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Quantum Mechanics for the 'lay person'

  1. Apr 4, 2008 #1
    Hi everybody. I'm a graduating med student interested in public health, medicine and engineering for the purpose of solving world problems (a very superficial description of my professional interests). To teach myself engineering in order to communicate with the engineers in these future interdisciplinary partnerships, I studied the Feynman lectures before studying engineering texts during med school. Feynman turned me onto Quantum Mechanics, and a while ago all the above led to a part of a conversation in a bar where some guy asked me to explain QM to him. I did so in an E-mail which I thought was reasonably good, and then, not to waste a happy opportunity, revised and clarified it for the purpose of using it somehow as a qualitative summary of the topic for the 'lay person' (high school graduate education level).

    I now put my head in the lion's mouth by posting it here to receive feedback on its clarity and accuracy (please note I didn't want to get bogged down in defining B-E and F-D statistics, the connection of F-D statistics to the Exclusion Principle, existence of quarks and gluons in QCD, etc, so when I mention "confined waves" for instance, it refers to electrons in their orbits, the mesons and nucleons which exhibit the physicist's "color confinement", etc... basically all matter as non-EM waves). I am also interested in symmetry in physical law, but mentioned relativistic effects as "weirdness at high speeds" rather than get into that here. My sources are several Feynman books (lectures, gravity lectures, QED, etc), a book by Einstein called "Relativity" (and his original Special Relativity paper but NOT a Gen. Relativity paper), an article by S. Lloyd, and Buckminster Fuller for my introduction to the word "generalization". I'm not trying to make money, just to spread the joy of learning about this neat subject to those otherwise turned off by math and physics. Thank you for your feedback; sorry for the long post.


    I'd like to discuss this in the context of the unique human capability to "generalize", which in science terminology means to identify a physical principle as being true, in other words exceptionless. Another way to think of generalization is as the process of refining our understanding of nature by extending the range of examples over which principles are known to hold true. If any exception to some principle is found, an explanation must account for it which may drastically shift our fundamental understanding of, say, motion through space and time which is what relativity's all about. Einstein broadened our understanding of motion to explain weird stuff occurring at speeds close to the speed of light that Newton's laws of motion failed to explain. In this way Einstein generalized the laws of motion further to fit them with other known phenomena (the weirdness at high speeds). This predicted the fact that there is no real meaning to the word "still" in the Universe - everything is in motion. He then even further generalized them to the "General Principle of Relativity", where some thing’s gravitational pull and the presence of the thing itself both co-cause a curvy bending in the path of some other thing, even light, as those things all move through space-time. So you can see again how it was made more applicable to reality, as there is no known ‘place’ in the universe that gravity doesn’t act. At ‘places’ of maximum known curvature our ‘thing’ is a black hole from which even light only escapes as the hole dissolves. So the center of a black hole is in a sense actually a physical redefinition of the word “still”.

    This process of generalization, an apparently unique human function, is the heart of science. It’s how we sensibly unify what we understand about nature. For example, over time it became known after enough exceptions overturning principles that electricity, magnetism and light are 3 parts of the same thing, an electromagnetic (EM) wave (traveling by definition at light speed). Sound waves, for example, work differently (atoms carry the sound by knocking into each other in the atmosphere and ultimately your eardrum or until friction causes the sound to die out over distance), but are also a ‘wave’ or oscillatory pattern through a medium (water, atmosphere, metal, etc). The wave pattern in this case is the back-and-forth vibrations of the atoms that propagate the sound wave until it dies, and the friction is the wavy vibratory motion (“heat”) of jostled neighboring atoms. And so pressure, heat and sound are unified. EM waves through space-time don't die out, as there’s no friction for light... it's nature's clearest example of a pure wave. Otherwise it and sound waves are similar in principle. Waves can interfere with each other and an example is 2 water waves meeting... they might reinforce each other (constructive interference) or kill each other out (destructive interference) depending on the waves' heights at the point of interaction. EM waves quantum mechanically interfere to tie together some of the confined waves we call “matter” (or a sort of ‘counterclockwise’ matter called anti-matter, which when combined with matter causes both to transform into unconfined [EM] waves). An example of a way EM waves ultimately ‘tie’ together matter is plant photosynthesis. This is a simplification since some of the little bits of what we might call "matter" actually are their OWN anti-matter, a very confusing circumstance. An example of the unconfinement is P.E.T. medical imaging technology that interacts matter and anti-matter, then detects the freed waves.

