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Light, particle or wave?

  1. Apr 8, 2007 #1
    I have not only read many books on the subject of light as well as experiments done to determine whether its wave or particle. I've also actually built a device to test the two slit experiment results to see if I could duplicate them. Honestly the whole talk of things existing in two places at once, or better yet, neither, until someone attempted to measure them just didn't sit well.

    After doing many tests I wanted to share the results and see if any of you could explain them to me as they do not in any way line up with reported findings from any book or information I've dug up on the subject.

    It is stated that when you shine light through a slit, the light forms a diffracted spot, if you will, on the wall, but no real pattern to it. It was then discovered that by splitting the light beam, you'd actually get an interference pattern on the wall, as if it were water and interfering with itself on the other sides of the slits. I can in fact duplicate this. pretty neat stuff.

    However, its going farther that things get really interesting to me. It is said that sending a single particle through the slits also get an interference pattern after a period of time, even though you are only sending 1 particle through, so what is it interfering with. But before we get there lets take a look at another result from the experiment that I've not read.

    In fact, if you shine any light past an object such as a book, and you look close enough, you will see a pattern of lines on the back wall. You don't even need a slit and don't have to separate the beam at all. Just interfere with it.

    Given that every single book I've read uses the Thomas Young two slit experiment as a base test case for Quantum Mechanics to show how things doen't exist until we attempt to measure them and therefore pass through both slits at the same time and dah dah dah...

    Can anyone explain to me why I'd get a scatter pattern like I do without even having a slit? In fact, I can get a perfect pattern on the wall with perfectly spaced vertical lines just by interfering with my laser beam.

    Thanks,

    glenn
     
  2. jcsd
  3. Apr 8, 2007 #2

    DrChinese

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    What you are talking about probably makes sense to you, but I don't think anyone here is likely to have a clue to what you are really asking. I would definitely recommend that you read more, and then try asking a more focused question.

    Just saying that things don't sit well with you is not much of an objection to scientific theory. The truth is that quantum theory makes numerous specific predictions which have been tested and verified many times.
     
  4. Apr 9, 2007 #3

    jtbell

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    Sure. This is called "edge diffraction." It can be explained either by using the classical wave theory of light, or by using quantum-mechanical wave theory.

    When textbooks discuss interference, they almost always start by concentrating on the two-slit example, with the important condition that the slits are so narrow that you don't have to take into account the width of the slits. You can analyze it using two pointlike sources of light, and you simply add the two waves together.

    Then they move on to examples like a single slit with a nonzero width, or two slits with a nonzero width, or edge diffraction. In these cases you do have to take into account the width of the apertures. (With edge diffraction, you have a "semi-infinite" aperture.) In these cases, you have an infinite number of pointlike sources of light, because mathematically, any finite line segment contains an infinite number of points. Each of these sources produces a wave, so you have to add together an infinite number of waves using integral calculus.
     
  5. Apr 9, 2007 #4
    Thanks for the reply. So then, it makes sense that I'm seeing a wave pattern with only a single slit? Or no slit at all? ie: passing the beam of light past a solid object where its simply getting interfered with?
     
  6. Apr 9, 2007 #5
    I appreciate the response, however, asking questions is part of learning. Telling me to go read more tells me what? Not to ask questions? At what point can I start asking questions? When I've read 4 books? 10? I am still studying and trying to understand, just wanted to talk to people that understand more than me because sitting alone and reading books can get you twisted sometimes if you don't talk about it.

    Thanks anyway,

    glenn
     
  7. Apr 9, 2007 #6

    ZapperZ

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    Just in case you missed it, this is such a frequent question that we do have an FAQ entry on it in the General Physics forum. You may want to start there and see if, after that, you might alter a few things that you think you have understood.

