Well.. my whole argument was based on my understanding. Since you can entangle oscillating particles so that their oscillations match, you could check the momentum of one, and then the position of the other. That way you would get a composite image of where this 'particle' was and how fast it was moving. This will bring you a lot closer to beating hbar/2 than any other experimental method, I think.
Falsification Of Heinsenberg's Uncertainty Principle?
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Well.. my whole argument was based on my understanding. Since you can entangle oscillating particles so that their oscillations match, you could check the momentum of one, and then the position of the other. That way you would get a composite image of where this 'particle' was and how fast it was moving. This will bring you a lot closer to beating hbar/2 than any other experimental method, I think.
It is hard to come up with a specific reason why what you are suggesting cannot be done, aside from the fact that it violates Heisenbergs principle, without a more specific proposal for an experiment. There is a nice experiment that does pretty much what you're talking about, due to Popper. Wikipedia has an article on it:
http://en.wikipedia.org/wiki/Popper's_experiment
Unfortunately it gets a bit technical when they actually start going into the details of what's wrong with it, and I'm going to have to read it again myself to figure it out. I don't know of any other examples of this type of experiment though and I can't think of my own just now. If you'll accept two other non-commuting variables rather than position and momentum it might be easier to come up with an experiment (I'm thinking spin about x or z axis here). I have to go just now though, I'll try and think of something...
http://en.wikipedia.org/wiki/Popper's_experiment
Unfortunately it gets a bit technical when they actually start going into the details of what's wrong with it, and I'm going to have to read it again myself to figure it out. I don't know of any other examples of this type of experiment though and I can't think of my own just now. If you'll accept two other non-commuting variables rather than position and momentum it might be easier to come up with an experiment (I'm thinking spin about x or z axis here). I have to go just now though, I'll try and think of something...
Entanglement doesn't mean they are copies of one another, but that their properties are related in some way. For instance, if you entangle two photons such that their polarisations sum to something you know then if you know the polarisation of one of them you know the polariasation of the other. However, this does not avoid the UP, as the entanglement means that the uncertainty in one particle feeds through to uncertainty in the other. You'll find that in measuring one of them you disrupt the other in precisely the amount you'd need to get the UP to remain valid.
There's a lot of nifty things you can do with entanglement but entanglement is a fundamentally quantum mechanical system, its dependent on the fact $$[x,p] = ih$$. If you remove the UP by saying h=0 then you find you can't entangle things quantum mechanically.
Kurros is right, that it's hard to explain this if you aren't familiar with the mathematics of quantum mechanics, as much of QM is counter-intuitive. Such things as Bell's theorem and inequalities show that even if you assume that hidden variables exist and in principle could be measured (you do not need to specify how this would be done, entangled pairs or nifty detectors etc) then you must give up the concept of cause and effect, ie causlity.
It's a trade off as to which you dislike the most, the concept of causality or the universe being inherently non-deterministic. The problem with throwing causlity out the window is its very hard to then get meaningful predictions as things can happen before the thing which caused them! Kind of hard to predict the future when that happens.
Hmm, there seems to be more to this than I first thought. In 1999 Kim and Shih [1] actually performed Poppers experiment and found that the results didn't agree with Heisenbergs principle. It appears that things are actually more complex for entangled systems. Later Rigolin [2] came out with an explanation in which he derives a modified version of the uncertainty relation which applies to the entangled system, and reduces to the regular uncertainty principle in the case when there is no correlation between the particles. So it looks like you can actually do a little better in your measurements if you make use of entanglement, neat.
[1] Y. H. Kim and Y. Shill, "Experimental realization of Popper's experiment: Violation of the uncertainty principle?", Found. Phys. 29, 1849 (1999)
[2] G. Rigolin, "Uncertainty Relations for Entangled States", Found. Phys. Lett. 15, No. 3, June 2002
[1] Y. H. Kim and Y. Shill, "Experimental realization of Popper's experiment: Violation of the uncertainty principle?", Found. Phys. 29, 1849 (1999)
[2] G. Rigolin, "Uncertainty Relations for Entangled States", Found. Phys. Lett. 15, No. 3, June 2002
Well, before I read the articles : I told you so! 
Even if you figure out the properties of the entangled system, its position in the real, macroscopic world would not be very well defined. . . or,, isn't it that larger objects don't 'smear' as much due to the wave-particle duality? Or, is it just that its harder to notice in larger objects?
For this to be useful at all, you would have to have an entangled particle oscillating with a more massive object. This way the duality would not be as pronounced..?
Even if you figure out the properties of the entangled system, its position in the real, macroscopic world would not be very well defined. . . or,, isn't it that larger objects don't 'smear' as much due to the wave-particle duality? Or, is it just that its harder to notice in larger objects?
For this to be useful at all, you would have to have an entangled particle oscillating with a more massive object. This way the duality would not be as pronounced..?
voodoochile
Registered Senior Member
ZZZZzzzz
That's part of the idea, but the wave nature of quantum mechanics imposes strict limits on how little one quantity can be affected when you attempt to manipulate the other one. If you attempt to squeeze a particle's position wavefunction into a very narrow box (with a tiny bit of leakage/tunneling out the sides), the very act of squeezing it is mathematically guaranteed to cause an enormous spread in the particle's momentum wavefunction.
