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Yes, that is true, but it's NOT the complete explanation. Read the rest of the article.
Falsification Of Heinsenberg's Uncertainty Principle?
- Thread starter common_sense_seeker
- Start date
Yes, that is true, but it's NOT the complete explanation. Read the rest of the article.
Are you sure you're not taking all the QM propaganda too seriously? Thats exactly what they say- in the quantum world, the rational becomes irrational, and math is the only way of understanding. This way, the guy with the fanciest degree and the most papers has a monopoly on truth. I piss on this system.
Thats exactly what bohr and his physicists were relying on. They keep arguing long enough, they will outlast memory and their truth will be lodged into the heads of most.
However, I better read the rest ..
Monopoly?
Shit, I wish someone had told me I was one of the "in crowd".
That is exactly wrong. It is, as far as we know, a principle that describes nature.
In this context, principle means "a comprehensive and fundamental law". I would not call that "only".
This comes off as more than a little "scientific conspiracy theory," don't you think? If you have objections to the actual math/science, by all means bring those to the table, but the ad hominem quibbling in the above passages is hardly productive. Arguing against authority is no more valid than arguing from authority.
This is what Heisenberg himself argued:
"One way in which Heisenberg originally argued for the uncertainty principle is by using an imaginary microscope as a measuring device.[3] He imagines an experimenter trying to measure the position and momentum of an electron by shooting a photon at it.
If the photon has a short wavelength, and therefore a large momentum, the position can be measured accurately. But the photon scatters in a random direction, transferring a large and uncertain amount of momentum to the electron. If the photon has a long wavelength and low momentum, the collision doesn't disturb the electron's momentum very much, but the scattering will reveal its position only vaguely."
So, it is based on observation.
Once again- Can you show any principle that is based solely on the uncertainty principle? I doubt it. Because the uncertainty principle is an experimental aberration. Its an error!
Think about it in terms of this scenario.
You are drunk, and you are walking through an academic dormitory. You feel really sick and you feel like you are going to vomit, so you run into the first bathroom that you see. Since you are very drunk, you do not notice that it is a female lavatory. Behind the door, there is a shapely young lady without any clothes on. You stop, and stare, but you cannot grasp her full beauty because she immediately recoils and screams.
This is like the uncertainty principle. When you look, you cannot see. You have to be sneaky in your observation, and you cannot let the particles feel like they are being observed in order to know their nature.
I mean that QM is contrary to "common sense".
As human beings the reality of QM and Heisenberg is outside our everyday experience.
It is a facet of nature: whether or not it comes across as "logical" or "what you would expect" is neither here nor there.
This is actually a very important statement you made. Quantum mechanics predicts non-local effects, which is exactly what entanglement is, and to many that does imply some kind of faster-than-light signalling. The experimental confirmation of the Bell inequalities demonstrates that no local hidden-variable theory can explain such quantum effects. You can have a non-local hidden variable theory, but that again means some kind of faster than light signalling. Actually there is one way to have a local quantum theory, that being the many-worlds theory, but aside from that locality is screwed. Fortunately information transfer remains a local process despite non-local entanglement type effects so relativity gets to remain valid.
I actually have my own crackpotish type ideas about locality. I worked on a theory for my honours project in which the structure of space-time was described by a quantum graph network, i.e. where spacetime was literally made out of mathematical points joined by edges which were ideal two-state quantum systems (i.e. edge 'on' or 'off). The idea was to dream up energy conditions for the graph so that the lowest energy state would be an extended structure that on the large-scale would vaguely resemble a 3-dimensional manifold (time was tricky to worry about and this was just a toy model anyway). I found that for all the energy functions I (and some others working on similar stuff) could think of to do such a thing, there would be a lot of states near the lowest energy state (which I could only approximate because the space of possibile configurations for a graph on a fixed number of nodes explodes out combinatorically with the number of nodes, i.e. it is vastly vastly enormous) which still had a small population of "non-local" links in the graph structure, i.e. the graph formed a mostly extended structure but there remained a number of links which provided "short-cuts" across the graph structure. This basically meant there were "non-local" defects in an overall local structure. Obviously there would be a massive amount of work to do to try and relate such a structure to real spacetime and real physics, but it was kind of interesting to see. I wouldn't be at all surprised if there turned out to be some truth to the concept.
