[questionposter]

DrRocket, on 7 February 2012 - 04:36 AM, said:

See page 1. The ideas are is relatively easy. I tried, but after that it became clearly futile.

Quantum mechanics is stochastic. When one is dealing with someone who cannot grasp that simple idea, there is little that can be done.

That is absolutely not true. I've taught algebra to farm girls, music to graphic designers. All you have to do is put the effort into explaining it different ways. It still seems like your in the old way of thinking. I bet even mentally retarded people could have some kind of grasp of the properties of QM. You could show them the wave generated by a pebble in a pond, or run that wave through a panel with two slits to see how it acts for themselves. If you don't want to put the effort into explaining things in a better way, then instead of being rude, find a topic you want to post in.

This post has been edited by questionposter: 7 February 2012 - 04:46 AM

[DrRocket]

questionposter, on 7 February 2012 - 04:42 AM, said:

That is absolutely not true. I've taught algebra to farm girls, music to graphic designers. All you have to do is put the effort into explaining it different ways. It still seems like your in the old way of thinking. I bet even mentally retarded people could have some kind of grasp of the properties of QM. You could show them the wave generated by a pebble in a pond, or run that wave through a panel with two slits to see how it acts for themselves. If you don't want to put the effort into explaining things in a better way, then instead of being rude, find a topic you want to post in.

Graduate students I can help.

Interested and intelligent undergraduates I can help.

Kids from 7-18 I can help.

Farm girls are a breeze. (God help the ones that you have "taught".)

I can and have helped all of the above.

But you are beyond help. You have far too many serious misconceptions and a closed mind towards correcting them. There comes a point at which misconceptions are so numerous and so profound that one's knowledge is actually negative. You are way past that point. Your "explanations" of quantum theory only serve to prove this -- while mentally retarded people, as you state, might have some understanding of QM , you clearly do not.

The problem is not that you don't understand. The problem is that you don't understand that you don't understand. You compound that by offering instruction to others and that instruction is almost always just wrong. In fact, in the words of Pauli "It is not even wrong."

The best that can be done is to prevent you from confusing other innocent people who are capable of learning, and who are worth the time to try to educate.

[swansont]

questionposter, on 7 February 2012 - 01:10 AM, said:

Ok, you gotta stop doing this

!

Moderator Note

On the contrary, you need to stop dragging the post off-topic with this discussion. If a posted idea is contrary to accepted physics, one is within his/her right to call it rubbish.

Back to discussion of quantum mechanics vs determinism, please.

[questionposter]

DrRocket, on 7 February 2012 - 05:43 AM, said:

Graduate students I can help.

Interested and intelligent undergraduates I can help.

Kids from 7-18 I can help.

Farm girls are a breeze. (God help the ones that you have "taught".)

I can and have helped all of the above.

The problem is not that you don't understand. The problem is that you don't understand that you don't understand. You compound that by offering instruction to others and that instruction is almost always just wrong. In fact, in the words of Pauli "It is not even wrong."

The best that can be done is to prevent you from confusing other innocent people who are capable of learning, and who are worth the time to try to educate.

I already stated that what I said wasn't 100% accurate, and unless you can find someone that is saying that direct description is wrong, I don't see what's wrong with using it for this topic. If you have an easier description to understand, then as I already also said, post a link. Put the effort into progressing the topic if I'm actually wrong. Every time I've posted "instruction", all the staff members or scientists were free to correct it, and they didn't even after two weeks of so little posting that those posts were in the top "most recent" for two weeks, which leads anyone to believe they are at least over 70% accurate, so what specifically is wrong with my general description considering I already know it's only a very basic general overview?

DrRocket, on 7 February 2012 - 05:43 AM, said:

But you are beyond help. You have far too many serious misconceptions and a closed mind towards correcting them. There comes a point at which misconceptions are so numerous and so profound that one's knowledge is actually negative. You are way past that point. Your "explanations" of quantum theory only serve to prove this -- while mentally retarded people, as you state, might have some understanding of QM , you clearly do not.

Help progress the topic or stop posting. I asked someone to find what is generally wrong with my description and if you have a better one, so either do that, or stop being rude. I'm not the only person you do this with, you do this with other people whom oppose what your saying, just get over the fact not everyone automatically agrees with every single thing you say. I even interned for a real scientist and they weren't as bad as you.

