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Natural Science Forum / Physics / Relativity / March 2007two slit questions for experiment experts
these questions rose while reading "the theory of almost everything" of R. Oerter: 1) light send to the two slits is monocromatic? is it coerent ? what if it is sun light? 2) what is the distances source-slits-screen? 3) what is distance between slits, what is the slit whith? 4) using electrons and putting a detector on a slit the distroying of interference takes place at once? what if the detector varies is sensibility and let trough some electrons when the interference disappears ? As usual there are facts and there is the language-logic to describe them, what are the real problems and what are the problems generated just from language-logic misuse ??? I would like to have references on a classical explanation of the two slit experiment. tanks in advance for any help beda pietanza > these questions rose while reading "the theory of almost everything" > of R. Oerter: [quoted text clipped - 11 lines] > them, what are the real problems and what are the problems generated > just from language-logic misuse ??? Quantum theory is many decades old and has been analysed countless times by physicists and philosophers. You can bet there are no issues with language logic misuse. The issue is trying to understand it by reading popularisations that can not by their very nature convey the subtleties. The real issue with QM was formulated by Von Neumann in his famous Mathematical Foundations of QM and is known as the collapse of the wave function issue. Different interpretations have different resolutions of the issue - only some of which at this stage are experimentally distinguishable from the other. Except for those that have been experimentally excluded, such as the Bohmian mechanics, choose the one you like best. The actual details of one interpretation, Consistent Histories, is given here: http://quantum.phys.cmu.edu/CHS/histories.html A comparison is given here: http://en.wikipedia.org/wiki/Interpretation_of_quantum_mechanics > I would like to have references on a classical explanation of the two > slit experiment. See the Feynman Lectures on Physics. Thanks Bill > tanks in advance for any help > > beda pietanza Bill Hobba ha scritto: > > these questions rose while reading "the theory of almost everything" > > of R. Oerter: [quoted text clipped - 20 lines] > Mathematical Foundations of QM and is known as the collapse of the wave > function issue. this is what makes me wonder on the adequacy of the terminology used: has been there done a experiment on the wave collapse that rules out the possibility of erroneous conclusions due to the combine of probability of events and efficiency of detectors ??? I have the feeling that the collapse of wave functions is just the popping out of preesistent hidden informations that would not change within the given aleatory probabilistic outputs. > Different interpretations have different resolutions of the > issue - only some of which at this stage are experimentally distinguishable [quoted text clipped - 10 lines] > > See the Feynman Lectures on Physics. Thank you, time permitting I will make good use of your references, beda pietanza > Thanks > Bill > > > tanks in advance for any help > > > > beda pietanza > Bill Hobba ha scritto: > [quoted text clipped - 31 lines] > of events > and efficiency of detectors ??? I have no idea what you are trying to get at. Be specific - propose an actual experiment. And if you find that difficult, have you considered the possibility your concerns are not well formulated enough to be of any value? > I have the feeling that the collapse of wave functions is just the > popping out of > preesistent hidden informations that would not change within the given > aleatory > probabilistic outputs. That is hidden variable theories. Standard QM rules them out via the Kochen-Speker theorem, if you want the hidden variables to behave in a classical like manner ie are both value definite and non contextual. It is possible that QM is a limiting case of a theory that does not have this problem - a few have been proposed, but as far as I know only Bohmian mechanics has been experimentally tested - and ruled out. Thanks Bill >> Different interpretations have different resolutions of the >> issue - only some of which at this stage are experimentally [quoted text clipped - 22 lines] >> > >> > beda pietanza >> Bill Hobba ha scritto: >> [quoted text clipped - 30 lines] >> possibility of erroneous conclusions due to the combine of probability >> of events and efficiency of detectors ??? Sure, see for example http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments According to one expert that I asked one year ago, upto then no experiment had been done that was free of known loopholes. > I have no idea what you are trying to get at. Be specific - propose an > actual experiment. And if you find that difficult, have you considered [quoted text clipped - 13 lines] > problem - a few have been proposed, but as far as I know only Bohmian > mechanics has been experimentally tested - and ruled out. When was that? According to the most recent information that