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when is Schroedinger's cat dead, and when is it not?

 
 
DrewDad
 
  1  
Reply Thu 9 Jun, 2011 04:32 pm
@igm,
Well, by all means go study graduate-level theoretical physics and let me know what you learn.

Until then, I'll stick with what actual physicists can tell me.
0 Replies
 
talk72000
 
  1  
Reply Thu 9 Jun, 2011 04:33 pm
@igm,
I agree. What we have here is not an observation but an interaction. There is a difference. Observation is where the act of observation does not impact the observed object significantly to alter its natural or normal behavior. An interaction is where the object is responding. An observed criminal knowing he is observed will pretend to be nice and ham it up. His criminal behavior will be hidden. He will put on a smiling face much as Conrad Black is doing.
0 Replies
 
Zarathustra
 
  2  
Reply Thu 9 Jun, 2011 05:40 pm
Schrödinger’s Cat is not a paradox because QM or “the math is wrong”. It is a paradox because there is an invalid premise in it. The S. Cat is trying to demonstrate the construct of coherent superposition. An electron (any particle) exists only in potentia until observed. In other words it exists as a field and only becomes localized as the electron we know and love from pre-QM days after a measurement is made. So an electron in two places or 2 trillion places at the same time in potentia is possible (required) and all possible allowed results are each a unique super-positioning. The resultant localization is just the one that actually happens. It is actually necessary to calculate (tediously) these possibilities to predict the probability of finding the electron in any particular location. To get an exact answer would require an infinite number of these calculations, something that drove Feynman to distraction for years.

The “paradox” is introduced because coherent super-position is not seen in the macro world. In fact classic calculations have no way to calculate them even if they did exist. So while the electron is nowhere until observed (it actually may not even always be an electron but that is too much for one post) the cat certainly is. (Remember in QM NOTHING exists outside of an observation). The cat is either real or not, if real it is either dead or not. It cannot exist in a supper-position of 30% dead cat/70% live cat, subatomic particles can. (Classical physics tells us the cat is there between observations).

This is the same thing we face in relativity with the twin paradox. It is not a problem with relativity it is the experiment demonstrating the premise cannot be conducted in our reality in a way that adheres to relativity. Think about it: how do both twins each maintain a non-accelerating inertial frame of reference and yet manage to somehow meet up again. A pretty neat trick!

The paradox is not in our science but in our questions -- to paraphrase a certain English writer.
rosborne979
 
  1  
Reply Thu 9 Jun, 2011 06:48 pm
@Zarathustra,
Yes. Well said. Too many people still cling to the Bohr model of the atom.
0 Replies
 
maxdancona
 
  1  
Reply Thu 9 Jun, 2011 08:44 pm
@igm,
Quote:

We aren't debating if a given state is 1 or 0 or both at the same time but if a cat can be both alive and dead at the same time...I think it's more likely to be faulty mathematics.


The mathematics aren't faulty at all. They predict the behavior of subatomic particles very well. The mathematics are also productive. They are used to design the microprocessors that are powering the computer you are using right now.

The purpose of mathematics is to predict the behavior of subatomic particles and to provide a foundation for new technologies. You can't argue with success. More likely what is faulty is human intuition.


maxdancona
 
  1  
Reply Thu 9 Jun, 2011 08:53 pm
@Zarathustra,
Quote:
So while the electron is nowhere until observed (it actually may not even always be an electron but that is too much for one post) the cat certainly is. (Remember in QM NOTHING exists outside of an observation). The cat is either real or not, if real it is either dead or not. It cannot exist in a supper-position of 30% dead cat/70% live cat, subatomic particles can.


This is simply incorrect. Of course things exist outside of observation. Quantum Mechanics doesn't say they don't exist. Quite the contrary. Quantum Mechanics says things that aren't being observed exist as a superposition of possible properties. If you take a graduate level Quantum Mechanics class, you will spend a good deal of time calculating these superpositions.

