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I Double slit experiment

  1. Nov 25, 2015 #1
    I was watching a video about the double slit experiment because I found it interesting, However, watching this vid raised more questions than it did answer. I would like to know why did the outcomes of the experiment only change when we observed it... wasn't the electron interacting with anything else that could have collapsed the wave function... why does it wait for human observation.

    Also are there any explanations as to why the outcome of the experiment changes when it is observed.
  2. jcsd
  3. Nov 25, 2015 #2


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    Which video?

    The idea that wave function collapse depends on human observation was pretty much abandoned many decades ago.
  4. Nov 25, 2015 #3
    The video is the explanation of the double slit experiment by Dr. Quantum (cartoon character)

    The video didn't specifically say that human observation was necessary for wave function collapse that is just a question from me. I noticed that everything interacts with everything so wouldn't for example an atom make an observation. My question was that why does the outcome of the experiment change only when we try and make an observation.

    Can you please explain why that idea has been abandoned

    I know that is a lot of questions but i dont have a text book i can refer to for answers

    Thanks in advance :)
  5. Nov 25, 2015 #4


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    A fairly recent long thread here about consciousness and QM is this one:


    You can find many more by using the "Search" feature at the top right of this page. Enter the word "consciousness" and make sure the box is ticked that restricts the search to this forum.
  6. Nov 25, 2015 #5


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    To make an observation of something very small means that we have to alter it in some way during the measurement, with a polariser for instance. If only one side ( one slit) is measured the phases alter so that the interference pattern disappears.
  7. Nov 25, 2015 #6
    @nnope The electrons don't wait for human observation. Experimenters have to make sure that there is no interaction such that the information about the electrons leak into anything other than the detectors (not even the slit). It has to be done in vacuum, for starters.
  8. Nov 25, 2015 #7
    consciousness is just a level of awareness it has nothing to do with physics or wave function collapse @Truecrimson answered my question. A system can be observed or measured by anything it does not have to be a human. I think this whole consciousness talk stems from misunderstanding especially due to the terminology used.

    I didn't really want to turn this conversation about consciousness, the whole idea seems nonsensical.

    Ill give you an example... A while back I read a journal article ( yes a real journal article published in a journal) describing an experiement where a scientist took a bunch of meditators and had them concentrate on the double slit experiement. The outcome? the results of the experiement changed when the people concentrated on the experiment... they could control the experiement with their minds.

    Everyone I have seen who has talked about consciousness as if it is necessary seems to be the type of people who believe they have magical powers. Honestly QM is either one big lie or its filled with a lot misinformation and misunderstanding.
  9. Nov 25, 2015 #8


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    Not a journal that's an acceptable source at PhysicsForums, I'll wager :-)
    There is no shortage of very bad "journals" out there, they're basically just vanity publishers.

    The latter - there is a tremendous amount of misinformation in the popular press (Dr Quantum is an example, and far from the worst).
  10. Nov 25, 2015 #9
    So how do we separate the truth from the lies. I'm really sick of searching up some information the being told about how my consciousness is eternal and it controls the world lol :)
  11. Nov 25, 2015 #10
    The only way to be certain is to study quantum mechanics. :)

    Of course, not everybody has time to do that. One way is to ask people who know quantum mechanics. PhysicsForums is a good place for this since there are many active members who know what they are talking about. Otherwise, you might want to look at books aiming to counter such nonsensical claims. I can think of two off the top of my head: David Lindley's Where Does the Weirdness Go? and Victor Stenger's Quantum Gods. (I have not read any of them.)
  12. Nov 25, 2015 #11
  13. Nov 25, 2015 #12
    I also recently had a few questions about quantum eraser experiment. I've read a bunch of articles and saw a few videos myself including the (Dr quantum) one. It occurred to me after some investigation that some of these popular videos on the subject come from a certain angle with some spin on them. Turns out the (DR quantum) video comes from a documentary about (metaphysics) and although it contain some interesting truths and facts they are "spun" to support certain theological beliefs about reality being mostly subjective. Suggesting that the human mind is what changes the experiment. I agree that the effect observed in this experiment are strange. I personally thought that the reason that some times the interference pattern disappears is that the detection equipment some how changed the environment so that it caused this. A member of this forum set me straight. After further study on the subject it turns out scientist take measures so that the equipment used doesn't affect the experiment. All that being said I can see why this "spin" about consciousness is popular. It's because scientist don't really understand this effect either therefore it's hard to explain to a laymen how, what and why these phenomena occure. QM as a field of study is very interesting but unless you are in this field of study its extremely hard to put in laymen's terms in away that will not leave a question.
  14. Nov 26, 2015 #13


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    Simply come here.