    And just in case one of the main message of that FAQ is missed, I will emphasize that how and what you are asking makes a whole lot of different in the ability to answer the question. You have to know what is meant by a 'wave' and a 'particle' and how they are measured or determined, because it then makes a tremendous impact on how one would categorize something else. This is why you often hear people telling you that light or photons are neither wave nor particle. They are not being difficult, they're being accurate based on HOW we define what a wave and particle are.

    In physics, when you start asking questions like this, then the details are crucial here. In other words, since we now have to fine tune our definition, we can no longer be wishy-washy about what we mean and how we define stuff. If not, you'll get vague, ambiguous answer, both from nature and from the experts.

    Zz.
     
    Last edited: Apr 9, 2007
  8. Apr 9, 2007 #7
    I didn't know that and will check it out. Thanks a bunch,

    glenn
     
  9. Apr 9, 2007 #8

    jtbell

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    Yes. That's what I was trying to say in my posting.
     
  10. Apr 9, 2007 #9

    DrChinese

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    You should ask questions anytime you feel a person can help you get past something that you can't readily resolve yourself. You are in the best position to judge that.

    On the other hand, claiming to have read many books on the subject seems remarkable given some of your statements. You may find that a more orderly approach - going through the books from beginner to intermediate, start to finish, for example - will answer your questions more effectively.

    I will say that taking the time to do experiments on your own is impressive. :smile:
     
  11. Apr 10, 2007 #10
    You have touched upon one of the most troubling phenomological findings ever. The one particle two slit interference phenomenon has never been solved.

    First, photons travelling through two slits do create an interference pattern. One photon, or one electron, or one neutron also create a pattern over time on an appropriate receptor, emulsion, whatever.

    The idea that one electron or photon, knows that it is passing through a slit and should therefore interfere with itself is of course improbable.

    The solution is really quite simple. The photon is generating an electromagnetic wave that precedes it. In a sense the wave is travelling faster than the speed of light. It then passes through the slit and becomes discontinous with the source, so that once the actual photon passes through it is affected by and its motion is inteferred with.

    The whole idea that a photon can be deflected by a force, such as the sun, is of course a contradiction to the constant speed of light rule. For any force, hence acceleration, implies a velocity that is greater than the speed of light. Therefore, in a sense, the one particle, two slit phenomenon is a constradiction of this law.

    Look, you have to understand that the people you call the elite scientists, etc, have no clue what a photon really is. Ifit is an energy, what is energy? The underlying foundation of all of science rests upon Aristotles concept of matter. Matter alone is the underlying constant of the universe. To add another construct, i.e. energy, is completely unfounded and really scientifically irresponsible.

    If you were to put a divider of approximately 10 inches between the two slits, then a single electron, or photon would never be able to transfer an electromagnetic pulse through the other slit and an interference would never result. I have probably told you too much already.
     
    Last edited: Apr 10, 2007
  12. Apr 10, 2007 #11

    ZapperZ

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    Your "solution" creates even MORE strangeness than you solved. Considering the fact that there's no explanation for this "wave" that precedes your photon AND the fact that is has never been observed are enough to cast serious doubts to your model.

    This is incorrect. Just because QM hasn't said anything about the 1-slit vs. 2-slit phenomena doesn't mean we haven't understood anything. The FACT that we know how to describe light and make use of it means that we have understood plenty. Do we understand everything? Nope. But we don't understand everything in almost every single phenomena that you see. Even the physics that built the house you live in, there are still things about it we don't understand. It doesn't mean we "have no clue" on what it is.

    This is also incorrect. I can separate out the path that a supercurrent takes by MORE than 10 inches if I want to, and I can still get such superposition. Furthermore, I can easily use EM radiation with wavelength longer than 10 inches and get that same interference pattern. It has nothing to do with the separation length. It has everything to do with a setup that allows the particle in question to have a viable superposition of its path.

    Zz.
     
  13. Apr 10, 2007 #12
    I understand what you're saying. I am adicted to learning and you can't know that. I have in fact read many books on the subject as well as on Einstein and others. What I've learned however, (right or wrong), is that a lot of information is passed off as fact when in fact its an assumption and doesn't have a proven experiment to back it up.

