zensunni Posted September 14, 2008 Posted September 14, 2008 My skepticism is probably just because of ignorance, but.... Regarding the double slit experiment when observing particles before the slit: Since the observation of a particle before going into a slit is an interaction between the detector and the particle, could the change be just a result of the interaction, not really the observation, itself? In other words, could the reduction of the wave be just a physical result of the detector's interaction? What process do they use to detect the particle in mid-flight, anyways?
swansont Posted September 14, 2008 Posted September 14, 2008 You don't have to detect it mid-flight to know which path it took. You can use entangled photons and circularly polarize the light in opposite helicities for each slit. Measuring the polarization of the photon that went through the slits as well as the entangled partner tells you which slit it went through, and this destroys the interference pattern. http://grad.physics.sunysb.edu/~amarch/ The general class of experiment is called a "quantum eraser" experiment, in case you want to search for more examples.
blike Posted September 15, 2008 Posted September 15, 2008 There's also the delayed choice quantum eraser.
Cap'n Refsmmat Posted September 15, 2008 Posted September 15, 2008 There's also the quantum Wite-Out.
DrP Posted September 15, 2008 Posted September 15, 2008 There's also the quantum Wite-Out. That happened to me at a party once when someone spiked my drink - most umpleasent!
Norman Albers Posted October 10, 2008 Posted October 10, 2008 Isn't that the point, namely that you cannot disturb, or 'measure' the field prior to the interference? One question: don't the slits have to be close together, in some wavelength measure? We work on such different scales. With a lab laser, scales are centimeters or meters. With stellar astronomy, scales are lightyears, so the Wheeler was able to say, photons interfere with their own paths on either side of galaxies. The angle here is small.
redsaint63 Posted October 24, 2008 Posted October 24, 2008 if you notice the pattern that emerges after the experiment is 3 spots that emerge after going through 2 slits what if instead of it was going through the 3 other sections of the slit because there is a field making them go through the other 3 sections and impedeing them from going through the slits( maybe they warp with the slits)...
Klaynos Posted October 24, 2008 Posted October 24, 2008 if you notice the pattern that emerges after the experiment is 3 spots that emerge after going through 2 slits what if instead of it was going through the 3 other sections of the slit because there is a field making them go through the other 3 sections and impedeing them from going through the slits( maybe they warp with the slits)... The three (or more) dots are easily explained by interferance patterns.
Zolar V Posted October 28, 2008 Posted October 28, 2008 i was about to post something on this topic, and I'm glad someone beat me to it. But i still have a question, I have heard that the explanation of the double slit experiment was the outcome of the photon going through both slits at the same time. That the Photon was in fact violating reality by either duplicating itself or halting time to adequately go through both slits.
Norman Albers Posted October 28, 2008 Posted October 28, 2008 Reality shows our ignorance. I have written a study (URL below) on how there might be a localized EM disturbance, i.e., photon. It is based on a reasonable model of vacuum response to changing fields, or vacuum polarizability. This may or may not have to do with what is real! I am reading a series of papers gathered for me by my brother, and I have made a comment or two gleaned from these. The best minds today seem quite equivocal on the 'conspiracies' involved in Nature that manifest the lightfield.
Klaynos Posted October 28, 2008 Posted October 28, 2008 i was about to post something on this topic, and I'm glad someone beat me to it. But i still have a question, I have heard that the explanation of the double slit experiment was the outcome of the photon going through both slits at the same time. That the Photon was in fact violating reality by either duplicating itself or halting time to adequately go through both slits. The explinations you've heard are imo flawed. Photons, electrons etc... are not particles. They also are not waves, they are something else which can act like either. So the easiest way to think of this experiment as the photons being waves, get a tank of water and put a wall in it with two slits, create a water wave and you will get exactly the same effect as seen with the double slit experiment. This might seem childish but it actually explains it quite well... http://uk.youtube.com/watch?v=DfPeprQ7oGc
iNow Posted October 28, 2008 Posted October 28, 2008 This might seem childish but it actually explains it quite well... http://uk.youtube.com/watch?v=DfPeprQ7oGc While it comes from a movie that has some issues with accuracy (WTBDWK), I always liked that animation quite a lot.
swansont Posted October 28, 2008 Posted October 28, 2008 i was about to post something on this topic, and I'm glad someone beat me to it. But i still have a question, I have heard that the explanation of the double slit experiment was the outcome of the photon going through both slits at the same time. That the Photon was in fact violating reality by either duplicating itself or halting time to adequately go through both slits. I have no idea what "violating reality" means.
Norman Albers Posted October 29, 2008 Posted October 29, 2008 A quantum of energy proportional to the frequency of the light is absorbed at a particular "spot". We cannot tell much from one event (is this true?) but the pattern built up over many gives the interference pattern of the wavetank. I am still looking for discussion of the interference from more and more widely separated "slits". Isn't it weaker and weaker?
