Full list of physics concepts with circular definition?

Discussion in 'Physics & Math' started by dixonmassey, Aug 26, 2004.

  1. dixonmassey Valued Senior Member

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    There are physics concepts with circular definition. Like work and energy. For example: what is energy? Energy is capacity to do work. What is work? Work is energy being transfered to the system ....

    The same with charge, time. What else?

    Does existence of "circular" concepts implies that those concepts are 1) basic building blocks of universe; 2) we have little clue about them. However, we can use those concepts to describe world around us and make our lives easier.

    For example, in materials science, one can easily obtain a formula relating hardness of an alloy to its composition using design of experiment techniques. The formula will reliably predict hardness of the alloy. However, coefficients of that formula (and formula itself) are mostly meaningless.

    Does something similar occur in physics? "We have little clue what is energy. However, we can use that concept to our practical advantage".

    Is any hope to crack some circular concepts in the future?
     
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  3. PhysMachine MALLEUS SCIENTIARUM Registered Senior Member

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    Well, first of all you're giving really layman's definitions of what we talk about. Technically, work is defined as the line integral of a path through a force vector field, and we declare that F dr = dE where we don't really specify an interpretation of dE until we start dealing with the concepts of energy. If you pay close attention, the definition of the potential energy is carefully set so that we can deal with the conservation of a scalar quantity if a force has certain characteristics (irrotational, for instance).

    Really if you see mechanics derived straight from F dp/dt you get a good feeling for the unity in classical mechanics, similarly with Maxwell's equations. There really aren't that many "circular" definitions in physics except for when you're scratching the surface and don't really relate the larger picture to a few basic postulates.
     
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  5. dixonmassey Valued Senior Member

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    Ok, I am physics layman. OK, there is formula to substitute layman wording. Still, your formula and force field changes nothing principially. F*distance=Energy. Thus, definition of work or energy (smart or layman) are mutually related. Feynman, in his Physics, wrote that physicist do not really understand what energy is about. Therefore, they do not really understand what is work about. The same with charge, the same with time. The same with force and mass, after all. I never have met a satisfactory explanation what force is about. Only formulas which do not really explain much, just introduce new parameters (impulse, mass) and derive the definition of force from those parameters. And conversly, some books derive definition of mass and impulse from definition of force. Circle is closed. One may write bunch of formulas and use phisicist's lingo to hide this sad fact. But fact is: those formulas are circular and do not explain much (on the fundamental level). In about the same fashion as mat. sci. hardness formulas do not explain why hardness of an alloy is as it is, they just enable precise calculations of that hardness.


    The questions:

    What is energy?

    What is charge?

    What is force?

    What is mass?

    What is....?

    stand. Again, there are bunch of the simple and convoluted formulas relating those things. But, do they really give answers to the above questions?

    I think it was Einstein who told a famous sentence about simplicity in physics. I do not remember it precisely but the meaning of it was something like this: "If you cannot explain a physical phenomenon without using formulas, probably, you do not really understand that phenomenon yet."
     
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  7. Facial Valued Senior Member

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    That's why we have concepts. I am confident that my concept of mass is the same as yours. Physics doesn't start with math ; it starts with concepts.

    Having said that, I haven't fully grasped what energy actually is, lol.
     
  8. John Connellan Valued Senior Member

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    3,636
    What kind of answer would u expect? Language itself is circular. If u try to define something u have to do so in terms of something else. These are base concepts in the sense that explaining them any further will not make our understanding of them any easier. In other words, defining energy as the ability to do work is the simplest definition of energy and trying to explain it further will not make our comprehension better.

    Why do u have a problem with this definition?
     
  9. MacM Registered Senior Member

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    10,104
    I have not seen this quote before but I very much concur with it. It seems to say (more eloquently) what I have argued for a long time.

    "Our dependance upon mathematical concepts without an underlying Physical Model has lead us down ludricrus paths and we have, and are, wasting a great deal of time pursueing impossible and worthless concepts - i.e. time travel, infinities, etc."
     
  10. Quantum Quack Life's a tease... Valued Senior Member

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    unfortunately until we can let go of this "something" conceptialisation we will never find the answer to these questions. We only look at the effect not the cause.

    if I said to you that energy was an imbalnce in time past and future occuring in the now, you will say "prove that this is so" and I would say how can something that is essentially non-existent be proved.