    Now, the mathematics of a wave can be generalized to what's called the interference of probability amplitudes for any given thing in nature to occur, where a probability amplitude is like a "pre-probability". Mathematically, when the probability amplitude is multiplied by itself (“squared”) you get the probability. This is how quantum mechanics describes nature. The math works this way because the amplitudes can be negative or positive, which is how they're able to interfere with each other... by canceling themselves out (destructive interference) as well as amplifying themselves (constructive interference). When you square the total amplitude (if it’s negative this cancels its own negative sign for mathematic sensibility), it becomes a probability. It turns out this squaring process mathematically represents observing a thing in nature. The situation with quantum mechanics is that even the best theoretically-designed equipment to see what the interference pattern physically LOOKS like in nature knocks the amplitudes into a single definite observed state, even in the simplest case of only 2 possible outcomes interfering. So that there is no longer a perpetual interference, but instead some definite outcome for even the most delicate experiment designed not to disrupt the interference pattern, no matter how clever we are. The act of "seeing something happen in nature" smears the amplitude interference pattern a little to where they no longer interfere and we get a result. This is an unavoidable frustration a bit like trying to fake out your reflection in a mirror. How little is the smearing? As little as that which correlates to the energy content of one quantum, an otherwise abstract thing actually literally definable as the minimum energy difference between a pre-smearing and post-smearing result. Just in case you’ve heard of it, the Uncertainty Principle in physics mathematically describes the trade-off of information about tied-together aspects of things at the quantum scale. In other words, for instance, if you pinpoint the location of something with total precision you have lost all the information of the motion of the thing, and vice versa. The trade-off effect being true is why we have the problem with our experimental designs impacting that which is observed, although it's not a very deep explanation for anything, just a description of what happens.

    So to summarize, before we observe anything at all we have only an interference pattern of the amplitudes as pre-probabilities (and calculated from that, probabilities). And what we were trying to observe is continually changing because of so many tiny probabilities so rapidly. This ever-changing probability series is the same thing as motion. The amplitudes for very complicated situations have even been made compatible with the weirdness at high speeds (in other words made “relativistic”, which predicted the existence of anti-matter). The unconfined (EM waves) relativistic wavy quantum nature and some of the confined (matter/anti-matter) cases are all described by quantum electrodynamics (QED), or in the confined wave cases inside some other bits of matter such as atomic nuclei, quantum chromodynamics (QCD). String Theory is a candidate to unify these with gravity and curved space-time as described by General Relativity. To summarize the summary, quantum mechanics is probabilistic until something’s observably locked into reality. It’s a tightrope kind of like the difficulty of precisely and accurately defining the word "now", which, if you said or communicated it by any physical means would smear the definition’s precision (although into inaccuracy instead of into the clear focus of reality as quantum mechanics does). Teacher-physicist Richard Feynman explains the quantum mechanics above in one of his lectures with the aid of an experimental description which makes what I've written very clear.

    So the sticking point is, what the hell is observation? Is thinking about something that you or someone else already observed observation in some way? Is it unique to humans? Can a spider or a virus or a star observe something, or is it really that a quantum mechanical description of nature, a generalized understanding of mechanics (forces and motion) so far without exception, is dependent on human observation to lock nature into existence? Is it possible that if we're not looking, something isn't definitely occurring? Not to mention the only information you actually get from the observation is that the state the thing entered is not one of the other options. What, if anything, HAPPENED to the other options is not known. That's the unclarity of quantum mechanics that at least physicists have, and can only be currently explained in terms of the generalized wave-like patterning of nature, that seems to be delicately self-stabilized by probability amplitude interference.

