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The question here is the title:

Do physicists subscribe to Occam's razor? If so, how do you define 'all things being equal'?

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closed as primarily opinion-based by ACuriousMind, Gert, user36790, user10851, John Rennie Nov 21 '15 at 8:55

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ This is primarily opinion-based. Some will love Occam's razor, some will have other criteria to choose between theories all empirical facts being equal. There's no objective answer to be had here. $\endgroup$ – ACuriousMind Nov 21 '15 at 4:08
  • $\begingroup$ my actual question is what does 'all things being equal' mean in the given context... $\endgroup$ – Aaron Anodide Nov 21 '15 at 4:09
  • $\begingroup$ That the theories predict the same results for the same experiments? I don't see any ambiguity here. $\endgroup$ – ACuriousMind Nov 21 '15 at 4:09
  • $\begingroup$ I think you may have out-IQ'd me :) I think I might know what you're getting at but my brain won't materialize it for me :) $\endgroup$ – Aaron Anodide Nov 21 '15 at 4:13
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    $\begingroup$ Suppose you want to conduct an experiment to find the influence of A on B. Now since it's a reasonable suspicion that C, D, E, F etc etc may also have an influence on A, the trick is to keep C, D, E, F etc as constant as possible and only vary B in a controllable fashion. That's one meaning of 'all other things being equal'. It doesn't have much to do with Occam's Razor, AFAIK... $\endgroup$ – Gert Nov 21 '15 at 4:14
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Occam's raizor:

The principle can be interpreted as

Among competing hypotheses, the one with the fewest assumptions should be selected.

In this format it is continually used in the formation of physics theories. The simplest and more parsimonious the better. This resume about covers it:

In science, Occam's razor is used as a heuristic technique (discovery tool) to guide scientists in the development of theoretical models, rather than as an arbiter between published models. In the scientific method, Occam's razor is not considered an irrefutable principle of logic or a scientific result; the preference for simplicity in the scientific method is based on the falsifiability criterion. For each accepted explanation of a phenomenon, there may be an extremely large, perhaps even incomprehensible, number of possible and more complex alternatives, because one can always burden failing explanations with ad hoc hypothesis to prevent them from being falsified; therefore, simpler theories are preferable to more complex ones because they are more testable.

As for "all things being equal", it is not in the wiki definition. In physics it would mean, when all data are modeled/predicted by the theoretical modeling in all proposed theories, choose the simplest theory with the fewer hypotheses.

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    $\begingroup$ Nice answer. But a little critique of OR wouldn't go amiss here. $\endgroup$ – Gert Nov 21 '15 at 4:27
  • $\begingroup$ I would argue that OR is most useful in the development of embryonic theories and that when 'problems with the theory' develop, complexification is often needed. $\endgroup$ – Gert Nov 21 '15 at 4:34
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    $\begingroup$ @Gert well, then among complexified proposals the simplest should be chosen. $\endgroup$ – anna v Nov 21 '15 at 4:38
  • $\begingroup$ yes, I think that's correct. 'All things being equal' in my reading at least, refers to choosing experimental set ups that exclude uncontrolled influences by variables not actually under study. $\endgroup$ – Gert Nov 21 '15 at 4:41

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