The funny part of the Schroedinger's cat experiment is that it is set up with a trigger that exists in the subatomic world. This is the paradox-- a quantum mechanical superposition of possibilities controls the trigger that releases the cyanide-- meaning that in this contrived experiment, the strange quantum mechanical rules will effect the normal world.


maxdancona
 
  1  
Reply Thu 9 Jun, 2011 09:04 pm
@maxdancona,
A physics professor of mine was fond of this quote...
John Archibald Wheeler wrote:
If you are not completely confused by quantum mechanics, you do not understand it.


For everyone trying to claim that it is simple to explain, or that it would make perfect sense if we just understood on thing really don't know what they are talking about. It is not just the mathematics, it's the results of the experiments (over 50 years now) that confirm the mathematics. There is some weird things that break human intuition.

If you want to learn the science you need to accept this, the experimental results don't make sense to the human mind. This means you need to either drop the idea that things should make sense, or you need to abandon the idea that science should be based on experimental results and mathematics.

Scientists go with observation, experiment and mathematics.
0 Replies
 
Zarathustra
 
  1  
Reply Thu 9 Jun, 2011 09:45 pm
@maxdancona,
Quote:
Nothing exists outside of an observation...
is a basic axiom of the modern interpretation of QM. It comes from the Copenhagen Interpretation of QM (1927). Until an observation is made QM can say nothing, including about “existence”. (That is pretty basic).

By the way the reason the “sub-atomic” rigger was used was as a simple means of defining a completely random trigger. There is no other reason, it use produces no effect it is just a random starting point.
maxdancona
 
  1  
Reply Thu 9 Jun, 2011 10:18 pm
@Zarathustra,
Quote:
Until an observation is made QM can say nothing, including about “existence”. (That is pretty basic).


It is a bit funny that you put "existence" in quotes. I would argue that wave functions exist as do electrons passing through double slits.

From the Wikipedia page

Quote:
The subjective view, that the wave function is merely a mathematical tool for calculating the probabilities in a specific experiment, is a similar approach to the Ensemble interpretation.

There are some who say that there are objective variants of the Copenhagen Interpretation that allow for a "real" wave function, but it is questionable whether that view is really consistent with logical positivism and/or with some of Bohr's statements. Bohr emphasized that science is concerned with predictions of the outcomes of experiments, and that any additional propositions offered are not scientific but meta-physical. Bohr was heavily influenced by positivism. On the other hand, Bohr and Heisenberg were not in complete agreement, and they held different views at different times. Heisenberg in particular was prompted to move towards realism.[4]

Even if the wave function is not regarded as real, there is still a divide between those who treat it as definitely and entirely subjective, and those who are non-committal or agnostic about the subject. An example of the agnostic view is given by Carl Friedrich von Weizsäcker, who, while participating in a colloquium at Cambridge, denied that the Copenhagen interpretation asserted: "What cannot be observed does not exist". He suggested instead that the Copenhagen interpretation follows the principle: "What is observed certainly exists; about what is not observed we are still free to make suitable assumptions. We use that freedom to avoid paradoxes."[5]


http://en.wikipedia.org/wiki/Copenhagen_interpretation






0 Replies
 
igm
 
  1  
Reply Fri 10 Jun, 2011 02:10 am
@maxdancona,
maxdancona wrote:

Quote:

We aren't debating if a given state is 1 or 0 or both at the same time but if a cat can be both alive and dead at the same time...I think it's more likely to be faulty mathematics.


The mathematics aren't faulty at all. They predict the behavior of subatomic particles very well... More likely what is faulty is human intuition.