This post has been edited by questionposter: 7 February 2012 - 01:48 PM

[A Tripolation]

questionposter, on 7 February 2012 - 01:27 PM, said:

Help progress the topic or stop posting. I asked someone to find what is generally wrong with my description and if you have a better one, so either do that, or stop being rude. I'm not the only person you do this with, you do this with other people whom oppose what your saying, just get over the fact not everyone automatically agrees with every single thing you say. I even interned for a real scientist and they weren't as bad as you.

Quote

What the uncertainty principle actually says is that for two complementary observables (position and momentum are complimentary) that if one takes particles prepared in identical quantum states and then does repeated measurements of position x followed by momentum p (or momentum p followed by position x) that



where and are the standard deviations associated with the random variables x and p respectively.

Inherent in this statement are that position and momentum are not deterministic. They are random variables associated with a stochastic system.

It is NOT a statement that there will be any definite error in the measurement of either position or momentum. It is in fact a statement that there is no such thing as a definite measurable value of either position or momentum associated with a quantum particle.

This was already given to you. It is accurate.

[michel123456]

DrRocket, on 19 December 2011 - 10:54 PM, said:

It is in fact a statement that there is no such thing as a definite measurable value of either position or momentum associated with a quantum particle.

Bolded mine.
What is the word "measurable" doing in this sentence?

If I had to follow Dr Rocket, it could be: (paraphrasing Dr's statement)

It is in fact a statement that there is no such thing as a definite value of either position or momentum associated with a quantum particle.

[DrRocket]

michel123456, on 7 February 2012 - 03:18 PM, said:

Bolded mine.
What is the word "measurable" doing in this sentence?

If I had to follow Dr Rocket, it could be: (paraphrasing Dr's statement)

It is in fact a statement that there is no such thing as a definite value of either position or momentum associated with a quantum particle.

I think we are saying the same thing. A quantity in physics is "real" only to the extent that it is either directly measurable or is reflected in a quantity that it directly measurable.

If I recall the context (one sentence makes it a bit difficult to do this) the point being made was that quantum mechanics describes random variables that evolve in time -- a stochastic process. Measurements produce samples of that random process and therefore measurements are not reproducible in the deterministic sense, but only in the sense that the statistics of many samples are predictable. When you make a measurement you get a definite value, and that value will be an eigenvalue of the operator associated with the quantity measured. But you cannot predict with certainty which eigenvalue will be produced, but only the relative likelihoods of the possible eigenvalues.

[Xittenn]

Ok, be gentle with me please, my physics is poor and English even worse! What I can't follow with all of this is the following. Schrodinger developed wave equations that model particle behaviour at <macroscopic scale, and these behaviours also tend to be lost at >macroscopic scale. As far as I know or understand, these equations are built on the principles of standing waves. This would suggest to me that there is a defined position. But now HUP comes along and says that defining the areas that a wave-particle will occupy can only be accomplished statistically and through probabilities, which to me contradicts the proposition that such elements could therefor be standing-waves. I have Messiah's book, translated into English (I might like to get the original French version someday) but I can only manage the first few chapters as it stands.

[immortal]

You cannot come to such a conclusion. Alaistair I.M Rae in his book A beginner's guide for QM takes both the analogies i.e a particle in a box analogy as well as the standing waves analogy that can be formed in a pool to arrive at the accurate predictions made by quantum theory.

We need those two analogies because of the dual nature of matter, the position of the physical entity like an electron is defined by the particle concept where as the momentum which is associated with the wavelength of the matter waves is defined using the standing wave concept.

Both particle -->position and standing waves--> momentum can have a set of possible values. This is where uncertainty creeps in so that we can only predict the possible outcomes or values of a quantum system and we cannot simultaneously know both the values of position and momentum precisely as it will always have an uncertainty equal to (Dirac's constant(h/2pi))/2.

Therefore HUP is a direct consequence of standing waves of matter. One advice the postivist approach of Bohr gives is that we should not attempt to attribute some reality to the nature of the quantum system itself, we don't know what those elements are and the aim of QM is just to predict the possible outcomes of the system and not to predict the nature of the physical quantum system itself.

