Charge Invariant: Intuitive Reason?

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    Charge Invariant
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Discussion Overview

The discussion centers on the nature of electric charge as an invariant quantity in physics, exploring whether there is an intuitive rationale behind this characterization. Participants examine the implications of charge conservation and its invariance, particularly in the context of Lorentz transformations, while also addressing the philosophical underpinnings of such concepts in physics.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Meta-discussion

Main Points Raised

  • Some participants question the existence of intuitive reasons for charge being invariant, suggesting it is primarily an experimental fact.
  • One participant argues that the conservation of charge should be considered an axiom, while another counters that there are no axioms in physics, only experimental evidence.
  • There is a discussion about the ambiguity of the term "invariant," with some suggesting it refers to conservation and others to invariance under Lorentz transformations.
  • One participant mentions that the mathematical proof of charge invariance, starting from the continuity equation, is complex.
  • Historical examples are provided, such as Ben Franklin's assumptions about charge flow and Einstein's postulate regarding the constancy of the speed of light, to illustrate how concepts in physics have evolved from educated guesses to experimentally supported theories.

Areas of Agreement / Disagreement

Participants express disagreement regarding the characterization of charge invariance as an axiom versus an experimental fact. The discussion remains unresolved, with multiple competing views on the nature of charge and its invariance.

Contextual Notes

Participants highlight the dependence of the discussion on definitions of terms like "invariant" and "axiom," as well as the historical context of scientific assumptions and their evolution through experimental verification.

Swapnil
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Why is charge an invariant quantity? My professor once said that that is an experimental fact. I believe him. But is there an "intuitive" reason for why a charge should be an invariant quanity?
 
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Swapnil said:
Why is charge an invariant quantity? My professor once said that that is an experimental fact. I believe him. But is there an "intuitive" reason for why a charge should be an invariant quanity?
No, there is no intuitive reason that I know of. The conservation of charge is simply taken to be an axiom in physics.

Pete
 
I dislike that wording. There are no "axioms" in physics. There is only "experimental evidence".
 
Swapnil said:
Why is charge an invariant quantity? My professor once said that that is an experimental fact. I believe him. But is there an "intuitive" reason for why a charge should be an invariant quanity?
"invariant" here could be ambiguous. If you mean "conserved", that is an experimental question with overwhelming experimental verification.
More likely, it means invariant with respect to a Lorentz transformation. This can be proven mathematiclly, starting with the continuity equation
(which follows from charge conservtion).
The proof is a bit tricky.
 
HallsofIvy said:
I dislike that wording. There are no "axioms" in physics. There is only "experimental evidence".

There have been many axioms or assumptions (educated guesses in physics). For instance, Ben Franklin and his GUESS that it was positive charge that was free flowing in the wire. Positive charges DO flow in the direction opposite the electrons, but Franklin believed it was the positive charges in the wire that were the physical objects moving, which is the opposite of what we know now.

Also, the idea that the speed of light was constant was in fact an axiom (Einstein calls it a POSTULATE) in his original paper. There was no experimental evidence for this. Just as Newton assumed all of his laws are the same in all inertial frames, Einstein assumed ALL laws of physics, beyond Newton's, were the same.
 
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