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I Operational Reality of E field? (Bridgman)

  1. Jun 21, 2016 #1
    I'm reading The Logic of Modern Physics by P.W. Bridgman (1927). He states an operational definition of reality: something is a "good construct" if it has a one to one correspondence with a physical situation defined by observations, but it isn't "real" until it has multiple definitions--separate phenomena that yield the same concept. He says that stress is real, atoms are real, but electric field is not. I know it's a philosophical quagmire, but I was hoping someone could tell me whether there are independent ways of detecting an electric field besides the definition of "put a charge there and measure the force." Bridgman was an experimental physicist and knew electromagnetism, so I'm wondering whether a separate, compatible, operational definition of electric field exists now, thereby making E fields "real" according to Bridgman
     
  2. jcsd
  3. Jun 21, 2016 #2

    Dale

    Staff: Mentor

    I wouldn't worry about it. It seems like his definition of "real" is not so important. I cannot see any case where having multiple definitions is an advantage.
     
  4. Jun 21, 2016 #3
    (Not having read the book,) I think I understand where Bridgman is coming from. For example, energy appears in many subfields of physics with different definitions. If all the physics you knew was just basic kinematics, you might think that energy is nothing more than a bookkeeping mechanism. And you might regard it as not real, since we can always invent various potential energies such that energy is conserved. But, we also see energy turn up in relativity. When we have multiple definitions, it places more constraints on each definition. We can't modify the definition willy-nilly without creating inconsistencies with the other definitions.
     
  5. Jun 22, 2016 #4
    Khashishi, exactly. Stress in a transparent solid can be measured by measuring forces on the exterior, by measuring strains, by looking at the optical deformations, etc, so Bridgman says that stress is a real thing. He claims that there is only one way to detect an electric field, and that is by having charges feel force when exposed to it. This surprised me, as I assumed that the energy density of the E field, for example, might be detectable in some other way, but I trust that Bridgman knew electromagnetism well as it stood in 1927.

    Dale, thank you, but I find it very important. Quantum mechanics and the murky philosophy surrounding it is what ended my physics career before it began. This book is forcing me to rethink a lot, so I want to understand it well.
     
  6. Jun 22, 2016 #5

    Dale

    Staff: Mentor

    I don't see how. Using that definition of "real" the things that are "real" or not change as you change dictionaries. How is that important?

    Then not only is it unimportant, it is anti important. It is important for you to actively avoid it.
     
    Last edited: Jun 22, 2016
  7. Jun 22, 2016 #6
    Dale, if you are happy without thinking about philosophy, more power to you. For myself, I can't do physics without it. To me the whole *point* of physics is to understand the real world. So yes, the definition of "real" is vitally important. If physics is not about reality then I'm not particularly interested in it--it just becomes math but with less rigor. I'm not willing to ignore the problem. Physics went off the rails in 1926 and all the mystical hand-waving in the world isn't going to save it. A logically self-consistent ontology is required.
    People always assume I'm narrow-minded or something, as if I can't face new ideas, just because I can't understand quantum mechanics. I took to general relativity like a duck to water. I can do all the math for quantum. I have no problem with randomness and probability. I'm fine with learning new rules for how the world works, but there have to BE rules. You can't just say, "Oh, we're going to use x, y, z coordinates freely in our equations, but positions don't actually exist." It's one or the other. Reality, by definition, is not optional. Either something is real, or it isn't, and you don't get to tell me, "you're not allowed to ask that question right now," and then declare the question has an answer when you feel like it. Or if something is going to exist, then vanish, then exist again, you have to tell me the RULES for when it is going to vanish and reappear.
    If I were interested in taking things on faith I'd have been a theologian. I wanted to be a physicist. Instead I'm a tutor, doing damage control on many failures of the educational system, and trying without success to fix the ways the educational system failed me.
     
  8. Jun 22, 2016 #7

    Dale

    Staff: Mentor

    It seems like you couldn't do physics with it either. This isn't a criticism of you, it is a criticism of philosophy.

    I agree with this goal, but disagree with the value of philosophy in accomplishing it. Experiment is the tool to use for understanding the real world, philosophy is not equipped for the task as your own experience seems to demonstrate.
     
    Last edited: Jun 22, 2016
  9. Jun 22, 2016 #8
    Experiments gather data. Then we have to think about the data and make models, concepts, constructs, theories. We have to decide what the basic objects are. That's choosing an ontology. Newton stipulated absolute space, absolute time, masses, and forces, and then built a structure using those elements. Einstein postulated curved space. Electromagnetism experts postulated that electric charges and electric fields exist. Physicists DO philosophy, they just usually do it unconsciously, and lots of them like to pretend that they aren't doing philosophy at all. When things are intuitive they can get away with handwaving and it's okay because everybody is on the same page and can communicate and solve problems. In that situation only a philosopher would care about the philosophical issues remaining.