Haha ok that's enough about that from me.
Haha ok that's enough about that from me.
Yes, and the Uncertainty Principle further states that are absolute limits to how little measurements on one quantity can effect the other. Whether you find it plausible or not, the wave picture of quantum mechanics works, and its predictions have been experimentally confirmed, so you need to tell me why I should instead believe your notions which are based on purely macroscopic intuition. Why does the world have to work at the fundamental level in a way which agrees with your daily experience at much larger scales?
Faster than light signalling has been experimentally proven since the 1980's, and is considered a major boost to the probability wave interpretation of QM. This is one of the reasons why hidden variable theories, the type of theory you're trying to support, are not taken very seriously at present. Associated with faster than light signalling, entanglement is a proven fact- look up Bell's Theorem on Wikipedia, since you're spending so much time there. It's been shown that two entangled particles are capable of having a measurement on one particle instantly alter the properties of the other particle, meaning you can't use your scheme to simultaneously measure position and momentum, because a position measurement on one particle affects the other's momentum, and vice versa.
The catch is that in a hidden variable theory, such signals would carry information and hence the causality principle in relativity is violated. In a probabilistic quantum theory, all information in the signals is destroyed by statistical randomness, preventing any causality paradoxes from arising in relativity. But it can still be proven that a signal was sent, once the statistical results of the experiment are analyzed at both ends and compared.
No, it was only a dozen or so key players who came up with the bulk of QM's framework. Yes there were others who helped put together various bits and pieces, but don't forget that Einstein had this kind of help too- he worked with figures such as Minkowski and Hilbert, some of the greatest mathematicians in history, and these were just a couple of the many brilliant collaborators he worked with on his theories.
Quantum mechanics is a very powerful and flexible framework which contains fixed mathematical rules, and specific objects you can tweak and manipulate within these rules. The bulk of the other physicists who made their contributions to QM did so in the area of applying the rules of QM to specific physical models, i.e. atomic systems. It's the same as when Newton came up with his laws- the rules in themselves don't describe anything interesting, you have to come up with physical systems like orbiting planets or spinning tops, and it took thousands of physicists to construct mathematical descriptions of these various systems and to then apply Newton's rules to see how these systems would evolve. QM was not tweaked and massaged by tens of thousands of physicists until it worked- a small number of brilliant men constructed a powerful framework, and then thousands of physicists proceeded to find ways of successfully applying that framework to real physical systems.
I think you should learn more about the details of what Einstein and Bohr actually did before you make such blanket statements. Ad hominem attacks on Bohr and the means by which he spread his ideas look foolish when you don't even demonstrate a basic grasp of what you're attacking. Focus on the ideas, the theories and the experiments, not the people discussing them.
You talk as if noone since Bohr et al has managed to understand their work or examined it using experiments or been able to develop it further. The basic concepts in the uncertainty principle come up in first courses in quantum mechanics, typically something a second year undergraduate might do. While I don't deny there's a few people whose work is shrouded in so much mathematics its hard to get a handle on it they are generally not lone physicists, with a monopoly on the ideas they work with, there are other people who also do that work.
Going from the fact that $$[x,p] = ih$$ through to the uncertainty principle is about 10~15 lines of algebra which uses nothing more than expectations and standard deviations. Anyone with a grasp of linear algebra and basic calculus can get their head around the derivation, even if they don't like the concept. In the derivation it doesn't mention how you do the measurement but simply measuring something, ie taking the expectation value of an operator, gives the result.
This certainly isn't mainstream science, but I think that there is much to be learned using an alternative approach. Because we are taught to look at problems in a certain way, there may be some holes in our vision that we do not see because of our perspective. Switching perspectives and exploring the world in terms of another theory can be quite useful I think. But thats me being pompous
No reason, but if I do get some of these rules about entanglement straight, maybe there is some sense in what I am saying. . True, I do not have any training in quantum physics or anything above entry level calculus, but in this scenario (uncertainty principle) I think it is easy enough to understand. What got me now is the entanglement portion.
I don't think this is right. This would mean that you are transferring energy faster than the speed of light, and I don't really see how this wouldn't imply faster than light communication.