    For instance we measure light only by it's effect and yet we have no idea what it really is, or should I say isn't.

    We measure magnetic fields by their effect, Yet if I suggest that a negative pole is a Past bias in spacetime, it is discounted as fantasy becasue the past is non-existant.
    Yet some will argue that matter is compressed spacetime.....but what do they mean by this? Are they just using the words spacetime for fun or what?

    They say that it is conpressed spacetime but when a singularity is suf=ggested as a cause for this compression for some reason it seems ludicrous. Yet I ask what causes spacetime to fold so densely if not for a singularity. One that is governed by that very spacetime compression.
    Why is it so hard to understand that a singularity of absolute vacuum or nothing is responsible for compressing not matter, but space time to creat matter and it's inherent energies. and the gravity that pervades all teh universe.
    Why is that so hard to understand as a possible answer to those questions?
     
  11. AndersHermansson Registered Senior Member

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    334
     
  12. PhysMachine MALLEUS SCIENTIARUM Registered Senior Member

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    Yeah, the concept of "energy" comes from a mathematical treatment of Newton's laws.

    First, consider our force F. Now consider that force activing over a differential distance, dr. We define the work done by that force as dW = F*dr, which in turn we call dT, the differential change in kinetic energy. Now, the expression for kinetic energy comes from F = ma = m dv/dt, and dr = vdt, so then the above becomes

    dT = m dv/dt*v dt

    Integrating this gives that

    T = 1/2 m v^2

    the familiar equation for kinetic energy. Now dealing with the potential energy, we pull out some given theorems from vector calculus and invent a quantity defined so that T + V = E, a constant, for certain systems.

    If you're really interested in watching a solid discussion and derivation of classical mechanics, I'd recommend the Corben and Stehle "Classical Mechanics" 2nd Edition. It's in Dover, and it's extremely thorough for being so brief.
     
  13. lethe Registered Senior Member

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    2,009
    the quote is "You do not really understand something unless you can explain it to your grandmother." attributed to Einstein.

    i strongly disagree with the sentiment. i can't even explain how to work the VCR to my grandmother. does that mean i don't understand the VCR? I can solve a Rubik's cube in 1:30, but I can't explain how to solve it, even to very smart people, without hours to spare and a chalkboard.
     
  14. MacM Registered Senior Member

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    HeHe I would have to agree.

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  15. dixonmassey Valued Senior Member

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    You can explain principles of VCR's operations in two sentences/no formulas to the more or less prepared audience. Rubik's cube is not exactly a physical phenomenon but mechanical principles of its work (hinge joints and so on) could be explained without formulas. Solving the cube is totally another matter.

    Should math come in the front of the phenomenological understanding or not? Should you have the faintest grasp of the physical principles before writing tonnes of formulas and simulations in order to deduct the very same principles?

    In a graduate school, I had a direct boss - professor in the applied math. We worked together on the "basic materials science" project. Professor had superb knowledge of math/programming (she was a lousy teacher though, very lousy) and zero knowledge of physics/materials science. God, her "advanced" simulations (which, I guess, were done very well from a mathematician's standpoint) were utterly worthless otherwise. Eventually, somewhow she managed to play with bunch of stuff in her code to match experimental data and simulations. However, in my opinion, those "simulations" showed nothing/explained nothing except proving the obvious truth "when somebody plays with a code for a long time he'll get what he/she wants". 80-90% of professors/principal "investigators" out there are engaged in the similar worthless projects of the zero value for the science and technology (not speaking of the generating mountains of waste).

    I understand well all the math behind the Energy concept. Still, all the math does not explain the concept of energy per se. The only thing math does is to express energy in the terms of other concepts. The other concepts are expressed in the terms of Energy in order to explain them (In college physics books, at least).
     
  16. dixonmassey Valued Senior Member

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    2,151
    "Holy spirit, etc." and "Energy" concepts have at least two things in common: both are used to explain how world works (by different groups of people), neither group of folks can explain what exactly primary mover of their Universe is about.
     
  17. PhysMachine MALLEUS SCIENTIARUM Registered Senior Member

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    Energy is just that, it's a physical quantity related to work. It drops out mathematically from Newton's laws, and all of the other things that we do with energy can be derived starting from Newton's laws. So really energy is a quantity changed by a force acting on a system of particles over a given displacement, so that's what energy is.
     
