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Quantum mechanics has certainly changed scientific concepts (deterministic <-> probabilistic). But to which extent did it change the scientific method? Since I perceive the scientific method more as a loose collection of principles than a standardized procedure, I would guess that it is impossible to say not at all.

Empiricism was certainly in place before the development of quantum mechanics. What about the often quoted work about falsifiability by Popper? It appeared only after quantum mechanics, however I read that he opposed the Copenhagen interpretation which became the prevailing one in science.

Is there any other scientific principle which may have been influenced by quantum mechanics?

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Quantum mechanics freed physics /science from ontology. Science relates one set of observations to subsequent observations. It does not need to, and in fact can't, base this on 'things' that 'exist'. Previously it was thought that observed phenomena were explained by the existence of objects and their interactions over time. This introduced a philosophical problem though, physical reality became a metaphysical concept. By definition the physical objects could only be inferred from observations. It's a simplifying assumption and is the basis of common-sense notions and what is called classical physics.There is however no logical justification to go from the observed regularities to concluding that they are caused by interacting 'things'. The on-vent of quantum mechanics clarified the situation. Not only is there no logical requirement to postulate physical objects but it is actually inconsistent with quantum mechanics and gives predictions that disagree with quantum mechanics. Bell's inequalities and Aspect's experiments (and quite a few others) have confirmed this. Physics in particular has been freed from the impossible metaphysical task of determining what 'exists' to finding mathematical models that empirically describe observations over time.

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  • This sounds very plausible to me (At least in my sub-field of theoretical physics I would think that this effect is there.). But does it affect other fields and are there primary historical or secondary sources which support this?
    – highsciguy
    Commented Feb 5, 2016 at 12:22
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Broadly speaking, the scientific method in physics is

1) observation – 2) theory – 3) observation etc.

1) In the case of quantum mechanics the observation of spectral lines had to be explained.

2) The Schrödinger equation, embedded in the theoretical framework of quantum mechanics, explains the discreteness of the spectral lines and facilitates computing their corresponding frequencies for the most simple atoms like Hydrogen or Helium.

3) Further subtle observations of spectral lines detected the fine structure.

4) The introduction of electron spin allows to explain the fine structure. Quantum mechanics did not change this established scientific method.

Also Popper’s emphasis on the principle of falsification is not restricted to quantum mechanics. It is an idealized description of the relation between experiment and theory, which applies to all natural sciences. Falsification is independent from Popper’s opinion concerning the Copenhagen interpretation.

A paradigm for the revolutionary step of quantum mechanics is the Heisenberg uncertainty relation. It shows that the classical concept with physical observables, having always a definite value, has to be abandoned in the domain of microphysics.

Hence from the viewpoint of philosophy of nature quantum mechanics has created a lot of deep open questions, in the domain of ontology as well as in the domain of epistemology. Does the concept of individuality pertain to microphysics, do the values of certain observables originate in the act of observation, how to speak about microcosmos with our concepts from mesocosmos? Some of these questions are examined by Heisenberg in his lecture Physics and Philosophy.

The coincidence of quantum mechanics and of the successors like quantum electrodynamics with the observed values from observation is striking. But the interpretation of the mathematical framework is still discussed. The main challenge is to explain the transfer during the act of measuremen from the microcosmic world of possibilities to the mesocosmic world of definite results. The best explanation at hand is the mechanism of decoherence.

Hence quantum mechanics provides us with an example of a theory which makes very precise predictions. But simultaneously, quantum mechanics provides a challenge for interpretation for each generation since its development at about 1925.