    My questions may seem dumb to you, but to me its just part of my reasoning based on things I've read. I've already admitted that I'm not reading text books, but off the shelf book store books, so maybe that is part of the problem. Here are a few of the books I've read: The Elegant Universe by Brian Greene, Quantum Evolution by Johnjoe McFadden, E=mc^2 by David Bodanis, Introducing Quantum Theory by JP McEvoy, Physics for the Rest of us by Roger Jones and A brief history of time by Stephen Hawking.

    I've also read other books that are upstars and can't get to them, but the point is that I'm not talking about something in which I have not done. I've also done a tremendous amount of research on the web for a subject in which I don't work and have no experience in, other that studying on my own. Perhaps I'm way off base with my understandings, but I'm a very logical person and think through problems ( I like to think at least ) from step 1 to the end. I take no ones word for anything because more times than not I've seen people speak of things as fact that truely are not.

    Again, I'm really sorry that I am annoying you with my questions, but they are in ernest and not some guy trying to cause problems.

    Thanks,

    glenn
     
  14. Apr 10, 2007 #13
    Zapper, I never said that we didn't understand something about light or a particles path. ( I do realize your response wasn't to me ) However, I do believe that we've taken the predictions of QM and given it a hold on the universe as we know it. Instead of saying here are some wave functions that seem to work, we've gone a whole step farther and stated that nothing is as it seems. We've made up superposition because we can't explain what we see, but maybe we're looking at it from the wrong viewpoint.

    The experiments I've seen including Bell's Theory are in absolutely no way conclusive either way. I'm not saying QM is wrong, maybe one day you'll be proven 100% correct all along. However, at the point we now stand, I think its foolish to assume that you're any more right than anyone else.

    The facts seem to be: QM contains the math that make appropriate predictions in a number of areas, but we're not sure why. While it allows us to use things more efficiently than ever before, we're not sure why. While we can still not build the truck, we can crank it sometimes and get it to haul a load, but we still don't know why.

    I could go on but you get my point... maybe... :-) QM is a facinating subject to me, I'm just not yet buying into all this spooky stuff at a distance, but maybe I have rocks in my head...

    glenn
     
  15. Apr 10, 2007 #14
    Kong,

    Interesting link. It comes right out and says that these particles do NOT move as a wave but rather a particle. First time I've seen anyone come out and say it. I agree completely with the point though as I also feel light doesn't move as a wave at all. Look forward to your email as I love to discuss light. For some reason its my favorite subject... :-)

    glenn
     
  16. Apr 10, 2007 #15

    ZapperZ

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    But there is an inherent problem here with QM and your level of understanding of it. As I had guessed, the root of the problem here is that you are trying to apply your classical knowledge of the world you live in, which you understand, and extrapolate that to understand QM. I argued that that will never work. There is an abrupt disconnect between QM and classical mechanics, at least as far as our physical intuition goes. So if you are going to try to understand QM based on classical intuition, you WILL run into things that appear to be absurd. The only thing that saves us from dangling in mid air with QM is the mathematical formalism.

    This means that without understanding the mathematical formalism of QM, you really haven't even begin to understand QM. There's no way around this, at least not from my perspective of being in this field for this long.

    Zz.
     
  17. Apr 10, 2007 #16

    ZapperZ

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    Now isn't that strange. That link (which has been removed) has plenty of unverified, unsupported claims about QM and its various phenomena. I can even find several things wrong with the scenario presented. Yet, this is the first one you actually are comfortable with.

    What does that tell you?

    Zz.
     
  18. Apr 10, 2007 #17
    I agree to a point. First of all I fully recognize my own ignorance on this matter which is why I've gone back to school. I'm going to learn the math and the details, but can't wait until then to start thinking about things. It seems there is a problem with your suggestion as well though.