    I don't actually LIKE philosophy. I don't like pounding my head against unknowable or impossible concepts, I don't like argument for argument's sake, and I still think most of philosophy is a waste of time for my purposes. I don't care who came up with what idea or who hated who or microscopic trivia of dead languages and what somebody *might* have meant. I went to philosophy, reluctantly, looking for a list of Great Questions and Most Commonly Proposed Answers. What I found was a 2,500 year long barroom brawl. I just wanted the ideas. I was dragged into philosophy kicking and screaming by my determination to *understand*, not just parrot equations blindly.

    Philosophy is essential to physics. Everybody who does any physics is assuming some philosophy or other, some picture of the world and nature of reality, some idea of what is knowable and how to know it. Quantum mechanics invalidated the old concepts. Fine. That's not actually helpful if it doesn't give new concepts to replace them, something to build an ontology out of. I can handle an electron wave function being like a cloud of probability. I can handle nonlocal effects existing. I'm not denying any experimental facts, and I believe that they are the ultimate arbiter of truth or falsity of models of the world.

    But quantum mechanics gives no picture, no mechanism, no model, no connection to reality. Now, there has to BE one somewhere, or you physicists wouldn't be able to extract predictions for what actual instruments will read in actual experiments, but 7 different quantum professors all utterly failed to communicate to me even a beginning to how one DOES that. I can turn a classical problem from words into a picture into a model into equations, solve the equations, and turn things back and be able to tell you what will happen with those levers or magnets. But every single example that I've ever seen in 30 quantum textbooks that attempts to do that with real world situations utterly FAILS to get anything done without huge amounts of handwaving and sloppy mathematics.

    At this point, opening a quantum textbook at all sets my BS meter to 70%, and the first handwaving pegs the scale. (Students who care about logic and rigor should never learn any math from physicists!) I have to take it on faith that the emperor has any clothes at all. I look at the physics texts to see what math they are using, and then I go to math books to actually learn the math before returning. I have by the way worked every problem in the first 6 chapters of Bransden and Joachain. I can do the math, once I have learned it in coherent fashion elsewhere.

    I've crossed quantum field theory off of my bucket list as unattainable in my lifetime. I know I'll never get there. But oh how I wish I could find any book or person who could tell me WHY quantum mechanics cannot be understood, WHY we are supposed to just "shut up and calculate," and how on earth you can turn a physical situation into quantum equations in the first place. I've spent a lot of years painfully inching my way toward wisdom about quantum mechanics. I have figured out some things (like the vital importance of philosophy in doing physics) and learned some math. I vowed in college that I would understand quantum mechanics, or know the reason why. The first option was preferred, but either was acceptable. At this rate, I'll die with that vow unfulfilled.
     
  10. Jun 22, 2016 #9

    marcusl

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    Gold Member

    My advice is to take up something else--woodworking or sailing, for instance.
     
  11. Jun 22, 2016 #10

    Dale

    Staff: Mentor

    Why? If our model works then what does it matter which objects are classified as "basic" and which are not? As long as the model is accurate, reality is entirely indifferent about our ontological classification. So if the goal is to understand reality then why do we "have to decide" at all?

    Why? Philosophers say that like a wish that if they repeat enough might become true. But have any experiments been performed where some students were given a heavily phisophocal course and others were given a low philosophy course? If the two groups perform equivalent then it is not essential.

    On the "vital importance of philosophy in doing physics". I would like to see the experimental evidence supporting that.
     
    Last edited: Jun 23, 2016
  12. Jun 22, 2016 #11
    That is what most of philosophers of science say, and I think most of physicists disagree with it. And I think that what physicists say about physics is more important ;)
     
  13. Jun 23, 2016 #12
    In physics if we are careful enough we never say that a theory (and the elements of the theory let it be fields, particles, forces e.t.c) is true or real, all we can say is that the theory is consistent with observations and measurements. If we make a new observation and the theory is not consistent with that observation, we can safely call the (old) theory false, and evolve a new theory that will be consistent with the new observation , yet we cant call the new theory true but just consistent.

    It might be the case that there are two or more totally different theories that are fully consistent with all observations (such two theories might be quantum loop gravity and string theory for example) and since they are both consistent we might not be able to distinguish which is the true theory.

    Furthermore (stop reading here if you want cause what I 'll say it is not supported by experimental evidence) we cant be sure what is real and what is not, for example we might as well living inside a some sort of thing that resembles a digital simulation that is generated by some sort of thing that resembles a supercomputer and exists in the truly real universe which is totally different than this universe which we thing is real and we just try to make a theory that is consistent with.
     
  14. Jun 23, 2016 #13
    The only real that matters is predicting the results of an experiment.

    Philosophy when pushed always ends in the same useless place....solipsism, which is good for??

    Unless you are aiming to be omnipotent a "best fit" approximation of reality is good enough.
     
  15. Jun 23, 2016 #14
    Interesting that no one has answered your real question:

    Thanks for the tip on this book. I have enjoyed reading Bridgman ("Reflections of a Physicist" ...).

    Good Luck!
     
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