussy.

Poor pussy cat.
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Mikey

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Re: Schroedinger's Cat
« Reply #12 on: 28 May, 2008, 04:42:59 PM »
While it was initially proposed to show the inherent contradiction displayed in yer quantum physics,to me it always helps demonstrate the fact that when observing fundamental particles, the act of observation changes their behaviour.So,actually looking in the box forces one of the two possibilites into existence.

The parallel worlds aspect that allows all possibilities to exist is grooovy!

And the BBC4 doc on Hugh Everett was excellent too.

M.
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Hoagy

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Re: Schroedinger's Cat
« Reply #13 on: 28 May, 2008, 06:03:04 PM »
I think Shroedingers cat went only some way to explain the theory.

The cat being dead was a major flaw. because if the cat is literally dead the quantum mechanics fail to carry on, due to death being an ultimatum.

If the cat is dead it cannot follow that the cat will alternatively be alive next time the person looks(?)  

how this is affecting the theory is a bit muddy from here. Then the lead singer of the Eels' dad steps in with new mathematics to further this explanation.. something like that.
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Mike Carroll

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Re: Schroedinger's Cat
« Reply #14 on: 28 May, 2008, 06:22:05 PM »
The simplest way to understand quantum physics is - like everything else - through the form of a joke:

Heisenberg is speeding along the highway when a traffic cop pulls him over.

"Do you know how fast you were going?" The cop asks.

"No, but I know exactly where I was."

(OK, it doesn't actually explain anything, but trust me: this is a really funny gag for physicists).