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What is non-Modern physics called?

  1. Aug 19, 2012 #1
    Is there a specific way of referring to physics before relativity and quantum theory? Whenever I want to refer to this category of physics my tongue keeps slipping and I keep saying "classical physics." Every single time I have to correct myself. I was tempted to say Newtonian physics, but there was much of pre-relativity and pre-quantum physics for which Newton was not responsible for, for example, Hamiltonian & Lagrangian mechanics, Electromagnetism, Thermodynamics.

    So what do I call classical physics without relativity?
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  3. Aug 19, 2012 #2
    I too have felt a need to talk about physics before relativity. However, the phrase "classical physics" is misleading. You are correct.
    "Classical physics" is usually considered nonquantum physics. Classical physics can contain relativity. Furthermore, electromagnetic theory and thermodynamics are not 100% consistent with Newton's Principia.
    I use the adjective "prerelativity" for the type of physics that you are talking about. Since quantum physics developed after relativity, "prerelativity" physics includes all physics before quantum physics. However, I suggest that prePlanck physics may be better. It was Planck's work on blackbody radiation that really blew physics theory up.
    "Prerelativity physics" removes most of the ambiguity that we are talking about. Of course, it doesn't remove the ambiguity 100%. But it helps. The 1905 date of Einstein's paper in which he defines relativity is a nice sharp line for distinguishing prerelativity physics from "post relativity physics". If you have to chose an arbitrary date, then that is the date to choose.
    Maxwell's equations, thermodynamics and wave optics are all "classical physics" yet not "Newtonian". They also happen to have been developed before quantum mechanics.
    I count the birth of quantum mechanics as Planck's blackbody fomula, presented in 1900. So anything before the blackbody article by Planck is to me nonquantum. There is only a short span of time between the blackbody article by Planck's 1900 paper and Einstein's 1905 paper. I think that Planck's blackbody paper was a real milestone in modern physics. One or two papers by H. Lorentz occurred between 1900 and 1905. Lorentz pointed out that electrodynamics contradicted Newtonian physics to a degree. So I believe that Planck and Lorentz essentially killed "preModern physics".
    Einstein basically buried "premodern physics", but the other two physicists (Planck and Lorentz) murdered it in cold blood. So I think of any new laws of physics during or after 1905 as "modern physics" and any laws of physics before 1900 as "old fashioned physics.
    There are little fuzzy problems with the phrase "prerelativity physics". The theory of electrons, developed by H. A. Lorentz, is very close to relativity. Some argue that it is relativity. This I consider on the arbitrary line between postrelativity and prerelativity. If you want to discuss this physics, just call it "the theory of electrons".
    Note that the third law of thermodynamics contradicts Newtonian physics, but is consistent with quantum mechanics. There are also some other conundrums in "prerelativity physics" that had to be solved much later with quantum mechanics. Some of these prerelativity conundrums had to be solved years after the 1905 paper by Einstein.
    Try "prePlanck physics" for the physics that you are talking about. Anything before Planck's 1900 paper includes neither relativity nor quantum mechanics. However, prePlanck physics can contain wave optics, thermodynamics, and Newtonian physics. Anything after Lorentz's 1904 paper is "modern physics". Modern physics contains relativity and quantum physics. Lorentz can be called "transitional physics." Lorentz working with prePlanck physics, but opened the door to relativity.
    Last edited: Aug 19, 2012
  4. Aug 19, 2012 #3


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    When I hear or see "classical physics" somewhere, it (nearly) always means "nonrelativistic" and "without quantum theory", and I use it in the same way. It includes Newtonian mechanics with Maxwell equations and the Lagrange/Hamilton formalisms, thermodynamics, fluid dynamics and whatever else, as long as it does not require or use SR/GR or quantum mechanics.
  5. Aug 19, 2012 #4
    The textbooks on "classical mechanics" always include relativity. Maybe the reason is that H. A. Lorentz derived many "relativistic formulas" with small modifications of Newton's Laws. Relativity did not break as many conceptual barriers as quantum mechanics.
    Regardless, when shopping for textbooks one has to use the physics jargon. A textbook called "Classical Mechanics" always includes special relativity.
    I think we do need a term for physics without relativity or quantum mechanics. I suggested prePlanck physics in another post.
  6. Aug 19, 2012 #5
    If you're talking about using Newton's laws as the method for approaching problems, say Newtonian physics.

    If you're talking about using Hamiltonian/Lagrangian (non-relativistic) as the method for approaching problems, say Analytical Mechanics.

    You could lump SR with E&M if you wanted.
  7. Aug 19, 2012 #6
    So optics is part of relativity? Electrostatics is part of relativity? General relativity has nothing to do with E&M?
    I can see optics is part of E&M. However, relativistic optics is only a small part of optics. Most optics was developed long before Einstein's 1905 paper.
    I can see how electrostatics and magnetostatics are part of E&M. However, electrostatics developed a long time before Maxwell's equations. Benjamin Franklin was famous for his experiments in electrostatics.
    Even Maxwell's equations are not necessarily part of special relativity. Without electric current, Maxwell's equations are invariant to both Galilean (i.e., Newton) and Lorentzian (i.e. relativistic) transformations. What makes it either Galilean or Lorentzian is the effect of time delay on the dynamics of the electric current.
    General relativity does include the effect of electromagnetic forces. There are several optical effects studied that general relativity. SR isn't a logically complete theory because it doesn't include accelerating observers. Therefore, leaving GR out of this category wouldn't be advisable.
    The OP wants to separate the hypotheses of modern physics from earlier physics. Electricity and magnetism has been studied for far longer than special relativity. So lumping these things together is not convenient for historical discussions.
    For historic discussions, I suggest that it would be useful to set dates. All physical hypotheses made before Planck's 1900 paper on black body radiation is the "old physics." Any physical hypothesis made after Einstein's 1905 article on special relativity is "modern physics." Any physical hypotheses made between 1901 and 1904 inclusive should be called "physics in transition".
  8. Aug 19, 2012 #7
    I'll have to read that later, but if you're in a weak gravitational field (AKA using Newtonian gravity is okay) and travelling at relativistic speeds then you can lump SR with E&M.

    I'll add more to this later.
  9. Aug 20, 2012 #8


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    Since Eienstein's work was so early in the 20th century, it would be a good description to call it 19th century physics.
  10. Aug 20, 2012 #9
    I really do not know much about this to be honest, but having a quick look at wikipedia, it says that it depends on the subject at hand.

    But I am not sure how accepted or common this is. Also, what if you're having a conversation in general, which do you use? :/
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