About Bell's Theorem, I only read a bit. It seems that he is saying that if you have hidden-variables then you can indeed have faster than light communication. However, if entanglement is entanglement for entanglement's sake, with no hidden variables or strings attached, then it would not imply faster than light communication. (what is the difference between communication and signaling, anyhow?)
Yes, thanks for clarifying. It can still be proven that a signal was sent? This seems like information transfer to me! I'm sure we can think up of scenarios that would use this set up to transfer information. For instance - "If you see the signal, blow the bridge!!"
Also, I would like to point out that Einstein had a rivalry with the quantum physicists, and they were certainly going out of their way to ruin each others shit. Bell's theorem uses Einstein's argument against himself.. which is quite brilliant.
Yes, several set up the framework, and then hundreds of people made it possible to apply quantum mechanics to every possible scenario. Even xkcd has a cartoon showing how ridiculous it is - http://xkcd.com/26/
True, I was only trying to point out that there was a rivalry between the two.
I mean to say that the uncertainty principle is nothing more than an observational error! I do not think there is anything wrong with QM!!
I'm not sure how hbar comes into play here, but I think I understand the physical basis of the uncertainty principle. It is a reaction to observation. If an observation was not made, there will be no uncertainty principle. Wave-particle duality, sure, absolutely. Uncertainty principle, no.
I mean, is the uncertainty principle even that vital to QM?
Terrific, I am late to work!
Yes, it can be proven that a signal was sent, but the only way to detect that a signal was sent is by having the two ends of experiment compare their results by the usual slower-than-light methods, and to see that there was a correlation between the random statistical results at each end which couldn't be explained by a local hidden variable theory. That was Bell's stroke of genius; he found a way of experimentally proving that signals can be sent faster than light, even if they're sent in such a way that no information is transmitted and the past can't be changed. It took a couple of decades before they had the technology to put Bell's Theorem to actual tests, just to let you know (look up physicist Alain Aspect for details on the first actual experiments).
Also, I would like to point out that Einstein had a rivalry with the quantum physicists, and they were certainly going out of their way to ruin each others shit. Bell's theorem uses Einstein's argument against himself.. which is quite brilliant.
Well, I would say the quantum physicists were very enthusiastic about Einstein's relativity, it's just that the feeling wasn't mutual. Relativity stitches very nicely into quantum mechanics, the whole field of particle physics was pretty much born out of this combination (look up "quantum field theory"). It's only when they try to add general relativity's gravity into the picture that things become muddled, but the special theory of relativity blends with QM perfectly.
The conflict between all these physicists wasn't really a matter of ego in most cases. Einstein and like-minded followers felt that the universe ought to have a definite set of rules for how outcomes are decided, that no decision would seem arbitrary if only you knew all the variables nature takes as initial input. Quantum mechanics does away with this completely- nature just picks stuff at random, and all we can do is predict the shape of the probability distribution from which nature samples.
It would be ridiculous if all their efforts amounted to was cramming these physical systems into a box too small to even temporarily hold them. But if these hundreds of physicists are able to take very limited samples of data, apply the rules of quantum mechanics, and successfully extrapolate the results to much larger varieties of data, is this something to be laughed at? The periodic table of the elements opened the door to a great deal of understanding and progress in chemistry, by revealing the beginnings of an underlying pattern (incidentally, the periodic table can be explained and predicted entirely using QM). Similarly, quantum mechanical models in nuclear physics, such as the Shell Model, opened the door to a great deal of understanding and predictive power in describing atomic reactions and decays, which ultimately led to things not many people laugh about. Quantum models also led to the prediction and discovery of transistors and diodes, without which you wouldn't be reading this message.
To sum it up, the proof is in the pudding. QM is taken seriously because it works, end of story.
Oh yeah, I'm just saying that there has been a lot of work outside of the framework. I never knew you could rewrite the periodic table using the rules of QM. That is quite amazing! Anyways, I am still trying to find more direct evidence that the uncertainty principle is a law of nature rather than a law of man. It just doesn't jive with my understanding of the world.
I just figured out what I am arguing:
http://en.wikipedia.org/wiki/Quantum_decoherence
And perhaps it is measurable!