As for your complaints about the terminology we physicists use, I agree 100%. If the early pioneers of QM had been more careful with their language and communication, we wouldn't have so many people misunderstanding it and there wouldn't be cranks going on the Oprah Winfrey show telling millions of viewers that quantum physics is the key to their spiritual fulfillment.
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I guess I understand the first part; my point is that uncertainty is not so much a law of physical nature, but a law governing the way we perceive it. If we knew everything, perhaps there wouldn't be as much uncertainty...
I mean, sure, the uncertainty principle may hold to be a very useful principle in physics; however, it is not a principle that describes nature, but rather a principle that describes procedure. Perhaps this is why it is only a principle.
Communication can be very tricky, especially for people who prefer to study symbols and abstract concepts. You cannot hope to be good at everything. It is interesting how some scientists nowadays choose to specialize in communicating their ideas instead of thinking up new ones.
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No.
It's a property of nature, not of our observations.
?!?! Wait a second, what about popper's experiment?
So. We can know very precisely what the momentum of a particle is. Or we can know very precisely what the position of a particle is. Is this all right so far?
Now, we take 3 entangled oscillators. We simultaneously figure out the momentum on one, the position on the second. We then take both of these and assign them to the third entangled oscillator.
So. We can know very precisely what the momentum of a particle is. Or we can know very precisely what the position of a particle is. Is this all right so far?
Now, we take 3 entangled oscillators. We simultaneously figure out the momentum on one, the position on the second. We then take both of these and assign them to the third entangled oscillator.
What about it?
As Kurros stated: "Unfortunately it gets a bit technical when they actually start going into the details of what's wrong with it" i.e. there's a number of objections.
Look at the Wiki article -
One or the other with precision. Yup.
I'll have to think about that*, but my first reaction is "Huh? So how do you know the position of the third one from the other two, unless it's exactly where they are?"
*it's (oh shit!!) nearly 5 AM here - another all-nighter... Bed for me.
Yeah.. this isn't really useful other than for proving the principle wrong in this one scenario.
The point is that you can figure out exactly where the particles are relative to their oscillating ion. Here is a link on oscillation entanglement -
http://www.nist.gov/public_affairs/releases/jost/jost_060309.html
This is quite useless since then you have to figure out where the ion is relative to another object, and so on and on. This does not give a precise point and momentum in space, but a precise point and momentum in reference to the oscillator. Does this beat the uncertainty principle?
Ha ha, I am in america but jet lagged and in european time its 6 AM x_x
The point is that you can figure out exactly where the particles are relative to their oscillating ion. Here is a link on oscillation entanglement -
http://www.nist.gov/public_affairs/releases/jost/jost_060309.html
This is quite useless since then you have to figure out where the ion is relative to another object, and so on and on. This does not give a precise point and momentum in space, but a precise point and momentum in reference to the oscillator. Does this beat the uncertainty principle?
Ha ha, I am in america but jet lagged and in european time its 6 AM x_x
But it's a law that governs the way we perceive nature for any means by which we choose to perceive it. Doesn't matter what kind of detectors you use or how you utilize the apparatus, the uncertainty principle holds in every case. So if our perception of reality is consistent regardless of how we choose to measure it, how do we separate this perception from the underlying truth?
The uncertainty principle is a direct result of the mathematical rules in quantum mechanics, and we presently have no experimental grounds to question these rules. In fact, experiments such as the double slit experiment demonstrate uncertainty at work (narrowing the slits to get better position certainty causes a wider spread in particle momenta as they go through the slits), and there are other versions of the uncertainty principle (such as angular momentum uncertainty) that have also been tested.
I disagree, I think most scientists are actually quite excellent at communicating their ideas, the problem is they're trained to communicate with other highly trained people who already have at least a general background in the same field. They're very good at expressing and discussing ideas with people who can actually do something useful with those ideas. The problem you're citing has more to do with the lack of interest in communicating science to the general public.
The marvels of modern science have captured the public's imagination, but the ideas are actually far more complicated and detailed than they're made to seem in the typical layman's explanation. We need more people who are both willing to dumb things down into terms and analogies a layman can relate to, while at the same time taking a sufficiently nuanced approach so as not to give people the wrong ideas and set their minds whirring with possibilities that don't really fit into the realm of physics.
I think Brian Greene is doing an excellent job explaining physics to the layman, you should check out his Elegant Universe book or watch his PBS TV special (same title) on the internet. I downloaded an episode of the Art Bell show (late night American radio show where they talk about aliens, ghosts, witches, demons, spooks, etc., with virtually zero skeptical analysis) with Brian Greene as a guest, and I have never in my life seen or heard such a good, wholesome, healthy dose of scientific truth injected into such a muddled pseudoscientific cesspool. I'm also personally hoping to take a shot at writing a layman's book on science one day, it's been a goal of mine since I was a kid, when such titles were the only material I could access on what's actually being studied in modern physics (note: such books should NEVER, EVER be considered a substitute for doing the actual math and details as you would in a university).