[MigL]

I believe one of the best explanations was given by Richard Feynman in his lecture series ( They are very easy to find online and may even be here as a sticky ). It arises from the fact that the amplitude of the 'wave' is related to probability.

Only an infinitely long wave has a clearly defined wavelength, wave number and amplitude. This amplitude is related to a probability in QM, such that in this case the probability of finding a particle at a certain place is the absolute value of the square of the amplitude. And so, in this case, since the wave is infinitely long, it can be found anywhere; position is uncertain.

A wave packet on the other hand, has an increasing/decreasing amplitude BUT the wave number cannot be easily defined. so although the particle is more localised in this case, its energy and also momentum are more undefined.

It is basically a trade-off, shortening the wave packet locates the particle with more accuracy, but makes the momentum more indeterminate; conversely lengthening the wave packet introduces more uncertainty in the particle position, but makes the determination of momentum more accurate.

This post has been edited by MigL: 9 February 2012 - 09:39 PM

[Xittenn]

I'll keep these points in mind as I continue my studies; thanks guys!

[DrRocket]

Xittenn, on 9 February 2012 - 06:28 PM, said:

Ok, be gentle with me please, my physics is poor and English even worse! What I can't follow with all of this is the following. Schrodinger developed wave equations that model particle behaviour at <macroscopic scale, and these behaviours also tend to be lost at >macroscopic scale. As far as I know or understand, these equations are built on the principles of standing waves. This would suggest to me that there is a defined position. But now HUP comes along and says that defining the areas that a wave-particle will occupy can only be accomplished statistically and through probabilities, which to me contradicts the proposition that such elements could therefor be standing-waves. I have Messiah's book, translated into English (I might like to get the original French version someday) but I can only manage the first few chapters as it stands.

A few points.

1. The Schrodinger equation really describes the evolution of the state function over time. It is not a wave equation in the strict sense, and it has nothing to do with standing waves. The Schrodinger equation is completely deterministic and the stochastic nature of QM is not reflected directly in it. However, in order to obtain a measurement of a physical quantity what one does is apply the Hermitian operator correcponding to the desired observable to the state function, which will produce the probability of the measurable being one of the eigenvalues of the operator. It is the interpretation of the Schrodinger equation that results in the stochastic nature of quantum mechanics.

2. Contrary to much that you read the Schrodiinger equation is not the entire story, not by a long shot. The Schrodinger applies only to elementary non-relativistic quantum mechanics. It does not apply to the more accurate and sophisticated quantum field theories, which are relativistic.

3. QM is inherently stochastic. See my earlier post. And this is not a result of the HUP. In fact the real effect of the Schrodinger equation, combined with the operators that represent observables, is simply to describe the time evolution of probability density functions. The HUP simple reflects the fact that complimentary operators do not commute (the order in which you apply them makes a difference).

4. Messiah is a good book. But you might find reading the third voluem of the Feynman Lectures on Physics enlightening. It is accessible and lets you see quantum mechanics through the eyes of a true master of the subject.

5. I tend to like Feynman's perspective: There is no such thing as wave particle duality. Elementary particles are particles. But they are not Newtonian marbles.

[Xittenn]

DrRocket, on 10 February 2012 - 02:21 AM, said:

you might find reading the third voluem of the Feynman Lectures on Physics enlightening. It is accessible and lets you see quantum mechanics through the eyes of a true master of the subject.

I'll definitely give this a try, I often find I pick too difficult a text for a first read and I'm left baffled. Having an overview that allows me to reach the concepts first is probably best. I've been looking to Phys Chem texts to fill in the gap. I think however that these texts have been supporting the very views that you have just pointed out as being maybe too strict in their adherence to ideas that might be better stated in other ways. They also tend to put a good deal of emphasis on the Bohr model as it applies to ideas related to equipartition theorem and--as Swansont has mentioned before--this isn't a proper way to address QM.

Appreciated!

[John Salerno]

Gah, I really want to wrap my head around this but it just doesn't make sense! I've read these replies, I've read Wikipedia, I'm currently reading "The Grand Design," but I still don't understand this concept (from Wikipedia):

Quote

The uncertainty principle states a fundamental property of quantum systems, and is not a statement about the observational success of current technology.

