What is the current explenation for the double slit experiment?

Discussion in 'General Science & Technology' started by Awoken, Jan 4, 2013.

  1. Awoken Registered Member

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    It was brought to my attention that there already is a satisfactory theory explaining what was once considered an unknown phenomenon.
    What is it?
     
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  3. mathman Valued Senior Member

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  5. kwhilborn Banned Banned

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    Despite the fact Wikipedia presents The Coppenhagen Interpretation and it has been dissected in all corners of the planet to mean different things, the Sciforums consensus would make it decidedly unpopular to construe the Interpretation to having any of the ....

    Pssst! Fred Alan Wolf views...

    Just mentioning that name too frequently or mentioning any concept of consciousness causing collapse in regards to this experiment is frowned upon here, although there are many smart people who hold those types of opinions.
     
    Last edited: Jan 5, 2013
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Young, one of the first to do the double slit experiment with light died about 200 years ago. I believe Huygens knew the waves interferring explanation earlier. There is no problem in undestanding the double slit interference (or the 10s of thousands of slits that a grading in a spectrograph makes) The wiki link mathman gave is nearly correct but makes this serious error:
    "In the basic version of this experiment, a coherent light source such as a laser beam illuminates a thin plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate. The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen."

    There need not be any coherence in the light source - only that it approximates a parallel beam or plane wave front. Young certainly did not have a coherent light source! This is because EACH PHOTON (or electon) interfers only with its self. That they individually go by more than one path is not compatible with human experience so that part is never and never will be well understood by humans; not only that is beyound human understanding but when they strike a recording photographic film all their energy is given to one tiny crystal of the film* - the photo -electric effect - shows light or electrons at times act like particles.

    * Actually to only one or two atoms in the crystal.
     
  8. AlphaNumeric Fully ionized Moderator

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    There is no problem discussing his views, as well as others, but the need to temper considerations with actual knowledge is important.

    As for the DSE in mainstream models the Feynmann lecture books cover it in a very nice way, enough mathematics to see how it works but without having to know tons of quantum mechanics. It boils down to the superposition of wavefunction modes, which lead to destructive and constructive interference. However, when you measure which slit the particle goes through the collapse down to a single mode and you get the line seen in the experiment.
     
  9. GammaMatrix Banned Banned

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    Isn't his name... Fred Alan Wolf?

    Before making any criticism, which I don't mind, you really should get the name of the person right first

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  10. GammaMatrix Banned Banned

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    On a related note, we know that consciousness is not special in the sense of collapsing the wave function... after all, decoherence does it fine without anyone around to observe the system.
     
  11. Robittybob1 Banned Banned

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    Has anyone tried "The double double slit experiment". One set of double slits is followed by another set of double slits. The second set could be shifted to locations of expected bands of strength or weakness of the diffraction pattern.
    Has the photon lost energy after going through the slits? If sound waves or water waves were allowed through a slit only a portion of the energy in the wave would pass on in the part that went through the slit.
    Is some of the diffraction pattern parts of the photons that don't make it through?
     
  12. wellwisher Banned Banned

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    A photon is both a particle and a wave. Picture a ship that is making a wake/wave front. The ship can only go through one tunnel at a time, but its wake spreads out and can become wide enough to go through two or more tunnels. The diffraction patterns form from the addition of the two tunnel wave crests and troughs. The ship remains singular and will dock in one place; particle.

    This situation requires a medium so waves can be generated. The aether was one early theorized medium. I am not saying the aether is accepted or true, but the ship and wake analogy requires a water medium. Once a wave is generated it takes on a life of its own and can travel even with the source stopped; tidal wave.

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  13. Grumpy Curmudgeon of Lucidity Valued Senior Member

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    wellwisher

    No, it does not. It is the photon itself that is a wave, it only collapses into a single point when it is absorbed.

    The problem with analogies is that at some point they break down when taken too far. The ship is not the wave, nor is the wave the ship. This is not analogous to the photon, which IS both the wave and the particle, requiring no medium to travel through. Also, the light wave is not a delta, it is a flat line perpendicular to the direction of travel.

    Grumpy

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  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Absolutely correct and few know that. Most think of photons as very small packets of energy that are hard for humans to understand as show properties of both waves and particles.

    I have at least two posts explaining in detail how I used a two path interferometer to measure the length of some "Sodium D" photons from a moderate pressure lamp. My photons were ~30 cm long. If the photon comes from a very low density gas they complete their radiative transfer most of the time before some other atom comes near to the one radiating.

    That approaching atom (or ion) perturbs the energy levels of the radiator and makes small changes in the energy carried away by the photon. When many photons are measured for their wave lengths the “line shape” is broader than from a very low density gas. In very high pressure lamp, the line radiation becomes almost a continuum, as it is if the radiation from the densest of materials (solids).

    If you think about it and know Fourier analysis there must be a huge number of cycles if the wave length / energy is very well defined. Also it is a little more complex to explain, but radiation from will separated atoms with the transitions between atomic energy levels that are “first order forbidden” is very very well defined in energy /wave length. This is due to the uncertainty principle (delta E very small forces delta T to be very large) I.e. the time during which the radiation takes place is unusually large. I.e. the radiator is “pumping out cycles” for long time but the first few to leave it are going away at the speed of light.

    The source of the green and reddish light seen in the Northern Lights was speculated upon for years but finally it was understood that it came from forbidden oxygen state transitions. Those photons are extremely long (Many meters long! More than 10m. I think.) They get to compete their radiative transition in most case without any disturbing collision – all most all have exactly the same energy as the energy difference between the upper and lower states. I.e. by Fourier there must be “zillion after zillions” of EM wave cycles in each photon.


