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Quantum Theory, Causality and Determinism

 
 
Alan McDougall
 
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Reply Mon 11 May, 2009 09:05 pm
@Bones-O,
Bones-O! wrote:
Are you seriously suggesting I'm being hypocritical when I take you to task on copying and pasting highly mathematical Wiki content you don't understand and that wasn't relevant to the question as it stood if I then post comments in my own words that I do understand and is relevant to the question as it now stands? Can you seriously not see the difference between my post and yours? Alan, I often suspect that with you the important thing is to post anything rather than post something worthwhile.

BTW, Schrodinger outlined the cat thought-experiment to demonstrate that quantum mechanics was incomplete. His view was that the cat must be alive OR dead, and thus since QM predicts a superposition of each, QM must be incomplete. It was not a hypothesis, falsifiable or otherwise: it was an argument within the QM community about how to interpret the maths.


Did you see the LINK I gave I just pasted a tiny fragment from that LINK open your eyes


Uncertainty principle - Wikipedia, the free encyclopedia
Entropic uncertainty principle
0 Replies
 
Exebeche
 
  1  
Reply Wed 13 May, 2009 03:32 pm
@Bones-O,
Bones-O! wrote:

BTW, Schrodinger outlined the cat thought-experiment to demonstrate that quantum mechanics was incomplete. His view was that the cat must be alive OR dead, and thus since QM predicts a superposition of each, QM must be incomplete. It was not a hypothesis, falsifiable or otherwise: it was an argument within the QM community about how to interpret the maths.

I can hardly express how much i want to thank you for this statement, seriously.
I have seen a lot of discussions about Schroedingers cat, but i haven't seen even one that took in account that his thought-experiment was actually to demonstrate a contradiction in the theory.
So please correct me if i am wrong.
The way i would have expressed it was:
QT claims the possibility of a superposition, which i understand as the possibility of a submolecular something to be in more than one state at the same time. QT further claims that this superposition exists in subatomic dimensions only, whereas in the dimensions that we perceive it disappears.
Schroedinger decided to lead this idea into a paradox by creating this theoretical experiment, saying:
If the the superposition exists only in subatomic dimensions, a cat can never be in a superposition of being dead AND alive.
The cat's life totally depends on the condition that our radioactive element is at. So if that radioactive element is in more than one state even for only a short time, the cat would inevitably be in that same "superposition" during this time.
Which demonstrates clearly the contradiction: Not only do we assume that cats cannot be dead and alive at the same time, but even more important the experiment shows that a superposition can not simply be assumed to exist at a subatomic level but not our scale.
I think i even remember reading about Schroedinger that after he created his great equation he would have wished to never have created it.
Does that correspond somehow with what you know about him?
In any case: thank you so much, tausend Dank, muchisimas gracias.
0 Replies
 
Bones-O
 
  1  
Reply Wed 13 May, 2009 04:16 pm
@Darunia9,
Did you know that Schrodinger came up with that equation while having sex with his mistress on holidy (and I think he was married at the time)? Not pertinent, but it's important to remember that from small seeds great things may grow.

Superposition is a necessary part of QM. It is necessary for time-dependence: without it, everything would remain in the same state. It is also necessary because there is a certain relativism of states: being in one exact state of property X sometimes necessitates being in a superposition of property Y. Spin is an example: if you particle is measured to be spin up with respect to some axis, it must be both spin up and spin down with respect to a perpendicular axis.

So accept superposition, or reject QM - the most verified scientific theory of all time. But... it is not the only verified scientific theory of all time. Classical mechanics works fine on the macroscopic scale, so QM should provide a classical picture on that scale. The case of Schrodinger's cat, then, is a contradiction. If an isotope is prepared in an unstable state, it must sometime afterwards be in a superposition of that initial state and a lower one: the one in which radioactive decay has occurred. Thus the emitted ray (beta say) must be in a superposition of having been emitted and having not yet been emitted. If there is a beta ray detector in the box, it must be in a superposition of detecting and not detecting the beta. And so on and so forth: the detector fires a laser and doesn't fire it, the laser burns some string and doesn't, the broken string releases a hammer and doesn't, the hammer smashes a poison gas container, the gas kills and doesn't kill the cat. Thus while the isotope is still both undecayed and decayed, the cat is both alive and dead. But this is a macroscopic, classical system displaying quantum behaviour, which shouldn't happen. Thus quantum mechanics is incomplete.

Unfortunately, Erwin's point fell on deaf ears. This has yielded a theory that makes a special case of consciousness (the cat is alive or dead when an observer checks), that introduces infinite universes (the cat is alive in some, dead in others and probably non-existent in most), and violates physical laws that have never been seen to be violated (instantaneous collapse of the wavefunction esp. the EPR paradox)... anything to insist that the cat is both alive and dead.

