The Uncertainty Principle - is it real?

First of all, howdy folks! I've been browsing this board for a few months now and I'm really enjoying it. This is my first post on the board so I hope I'm not doing anything wrong. Okay, let's get into it.I'll start by saying that I'm currently not a physics student (I'm studying prep courses so I can study at university next year). However on top of the boring stuff I have to study for that, I have also spent the last couple of weeks reading Brian Greene's The Elegant Universe and Fabric of the Cosmos and just got started on Richard P. Feynman's QED.In Greene's books the uncertainty principle is very important in string theory and inflationary cosmology and is a part of the quantum physics that remains intact throughout pretty much the entire book. However, in QED there is an endnote on page 55 that says (I'll paraphrse);

quote:

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"I would like to put the uncertainty principle in its historic place: When the revolutionary ideas of quantum physics were first coming out, people still tried to understand them in terms of old-fashioned ideas... if you get rid of the all the old fashioned ideas and instead use the ideas that I'm explaining in these lectures - adding arrows for all the ways events can happen - there is no need for an uncertaintly principle!"

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My question is this - is the uncertainty principle real? This one endnote has me pretty confused so I was hoping some of the very intelligent people on this forum could help me.I would also appreciate it if someone could explain to me the experiments that have been performed that have shown us that the uncertainty principle is, in fact, real (if any). I would expect this topic (if accepted) would belong in the Big Bang/Cosmology section of the science forum.

Welcome Martin,This seems like an interesting topic, and as you say the Big-Bang/Cosmology forum seems most suitable.One small point, you say you are going to paraphrase and then appear to provide a direct quote? Which is it?TTFN,AW

Thread moved here from the Proposed New Topics forum.

I have always wished that the Uncertainty Principle had been called the Tolerance Principle.If you buy a piston for your car, it will be dimensioned at some diameter some tolerance. The actual diameter really doesn't matter as long as it is within those bounds.

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Aslan is not a Tame Lion

Why do the good questions come up when I'm so busy...???The quick answer is that there are several equivalent formulations of QM; the important ones for this are wave-equation evolution via the Schroedinger equation, and Feynman's path integral formalism. In the latter, the idea of wavefunction is absent (although it is recoverable) and the operator* formalism is not apparent. As the UP is essentially a statement regarding the non-commutability* of operators, the UP does not arise. But it is still there. Feynman was not being deep, just obtuse. Usually he was both * Position and momentum in QM are not properties, but actions of measurement or "operators". You "operate" on the wave-function and receive a value (an observable), while changing the wave-function via the operation. Only if the the wave-function is in an "eignestate" of the operator will the operation not change the wave-function, in which case the observable is what we would normally call the "property". A wavefuntion cannot be in an eignestate of position and momentum at the same time.Operators do not commute in general... in other words, performing them one way round will result in something different to the other way round. Think of rotations: fix a set of 3d axes and define roll, pitch and yaw to these axes. roll 90 degrees left and pitch up 90. Try again, picth up 90, and roll left 90. You are in a different orientation to the first time: 3d rotations do not commute.Ugh, sorry you asked? If you are interested I can try and make this more palatable a little later. It will obviously be much longer

Hi, Heh, that is a great pun. Intended or not.Determinism states that if given enough information the outcome of a event can be accurately predicted. So macroscopically speaking Newtonian phyisics holds out.The founders of QM and UP, Dr. W. Heisenberg, and N. Bohr and even Dr. Einstien' who historically hated the concept, showed mathmatically and experimentally the way nature behaves on a quantum level is not 100% predictable. It is said that Dr. Einstien spent the rest of his life trying to reconcile this qurk in nature. There is a element of uncertainty because at a quantum level things do behave differently than on a macro level . Schrodingers equation allows for extremely accurate predictions of the problemistic wavefunction, although as far as I know reality still refuses to be boxed in a corner.

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"One is punished most for ones virtues" Fredrick Neitzche

True Jar,
But mathmatically,(however slight) there is a probability that given enough time; the piston vanishes from your crankshaft and ends up in some China mans tea pot. **edit spell.This message has been edited by 1.61803, 01-11-2006 12:49 PM

It's not a direct quote, I omitted a bit in the middle of the endnote which I considered reasonably irrelevant

I'd be lying if I told you I fully understood all of what you said, but give me a bit more time and I'm sure I can digest the bulk of it - of course if you find you have the time I would very much appreciate it if you could give me the "long version."

I have a follow up question which I seem to recall was covered briefly in Fabric of the Cosmos, but which I would love to hear your opinions on.Do you think the uncertainty principle is a consequence of the limits of our technology and/or methods involved in measuring particles, or an intrinsic property of nature at an ultramicroscopic level?

Well, the vast majority of experiments investigating Bell's Inequality suggest that the Uncertainty Principle is a fact of the real world, not just a physical limitation to experimental measurements.

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"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt

As Chirop mentioned, the UP is fundemental, not just an experimental limitation. And I will try to get back to this by the weekend, with a slightly more coherent post...

Hello MartinDomes,First off I agree with Chioptera and Cavediver. The problem with the whole thing is that things cease being "things" @ a quantum level. Dr. Einstien opened up a can of worms when he discovered and showed that light exist as discreet little packets of energy. Reality is quantized. Hence the naming of quantum mechanics. His photoelectric effect showed that light is a particle as well as a wave as previously believed.
When Prof. W. Heisenberg conducted experiments he found out that any measurements of these "thingys" would affect the data. Why? Because. The same reason reality is made up of bits of information rather than a smooth continum. For the same reason a electron can vanish in a valance and reappear in another at a different energy state. Why? How? Nobody knows.Thats why when you ask is the Uncertainty Principal real, I chuckled, because at a quantum level nothing is real. Everything is zinging around in a state of possibilties. A quantum foam so to speak. Prof Einstien refused to accept this. He believed that there was a simple elegant answer to this seemingly bizzare reality at the quantum level. That given enough time and information the Uncertainty principal could be reconciled as a mathmatic formula.
Well we still do not know why light is quantized, we still do not know what exactly energy is, and we still have not found a way to make gravity and electromagnatism physics make sense together. Is the U. P. real yes. is it due to us not being able to resolve the uncertainty no. I believe it has more to do with the limitations of not being able to take ourselves out of the formula than the limitations of what we can measure.

The best way of explaining the uncertainty principle, at least in my opinion, is as follows.Every Quantum Mechanical system is described by a function called the wavefunction, usually represented by the Greek letter "". is a complex valued function, meaning it attaches a complex number to each point in space.
What is it a function of though?
Usually we make it either a function of position "x" or momentum "p".
So lets say we have a system which consists of only a single electron moving in a straight line.
We can write down its wavefunction a function of momentum "(p)" or as a function of position "(x)".When we measure something's position to good accuracy, the wavefunction becomes very neat in terms of x. Which means "(x)" becomes very neat, peaking at the value for position you measured, with very little "trail off" into other values.
However "(p)" becomes very messy, trailing over many values of p.When we measure momentum the opposite happens. "(p)" becomes neat and "(x)" becomes messy.
So the neater the wavefunction looks in one representation the messier it looks in another.
The uncertainty principle basically shows how the untidiness is spread between the two representations.

The possibilities are real. The information is real, and the physical form is derivative, right?