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Variables & Dimensions (total noob)

  1. Jan 24, 2015 #1
    So, I have some questions regarding 'dimensions' and 'parameters' in physics. (there are differences in the meaning between physics and mathematics, as far as I understand it)
    As far as I understand it, we live in a 4-dimensional world, consisting of 3 space and 1 time dimensions. Yet we combine them to form 4 dimensions of spacetime?

    Does this mean that we only need 4 points to describe where a particle is?
    If so, that raises (at least to me) the following question:
    What are the amount of variables needed to completely describe a particle? Is that even possible?
    It would seem to me you need more information than just these 4 dimensions to describe something fully. Namely not only where it is, but also what it is.
    So what else do we need? Mass, probably? Charge? What else? Can we even assign these things, or do they only appear in relation to other objects? Can we describe a particle fully? If not, what is the maximum amount of information we can have about a particle at any given time?
    Now, let's assume we could describe a particle fully and completely with just 6 variables. 3 for space, 1 for time, 1 for charge and 1 for mass.

    What is then the difference between space & time on the one hand, and charge & mass on the other? What makes space & time dimensions, but the other's not?

    I hope somebody a little smarter than I can explain these things to me, or explain to me why I am not asking the right questions if that's the case.
  2. jcsd
  3. Jan 24, 2015 #2

    Stephen Tashi

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    Physical theories apply to certain aspects of the world, not to all aspects of it at once. When a aspects of a physical system are analyzed, the analysis defines what a "state" of the physical system is. In some physical theories, the definition of "state" says you need to specify only 6 variables per particle. I don't think such theories can completely explain the behavior of atomic particles.

    Sometimes technical terms convey technical meanings and sometimes they are just a result of tradition and culture. For example, in mathematics, the "dimension" of a vector space has a different definition that the "dimension" of a fractal object, but historically speaking, one definition motivated the other one. An explanation of why certain variables are "dimensions" can be a question of linguistics and the history of science. I don't know the historical background for why certain variables are traditionally called "dimensions" in various theories.

    To pose your question precisely, you need to specify which physical theory or theories you are talking about. To say you are talking about "the real world" doesn't say which specific theory of it you are asking about.
  4. Jan 24, 2015 #3
    Such as?

    Standard model. Does that qualify?
    If not, then what theories exactly do you mean?

    (If this is about the fact that I posted in 'beyond the standard model', that is solely because on similar forums where I have posted in the past, general models were for serious questions about physics and the maths behind it, and forum sections such as this one more about philosophy and questions for uninformed people like myself. If this was wrong I apologize)
  5. Jan 24, 2015 #4


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    Presumably, at least one day, the only other properties we will need to specify about a point are the values of the four fundamental forces. I am no expert but it seems to me, the nature of fundamental forces is that all other physical properties can be derived from those.
  6. Jan 24, 2015 #5
    Yes, thank you. That was exactly what I was thinking too. Well, those and the 4 dimensions of spacetime. Or don't we need those?
    Because again, if that is the case, what is then the difference between these 4 dimensions and these 4 forces? Is the difference purely semantics, to better explain their 'use' in our everyday life?
  7. Jan 24, 2015 #6


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    I am a little outside my comfort zone here, so take what I say with a grain of NaCl, but it seems you'd need all 8 parameters: 4 space-time coordinates and 4 force values.
  8. Jan 25, 2015 #7


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    Hi wubs23,
    maybe this article will be interesting for you to read:
    How Many Fundamental Constants Are There? (John Baez)
    (please note that the article is from 2011 so it does not reflect the Higgs detections in 2014)

  9. Jan 26, 2015 #8


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    Sorry, wrong year haha, I should have said "2012".
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