I have, Bohmian mechanics and its variants have not been ruled out. Perhaps something important happened over the last year that I don't know of? Thanks, Harald >>> Bill Hobba ha scritto: >>> [quoted text clipped - 58 lines] > Bohmian mechanics and its variants have not been ruled out. Perhaps > something important happened over the last year that I don't know of? See http://arxiv.org/abs/quant-ph/0206196 Thanks Bill > Thanks, > Harald Bill Hobba ha scritto: > >>> Bill Hobba ha scritto: > >>> [quoted text clipped - 61 lines] > See > http://arxiv.org/abs/quant-ph/0206196 download of it din't work, could you sent me a copy of the paper ??? beda-pietanza@libero.it thanks in advance beda pietanza > Thanks > Bill > > > Thanks, > > Harald > Bill Hobba ha scritto: > [quoted text clipped - 87 lines] >> Thanks >> Bill Thanks Bill (I missed your post but found it contained in here), download worked for me and I will read it. Note however: apparently this has not been published in journal, which indicates that their work probably did not stand up to review (obviously, lack of novelty can't have been the reason for rejection, it would have been a break-through). Harald >> Bill Hobba ha scritto: >> [quoted text clipped - 96 lines] > lack of novelty can't have been the reason for rejection, it would have > been a break-through). Correction and addendum: As it seems to be a serious and high-quality paper I tried with Google. Although not shown in their preprint, it has been published: "G. Brida, E. Cagliero, G. Falzetta, M. Genovese, M. Gramegna, C. Novero A first experimental test of de Broglie-Bohm theory Journal of Physics B: Atomic, Molecular and Optical Physics, Vol. 35, p. 4751, 2002. Quantum Mechanics is a pillar of modern physics, confirmed by a huge amount of experiments. Nevertheless, it presents many unintuitive properties, strongly differing from classical mechanics due to its intrinsic non-epistemic probabilistic nature. Many attempts have been devoted to build a deterministic theory reproducing all the results of Standard Quantum Mechanics. One of the most successful attempt in this sense is de Broglie-Bohm theory. This theory is built in order to reproduce almost all SQM predictions. However, recently it was suggested that different coincidence patterns are predicted by SQM and dBB when a double slit experiment is realised under specific conditions. In this paper we present the first realisation of such a double slit experiment with correlated photons produced in type I parametric down conversion. We observe a perfect agreement with SQM prediction, whilst our result is far almost 8 standard deviations from dBB prediction. " Thus indeed, dBB seems to be out of the game now. Thanks, Harald Dear beda pietanza: > these questions rose while reading "the theory of almost > everything" of R. Oerter: > > 1) light send to the two slits is monocromatic? It doesn't have to be, but it is a whole lot easier if it is at least a single gas source. > is it coerent ? This is not important. > what if it is sun light? Lots of lines to sift through. Makes it much harder. > 2) what is the distances source-slits-screen? Source-to-slits should be >> slit spacing. What ever you require to discern separation between maxima for slits-to-screen. Note that as you move the "detection screen" away, the lines get dimmer. > 3) what is distance between slits, what is the > slit whith? The slit width is as small as practical. The slit spacing should also be as small as practical, and on the order of 5x the slit width. > 4) using electrons and putting a detector on a slit > the distroying of interference takes place at once? Yes, and propagates to the screen. > what if the detector varies is sensibility and let > trough some electrons when the interference > disappears ? As your resolution on what passes through one/both slit gets better and better, the pattern becomes more and more just "bullets passing through one slit or the other, but not both". > As usual there are facts and there is the > language-logic to describe them, what are the real > problems and what are the problems generated > just from language-logic misuse ??? No, it is just a weird as it sounds, beda. In any language. > I would like to have references on a classical > explanation of the two slit experiment. > > tanks in advance for any help OK. Everything propagates as waves, when the apparatus requires / allows it to act as waves. So the classical explanation is the wave model applies. And it applies to photons, electrons, and even molecules larger than C60 buckyballs. David A. Smith N:dlzc D:aol T:com (dlzc) ha scritto: > Dear beda pietanza: > [quoted text clipped - 47 lines] > > No, it is just a weird as it sounds, beda. In any language. what sounds weird to me is just the collapse of the wave funtion, which appears to me more as a retarded discovery of preesistent hidden informations then what seems a action at distance. > > I would like to have references on a classical > > explanation of the two slit experiment. [quoted text clipped - 5 lines] > wave model applies. And it applies to photons, electrons, and > even molecules larger than C60 buckyballs. Agree, and I find it rather sensible: the particles