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Reality of Universe

  1. Mar 23, 2014 #1
    In universe we afffect everthing.Observers (us) measures something and we changed something.Example If we want to measure a electron's momentum than we can't measure its location Physics says this is real so it means it is not an experimental mistake.How they know it.How can physics says that this is real and not a experimental mistake.
    I think this can be answer but I am not sure an this is my idea.Copenhag Interpretation says that measurement affects reality so our measurement affects universe
     
  2. jcsd
  3. Mar 23, 2014 #2

    Nugatory

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    There's no easy answer to this question. If you learn quantum mechanics, the answer will show up in the math with absolute clarity, so the question comes down to asking how we know that quantum mechanics is a correct theory. That's an easy question to answer - there's more experimental evidence in favor of QM, and less experimental evidence against it, than for any other physical theory ever.

    However, for this to be answer to your original question, you have to learn quantum mechanics... And that's going to take some time and work, and a fair amount of mathematical background. Figure a year or so of college-level work after you've nailed classical mechanics and elementary differential equations. That's why I say there's no easy answer.
     
  4. Mar 23, 2014 #3

    ZapperZ

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    Please note that unless this thread has substantial physics content and not just philosophy, it will be closed, per our PF Rules and the restriction on purely philosophical discussion.

    Zz.
     
  5. Mar 23, 2014 #4

    BruceW

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    Interpretation is ... messy for quantum mechanics. It is better to learn the mathematics, and how to apply quantum mechanics to certain problems. Then let interpretation come afterwards. At least, that is how I have been taught it, in undergraduate physics.
     
  6. Mar 23, 2014 #5
    Because the experiments are not done just once! Remember, everybody can't be wrong.
     
  7. Mar 23, 2014 #6
    So math says this is real.Its strange
     
  8. Mar 23, 2014 #7
    How come its strange? only facts are proved and published. Yeah..your right no one has seen an electron..but you can observe that there is something in for example a particle. Science is just facts. Though it keeps updatin
     
  9. Mar 23, 2014 #8

    Nugatory

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    Yes, it is strange, but also utterly fascinating. Learning QM is a fair amount of work, as I said above, but it's worth the effort - that's why people do it.
     
  10. Mar 23, 2014 #9

    ZapperZ

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    Mathematics cannot say something is "real". This is a fallacy.

    What makes it "real" is that this concept is verified by experimental evidence. That is the only way for something to be valid. Once the theory matches the experiment, then we know that we have a good understanding of a phenomenon.

    Quantum mechanics arose out of classical theory not matching experimental observation at the time. Remember, you can also use math with classical mechanics to derive at a number of things. Doesn't mean these were "real" even when the mathematics said so. And the fact that these classical mechanics predictions didn't match experimental observations was a big clue that classical mechanics was missing something.

    Mathematics alone is insufficient to show if something is "real". You are missing out on an extremely important component of science - experiment!

    Zz.
     
  11. Mar 23, 2014 #10
    @Nugatory However, it is a shame that most people aren't interested in physics.. Most people have never heard of quantum mechanics and its bizarre rules and the weird behavior of particles. Go talk to random strangers on the street and ask them if they know what the wave particle duality is and how the measurements of an experiment can alter its results, etc. You'll be lucky if one of them at least knows what you're talking about. However, I don't really blame them because it is really hard and confusing. Even Einstein could get his head around the quantum theory, then why should "normal" people do?

    cb
     
  12. Mar 23, 2014 #11

    bhobba

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    That isn't really what it says.

    What it says is quantum objects do not have properties independent of observational context. Also note in QM observation is anything that has some kind of outcome here in the common-sense macro world - nothing to do with a concious observer.

    I suggest you start at the beginning with its conceptual core:
    http://www.scottaaronson.com/democritus/lec9.html

    Once you understand the detail its less bewildering and much more beautiful.

    Thanks
    Bill
     
  13. Mar 23, 2014 #12

    bhobba

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    Nor do I - but popularisations and even some actual textbooks IMHO don't help by being a bit vague on some points eg they don't make clear an observation is something that occurs here in the common-sense world - concious observer not required.

    IMHO it doesn't require much effort to dispel the misconceptions - but, possibly because it makes it more mundane and less sensationalist, it's not done.

    Thanks
    Bill
     
  14. Mar 23, 2014 #13

    phinds

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    To just add one thing to what zapper and nugatory have said, it is experimental fact that makes QM "real", not the math, and at least 40 years ago Feynman was fond of pointing out the the experimental results of measurements made in support of QM were accurate to the same degree as measuring the width of the United States and getting it right to within the width of a human hair.

    And keep in mind "within the width of human hair" does NOT mean that it is off from the theory by that much but rather that that is the range of measurement error. This is a terrific agreement between measurements and theory.
     
  15. Mar 23, 2014 #14

    Nugatory

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    This is something of a glass-half-empty/glass-half-full thing. I'm a total and irredeemable Pollyanna, so I look at the level of traffic here at physicsforums.com as evidence that there are a lot of people who are interested in physics. Also, the guidelines and mentor activity screen out the intellectually lazy - so I see a lot of people who are not only interested but also willing to put a fair amount of their energy into understanding physics.

    I'm much more unhappy about the poisonous effect of the populizers who exploit these interested and motivated people. Aside from an unnecessary upper-case 'H', I agree with Bhobba:
     
  16. Mar 23, 2014 #15
    A lot of people interested in getting their boring homework done.

    cb
     
  17. Mar 24, 2014 #16

    phinds

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    Yeah, but they don't stay around. If you stay around you'll find that there are a lot of people with more than the dozen or two posts that is usually the max for someone who just comes here for a homework question or two. There are probably a LOT of "registered users" who only have a couple of posts at most, but last time I looked there were over 350,000 registered users and that doesn't count the lurkers who haven't posted yet.
     
  18. Mar 24, 2014 #17

    bhobba

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    Yea - too true.

    I didn't really get into QM until I got away from this business of passing exams, doing assignments - yada, yada, yada.

    Thanks
    Bill
     
  19. Mar 24, 2014 #18

    BruceW

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    well, quite a few seem interested in their homework. Or at least they need to do it, but also don't find it a completely mundane task.
     
  20. Mar 24, 2014 #19
    We have uncertaninty principle because experiment show us that ,we cant measure both of them(momentum and location).But How can we sure that this is works in real universe.Nugatory answered my question and he says beacuse of math now you are talking about experiment. Experiment results are cant say us about real world Because experiments changes real world.Like Double slit experiment.I am confused
     
  21. Mar 24, 2014 #20

    BruceW

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    when you say "is this real", you mean (in more precise words) "is this a physical phenomena in it's own right in quantum physics, or is this just due to our equipment being not precise enough?" And the answer is that this is a physical phenomena in it's own right. According to quantum mechanics, we cannot measure both momentum and position of an electron (simultaneously) with arbitrary precision, no matter what kind of equipment we are using.
     
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