    We have many science advisor's that know the facts.

    On this issue here is THE technical reference that explains exactly what's going on just in case you want to see one so you know its backed up by standard textbooks:

    To be fair it must also be said this is an area of physics that beginning textbooks, some of them otherwise very good, are not clear on. It done so as not to confuse students - but sometimes has the opposite effect.

  15. Nov 26, 2015 #14


    Staff: Mentor

    [Mentor's note - this post has been edited to remove a quote from a subsequently deleted post]

    To understand why a human requirement for wave function collapse was considered and then abandoned you need know how it started in the first place.

    It dates back to a seminal work by the great polymath John Von Neumann who most have heard of because he made important contributions to many areas - not just physics.

    He presented an analysis that he thought showed collapse occurred by human conciousness. It was weird even then, but its even weirder now because of the rise of computers that blurred exactly what a conciousness was. It didn't catch on much, but a few bought into it, the most notable being the great mathematical physicist, Wigner. Anyway progress in QM is inexorable, and Von Neumann unfortunately died young so wasn't around to see the early work on decherence by Zurek and others. Wigner however was and after seeing some early papers by Zurek did a 180% about face realizing the reason Von Neumann gave was no longer valid.

    If anyone wants to know the error made by Von Neumann start a thread about it and myself and others will be only too happy to explain. BTW it was an excusable error because QM was in the early stages.

    Last edited by a moderator: Dec 2, 2015
  16. Nov 26, 2015 #15
    @bhobba you seem like you do know the facts that is true, however it doesn't seem like everyone here knows, some people just seem as confused as I am, I will start that thread you talked about however I fear it will attract users that might confuse the situation even more for me. would u mind giving a little more of an explanation here on this thread. If that's alright with you

    thanks in advance
  17. Nov 26, 2015 #16


    Staff: Mentor


    Von Neumann showed the quantum classical cut can be placed anywhere up to the the conciousness of an observer - technically its called the Von Neumann regress. Since everywhere else was equivalent he placed it at the only place that was different - human conciousness. Since then a lot more work has been done on decoherence and there is a place that is different - just after deoherence. If you place it there - poof - all problems gone. Why doesn't everyone do that? There are other ways of resolving it and different strokes for different folks.

    The main point is there are many many ways of resolving QM issues - conciousness being involved is a very very fringe one - but it cant be disproved.

    BTW you can trust any of the science advisor's, homework helpers, or staff mentors.

  18. Nov 27, 2015 #17
    @bhobba I don't understand why it can't be disproven or why it is even considered. What is human consciousness anyway? Isn't consciousness just the awareness of our surroundings, why is it so special. Considering human consciousness as the cause of anything and then asking it to be disproved is like asking someone to disprove the claim that our life is just an illusion and that we really live on mars and aliens control our brains.

    perhaps there is something else that controls the collapse of wave functions, maybe when we make an observation more is happening than we perceive. Why are people resorting to magical stuff? I'm seriously confused
  19. Nov 27, 2015 #18


    Staff: Mentor

    A few points.

    Many of the issues you raise are not physics but philosophy and we don't discuss that here. Besides I am not trained in it anyway having just done an introductory philosophy course - if you want to chat about that best to go elsewhere.

    The other issue is collapse is an interpretation thing - its actually not part of the formalism so doesn't require explanation:

    Regarding the mystical tripe about QM in books like What The Bleep Do We Know Anyway I think its pretty obvious they have a new age touchy feely view of things and want to evoke QM to justify it. Forget about it - its rubbish.

    At the beginner level here is the book to get about this stuff:

    If you want to go deeper then that is a longer journey and this is the book to start with:

    Last edited: Nov 27, 2015
  20. Nov 27, 2015 #19


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    To disprove any hypothesis we have to construct an experiment that gives different result according to whether the hypothesis is correct or not. So far, no one has been able to propose such an experiment.
    It's not. With a few exceptions that are far from the mainstream, the idea was abandoned decades ago.
  21. Nov 27, 2015 #20
    Anyway thanks alot for the help guys i geuss i will end it here since it is getting philisophical. I really apreciate your help. it has allowed me to remove alot of misconceptions from my thinking and i will go through the books suggested. Thanks guys
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