    -Gerrit Ockerse
    Last edited: Apr 4, 2008
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  3. Apr 6, 2008 #2

    With 79 views I'd think someone had an opinion (e.g. "this sucks", or "unclear", or "accurate", or "here are specifics on why it is inaccurate...", etc). I'm game for criticism from you smart pros (for clarity and/or accuracy) or the non-physicists (for clarity more than accuracy) who ask and answer questions on these boards. Anyone..? This is meant to be improved with feedback for the purpose of education, so almost any comments are helpful.
  4. Apr 6, 2008 #3


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    Hi Gerrit:

    we are not accustomed to 1200 word essays to evaluate, but questions expressed somewhat more succinctly.

    If you're talking about SR - it is more than just 'weirdness at high speeds'.

    No prediction was involved. It is a postulate of SR that "a state of rest cannot be distinguished from a state of uniform motion".

    Eh ? How so.

    Well, I'm too bored to go on. I've read it all but your attempt to summarize the state of science and scientific philosophy is confusing and I think a layman would emerge with a spinning head from reading this.
  5. Apr 6, 2008 #4
    Thanks for the reply...

    And your input. It's the confusion I'd like to clear up and you've helped a little with that, so thanks. I'm not much of a writer and no physicist, but this is my attempt to reduce topics I found very interesting to a couple pages other non-physicists could read. I hate the divide between 'scientists' and 'non-scientists' and will do what I can to bridge it. I guess you could think of me as a tenacious journalist.

    This 'still' and 'moving' business...
    I know SR's more than "weirdness", but I tried to cap this at 2 typed pages and so didn't elaborate on symmetry in physical law, etc. Since SR invalidated absolute "stillness", and since SR is a limiting case of GR, which involves gravitational accelerations and curved space-time, aren't the traditional definitions of "stillness" and "straight lines" in the universe known to be just convenient approximations of reality since Einstein hit the scene? Just as quantum mechanics seems to have invalidated the word "solid". That's how I think of it at least, maybe wrongly. I thought the curvature of a black hole locking perpetually moving EM waves within it could in a sense conceptually redefine stillness, though a real redefinition would I guess describe an inert reference frame coasting through constantly curved space-time.

    Well, thanks again for your feedback. Criticism of paragraph 1 duly noted.
    Last edited: Apr 6, 2008
  6. Apr 6, 2008 #5


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    Hi Gerrit,

    I always thought of 'stillness' as an attribute as in 'still water', and motion as an observer dependant state. I think the key thing in SR is that there is no such thing as stillness or 'stationaryness'. You talk of stillness being redefined, but actually it's shown not to exist in an absolute sense. Now you've got me splitting hairs.

    The problem is that physics is based in equations and mathematical definitions and the meaning of these is not always clear even to physicists. You talk about the inside of a black-hole - but no-one has ever seen a black hole, never mind the inside of one. So everything we might say is based on some persons interpretation of the equations.
  7. Apr 6, 2008 #6
    Response to Mentz comment

    Mr.(?) Mentz(?),

    I love to talk about this stuff: splitting hairs seems essential for interpretation. It seems to me you're pointing out my inconsistency when I say "everything is in motion" and then "the center of a black hole is in a sense actually a physical redefinition of the word 'still'". That is true; until the Large Hadron Collider or something better shows something, nobody can say light is immobile within a black hole. For all anyone knows it's still pinging about the physical representation of the singularity at the speed of light. Furthermore, if black holes move then the contained light would too. In fact, speculated particle/antiparticle mechanism (or so I've read from Seth Lloyd) of Hawking radiation aside, maybe the light does escape the hole in some weird way. Hell, maybe black holes are wormholes as in sci-fi. For consistency I shouldn't assume anything about the behavior of light within a black hole. I'll omit that sentence. Thanks for pointing this out.

  8. Apr 6, 2008 #7


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    While this thread started out with you trying to see if you got the ideas right, it appears that you're now trying out your own speculative ideas. Please re-read the https://www.physicsforums.com/showthread.php?t=5374" in case you've missed it the first time around.

