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There is possibly some idiom or saying like this, "If you try too hard for something, you will never get it. If you do not aim for something, it may fall on you accidentally, not as you originally planned."

In physics, or generally in science, there are many moments where success and triumph come from the accidental, unplanned attempts. Moreover, there are some cases that originally were attempts for one specific question or a goal, but solved another seemingly unrelated problem, or reach seemingly opposite goals. There are these kinds of moments leading to a breakthrough of physics or science.

For example,

  1. Yang-Mills theory: The original paper has attempted to explain a theory of nucleons, such as neutron and proton interactions with isospin symmetry, but it turns out that Yang-Mills theory as a non-Abelian gauge theory is suitable to describe a more fundamental subject, the gauge fields coupled to quarks and leptons in the standard model (EM, and especially the weak interaction and the strong interaction.)

  2. $Z_2$ topological insulator in 2+1D: the original paper of quantum spin hall effect from Kane and Mele is about graphene. But it turns out that the phenomenon is not present in graphene (C Kane jokes on this accident himself), but the physics is profound and correct, and later realized in CdTe/HgTe/CdTe quantum wells with a 2D film HgTe sandwiched.

[Question]: Can any of the readers here list more? Both in theory or in experiments. Making an inspiring list for eager-minded scientists at Phys.SE here. To give us some inspiration and high motivations to be subconsciously aware of those random accidental moments.

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closed as too broad by John Rennie, dmckee Aug 22 '13 at 14:31

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ I'm sure it used to be that list questions were explicitly banned, though I've had a quick look at the faq and I can't see anything to that effect. However I'd guess the question will be closed on the grounds of being too broad. $\endgroup$ – John Rennie Aug 22 '13 at 10:51
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    $\begingroup$ The relevant meta question is, I think, Good list, bad list. $\endgroup$ – Emilio Pisanty Aug 22 '13 at 10:55
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    $\begingroup$ Should be made community wiki. $\endgroup$ – Deer Hunter Aug 22 '13 at 13:25
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    $\begingroup$ @dmckee and such questions do the site a better service in attracting new good experts because they are interesting than the lazy effortless low-level one-liners it gets flooded with and which are allowed to hang around and get answers of the same kind ! $\endgroup$ – Dilaton Aug 22 '13 at 15:10
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    $\begingroup$ I will be happier to see this question to survive here, instead of being closed or removed. This question does the job to examine those important physics breakthroughs - how accidental the discoveries were made. It is totally a nontrivial creative question, because "accidental" and "breakthrough" together are nontrivial. You can have many accidents, and you can have some breakthroughs, but usually not together. I will bet that the list of these accidental important breakthroughs is finite many, possibly an order of 100, much less than 1000. $\endgroup$ – wonderich Aug 23 '13 at 10:28
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A few more here:

Fractional quantum hall effects: had heard that the large magnetic field is originally aimed to see the Wigner crystal effect, instead of testing quantum hall physics.

Asymptotic freedom (QCD running couplings to small at high energy): from Wilczek's book ``Longing for the Harmonies,'' at that time David Gross originally aimed to prove that QFT cannot explain the Bjorken scaling, i.e. prove that (non-Abelian) QFT always lead to large coupling at high energy, simply that QFT cannot explain the couplings run to small at high energy. But the final result is the opposite. And they won the Nobel Prize.

String theory: originally aimed for explaining strong interaction, but not as successful as QCD. String had then been abandoned for a long while. Later string theory turned out to be a candidate for a theory of everything.

Inflation(cosmology): Alan Guth firstly studied particle physics and magnetic monopole in grand unified theory(GUT). He encountered the magnetic monopole problem (the sparsity of magnetic monopoles in the universe). Initially there is no significant progress. But he and colleagues turned out to detour to use a theory of supercooling to understand the phase transition of the early universe, which produces a false vacuum then decay to produces Inflation. This new idea discovery of Inflation goes backward solving the magnetic monopole problem.

The non-existence of luminiferous ether: Michelson and Morley had initially hypothesised that luminiferous ether exists, but they ended up showing otherwise.

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The Stern-Gerlach Experiment: originally setting out to corroborate the Bohr-Sommerfield hypothesis that the direction of the angular momentum of an atom is quantized, it was eventually realized that the proper interpretation of the observations was as the first evidence of particle spin and that the electron is a spin-1/2 particle.

The Spin-Statistics Theorem: I can't imagine anyone expected this jewel to pop out of the union of quantum mechanics with special relativity.

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  • $\begingroup$ actually Spin-Statistics Theorem may not need to have special relativity. What you implied may be is the CPT theorem derived in QFT. For Spin-Statistics, Quantum mechanics alone is good enough to derive. ps. In 2+1D, using fermions as the string ends, doing the trick of Feynman's plate also can show Spin-Statistics Theorem. Levin-Wen String-net also does the job to show Spin-Statistics Theorem. It will also be better to say what this is accidental and unplanned from a historical viewpoint. $\endgroup$ – wonderich Aug 23 '13 at 10:22
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Discovery of X-rays: it happened when Röngten discovered that some photographic plates received radiation even if they were unexposed.

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    $\begingroup$ Pls check this: I'm pretty sure you're confusing Röntgen with Becquerel $\endgroup$ – WetSavannaAnimal Aug 22 '13 at 13:37
  • $\begingroup$ @WetSavannaAnimalakaRodVance Becquerel discovered radioactivity, Röngten X-rays $\endgroup$ – chuse Aug 23 '13 at 13:12
  • $\begingroup$ Agreed, but I seem to recall the photographic plates were Bequerel's detector, whereas Röntgen I think used something different. $\endgroup$ – WetSavannaAnimal Aug 23 '13 at 13:14

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