I just don't see how the uncertainty principle is anything other than a description of the problems with measuring techniques, rather than an inherent property of the system being measured. I fully understand how measuring a particle's position, for example, will affect it's momentum, but that still seems like a problem with current measurement technology rather than with the properties of the particle itself. Why isn't it the case the particle still really does have a specific position and momentum, and the problem is simply that we cannot measure them both simultaneously? I don't understand why the uncertainty principle HAS to mean that a particle never has a specific position and momentum at any given time.

Finally, in reading "The Grand Design," a distinction seems to be made between the uncertainty principle and the idea that measuring something will necessarily change it. Are these two different ideas, or are they the same thing? I thought that the uncertainty principle was basically saying if you measure one thing, it changes something else. But the book seems to be suggesting these are two distinct ideas in quantum physics.

Thanks.

[MigL]

Uncertainty is an inherent property of quantum reality. The measurement problem is used to explain the situation because most people find it very hard to believe reality is so strange. Go back and re-read some of the excellent guidance you've been given in previous posts. Oh, and a very good authority says 'The Grand Design' is a sell-out and not up to the standard of his previous books ( I haven't read it yet myself ), and you'd be better served by the Feynman lecture series ( which I have read and are excellent ).

[John Salerno]

MigL, on 27 February 2012 - 09:57 PM, said:

Oh, and a very good authority says 'The Grand Design' is a sell-out and not up to the standard of his previous books ( I haven't read it yet myself ), and you'd be better served by the Feynman lecture series ( which I have read and are excellent ).

I don't know who that "authority" is, but thus far I'm finding the book to be very similar to A Briefer History of Time. It covers a lot of the same material, but it also discusses M-theory in more depth (which I think is the topic of the next chapter I have to read). I guess it depends on what is meant by "sell-out."

[juanrga]

John Salerno, on 16 December 2011 - 08:56 PM, said:

I'm currently reading Stephen Hawking's book "A Briefer History of Time" and I was a little confused by the suggestion that the uncertainty principle undermines determinism, as stated in this sentence from the book:



As explained in the book, the uncertainty principle states that the more accurately the position of a particle is measured, the less accurate the measurement will be of the particle's velocity. Therefore, the "initial conditions" of the system can never be accurately known in order to determine the past or future state of the universe.

This much is easy to understand, but it seems that the uncertainty principle really only undermines our ability to calculate these past or future states of the universe, not that it actually undermines the fact that the universe still is deterministic (not that it necessarily is, but the uncertainty principle as stated above doesn't seem to suggest otherwise), even if we can never calculate any given state of it because of this uncertainty.

However, I have seen elsewhere that perhaps the uncertainty principle suggests more than the simple explanation given in the book. That, in fact, it explicitly says that the position or velocity of a particle is not actually determined at all until it is measured. This seems to really hurt determinism, but is that really what the uncertainty principle says? That a particle's position or velocity essentially doesn't exist at all until we measure it, or is it simply that we can never know a particle's position or velocity for sure until the time of its measurement?

Basically, my question comes down to this: even given the uncertainty principle and the probabilistic nature of quantum mechanics, couldn't it still be the case that the universe is perfectly deterministic, even if we can't accurately make the measurements to determine these past or future states ourselves? Doesn't a particle still have a certain position and velocity at any given time, even if measuring one of these will then change the other?

Hawking hints at this idea:



Frankly, I think the mention of a "supernatural being" unnecessarily muddies the discussion and makes Hawking dismiss the idea too easily. It's not necessary to postulate anything supernatural in order to retain determinism.

The above quote could easily have been stated as something like this: "We could still imagine that there is a set of laws that determine events completely, despite our inability to measure the present state of the universe without disturbing it." Then the second sentence would be irrelevant, because it would be of interest to us to know that it is possible for the universe still to be perfectly deterministic, even if we can't (yet) discover all the laws.

Yes quantum theory undermines determinism, but it has nothing to see with the uncertainty principle, but with the non-unitary evolution of the quantum state (vonNeuman postulate).