appears only when we force them to "materialize" with a detecting apparatus thanks a lot, also for your clarity beda pietanza > David A. Smith Dear beda pietanza: > N:dlzc D:aol T:com (dlzc) ha scritto: > [quoted text clipped - 57 lines] > discovery of preesistent hidden informations then what > seems a action at distance. I think of this "wave function collapse" along the lines of this joke: How do you shoot a purple elephant? With a purple elephant gun. How do you shoot a pink elephant? Hold his trunk until he turns purple, then shoot him. We look for wave behavior, we see and measure wave behavior. We look for particle behavior, we see and measure particle behavior. Any quantum particle has no "shape" in the wave-particle space... until we "hold its trunk". The "hidden information" is information we "impress" (or suppress the other behavior). >> > I would like to have references on a classical >> > explanation of the two slit experiment. [quoted text clipped - 10 lines] > appears only when we force them to "materialize" > with a detecting apparatus But whatever these "wavicles" or "wavelettes" have, they are discrete in the amount of momentum they carry. And they arrive at discrete locations, and only at (path length / average speed) seconds. The problem is the "language" our macroscopic experience uses to describe the very small. > thanks a lot, also for your clarity And you your patience. David A. Smith On Mar 21, 8:11 am, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: > Dear beda pietanza: > [quoted text clipped - 73 lines] > until we "hold its trunk". The "hidden information" is > information we "impress" (or suppress the other behavior). Cutely said. Bohr tried to impress on everyone that would listen that the inherent -- and this word "inherent" is important -- complementarity of quanta is intimately connected to a fundamental inseparability between the objects observed and the observer. That is, a particle does not HAVE a reality that we can lay hands on independent of our measurement of it, and how we measure it is enmeshed with the picture of the particle's reality we obtain from it. Up until Bohr, the approach had been basically Galilean: Make a bunch of measurements and estimate the perturbation that the observer introduces into each measurement, and then extrapolate to nail down what nature does without any observer at all. Bohr demonstrated that, at the quantum level, this strategy breaks down in a hopeless way. PD > >> > I would like to have references on a classical > >> > explanation of the two slit experiment. [quoted text clipped - 26 lines] > > - Show quoted text - PD ha scritto: > On Mar 21, 8:11 am, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> > wrote: [quoted text clipped - 89 lines] > what nature does without any observer at all. Bohr demonstrated that, > at the quantum level, this strategy breaks down in a hopeless way. OK, but the quanta speculations are even more hazardous then the risks related to the Galilean approach. regards beda pietanza > PD > [quoted text clipped - 28 lines] > > > > - Show quoted text - > PD ha scritto: > [quoted text clipped - 94 lines] > OK, but the quanta speculations are even more hazardous then the risks > related to the Galilean approach. Which is one reason why Dirac (although often attributed to Feynman - who without doubt would have agreed with it) said 'shut up and calculate'. But if you do that then you can't ask the type of questions your asking - you can't have it both ways. Thanks Bill > regards > [quoted text clipped - 32 lines] >> > >> > - Show quoted text - > > PD ha scritto: > [quoted text clipped - 103 lines] > if you do that then you can't ask the type of questions your asking - you > can't have it both ways. This applies to a scientist, science is too important to leave it to the scientists exclusevely. Questions wrongly made should be the easiest to answer. regards beda pietanza > Thanks > Bill [quoted text clipped - 39 lines] > > - Mostra testo tra virgolette - >> > PD ha scritto: >> [quoted text clipped - 108 lines] > the > scientists exclusively. So what you are saying is that we should not trust those that have devoted their career to something and not give it greater weight than what some casually interested person might think? Of course you not should accept things just because some professional says so - but the fact a professional says it means you need to give it greater weight and require evidence of greater weight to reject it. > Questions wrongly made should be the easiest to answer. Your exact reasoning for that remark is beyond me. For example, in mathematics, you have what is known as the existence issue. Sometimes it is very easy to prove a theorem if you assume something exists (eg every set can be well ordered). Trouble is proving that possibly wrong assertion (ie question) often turns out to be some of the most difficult problems in mathematics leading to some very profound insights eg look up the axiom of choice. Thanks Bill > regards > [quoted text clipped - 43 lines] >> >> - Mostra testo tra virgolette - > >> "beda pietanza" <beda-pieta...