This reminds me of an argument Neils Bohr and Albert Einstein had going on in the 1930's, back and forth both in person and by mail. Einstein tried to come up with various schemes such as the one you're suggesting, as a means of "beating" the uncertainty principle. The whole point of entanglement is that if you take a particle at rest with a precisely known position, then let it decay into two particles with equal and opposite momenta, those two particles get entangled in a single unified wave function. If you attempt to alter the position or momentum of one particle, it instantly affects the position and momentum of the other particle, no matter how far away it is. Quantum physics doesn't respect the principle of locality, and faster than light (nonlocal) phenomena in QM have already been demonstrated by several experiments. Of course there is a catch, which is that although we have proven faster than light phenomena in QM, these phenomena can't be used to transmit actual information in a way that could violate causality, hence relativity is still protected.
This is what wikipedia says-
"This means that the uncertainty principle is related to the observer effect, with which it is often conflated. The uncertainty principle sets a lower limit to how small the momentum disturbance in an accurate position experiment can be, and vice versa for momentum experiments."
and that
http://en.wikipedia.org/wiki/Heisenberg's_microscope
So, it seems that the uncertainty principle is all about measurements.
http://www.sciforums.com/showthread.php?t=93587&highlight=entanglement
This is where I get some of my understanding of entanglement. It seems that entangled particles start out with the same 'motor', but as soon as they are disturbed their motors start to run differently. This way you can tell what the other particle is doing when you measure the properties of its entangled twin.
It makes me angry when people choose not to distinguish truth from observation. Just because we can't measure it doesn't mean its not there. Bohr didn't really care about the truth, he only cared about the scientific method and it's limitations; he was very practical. Einstein had some kind of vision of the universe that he adhered to, and uncertainty would not be a part of it. This is what I got from the wikipedia article.
I agree with Einstein. There is more to the world than quantum mechanics can explain.
"This means that the uncertainty principle is related to the observer effect, with which it is often conflated. The uncertainty principle sets a lower limit to how small the momentum disturbance in an accurate position experiment can be, and vice versa for momentum experiments."
and that
http://en.wikipedia.org/wiki/Heisenberg's_microscope
So, it seems that the uncertainty principle is all about measurements.
http://www.sciforums.com/showthread.php?t=93587&highlight=entanglement
This is where I get some of my understanding of entanglement. It seems that entangled particles start out with the same 'motor', but as soon as they are disturbed their motors start to run differently. This way you can tell what the other particle is doing when you measure the properties of its entangled twin.
It makes me angry when people choose not to distinguish truth from observation. Just because we can't measure it doesn't mean its not there. Bohr didn't really care about the truth, he only cared about the scientific method and it's limitations; he was very practical. Einstein had some kind of vision of the universe that he adhered to, and uncertainty would not be a part of it. This is what I got from the wikipedia article.
I agree with Einstein. There is more to the world than quantum mechanics can explain.
What can we say about reality other than that which we can measure? Noone said a hidden variable theory of quantum mechanics couldn't be constructed in which everything's pre-determined but some details are hidden from us. The problem is that it's already been experimentally proven that any such theory would have to include faster than light signals, and in the case of hidden variable theories, these signals would have to carry information and thus violate relativity. So you can believe whatever you want about the underlying roots of the uncertainty principle, but I'll assert once again, as Oli has been doing, that this principle applies to everything we measure and by every method we choose to measure it, unless something is fundamentally wrong with the math of quantum mechanics. And when a reality manifests itself in a universally consistent manner, what's wrong with finding it plausible that the manifestation is itself the reality?
Your understanding of entanglement is totally wrong, that's the first problem. Entanglement involves setting up a system of particles in which certain collective properties of the system are known (i.e. momentum, angular momentum, electric charge). When you make a measurement on one of these particles, quantum mechanics guarantees that the other particles will have their values adjusted in such a way as to preserve the net properties of the system as a whole. If you entangle two particles such that they have opposite momenta, and you measure the momentum of particle A, it will automatically force a momentum measurement on particle B. The resulting entangled measurement on particle B will disrupt its position wavefunction, which means measuring particle B's position gives you no info on where particle A would have been found if you had measured its position instead of momentum.
Its not plausible. It simply does not make rational sense!! Its the measurement that distorts the system, not the system being distorted in the first place!! Even the wiki says this-
"The measurement of position necessarily disturbs a particle's momentum, and vice versa"
Their values adjusted? No, this would mean faster than light signaling! The particles are not in any way connected, they are simply wound up to work the same.
Quantum mechanics is an incredibly useful and broad field, because tens of thousands of people collaborated to make the theories work in every possible way. There was only one gifted, genius visionary Einstein that out of his little pinky finger pulled up a new field of physics.
The way I see it, Einstein was a visionary genius, while Bohr was an organizational genius. Einstein envisioned something and then made some bold calculations. Bohr got the whole world thinking and working exactly like he did. Which is greater?
Its like comparing a war hero who rescued 50 of his comrades in one night to a general that fine tuned and adjusted every facet of his war machine in order to win the fight. There is simply no comparison because both men were working under different motives and in different fields, and for various purposes.