Royston Posted October 31, 2008 Posted October 31, 2008 I am still looking for discussion of the interference from more and more widely separated "slits". Isn't it weaker and weaker? Depends what you mean by weaker...intensity ? Maybe I'm misreading your question, because (not meaning to sound rude) surely you know this ? In any case, I'm killing time before going out... Constructive interference will cause high intensity, where the path difference between the two waves is [math]d\ sin\theta[/math]. d being the distance between the two slits. Compare two waves, and the path difference would mean constructive interference at any given point is a positive integer of wavelengths i.e [math]n\lambda[/math]. Destructive is therefore [math]n + \frac{1}{2}[/math], so... [math]d\ sin\theta = n\lambda[/math] Now it's just a case of plugging in some numbers, however you'll find that as the distance between the slits increases (providing the wavelength is constant) then [math]\theta[/math] must decrease causing the interference fringes to be closer together. So the intensity decreases, as the angle of maximum intensity has decreased...i.e less constructive interference, if that's what you meant by 'weaker' ? But again, I may have misread your question.
Norman Albers Posted November 1, 2008 Posted November 1, 2008 (edited) You are right on, thank you Snail. As usual when we ass'u'me that someone knows things we risk mistake. I know some things really well and others dimly. If the "slits" are "widely" separated, then you are out in the lower interference amplitudes. I need to look up a source like Feynman Lectures, but you are on it. What do you mean by "...angle of maximum intensity has decreased"? Edited November 1, 2008 by Norman Albers multiple post merged
Royston Posted November 1, 2008 Posted November 1, 2008 What do you mean by "...angle of maximum intensity has decreased"? You can calculate the intensity for any value of [math]\theta[/math], and from there you'll know the maximum...no offense, but I'm not sure where to start with the math i.e I'm not willing to spend several hours on a post explaining it. I'm confident you can look this up yourself. As an afterthought, this phenomena is not constrained to a lab...far from it. Any crystalline structure where there's regular spacings will display such effects, in fact it was this discovery that lead to the use of X-rays in medicine (as one example.) TBH I get very niggled when QM is represented as something that's solely reproducible in a lab, when it's effects are predicted and observed outside a laboratory...Yay, thanks to QM my mobile phone has better resolution <sigh>
Norman Albers Posted November 1, 2008 Posted November 1, 2008 Cool, I'll see it when I spend time on my homework.
scalbers Posted November 2, 2008 Posted November 2, 2008 You are right on, thank you Snail. As usual when we ass'u'me that someone knows things we risk mistake. I know some things really well and others dimly. If the "slits" are "widely" separated, then you are out in the lower interference amplitudes. I need to look up a source like Feynman Lectures, but you are on it. What do you mean by "...angle of maximum intensity has decreased"? My guess is that the fringes are closer together, hence one would need narrower slits (yielding lower intensity) so they wouldn't get washed out (and look "weaker"). Perhaps with an interferometer using collimated mirrors and such you can get the wider beams again to give more intensity.
Norman Albers Posted November 2, 2008 Posted November 2, 2008 Thanks, scalbers. I know the problem is "just pathlengths projected into angles" and I am now getting a feel for it. Bear in mind that this manifests in such different scales and situations. I see Feynman has a whole chapter on diffraction that I've not ever read. I'm glad the winter rains just came.
Harlequinne Posted December 16, 2008 Posted December 16, 2008 My skepticism is probably just because of ignorance, but.... Regarding the double slit experiment when observing particles before the slit: Since the observation of a particle before going into a slit is an interaction between the detector and the particle, could the change be just a result of the interaction, not really the observation, itself? In other words, could the reduction of the wave be just a physical result of the detector's interaction? What process do they use to detect the particle in mid-flight, anyways? Hi............I have a full description of the double slit if you'd like it. If light is a pulse or spherical in shape,like a ballon expanding at light-speed, the particles are not that at all,they are the 'tip' of a sphere! ask me another...........
truedeity Posted December 16, 2008 Posted December 16, 2008 Originally Posted by zensunni What process do they use to detect the particle in mid-flight, anyways? My Response: Based on my understanding Richard Feynmans covered this in his lessons. The position of a particle cannot be determined exactly. However, the probability of its position(s) can be estimated. (I believe there is a good reason, see below.) Which is the best answer I can credibly offer you. Then again, it is my speculation that there are no particles in the universe...
Klaynos Posted December 16, 2008 Posted December 16, 2008 Hi............I have a full description of the double slit if you'd like it.If light is a pulse or spherical in shape,like a ballon expanding at light-speed, the particles are not that at all,they are the 'tip' of a sphere! ask me another........... Could you describe that mathematically, and explain predictions it makes that alters it from other descriptions?
Harlequinne Posted December 16, 2008 Posted December 16, 2008 My skepticism is probably just because of ignorance, but.... Regarding the double slit experiment when observing particles before the slit: Since the observation of a particle before going into a slit is an interaction between the detector and the particle, could the change be just a result of the interaction, not really the observation, itself? In other words, could the reduction of the wave be just a physical result of the detector's interaction? What process do they use to detect the particle in mid-flight, anyways? If you would like an interpretation of it I will gladly tell you what is going on.Theoretical Physics couldn't be more wrong about particles of light if it tried.How to have half a particle?If you were to spray the light from a torch left and right all over a wall,you would not see dots/particles unless the torch moved faster than light.
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