Which is a shame, because the more fascinating question would be: when is it decided that the cat lives or dies? A colleague of mine is looking into this problem with some success at showing that while superposition is possible, superposed systems interacting with other systems tend determinstically toward a (mostly) single state (this is all that is required: an absolutely exact state isn't necessary for the classical limit), and the larger the system, the faster this occurs. A cat is, by his standards, incalculably large.

There are other reasons to believe the cat is alive or dead. Part of my research has been looking into an aspect of quantum tunnelling. A particle presented with a sufficiently small barrier both tunnels through it and is reflected by it: i.e. goes from a single state to a superposition. However, when you have two such barriers next to each other, it seems like the particle is either completely reflected or tunnels completely through it. This is semi-classical behaviour on the quantum scale. It could be that the beta particle in the cat experiment acts similarly.

The most important argument in all this is that it is a thought experiment. People ignore the actual interactions between the beta, the detector, the laser, the string, the hammer, the gas container and the cat when talking about the outcome. These are a lot of factors to ignore. So it may well be that the theory is complete, and yet the cat is still alive or dead. This is where I'll put my money on the next theoretical advances being made. Increasing computing power is allowing us to simulate more complex systems and see roughly how things might really work. We're a long way off cats, but as mentioned above, we may already be seeing evidence of a deterministic quantum theory.
Exebeche
 
  1  
Reply Thu 14 May, 2009 04:02 pm
@Bones-O,
Bones-O! wrote:
Not pertinent, but it's important to remember that from small seeds great things may grow.

:bigsmile:
Hello Bones-O

Thank you for that witty answer, your competence mixes very nicely with your humour.
It is very nice to see this even combined with patience for wannabes like me.
I wonder if it would be overstretching your patience if i came up with one of these "I'm the new Einstein"-ideas.
What i mean is: I am quite conscious that the idea itself is likely to be just another example for how a student has not understood a major point of his studies but, i don't know, i would really like to hear somebodys opinion who is competent to tell me why it doesn't fit.
First of all we probably all know explanations of higher dimensions that are trying to make things more understandable by describing a world of twodimensional beings.
For the twodimensional beings a threedimensional being could probably do things that seem impossible to the twodimensional ones. The threedimensional one might for example be able to fold the paper, which is what the twodimensional ones call the world, because they only see this part of the universe. The 3-dimension one could then hop from one point to another and this way just appear and dissappear wherever he wants.
This example has been picked up by many science fiction authors, so it's nothing new, and there's a bunch of other ideas we all have already heard of and which lead into unexplaneable phenomenons for the 2dimensional creatures.
What i am trying to explain here is not how we could try to figure higher dimensions.
The point i am making is in the first place: Phenomenons based on dimensions that are higher than what a creature can perceive tend to create effects that seem to be unexplanable or even paradox and irrational to this creature.
My idea is basically that the wave particle dualism is such a phenomenon.
What if we are actually observing something that takes place in more than 3 dimensions, actually more than 4 if we include timespace?
The equation that Schroedinger developed obviously provides an excellent tool for describing the processes taking place. But the fact that his equation is a solid peace of mathematics doesn't mean that it contains ultimate truth.
It may describe a part of our reality but at the same time it may describe only a slice of it.
I noticed a wave-phenomenon, that is based on an optical illusion:
Do you have one of these ventilators (like on your table e.g.) that keep moving from one side to another and are surrounded by these wires, that protect you and your children from getting their fingers in danger? If you have one of them next time you turn it on observe it consciously, but don't look at it, rather look through it. You will notice that there is a slight optical illusion taking place, because you will have the impression of seeing the wires creating the impression of a wave.
This is only the result of two different movements creating an overlay and can also easily be observed by simply putting two layers of transparent curtain over each other and moving them. Waves seem to occur.
Our eyes watch a threedimensional event and read it as something twodimensional.
Such overlays of movements can also be observerd in acoustics where it would be called a beat .
http://en.wikipedia.org/wiki/Beat_(acoustics)
What if the wave-nature of particles that we observe in the double-slit experiment is a three dimensional illusion of a process that is actually (at least) 4 dimensional? Plus, if i wonder what would happen, if i tried to measure the wave i observe in my ventilator, i would definitely never manage to get the wave into my hands, but always only one of the wires.
Which is what happens when we apply a measureing in the double-slit experiment: As soon as we try to get a hold of the wave it turns out to be a particle. Our measuring can not take place in more than 3 dimensions, so we can never catch more than the wire.
H.P. Stapp said a sentence which i am going to translate as precise as possible into english:
"A subatomic particle is not an independently existing analysable unit. It is basically a number of interrelations which stretch to the outside, towards other things. "
I think this translation should be somewhat precise enough.
This could as well be a description of a wave that only appears when an overlay of several movements take0 place.
Now, if i take the curtainlayers as a basis, there is actually two different movements. If however i look at the ventilator, there is only one movement, and the appearance of the wave totally depends on the perspective of the observer.
Bones-O
 
  1  
Reply Thu 14 May, 2009 04:38 pm
@Exebeche,
Exebeche wrote:
:bigsmile:
Thank you for that witty answer, your competence mixes very nicely with your humour.
It is very nice to see this even combined with patience for wannabes like me.

