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The Basic premises behind quantum mechanics

  1. May 29, 2010 #1
    *I am just a novice who has done one or two undergrad courses in Physics, so forgive me if my questions seem to be silly.*

    According to Heisenberg 's principle , the exact location of an electron can't be ascertained as whatever radiation we use displaces it. Furthermore , there is an irony that for smaller wavelengths of the radiation used , the energy of the radiation is high , so this causes greater displacements of the electron . So we can only speak in terms of probabilities of the electron .

    I would like to know , what is the scientific explanation that this is the only way one can detect particles , viz using some sort of radiation ? We have got 5 senses viz Eye , touch , nose , ear , taste , so any input that we get through these is definitely depended on some sort of wave or the other .

    But how does this rule out some other being on some distant planet not being able to detect particles using some other means ?

    Even if it is theoretically impossible for humans to do so , how does that rule out the real picture ?

    I am particularly uncomfortable with the statement :-GOD DOES PLAY DICE . Now I am neither implying the existence nor non-existence of God . But , all I am saying is suppose there is a God outside the bounds of our universe , and he/she/it has a means of detecting particles without making use of radiations , won't he/she/it be able to speak of electrons entirely in terms of particles ? Shouldn't we be saying:- GOD MAY OR MAY NOT BE PLAYING DICE , BUT FOR US , HE/SHE/IT SEEMS TO BE PLAYING DICE.

    I would be glad if someone told me about theories or websites where such issues are discussed .

    Also , I would like to know some good books or websites where the basics of the maths behind quantum mechanics are given , so that I can begin getting to know this amazing branch of science.
  2. jcsd
  3. May 30, 2010 #2


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    The uncertainty principle is a loosely stated idea that predates QM. It's one of the ideas that were used to find QM. The point of a "principle" is to help us guess what mathematical structure to use in a new theory. The idea is to only consider theories in which there's a theorem that resembles the idea expressed by the "principle".

    So you shouldn't be concerned about what the "principle" is saying. Those words were chosen by someone who at the time didn't understand QM. You should be concerned with what quantum mechanics is telling you. QM isn't telling you that a particle always has a well-defined position and a well-defined momentum, that we just can't determine at the same time. It's telling you that a) a particle never has a well-defined position nor a well-defined momentum, and b) when you make a large number of measurements of either position and momentum of identical particles that have gone through the same state preparation procedure, the results will be distributed around the mean values as described by the theorem that corresponds to the uncertainty principle. [Note that a) doesn't have anything to do with the uncertainty theorem].

    These are some other posts that might be useful.


    In that second one, see also my posts below the one I linked to directly, and ZapperZ's post #14.

    If you think about what our senses do, I think you'll agree that all they do is produce signals to our brains that tell us that some interaction has taken place. Measuring devices are just an extension of that. They produce signals to our sensory organs that tell us that an interaction has taken place. Aliens might have a different set of sensory organs, but that doesn't really change anything.

    What real picture? If you're thinking that superpositions are just fancy talk for the system being in one of the eigenstates with probabilities that can be calculated from the wavefunction, that idea might have seemed plausible before the discovery of Bell inequalities and the fact that QM predicts Bell inequality violations. But it has been completely ruled out.

    It's possible that there's a more fundamental theory underlying QM, in which the fundamental variables aren't observables, but it seems pointless to speculate about such things.

    The philosophy section of this forum perhaps? As long as you don't get into religion, I think questions like this are OK (=not in violation of the forum rules).

    I think Isham's book is a good start. It's also pretty cheap. If you haven't already studied a standard introductory textbook like Griffiths, you should probably get one of them as well.
  4. May 30, 2010 #3
    Thanks , for the reply , I will definitely refer the books you stated .
    No , I wasn't intending to do that.:smile: I actually asked the GOD question so as to know , how the reality would be perceived by a being not bound by the same laws as us .i.e I wanted to know whether the theory is observer dependent.

    I read some initial parts of Griffiths book , and it seems my doubt was quite same as the realist approach to QM.

    But I will take Griffiths advice and go into the interpretations only after I have had some mathematical background on the subject
    I will return to this forum after I do some study.
    Last edited: May 30, 2010
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