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Featured Can modern physics be understood qualitatively?

  1. Dec 28, 2016 #1
    I'm curious on just how much modern physics can be understood qualitatively, without equations.

    I know that people can understand F=ma with just words. For example, the acceleration an object experiences is directly proportional to overall force pushing or pulling on the object. The more force the more acceleration and vice versa. Of course, this ignores the fact that its a differential equation, but thats a minor detail compared to the overarching concept.

    Why can't a similar approach be taken with more modern physics? I've heard that lots of the popular science books for layman dumb it down so much as to be inaccurate. Why? Could it be that the equations have so many parameters and mathematical concepts that expaining them would be impossible? If that is the case, then why even read the books then? If the rubber sheet analogy is wrong, when what is the point? Is it because it's wrong but just not so terribly wrong what knowing it is better than not knowing anything about it at all?
     
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  3. Dec 28, 2016 #2

    phinds

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    There are instances where English just is not adequate for describing what's happening. An example of this that very frequently crops up is the concept of "virtual particle pairs" being an explanation for Hawking Radiation. You pretty much ALWAYS hear that explanation in pop-science but Hawking himself has specifically said that it is NOT a correct explanation and in fact was simply the best he was able to come up with to explain in English a concept that really can only be discussed properly with math.
     
  4. Dec 29, 2016 #3

    robphy

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    One thing to consider is that many aspects of "modern physics" are not intuitively obvious
    since they may occur at very small or very large scales, high speeds, or many particles (which may not behave like "everyday objects").

    This famous lecture by Feynman seems appropriate here.

    A fuller reference is below (with an interactive transcript).
    This version on YouTube has the intro trimmed and gets right to the lecture.


    A useful passage [at about 3m08s above, or 4m12s below]:

    For more info on this series of lectures:
    http://www.cornell.edu/video/richar...ty-uncertainty-quantum-mechanical-view-nature
     
    Last edited: Dec 29, 2016
  5. Dec 29, 2016 #4
    Do you see all the people without a math background asking questions about quantum physics based on watching Michio Kaku documentaries?
     
  6. Dec 29, 2016 #5

    robphy

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    What got me to pursue degrees in physics is my frustration with pop science books trying explain relativity. They were good for attracting my interest... but not to fully understand or at least get a working knowledge from them. So pop books have a role to play.
     
    Last edited: Dec 29, 2016
  7. Dec 29, 2016 #6

    phinds

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    Absolutely. I love pop-sci books and TV shows to sort of learn what the questions are, but I know better than to take them too seriously about what the answers are.
     
  8. Dec 29, 2016 #7

    Andy Resnick

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    This is a fallacy: 'Force' cannot be understood without it's precise (mathematical) definition; using words alone leads to mis-use ('force of impact'). The same can be said about many other words: stress and pressure are two obvious ones.
     
  9. Dec 31, 2016 #8
    Touche.

    But still, the qualitative description captures some aspect of it. Just not completely.
     
  10. Dec 31, 2016 #9
    Well, to be fair, my mind was blown after learning about the double slit experiment for the first time from popular science book. This was way back in high school.

    Now, after reading some of the math behind it( basically vectors in hilbert spaces and fourier series), things aren't really all that much more illuminating. But I've only recently started studying it, so maybe there's still more to see.
     
  11. Jan 1, 2017 #10
    Well, you start out having your mind blown and then there's a sort of illusion of competence that goes along with it. When you study the subject (any subject) formally in school you basically will get smacked in the face with how little you understand.
     
  12. Jan 1, 2017 #11

    phinds

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    Exactly. Personally, I persist in the illusion of competence despite being CONSTANTLY smacked in the face here on PF with obvious examples of my ignorance. I never let a little thing like not knowing what I am talking about get in the way of a good discussion. :smile:
     
  13. Jan 1, 2017 #12
    Mathematics is just a type of shorthand. It has been described as a way of expressing the longest train of thought possible in the minimum number of symbols possible. Lanczos liked to test how well his students understood an equation by asking them to explain it in words. This may involve a rather long and at times convoluted train of thought, but it helps people think about what the equation means, as opposed to simply developing a facility for manipulating symbols according to a set of rules.
     
  14. Jan 1, 2017 #13

    phinds

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    No, it is a language all its own. I understand what you mean but you are oversimplifying. Reread post #2.
     
  15. Jan 2, 2017 #14

    Andy Resnick

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    Sure- there's a time and place for qualitative analysis. But in the hard sciences, it can't replace quantitative analysis.
     