So, when you measure the momentum of one part of an entangled set, it automatically measures the momentum on the other ? Does this break entanglement of the whole set, or just that one particle? Ooooh, I'm feeling lucky. Please, answer the above question and I will post something seemingly profound.
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That's only scratching the surface- QM is an extremely useful, powerful and descriptive theory. It's not just some philosophical game for people to play while they sit in their armchairs smoking their pipes.
When I was a kid, I hated relativity after my dad explained why things can't go faster than light (in the information sense, as we discussed earlier). But the evidence to support it is just too damned good, and the math is practically inevitable once you accept the laws of electromagnetism. Basically, I don't think you should try too hard to disprove something just because you don't like the consequences it implies. Nature didn't really ask for or need our input when it drew up its rules.
No, I'm pretty sure you're misunderstanding the whole article. It's not talking about a particle having an absolute position and momentum at the same time, it's actually the opposite in a sense. Quantum decoherence is a means of explaining how our experimental devices can make waves collapse and appear to behave like particles. It actually suggests that particles exhibit wavelike behaviour even in experiments where their wavefunctions seemingly appear to collapse, which would preclude any possibility of exact measurement.
The answer depends on how much you know about the system as a whole, at the start of the experiment. A pair of particles gets entangled when knowledge of one particle's quantum properties implies some knowledge about the other particle's properties. An example of an entangled system would be a stationary, neutral pion known to have zero spin, decaying into two photons which shoot off in opposite directions. The total angular momentum of that system of two photons must still sum to zero, so if you measure the angular momentum of one photon, the other one must have opposite angular momentum with respect to the system's centre of mass.
Once a measurement is made, the entanglement is broken, although entanglement can then be formed between the entangled objects and the device performing the measurement.
I believe it is a very useful theory that requires enormous time investments and understanding to comprehend. However, I am sure that there is some intellectual corruption in quantum mechanics just as there is everywhere else.
Funny thing, I first started hating the uncertainty principle because my dad told me nothing is certain. Ultimately I am not trying to undermine this principle just out of whim, but because i think I can, and because I think it is a stupid principle. For god's sake, its just the observer's effect!
I look at the math in that article, and all I can say is :bugeye:
I do not disagree that particles exhibit wavelike behaviors. Wave particle duality is firmly lodged in my head as true. The article says that Quantum Decoherence provides a reason why one may observe wavefunction collapse.
http://en.wikipedia.org/wiki/Collapse_of_the_wavefunction
"The reality of wave function collapse has always been debated"
and
"In recent decades the quantum decoherence view has gained popularity."
This isn't really proof for my argument, since I want solid definitive evidence that the uncertainty principle is an aberration. However, it does give me some room for argument and may even be the basis for some experiment (if I ever choose math..).
Yeah, this sounds right to me. Entanglement isn't really that extraordinary, it can be achieved on the macroscopic scale to I believe. Entanglement is broken because the starting parameters are altered (due to measurement).
Suppose the pion splits into three photons (whether it is possible or not..). If you measure the momentum of one, you know the momenta of the other two. If instead you measure position, you know the position of the other two (relative to the starting point/ center of mass). Now, if you measure the position of one and the momentum of the other, you will know both for the third. Am I right or am I right?
And if the math of quantum physics is correct, it doesn't matter whether it's a natural principle or a mere observer effect, the point is there are limits to how precisely you can determine position and momentum at the same time. So if you want to believe the Uncertainty Principle is stupid, that's your prerogative, but I can't see any factual reasons to consider the math behind QM to be stupid or irrelevant.
One of the main points of quantum decoherence is that wave functions never completely collapse. So from this viewpoint, the idea of the point particle is only good as an approximation, but in reality everything is made of waves.
I don't see how it says anything whatsoever about being able to determine position and momentum to arbitrary precision at the same time. Like I and others have been saying, the Uncertainty Principle follows directly from some of the most basic axioms found in quantum mechanics. You can't get rid of the Uncertainty Principle without getting rid of the mathematics at the same time, and those mathematics work too darn well in the real world to be dismissed as a lucky fluke.
I don't think that's the case. Individual particles get entangled all the time, but on the macroscopic scale you have measurements being done all the time which would break any efforts to get a meaningful entanglement on such scales. There's a lot of rubbish published in the popular media about entanglement, so one has to be very careful what they read about it and from where.