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  • Here is another thought: Many physics students find it more difficult to digest quantum mechanics, even though elements of the scientific method appear to be common sense for them (not a lot of time is spent on these or their history in the physics curriculums I know). Is this difficulty perhaps due to that quantum mechanics enforces deductive reasoning (while classical mechanics or electrodynamics can be approached in an intuitive inductive way)? And may the development of quantum mechanics have increased the acceptance for the deductive approach which is common to other modern theories?
    – highsciguy
    Commented Feb 3, 2016 at 20:10
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    @highsciguy The classical course in theoretical physics comprises 4 classes: Mechanics, Electrodynamics, Thermodynamics, and Quantum mechanics. In my opinion, each class requires a similar deductive reasoning: Lagrange formalism, Maxwell equations, Boltzman Stosszahlen-approach, First Quantisation.
    – Jo Wehler
    Commented Feb 3, 2016 at 20:18
  • Sure, but in Mechanics, Electrodynamics and Thermodynamics an alternative deductive (or historical) approach is also possible. For example, one can revert to school physics to obtain much of the results computed based on the Lagrange formalism. (I agree that the Lagrange formalism is taught, but maybe more for the reason that it is needed for modern theoretical physics)
    – highsciguy
    Commented Feb 3, 2016 at 20:53
  • You can't start with observation since without a guess about what's going on you don't know what to observe. You start with a problem: a flaw with an existing idea, you guess solutions to the problem, and then you criticise the guesses. This was pointed out by Popper in many places, e.g. - "Objective Knowledge", Chapter 1.
    – alanf
    Commented Feb 10, 2016 at 9:26
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    @alanf I am not quite convinced: People look up in the sky in the night. They wonder what they observe.
    – Jo Wehler
    Commented Feb 10, 2016 at 9:48
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Quantum mechanics did not much change the scientific method. Rather, it was interpreted in the light of many bad ideas about the scientific method that still have a lot of adherents today.

Instrumentalism claims that if a scientific theory predicts the results of experiments, then you can disregard the need to explain what's going on. This is an extremely bad idea since if you took it seriously you would regard experimental results as primitives that can't be questioned. But experiments are difficult to do, and you can't get anywhere with them unless you think about what's going on in reality to bring them about.

Another development was the rise of subjectivism: interpreting every idea as being about the subjective experiences of observers. Subjectivism led many physicists to think that quantum systems weren't real until they were observed, and all sorts of nonsense along those lines. As evidence, I offer one of the answers above.

Quantum mechanics can be understood as a description of how the world works, see "The Fabric of Reality", chapters 2 and 9 and "The Beginning of Infinity", Chapters 11 and 12 by David Deutsch. See also

http://www.daviddeutsch.org.uk/many-minds-interpretations-of-quantum-mechanics/.

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  • But, in physics today (I don't know about philosophy), the Copenhagen interpretation is mainstream. I think that this cannot be said about physics at the dawn of quantum mechanics. Apparently those big minds where reluctant to accept to accept this interpretation as a scientific theory.
    – highsciguy
    Commented Feb 10, 2016 at 11:32
  • As I said, quantum mechanics did not change the scientific method. Rather, it was interpreted by most physicists in the light of bad ideas about science including instrumentalism and subjectivism. The Copenhagen interpretation is both instrumentalist and subjectivist and was adopted as a result of those bad ideas. Saying that the CI is accepted today is not evidence against my point that QM made no difference to ideas about the scientific method.
    – alanf
    Commented Feb 10, 2016 at 23:19
  • I am saying that with respect to QM something changed. Physicists today seem to view QM differently then they did at the time it was found. At least for some of the founders the Copenhagen interpretation was difficult to swallow. If this has made it easier for scientists to accept this sort of interpretation then I would think that it has affected the scientific method. I do not know, however, if this can be said (are there examples for other modern concepts which Einstein's contemporaries would find difficult?). Whether the Copenhagen interpretation is good or bad is a separate question.
    – highsciguy
    Commented Feb 11, 2016 at 9:36
  • The fact that the founders of the Copenhagen interpretation swallowed the CI at all instead of working out what QM actually implies about how the world works implies that they already had bad ideas about how to do science. QM didn't change that: it just revealed a pre-existing problem.
    – alanf
    Commented Feb 11, 2016 at 11:19

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