    BTW just ignore Wellwisher - he usually makes up plausible sounding BS as knows very little about the subjects he post on. Sometimes, like now, he does give me the opportunity to teach a little physic without being too pedantic, so I thank him for that.
     
  15. Robittybob1 Banned Banned

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    I was hoping we could discuss how a "double double slit experiment" might work. The results of the double split are very mysterious, when the look at the split closely then the photons become particle like. Is it really looking at them that makes the difference?
     
  16. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    There is no energy loss when light is re-distributed in space differently only by (self) interference - this is not true if it reflects off mirror etc. Also there is no memory in the photon. When it arrives at Earth from distant star it does not know it has been traveling many years.* Thus the 2nd double slit, if placed so both slits are equally illuminated by one of the constructively interfering beams from the first double slit will make same spatial spread interference pattern that the first did. If you were thinking it should go "straight as a single beam" after the 2nd slit, that is wrong.

    *It may have lost some energy during the trip due to expansion of the universe but does not know it was once blue and now is red.
     
  17. Robittybob1 Banned Banned

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    I was thinking it couldn't form the interference pattern after the first set of splits as that would be like looking at it. For it might have to go through the second split therefore it would NOT spread out, losing energy in areas of destructive interference.
     
  18. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    No. "looking at it" happens only when the photo dies -is absorved - ceases to exist, became particle like, giving all it energy to one atom. Again the photons coming to the 2nd slit pair have no memory of the first slit pair.

    Until the photon does die, it is best to think of it as a field of energy with some distortions of that field even by object far to the side of its line of travel. These "distortions" build as the point of closest approach to the distrubing object is approached and then generally undo /reverse as the photon passes further away form the object. Compton scattered photons do leave with less energy as some is now in the recoiling atom. Likewise the TV signal "photons" also leave your antenna with some energy transfered to the antenna, but it is a little stange to say this, this way, but it sure drives home my POV that until the photons dies it is a 3D field.

    For example the stellar photons that passed near the sun and had their path ever so slightly bent to prove Einstein was correct were of slightly higher energy (more blue) for a while as the passed by the sun, but that energy disturbance was completely undone later.
     
  19. Robittybob1 Banned Banned

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    Have you heard of the double double slit experiment? No doubt it has been done but I could not find it on a Google search. Searches work best if you know the proper name of the set up.

    The Delayed-Choice Double Slit Experiment
    http://www.youtube.com/watch?v=3A6ageOaS-E
    Gives a similar choice to the photon. When the light can go into the telescope it remains as particle in nature.
     
    Last edited: Mar 29, 2013
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    No, but if you have a modern (made inlast 60 years or so) camera you do something very much like it every time you take a pictures as it has a multi-layer dielect coating on the lense. Alternate layers are a different dielectric. At each layer interface some light is reflected and some is transmitted. The layer thickness and their index of refraction are such that the reflection from interface "n" and interface (n+1) destructively interfer so instead of losing ~4% of the incident light to reflections with a simple glass lense, almost all goes on to expose the film (or now days do its work in solid state pixel array). This is much like many slits stacked one after another.

    I.e. interference devices are of two types: beam splitting or wave front division. The double silt is more like the beam spliting type. I.e. there are two possible paths but each photon in some sense "passes thru both", but in all types of interference devices, each photon ONLY interfers with is self, not other photons. Most source of light (but not lasers) produce incoherent light and then photons of that type of light can not completely cancel out a different photon - only themselves in the destructive direction.

    I won´t go into details but reason why laser light (all photon waves in phase) travels without significant spreading is any photons trying too go a little off the beam direction are mutually and self interfering in the null energy path direction. In some sense, all lasers are constructive interference devices.
     
  21. Dinosaur Rational Skeptic Valued Senior Member

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    While there is much in Quantum Theory which is weird & counterintuitive, one of the experts said:
    The above is a paraphrase not an exact quote. The person who said it did not claim that it took away all the mystery, but at least it made such behavoir less mysterious.
     
  22. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Not a bad first cut, but makes understand all I described in post 11 very difficult. I.e. the long photon is "pumped out" over time, etc.
     
  23. Undefined Banned Banned

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    Sorry if this is off-topic but I don't know which thread to post this in, so I put it here because it sorta connected with the topic of wave properties of electromagnetic radiation. If moderator knows which thread is better, can you move it there please?

    Talking of wave nature of photon propagation, I can't stop thinking about the statements about the photon having no time and its passage is instantaneous in its own frame and such. Relativity people even say that photons see the distance between one side of the universe and the other as infinitely contracted to effective zero even though they travel form one point in the universe to the other at finite speed.

    How can a photon not have internal time? My naive understanding is that in order to propagate a photon's electric and magnetic fields oscillate at a given rate. The internal oscillation is described in WIKIPEDIA:
    If the electromagnetic field exists between ends of the universe and photon propagates by fixed rate oscillations of the field which makes up the photon wave, then an absolute time photon clock exists within the photon doesn't it? And if this internal clock oscillates to make a time tick count during the crossing space, then how can the photon see the space contracted to zero but still have a definite count of oscillations made over the electromagnetic field along which it waved?

    I am confused by statements of timeless photons but oscillating fields which make the propagation possible. Can somebody give a reason why the oscillation is timeless but the oscillation must occur or the photon can't move across electromagnetic field from one end of universe to the other? And why it sees distance contracted to zero when it has internal oscillations which happen so many times per unit distance if propagation and oscillation must be logically and physically connected in real time if photon is moving? Because a internal fields oscillation process is happening in real time to oscillate and move or not?
     

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