  18. dixonmassey Valued Senior Member

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    2,151
    then, what is force?
     
  19. PhysMachine MALLEUS SCIENTIARUM Registered Senior Member

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    Force is something we take as a postulate that, through experimental work, has been shown to be equal to the mass times the acceleration. We just assume it in Newton's laws, and experimental evidence has supported that it works time and again. It's fundamental, so you can't "derive" Newton's laws from anything more fundamental. Nobody has any idea why Newton's laws work, it's just that they do.
     
  20. Silas asimovbot Registered Senior Member

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    1,116
    Newton didn't invent the terms "Force", "mass" and "Energy", but having found clear mathematical relationships in the movements of bodies, he applied those terms to the various mathematical parts of his equations.

    You have a ball on a table. If you apply a constant pushing motion the ball will accelerate. We can measure acceleration precisely using distance and time, two absolute fixed values. Using the same constant force we push different sized balls, until we discover a ball which when pushed has precisely half the acceleration of the first one. This ball has exactly twice the amount of "matter" in it as the first one. Now we can measure "mass", and by creating a combination of different masses we now have something we can put on a balance and measure the masses of other objects. Now we take a mass and we apply different pushes to it until we have a push which accelerates the 2 x m object at the same rate as the first object. Therefore a force twice as large was being applied, and we have a means of measuring force. All of this implies the ability to apply forces, and the amount of force-applicability of something is a limited supply. Allow a spring to pull an object, and eventually the spring will reach equilibrium and stop pulling the object. Allow a ball to roll down a slope and up another slope, and the ball will slow down (due to the opposing force of friction) and finally whatever it is about the position of the ball that allows it to move will "run out". The Use-up-ability of the moving forces is what we call energy.

    So lets return to the questions:

    What is energy?

    What is charge?

    What is force?

    What is mass?

    What is....?

    The answer is that "energy" is the term we use to describe the amount we can move objects using force. We plug this "energy" term into our equations and we know how long we can move stuff for. "Charge" is the term we use to describe the affectability of an object to an electromagnetic field. We plug this "Charge" term into our equations and we know how much a forcefield will move a charged object like an ion. "Force" is the term we use to describe how hard we can push stuff to move it. We plug this "Force" into our equations and we know how much acceleration a given mass will achieve. "Mass" is the term we use to describe how hard we must push something to get it to move as we want - objects with more mass are harder to push. We plug this "mass" term into our equations and we know how much force to apply.

    My point is this: We don't know what "energy", "charge", "mass", "force" are - but if we did know, we wouldn't be able to do anything with that! The words are what we plug into mathematical equations to get answers. It is the mathematical equations that are useful, that are practical. Asking "What is force" doesn't help you apply your knowlege. But F=ma does help.

    Richard Feynman ran into this problem when assessing physics text books for use in schools. There was a page showing, i don't know, the sun, a windmill, a boy on a bicycle, and asking of each of them, "What makes it go?" And he thought he had a good idea of how it was going to explain how the heat of the sun moved air in the atmosphere, moved a windmill which ground corn to make food to feed the boy, or whatever. But when he turned the page he found it just said, for each illustration, "Energy makes it go". But that doesn't tell you anything! You might as well say, "Pixies make it go"!

    At the end of the day, there are only equations. Stephen Hawking said, "Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?" That is a fundamental question, but it may be unanswerable. The only way to a unified theory is to continue with the mathematical work. The fact that our descriptions of phenomena are all mathematical does not mean that we cannot discover answers through them. In fact the reverse is true. We cannot discover a unified theory without a fundamental understanding of the existing theories, that they are right as far as they go, and that they work as far as they go.
     
    Last edited: Sep 2, 2004
  21. MacM Registered Senior Member

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    10,104
    Unfortunately, this only tells us what energy can do or has done. It does not tells us what energy is.

    If I had to make some sort of guess or give a description I would think it is some form of excess pressure generated at the time of the Big Bang or an ongoing creation of space which seeks to stabilize at its lowest common level - i.e entrophy. That suggests a flowing space causing gravity and the illusion of time flow.

    Could be BS but then I haven't seen anyother descriptions.
     
  22. Paul T Registered Senior Member

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    Yep...it is a BS guess!
     
  23. MacM Registered Senior Member

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    10,104
    Yep, and as I stated I don't see your description. Perhaps you could enlighten us with a better one.
     

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