No, I think I should try to explain this in more detail. Particles get entangled when you set things up so that the system to which they belong has some well-defined properties, such as total angular momentum. If there is more than one arrangement these particles can take in order to maintain such properties, the particles usually become entangled in a superposition of several such arrangements. So when you make a measurement on one of these particles, there are multiple possible outcomes, but once an outcome is selected, all possibilities for the remaining particles that don't add up to the required values will be removed.
Suppose the pion splits into three photons (whether it is possible or not..). If you measure the momentum of one, you know the momenta of the other two. If instead you measure position, you know the position of the other two (relative to the starting point/ center of mass). Now, if you measure the position of one and the momentum of the other, you will know both for the third. Am I right or am I right?
No, I think you're wrong about this. For instance, if you measure the momentum of one photon, it constrains the combined momentum of the other two photons but doesn't completely determine their individual values. In any case, going back to the case of 2 photons: measuring the momentum of one photon would instantly affect the momentum of the other one, which then screws up the certainty in its position. The positions you would subsequently measure don't correspond to the positions the particles had when their momenta were determined.
You should be aware that this is all a highly simplified picture. Particles never have a single well-defined momentum, they always have a continuous spread of momenta combined into a single state known as a wave packet. You don't measure an individual particle's exact momentum, rather you get a statistical picture of what the particle's most likely momentum is, and you usually have to repeat the experiment with the same conditions over and over to figure out the shape of the wave packet. It's a very complicated subject, and I don't pretend to be an expert in this area. It's much easier to deal with the Uncertainty Principle as it applies to quantum spins- this is much, much, much easier to calculate, understand and test.
Yes, I am sure it is. I don't doubt that there is plenty that I do not understand, but I think that simple logic should always be allowed to make it's points. If a theory cannot take a hit of simple logic, it is a very weak theory. I am not saying the QM theory is one of these, just that there may be some facets of it that have an over-inflated importance.
Sure, but the underlying truth may be that there is no 'uncertainty', maybe at least for the particle model. If you take a wave, I am sure you can define it's 'center of energy' but this will not be very truthful, so perhaps there is some uncertainty.
Its the wave particle duality, so we can describe the world in terms of particles or waves. However, it seems that quantum decoherence indeed implies there are no particles, only waves.
Like you say, the uncertainty principle follows, it does not lead to anything. Its just a measurement aberration. Its not a law that shapes others, its just a handy principle.
The fact that you cannot measure both very accurately must have been incorporated into QM since otherwise the whole thing would be worthless! If you needed certainty, then QM would only be a theory. However, relying on the Uncertainty Principle, QM was experimentally verifiable. Quantum mechanicists worked with their inaccurate measuring devices and found ways to go around these inaccuracies mathematically. This is exactly why the uncertainty principle must be incorporated in all the equations of QM - because it is a theory that is real, and aberrations are a reality.
By no means a lucky fluke, it is a powerful theory of reality with experimental proof. However, if one found a way to go beyond the uncertainty principle, there would be much math to rewrite. (of course, only if there was any good reason to. perhaps QM is solid enough that there is no need for certainty)
This is a good point. It seems that a macroscopic system would constantly be affected by photons, destroying any entanglement.
However, this is mechanical entanglement:
http://blogs.physicstoday.org/update/2009/06/entangled-mechanical-oscillato.html
Its only two atoms per oscillator, so its by no means a large system.
Yes, I got it. But there is no real and permanent effect on the other particle by measuring one. If there was, faster than light communication would be possible.
Also, picture this scenario:
One photon is used to measure the position of an entangled particle. This photon only has a certain amount of energy and momentum. To assert that this one photon can then affect any number of entangled twins is ridiculous! It would require more and more momentum to have the same effects on more and more particles!
Well, it seems that here you contradict my above statement. So there is real and permanent change?
This can't be true, because you would be transferring energy faster than light. It's not even a signal, its outright force (otherwise no change in momentum).
It seems that entanglement is 100% precise when measuring spins (as in perfect correlation), and so it is 100% accurate when measuring position (in mechanical entanglement .. yes, big assumption).