    Last edited by a moderator: Apr 23, 2017
  9. Apr 6, 2008 #8

    Then please let me rephrase that post as "Everyone agrees nobody knows what happens in black holes".
    Last edited: Apr 6, 2008
  10. Apr 6, 2008 #9


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    Hi Gerrit,
    "Mr Mentz" is correct but too formal, "Mentz" will do. Further to what I was saying about interpretation, one should be careful to realize that the mathematical entities used to calculate effects sometimes have a shadowy ontological status. Is space-time actually 'curved' ? Is the wave-function real ( it 'exists' in a multidimensional space quite unlike our 4D space-time) ? So philosophical insights based on the absolute reality of these things could be completely wrong.

  11. Apr 6, 2008 #10


    Agreed. I couldn't qualitatively describe a probability amplitude any better than as a "pre-probability" for that 'shadowy ontologic status' reason. I hope by your and others' judgment I haven't mistranslated the physicists' current consensus of nature's version of the math elsewhere in my 'paper', though to find that out was ultimately the reason for posting it on this forum. What I most worried about were:

    1) the light-in-a-black-hole as a sort of 'stillness' (thanks again),
    2) rather arbitrarily defining "matter" as confined, non-EM waves (i.e. non-photon particles),
    3) interpreting series' of observed probabilities as motion,
    4) the sentence: "It turns out this squaring process [of a probability amplitude] mathematically represents observing a thing in nature", since that's the lynchpin of my quantum mechanics description.

  12. Apr 6, 2008 #11


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    Hi Gerrit,
    I have to comment on point 4) because it is a bit off-beam. Squaring the wave function gives a probability distribution of position, momentum or some observable and is not equivalent to 'observing'. Observing is associated with the 'collapse of the wavefunction'. So after you've developed the film and determined where the particle was, at that moment the wf collapses (?). My belief is that the wf does not exist and so cannot collapse, but that is the subject of much discussion.

    2) is oversimplified. Matter may well be described by wave functions in some situations, but it is still matter and may have fermionic and electronic properties that hurt if you bang your head on it.

  13. Apr 6, 2008 #12


    You're a clarity-saver.
    Yeah, despite calling it my lynchpin, the wording of my point 4 above isn't even consistent with the rest of my original post. When I wrote:
    "It turns out this squaring process [of a probability amplitude] mathematically represents observing a thing in nature", I didn’t mean I think amplitude squaring is equivalent to observing something, but that squaring to obtain a probability takes a variable's certainty as far as it can go mathematically, whereas observation takes the certainty as far as it can go physically (collapse). Of course, that's clearly not what I had implied. Hooray for feedback, huh?

    As for point 2, as I barely understand, fermions have half-integer spin and so exhibit antisymmetry. You probably know Feynman gave a cool Dirac memorial lecture on this. I know this produces the Exclusion Principle, which (along with the Uncertainty Principle) is why we bang heads on things and don’t fall through floors. I didn’t include this because I didn’t know how to put it in ‘lay terms’, as I sort of said in the little header to my post.
    Does anyone reading this have any idea how to phrase an easy explanation of this?

  14. Apr 7, 2008 #13
    If you move a box with internal reflecting walls, the contained light will move too. Where is the problem?
  15. Apr 7, 2008 #14


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    this is an excellent little paper written by students comparing different flavours of quantum mechanics

    http://hubcap.clemson.edu/~daw/D_Realism/AmJPhys.v70p288y02.pdf [Broken]

    Posted by CarlB in another thread.

    Last edited by a moderator: May 3, 2017
  16. Apr 8, 2008 #15
    Light Arrow and Mentz

    L.A.: Yeah, that makes sense to me, but I didn't know enough about our observations of black holes to know whether they can be said to move in any reference frame, since they just suck everything in. Although if some are speculated to be at galaxy centers, as I've read, then of course they'd act as a light-containing box. My bad.

    Mentz: Thanks for the paper link.
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