    If one has no way to relate to a matter, then how is he/she suppose to determine if the matter is true or false? For example: There are those that will argue that the Bible is true because God said so. I argue its hogwash, because it doesn't fit with what I see. They say I'm going to you know where because I don't believe. That I can't understand it if I'm looking at it through the eyes of the world. I have to have faith.

    Its not possible according to you for anyone to understand it unless you understand the math behind the madness. But are you not yourself placing your beliefs in something that you can't explain?

    For example: Can you list for me a single experiment in which QM predicted something that could not otherwise be true? Something that my world views could not possibly explain? Because, such an experiment would at the very least cause me to lean closer to your side and accept that I don't and can't understand it with my current knowledge set.

    The problem is, (and I'm by no means saying I've read them all) of all the experiments that I've looked at and listened to people talk about, they all have possible classical explanations as well. They don't have to be black magic that is only predicted by mathmatical formulas but can't be understood by anyone.

    It almost seems to me that QM folks have accepted it as true, despite the fact that they can no longer explain what truth is, and have abandoned any concern of explanation. As if the concept is so far out there that we've decided openly that an explanation is impossible and therefore not important.

    As another example: Bell's Theorem is probably the most appreciated and some would think nails the final nail in the classical coffin. I however don't see a single experiment to back up his claims. I do agree with him, if they are true then it would be that simple. But the fact is, you can't setup an experiment to prove it.

    We understand water, current drift and so on, but if I were to drive you out over the Atlantic, drop a marble in the water and ask you for a precise spot on the bottom where it will touch, you can't give it to me. Not because you can't understand the problem, but because the data is too overwhelming to try to calculate. Does that mean that we really don't understand how a marble will fall through water? Or should we assign some superposition to the problem and state that unless we measured the marble all the way to the bottom that it would esentially hit the entire ocean floor?

    But again, I'm still learning so maybe I"m going to come to a revelation one day and sit at your side of the table...

    Thanks,

    glenn
     
  19. Apr 10, 2007 #18
    lol, well, it tells me that you are perhaps looking at things a little cross-eyed yourself. Have you ever stopped to realize that you can't explain anything related to the two slit experiment? You simply tell me that QM predicts how it will go, and that you can't understand it. That light doesn't move as a particle or a wave as you can't ask the question as it makes no sense. Yet this makes sense to you?

    I need to be careful as I"m really not trying to offend anyone here. I'm honestly enjoying the debate. However, I don't understand how you can tell me I don't understand something, yet you can't provide explanations. You simply tell me I'm not intelligent enough in the subject matter to understand. This is why earlier I spoke of QM being like a religion. It takes on that "you just have to believe" air to often.

    Again, I'm not trying to offend you at all and hope you aren't getting upset with me. I would like to know what specific experiment did you read or do that caused this blind faith that you seem to have? I'd love to be convienced there is more to it than conventional ideas can portray. But I haven't seen or heard of one. Obviously there is something though...

    Thanks and please don't get upset with me as I"m just speaking out loud.

    glenn
     
  20. Apr 10, 2007 #19
    Zapper, what happened to that original post with the link in it from Hong? I hope I haven't found another website where the managers of the site delete content they don't agree with. If thats the case maybe I should start looking for another forum for ideas.

    glenn
     
  21. Apr 10, 2007 #20

    ZapperZ

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    Empirical evidence! That is why a large portion of physicists are experimentalists.

    If you think very carefully and examined your world, you will notice that everything that you think you can "explain" is really, at the very fundamental level, a "description". Every single "explanation" becomes a description at the very end of that line of explanations. For many people, science's role is simply to describe things at the most fundamental level. This is true even for classical physics, which, presumably, you have no problem with. Don't think that's true? Try to "explain" the classical Coulomb's Law.

    Easy. Superconductivity. It is the clearest manifestation of quantum mechanics at the macroscopic level that has zero classical explanation and description.

    Zz.
     
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