@libero.it> wrote in message > [quoted text clipped - 119 lines] > says it means you need to give it greater weight and require evidence of > greater weight to reject it. Agree, but consider that a "great true" is like a strong lively plant, which is bond to generate and to house a lot of parasites, so a "great true" generates spurious thinkings some of which might be very suggestive that eventually completely take over the scene: this could be the fallouts of the "ipse dixit" of a careless scientist. > > Questions wrongly made should be the easiest to answer. > [quoted text clipped - 5 lines] > mathematics leading to some very profound insights eg look up the axiom of > choice. yes you are right, I only meant those wrong questions that can be settled just using a common sintetic a priori judgment bets regards beda pietanza > Thanks > Bill [quoted text clipped - 50 lines] > > - Mostra testo tra virgolette - Dear beda pietanza: > PD ha scritto: ... >> Cutely said. Bohr tried to impress on everyone that >> would listen that the inherent -- and this word [quoted text clipped - 19 lines] > hazardous then the risks related to the Galilean > approach. Hazardous in what way? The fact is, in the quantum realm, space and time don't exist... or at least are not meaningful. This means that "wave" (invokes frequency and wavelength... time and distance) and "particle" (invokes location, path and velocity... 4D spacetime) are something impressed on these "poor" quanta *by the system that measures them*. The hazard lies in not realizing that it is mostly *ourselves* that are being measured, when we require a definition of wave or particle. It is the system we learn more about, not the individual. http://www.physics.carleton.ca/~watson/Neut_cent_talk/Neut_cent2.html ... only mildly related to the topic at hand, but what would you bet the "quantum bounce" was actually diffraction? David A. Smith On 22 Mar, 01:30, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: > Dear beda pietanza: > [quoted text clipped - 25 lines] > > Hazardous in what way? In the past centuries science has lead the way to good willings and helped them to protect umanity from the worst always at bay. Science is not just to run ahead to the most effective experiment but also the best means to light the path of human future, so, the task of a good scientist is to care for the social implications and for the preservation of soundness of human language; and this must be done working side to side with philosophers and politicians and religious people. Some scientist do so, some don't. Since the wrong ways are the easiest, these are taken first > The fact is, in the quantum realm, space and time don't exist... > or at least are not meaningful. This means that "wave" (invokes [quoted text clipped - 7 lines] > particle. It is the system we learn more about, not the > individual. Yes it is surely so, the hazard remain more subtle than ever for we cannot get rid of *ourselves*: the hazard stays, it goes all the way down We don't solve it with funambulims but striving to stay put on the ground of shared soundness. EI: the correct statement is not: "in SR one way speed of light is C" but: "in SR one way speed of light is made C by apposite synchronized clocks". Again some do, some don't, it is true though, that at a certain level of sophistications of the issues, it is hard to tell who is who. best regards beda pietanza > http://www.physics.carleton.ca/~watson/Neut_cent_talk/Neut_cent2.html > ... only mildly related to the topic at hand, but what would you [quoted text clipped - 3 lines] > > - Mostra testo tra virgolette - Dear beda pietanza: > On 22 Mar, 01:30, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> > wrote: ... >> > OK, but the quanta speculations are even more >> > hazardous than the risks related to the Galilean [quoted text clipped - 5 lines] > good willings and helped them to protect umanity > from the worst always at bay. These are the centuries where nerve gasses, and "area denial weapons" were invented, right? > Science is not just to run ahead to the most effective > experiment but also the best means to light the path [quoted text clipped - 3 lines] > this must be done working side to side with > philosophers and politicians and religious people. It seems to me that science has to evade all those groups that you seem to think they work with. Science has to mold specific words, and protect them from the vagaries of popular usage. Human language is mercurial. Science builds upon the "shoulders of giants" and if the basic language changes... older meanings are lost. Philosphers have access to Truth, but Science does not. And Philosophers don't seem to understand this about Science. Politicians hold the purse strings, but tend to be the ones that ask for nerve gasses and "area denial weapons". In Religion, you do not get to test the limits of Sin, but in Science you test for areas forbidden by your theory. Because otherwise you don't learn. > Some scientist do so, some don't. > > Since the wrong ways are the easiest, these are > taken first Wrong ways are like Edison's 9,999 types of light bulbs that don't work. >> The fact is, in the quantum realm, space and time >> don't exist... or at least are not meaningful. This [quoted text clipped - 14 lines] > *ourselves*: the