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I Most fundamental quantity in physics

  1. Dec 20, 2016 #1
    So out of the concepts such as mass, momentum, angular momentum, fields, etc what is the most fundamental in physics?

    I'm thinking energy since the lagrangian shows up almost everywhere, not just in classical mechanics.

    But I'm not sure since I haven't looked deeply into all fields of physics yet.
     
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  3. Dec 20, 2016 #2
    I am thinking energy and field, since all particles of the standard model correspond to excited energy states of the underlying field. Also all the particles gain mass (and with mass (and velocity) comes momentum linear or angular) by interaction with the higgs field.
     
  4. Dec 20, 2016 #3

    sophiecentaur

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    My opinion is that Physics is the study of relationships between quantities so you would need at least two.
    It's not a beauty contest, though.
     
  5. Dec 20, 2016 #4

    Vanadium 50

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    If you search for this here, you will find dozens of threads on this, mostly closed. Closed because it is an ill-formed question. Unless you can come up with a metric where someone else can show that resistance has a fundamentality of 6 and reflection has a fundamentality of 11, it all boils down to "how fundamental does FallenApple think it is?" We're not mind readers, so this never works out.
     
    Last edited: Dec 20, 2016
  6. Dec 20, 2016 #5
    Just as Occam's razor fails due to a lack of widely applicable definition for "simple" this discussion fails for lack of a widely applicable definition of "fundamental." Those who define simple and fundamental one way will come to different conclusions from those who define simple and fundamental a different way.

    Terms like "simple" and "fundamental" are really more like "beautiful" than they are like "energy" or "mass."

    Lots of folks think they know what they are, but it is very challenging to formulate a definition that will get enough widespread agreement to be useful.
     
  7. Dec 21, 2016 #6
    Quantity of people studying physics. Most important number.

    -Dave K
     
  8. Dec 21, 2016 #7

    ZapperZ

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    This is VERY confusing. Your title does not match the content of your post. "mass", "momentum", "energy", etc. are QUALITIES, not QUANTITIES. Quantities are "numbers", "values", such as physical constants.

    A very valuable lesson that can be learned form PF is the realization that your question is almost as important as the answer that you seek. Vague questions will receive vague, unspecific answers. Undefined questions do not have any meaning.

    So what exactly do you want? And what is the criteria for something to be "most fundamental"?

    Zz.
     
  9. Dec 21, 2016 #8
    I mean what subsumes the others? For example, ice is just a instance of H2O. So the idea of H2O is more fundemental.

    I guess my question is, are some of those qualties just special cases of some others.
     
  10. Dec 21, 2016 #9

    ZapperZ

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    Unfortunately, that doesn't clarify anything. I could say that "ice" is a different NAME given to H2O, the same way water and water vapor are different names given to H2O in different phases.

    If you say that H2O is the molecules that MAKE UP ice, water, water vapor, and thus the MOLECULE itself is "fundamental" by your definition, then its another matter (no pun intended). However, just because H2O molecules make up ice, water, and water vapor, knowing that alone is INSUFFICIENT to allow you to describe ice, water, and water vapor. So, does this make H2O molecule "fundamental"?

    In elementary particle physics, CPT symmetry is often checked for all processes and interactions. From this alone, you can see that each of these can't be "subsumed" into the other, or else we wouldn't be carrying all 3.

    Zz.
     
  11. Dec 21, 2016 #10
    I think your question is understandable, but that the answer cannot be arrived at through scientific inquiry and is more a matter of philosophy, since "fundamentalness" is not a measurable quantity.

    -Dave K
     
  12. Dec 21, 2016 #11

    Oh ok I see. So ice isn't just H2O. It's H2O combined with the right pressure and temperature. So ice is just a combination of concepts. To say something is ice, we need to know more than it's just made of H2O.

    So for particle physics, saying that an electron is just an instance of the EM field is wrong. Because while the electron is an excitation of the EM field, it needs other things such as mass, which it gets from something else( like the Higgs field). So it's somewhat analogous to the ice example in that it gets it's structure from multiple concepts.
     
  13. Dec 22, 2016 #12
    Why cant we just agree that energy is the most fundamental(if not fundamental maybe central) concept in physics since all phenomena that exhibit time evolution involve the exchange or transform or flow of this quantity/quality/concept between different parts of the system, between particles and/or fields. Energy is what drives motion and change.

    Of course there are the static systems under study as well, but I believe static systems can be considered only macroscopically. In the microscopic world nothing is absolutely static.
     
  14. Dec 22, 2016 #13
    What about 'amount of substance'? It's just counting, which is fundamental in the sense that it's the foundation of our mathematical systems.
     
  15. Dec 22, 2016 #14
    Because we haven't defined fundamental or central.

    Intuitively I agree with you about energy. But someone else might have a different intuition.

    -Dave K
     
  16. Dec 22, 2016 #15
    True, but science is in part philosophy. For example, the common use of occams razor to settle disputes between two models is philosophical in nature.

    I think in some cases it's more clear what is more fundamental once a clear definition is reached by consensus.
     
  17. Dec 23, 2016 #16
    Science is the part of philosophy where we define things as unambiguously as possible. :)
     
  18. Dec 23, 2016 #17

    ZapperZ

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    Again, what is the criteria that you are using to categorize something to be "fundamental"?

    Is energy "fundamental"? The lagrangian and Hamiltonian have to be written down in terms of position and momentum, and the rate of change of these with respect to time. Someone who doesn't know the physics, but just looking at the math, will come to the conclusion that if "A" can be broken down and described by other varaiables, then "A" is not fundamental.

    This is why "... we can't just agree...."

    Zz.
     
  19. Dec 23, 2016 #18

    russ_watters

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    I certainly wouldn't. Though "fundamental" isn't well defined (as others have said), energy is a quantity derived from other quantities that seem to be more directly relatable to an object. Energy requires relating multiple properties and often multiple objects and reference frames, which not only makes it dependent on other things, but also, more importantly, it is totally arbitrary.
    I'm not sure I agree, but in either case:
    I'm not sure in what sense, but consider mass. Is the mass of an atom static or does it change over time? Can I change the mass of an atom by bringing another object near it (like I can with energy)? Can I change the mass of an atom by arbitrarily assigning a height to it? As I just said in another thread, I think this all makes energy nothing more than a convenient (and therefore unnecessary) bookkeeping quantity. A human convenience, not a property of an object -- though a property of human-defined systems.

    I think people place more "fundamental" (even mystical!) importance on the concept of energy than it deserves because it is so useful.
     
  20. Dec 23, 2016 #19

    Vanadium 50

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    First, action is clearly more fundamental than energy. :smile:

    Second, we can only have this discussion if we all agree on how to define fundamentality. We clearly don't.
     
  21. Dec 27, 2016 #20
    I still think my answer is the best. The most fundamental quantity in physics is the number of people studying it. If the number were 0 we would not be able to have this conversation.
     
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