My friend, the tendency toward understanding is what this site is here to encourage, and I'll think you'll find this attitude is across the board with pretty much all of the members of this forum who are here to discuss, rather than to disclose, irrespective of your current knowledge base. You'll find this point very useful on a forum open to everyone when it comes to separating the wheat from the chaff, so long as you are similarly inclined. Impatience is generally a trait of ignorance - you will find you have the ear of many people wiser than I when you display a willing to understand. That said...


Exebeche wrote:
The equation that Schroedinger developed obviously provides an excellent tool for describing the processes taking place. But the fact that his equation is a solid peace of mathematics doesn't mean that it contains ultimate truth.

Schrodinger's equation probably is true, for the right questions. Only one person has come up with a more powerful equation, and that was built upon Schrodinger's.

I say this having been a non-physicist and now being a physicist, when looking to X for the truth of Y, it is important to consider how they relate. Schrodinger's equation has proved its worth, but it's not the final word.

As for your discussion of higher dimensions, you raise points and questions worthy of their own thread and, alas, quite out of keeping in this one. Please, by all means, post a thread on the topic if: a) you are interested in talking about the matter further, and b) there doesn't exist a current thread on that topic (and from memory I don't think there is one, so you're clear). If you do, I'll be around to dig in where I can.


Exebeche wrote:
Plus, if i wonder what would happen, if i tried to measure the wave i observe in my ventilator, i would definitely never manage to get the wave into my hands, but always only one of the wires.
Which is what happens when we apply a measureing in the double-slit experiment: As soon as we try to get a hold of the wave it turns out to be a particle.


There's a universal misunderstanding here that I've been rather missionary-minded about setting right, so forgive me if I get on my soap box. This isn't the fault of the non-physicist. I'm a huge antagonist to the way theoretical physics is explained to the public, which is almost always WRONG! One such myth is that that a wave-particle, when measured, is always particle-like, i.e. like a point-particle. This is not true generally, only when one attempts to measure the position (or some variable compatible with position) of a particle. If one measures the momentum of a particle, one finds that it is indeed a wave, insofar as it has a wavelength. The 'paradox' of measurement in QM is not as it has been presented to the public. I do hope this trend of mystifying QM will, at some point, come to an end, not least because it will rid us of all the new-age nonsense surrounding its representation.



Exebeche wrote:
"A subatomic particle is not an independently existing analysable unit. It is basically a number of interrelations which stretch to the outside, towards other things. "
I think this translation should be somewhat precise enough.
This could as well be a description of a wave that only appears when an overlay of several movements take0 place.

The wavefunction, that is the solution to the Schrodinger equation that describes a particle, is a complex entity. I don't mean complex as in complicated, I mean complex as in it has real and imaginary components. Imaginary components are often treated as another dimension. Again, there is a whole thread's-worth of discussion here, but this is not the right thread. The discussion here is strictly about causality and determinism. As I said before, you've enough to warrant you're own thread, and I will be around to help if I can, as will others.
Darunia9
 
  1  
Reply Fri 22 May, 2009 06:00 pm
@Bones-O,
Bones-O! wrote:

There's a universal misunderstanding here that I've been rather missionary-minded about setting right, so forgive me if I get on my soap box. This isn't the fault of the non-physicist. I'm a huge antagonist to the way theoretical physics is explained to the public, which is almost always WRONG! One such myth is that that a wave-particle, when measured, is always particle-like, i.e. like a point-particle. This is not true generally, only when one attempts to measure the position (or some variable compatible with position) of a particle. If one measures the momentum of a particle, one finds that it is indeed a wave, insofar as it has a wavelength. The 'paradox' of measurement in QM is not as it has been presented to the public. I do hope this trend of mystifying QM will, at some point, come to an end, not least because it will rid us of all the new-age nonsense surrounding its representation.


Your right, when I first had the idea for this essay I had in mind some of those misrepresneted views, not as they are to most people as I knew some aspects, but as I've read more I'm seeing how wrong poplar view is. And how even more interesting the real physics is.
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