hazard stays, it goes all the > way down The hazard does not go "all the way down", unless we take it with us. If I understand your meaning, the hazard is in what we *do*, not what Nature really is. No? > We don't solve it with funambulims but striving to > stay put on the ground of shared soundness. [quoted text clipped - 3 lines] > "in SR one way speed of light is made C by > apposite synchronized clocks". Using the Moon as a shutter, there is no anisotropy in the speed of light regardless of the motion of the source. Maxwell provides a one way speed of light = c. SR simply says "OK, given that... " > Again some do, some don't, it is true though, that > at a certain level of sophistications of the issues, > it is hard to tell who is who. David A. Smith On 23 Mar, 05:12, "N:dlzc D:aol T:com \(dlzc\)" <d...@aol.com> wrote: > Dear beda pietanza: > [quoted text clipped - 13 lines] > These are the centuries where nerve gasses, and "area denial > weapons" were invented, right? It could have been much worse if some of the Six Sages gave up. > > Science is not just to run ahead to the most effective > > experiment but also the best means to light the path [quoted text clipped - 21 lines] > Science you test for areas forbidden by your theory. Because > otherwise you don't learn. the reasons you mention are the very reasons for which scientist must stay and work very closely to philosophers, politicians and religiuos not to give them chances to swindler. And for philosophers, politicians and religiuos to keep a close eye on what scientists do. > > Some scientist do so, some don't. > [quoted text clipped - 26 lines] > us. If I understand your meaning, the hazard is in what we *do*, > not what Nature really is. No? We look at Nature with our eyes, we dream of the Nature, our dreams are guided from Nature. Our dreaming attitude, that generate the our perceived reality, can go on his own and generate just suggestive scenarios: sort of mental attractors and be trapped. > > We don't solve it with funambulims but striving to > > stay put on the ground of shared soundness. [quoted text clipped - 8 lines] > Maxwell provides a one way speed of light = c. SR simply says > "OK, given that... " OK, given that...we synch the clocks to obtain it. thankful if you provide me a reference to "the Moon as a shutter...." best regards beda pietanza > > Again some do, some don't, it is true though, that > > at a certain level of sophistications of the issues, [quoted text clipped - 3 lines] > > - Mostra testo tra virgolette - > PD ha scritto: > [quoted text clipped - 98 lines] > OK, but the quanta speculations are even more hazardous then the risks > related to the Galilean approach. The hazards are not important if one has the simple ability to check guesses against what is *measurable* in experiment. This is the *sole* assessment of whether or not an approach is workable. > regards > [quoted text clipped - 36 lines] > > - Show quoted text - > these questions rose while reading "the theory of almost everything" > of R. Oerter: [quoted text clipped - 11 lines] > them, what are the real problems and what are the problems generated > just from language-logic misuse ??? Since this is something that is easily reproduced as an experiment in your basement or garage, I suggest that there is no substitute for personal exploration of the real phenomena. You will need the following things: - A $10 laser pointer - A small C-clamp - A piece of scrap glass - A small can of spray paint - A utility knife - A ruler With this $20 expenditure, you will be able to perform a week's worth of experiments, with which you will gain a better understanding of what really happens. PD > I would like to have references on a classical explanation of the two > slit experiment. > > tanks in advance for any help > > beda pietanza > Since this is something that is easily reproduced as an experiment in > your basement or garage, I suggest that there is no substitute for [quoted text clipped - 10 lines] > of experiments, with which you will gain a better understanding of > what really happens. Good point. One comment: It probably is not possible to scribe two slits close enough together with a utility knife and ruler. But I believe that two razor blades held together can do so in one swipe along a ruler. You spray the paint onto the glass, let it dry, then scribe the slits in the paint. DO NOT LOOK INTO LASER WITH REMAINING EYE! (project onto a wall and look at the image) Tom Roberts > > Since this is something that is easily reproduced as an experiment in > > your basement or garage, I suggest that there is no substitute for [quoted text clipped - 21 lines] > > Tom Roberts Actually, what I suggest is a narrow "X" made with the ruler and the utility knife. It is straightforward to mark two notches about a mm apart at one edge of the painted glass, and another pair at the other edge, and then scribe a line from the top-left to bottom-right notch, and then another line from the top-right to bottom-left notch. With this scheme, you can investigate the effect of varying slit separation and one can even investigate, with some care, single-slit diffraction. PD |
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