  16. Jan 3, 2017 #15
    You mean I am oversimplifying about shorthand? Perhaps, but I don't have time to think about it now. I won't even say who I am quoting. Yes, NL etc. but in accord with one of my New Year's resolutions I am not going to drag in that old appeal to authority any more.

    I'm getting fed up with words anyway. "Show me your equations." (mystery quote). I wonder how that fits in with this forum?

    :smile:
     
    Last edited: Jan 3, 2017
  17. Jan 3, 2017 #16
    Aren't there many situations where no analytical solutions can be found and costly to implement numerical solutions?
     
  18. Jan 3, 2017 #17

    ZapperZ

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    But what does that have to do with the requirement that it must have a quantitative description? Setting up the Hamiltonian, even if one can't find the most general, closed-form solution for it is still extremely important. It is like setting up the force equation. It tells someone else what one is accounting for describing something. Without this, it is just hand-waving.

    In addition, area of study such as Many-Body physics, often deals with situation where you can't have an analytical solution to each individual interactions. So we know how to deal with something like that.

    I've said it a thousand times, and I'll say it again. Physics isn't just saying "What goes up must come down". It must also say "When and where it will come down"! A lot of people seem to forget that it is the quantitative aspect of it that makes it testable, and that experimental verification is central to any idea in physics for it to be considered to be accepted.

    Zz.
     
  19. Jan 4, 2017 #18
    Not much. Chemistry and Physics are fundamentally quantitative sciences. They are all about making quantitative predictions about what will happen in quantitative experiments making accurate quantitative measurements.

    There are some aspects of new theories that can be explained as qualitative differences from the older theories that they surpass. But if a student in incapable of using the new theory to make quantitative predictions, then they are just parroting qualitative descriptions without real understanding.

    "Conceptual Physics" is an oxymoron.
     
  20. Jan 4, 2017 #19
    It may be worth pointing out that Aristotle (a) worked without math, using only words, b) and never bothered to check his descriptions of how nature operated. The connection is that he would have needed math to implement the measurements that he would have used to check those descriptions.

    So you can strip the math out of a second-hand account, sure; but this leaves readers unable to verify even the simplest of assertions for themselves, including F = ma. So for all they really know, they could be reading total make-believe. Yes, we tend to trust authority because we must; e.g. like all humans, I don't have the time nor the expertise to verify the vast majority of descriptions of reality that I have encountered, from childhood on; but one of the things that makes science what it is is verifiability by others. Those outside the community of science (definitely including me, at present) who can read only pop science books can't verify that what we are reading about is actually science; we can only trust & hope.

    Also, consider metaphor. It's frequently used to provide context for mathematical models; but appropriate metaphors must be chosen & inappropriate or misleading ones discarded; e.g. see the well-known video of Feynman explaining to an interviewer why rubber bands aren't an appropriate metaphor for magnetic attraction. Beyond that however, even the most useful metaphors (I am guessing here, but am pretty certain I'm right) have sharp limits beyond which they become inappropriate; only by knowing the math could you know what the metaphor helps make clear & what would be a misleading interpretation. Thus such metaphors wouldn't be much use to non-math readers.

    So to me it seems that to "know" even a small bit of physics ("know" = prediction & control), rather than rely only on argument by authority, requires more than just verbal descriptions. Physics is made up of models & these models require both the math and the surrounding verbal/situational context. Take away either and you don't have a science. You can have a purely verbal description of the thing, but not the thing itself.
     
    Last edited: Jan 4, 2017
  21. Jan 4, 2017 #20

    ZapperZ

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    A while ago, in this thread, a PF member who is no longer with us, used gravity to explain why two sheets of glass plates stick together. This member had a "conceptual understanding" of gravitational attraction, but lack any understanding of the quantitative aspect of it. He/she could not estimate the gravitational force between 2 typical glass plates, and whether the force from it is sufficient to provide such a "glue" to make them stick together. This is before considering that if the glass surfaces were wetted, the sticking is even stronger. Maybe gravity changes strength with added thin film of water.

    This is a common occurrence. When people only think that they know the qualitative or conceptual aspect of something, but lack the quantitative or mathematical description of it, then they tend to use highly improbable or minuscule effects to explain very common observations. This is because they lack the ability to estimate the order-of-magnitude numbers associated with these effects. They are aware that two masses, such as glass plates, have gravitational field, but are not able to figure out the strength of the field and whether it can explain what has been observed. To be able to do the latter, the physics understanding must be accompanied by an underlying mathematical description.

    Without the mathematics, at best, one can only claim a superficial understanding of physics. One cannot claim to have a useful, usable understanding of physics.

    Zz.
     
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