Isn’t it that this thought experiment highlights the inadequacies in the axioms of QM and the math that follows from them, highlighted by showing a paradox because we don’t have a unifying theory between QM and GR? Didn’t you say this your self in previous posts?
maxdoncona wrote:

Schroedinger's cat was not invented to explain anything. It was invented to show the apparent absurdity of the implications of the mathematics behind Quantum mechanics. It is an obvious paradox.

zt09
 
  1  
Reply Fri 10 Jun, 2011 03:43 am
The experiment is just not quite ... correct?

Quote:
Until an observation is made QM can say nothing, including about “existence”.


So we can't say anything about the cat until we interact with it! We may only guess.

And one cannot completely isolate all the particles the cat consists of, their interaction (electromagnetic, gravitational for example) with environment . And so there are other potential ways to determine what's going on in the box for some potential observers. The more ways to measure the state, the less unsertainty, isn't it? Let's just replace the steel box with a glass box. Don't we know when the cat is dead?
DrewDad
 
  1  
Reply Fri 10 Jun, 2011 06:41 am
@zt09,
Just replace "cat" in your last sentence with "horse."
0 Replies
 
maxdancona
 
  1  
Reply Fri 10 Jun, 2011 06:55 am
@igm,
Quote:
Isn’t it that this thought experiment highlights the inadequacies in the axioms of QM


I wouldn't say that at all. QM is what it is, a set a mathematic equations that have been extremely effective at making predictions and is the basis of cool new technology.

Inadequacies? No.

The thought experiment demonstrates that QM flies in the face of human intuition. The math is what it is. If there are inadequacies I would bet they are on the human intuition side.


maxdancona
 
  1  
Reply Fri 10 Jun, 2011 06:56 am
@zt09,
Quote:

So we can't say anything about the cat until we interact with it! We may only guess.


In chemistry we speak of electron clouds. I don't believe anyone claims that electron clouds don't exist.

Quote:
Let's just replace the steel box with a glass box. Don't we know when the cat is dead?


Looking inside a glass box is a measurement. In this case the wave function (i.e. the superposition of all possible outcomes) collapses (i.e. becomes one outcome). If you look in the box, then the cat is either alive or dead. Before this point, it is a superposition of alive and dead.
igm
 
  1  
Reply Fri 10 Jun, 2011 07:53 am
@maxdancona,
Just to lighten things a little. If what SC stands for is correct then from the cat’s point of view before it sees us we are in a state that is simultaneously alive and dead due to the math derived from the axiom called the 'Superposition Principle' and the axiom called the 'Measurement Principle' closely followed by the axiom called 'Unitary Evolution'. Since we all must be unviewed by at least some others we must all be in a state of being both dead and alive at the same time all of the time lol!

Newton’s laws give us practical science but that doesn’t mean the axioms were correct or the math derived from it, but it was useful enough for practical usage whilst throwing up the odd paradox.

As shown by the philosopher ‘Popper’ another set of axioms will show different results which can have predictive results and be used in practical science but can both sets of axioms be true (no) and are they based on assumptions (yes).
0 Replies
 
zt09
 
  1  
Reply Fri 10 Jun, 2011 09:22 am
@maxdancona,
Quote:
Before this point, it is a superposition of alive and dead.


I cannot agree with that. Because the cat is not isolated enough from the ouside world. What if somebody else had already measured the state (for example with X-rays) of the cat? He knows the cat is alive. And we think it's superpositioned. Rolling Eyes
DrewDad
 
  1  
Reply Fri 10 Jun, 2011 09:58 am
@zt09,
You do realize that it's not actually a rigorous experiment, right?
zt09
 
  1  
Reply Fri 10 Jun, 2011 10:30 am
@DrewDad,
Quote:
You do realize that it's not actually a rigorous experiment, right?


So do you argee, it's not a flawless one?
DrewDad
 
  1  
Reply Fri 10 Jun, 2011 11:33 am
@zt09,
It's a visualization aid. It's not a real experiment.
0 Replies
 
JLNobody
 
  1  
Reply Sun 12 Jun, 2011 10:42 am
@maxdancona,
Clearly a feral cat.
0 Replies
 
 

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