Can Calculus Effectively Handle Discontinuous Fundamental Quantities?

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Discussion Overview

The discussion revolves around the applicability of calculus to discontinuous fundamental quantities in physics, particularly in the context of energy and quantum mechanics. Participants explore the implications of using calculus for functions that may not be continuous and consider alternative mathematical frameworks.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant questions the compatibility of calculus with discontinuous fundamental quantities, suggesting a potential conflict when applying derivatives like dE/dt.
  • Another participant asserts that mathematics is distinct from physics and acknowledges that no mathematical model can be expected to work perfectly, which is considered in model development.
  • A subsequent reply challenges this view, asking for clarification on the implications of mathematical inconsistencies in general relativity (GR) and quantum mechanics (QM), and whether mathematics is a discovery or an invention.
  • It is proposed that physics can be conducted without continuous quantities, although it may be more cumbersome, and that real numbers and calculus serve as shorthand for larger, well-regulated structures.
  • One participant wonders if there have been attempts to redefine calculus for discontinuous functions, particularly in relation to Planck's constant and its significance in quantum mechanics.
  • Another participant introduces the concept of discrete differential forms in differential geometry, noting their application in numerical simulations and the discretization of computations.
  • It is mentioned that discrete analogs for derivatives and integrals exist, such as finite difference operators and discrete summation, but that continuous methods are often preferred for their simplicity and reasonable results.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between calculus and discontinuous quantities, with no consensus reached on the effectiveness of calculus in these contexts or the potential for alternative frameworks.

Contextual Notes

Participants highlight limitations in applying traditional calculus to discontinuous functions and the potential need for redefined mathematical approaches, particularly in quantum mechanics. The discussion reflects ongoing uncertainties and assumptions regarding the nature of mathematical models in physics.

meaw
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i wondered at the idea that calculus works for continuous functions and in reality fundamental quantities are discontinuous. For example energy or an electron can't asume all values. Therefore isn't there a conflict when we work on a equation like dE/dt or something similar which involve calculus of discountinous things ?
 
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Mathematics is not physics. No mathematical model can be expected to work perfectly. That is taken into account when developing a mathematical model for a physical situation.
 
"No mathematical model can be expected to work perfectly" - you mean it really ? Then why are we so bothered about mathematical inconsistencies when GR and QM are put together ? Unless you are hiniting at thephylosophical question of whether maths is invented or discovered, the general believe is that Maths is reality. Maybe I misread you. Can you clarify ?
 
It is certainly possible to do physics without ever introducing continuous quantities, but it's just that much more cumbersome. In a way, we use things like real numbers or calculus as shorthands for large structures which are well-regulated. The fact that this is often ignored is an unfortunate state of affairs, but textbooks have to draw a line somewhere. In practice, physicists will often do things like use integration when they are talking about discrete sums, as long as the results are reasonable.
 
right you are. I am wondering whether any attempts have been made to redefine calculus for discountinouous functions where the discontinuity is of the order of plank's constant which can be ignored for general physics but not so for quantum mech.
 
Inside differential geometry (which is basically just calculus on curved manifolds) there is a large combinatorial, simplicial structure. Google for "discrete differential forms". These have found good use in numerical simulations, where things have to be discretised for computation. Similarly, things like lattice QCD or Regge calculus in GR have similar backgrounds.
 
There are discrete analogs for the derivative and the integral: the finite difference operator and discrete summation. It's just that a lot of the time, its much easier to do the continuous version, and the results are reasonable.
 

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