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Recently I've read a debate over the futility of demanding "usefulness" from research endeavors, since the potential outcome is unpredictable. As evidence for this statement, a list of random papers of apparently useless or just of academical interest followed. One of them was the development of quantum theory at the beginning of the 20th century.

I don't want to focus on the topic of the debate itself. Instead, I wondered if that premise, that "quantum theory originated as a purely academical/intellectual work", is actually true. It's a post-industrial revolution world after all and patents dealing with heat/electricity maybe were driving a society's need... or maybe not. I couldn't find any evidence for or against it anywhere. I will turn, then, to people more knowledgeable than I.

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    Quantum theory originated with Planck's 1900 paper on black-body radiation, and Einstein's 1905 paper on the photoelectric effect. AFAIK, there weren't any real practical applications until perhaps half a century later, with the invention of transistors. – jamesqf Feb 11 '18 at 19:40
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    People voting to close as unclear, what is unclear about the question? I don't know if it's the type of question that admits a simple yes/no answer, but I do think it's a question that admits an answer, and I don't have any problem understanding what the OP was asking. – Ben Crowell Feb 11 '18 at 20:59
  • Indeed, both works are relevant, but electricity companies began operating around two decades earlier in Europe and the US. In that scenario, the photoelectric effect could be linked to industrial concerns of that time. Or maybe the way science was conducted in Europe by the end of the 19th century was quite detached from industry... that's my question. – one_teach_wonder Feb 11 '18 at 21:09
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    I'm voting to close this question as off-topic because it would do better on History of Science & Mathematics – Lars Bosteen Feb 16 '18 at 5:35
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As far as I can tell from the history, it would be inaccurate to claim either that quantum theory originated completely as pure research or that it had its origins in applied science. To set the stage, there are basically three time periods involved:

1900-1913: Planck's paper on blackbody radiation (1900), Einstein's paper on the photoelectric effect (1905).

1913-1927: The old quantum theory, Bohr model, BKS theory.

1927: Within the space of about a year, a new quantum theory is produced, which is essentially the theory in its modern form.

Planck was working almost totally in his own theoretical world, and his work was considered extremely obscure at the time. He made his bread and butter as a theoretician at a university. (Claims that Planck was funded by lightbulb companies appear to have been false.) Although Einstein was a fairly competent experimentalist, inventor, and engineer, and worked for a while at the Swiss patent office, his work on quanta was way ahead of its time, and seems to have been pure research, unmotivated by any applications.

As we get into the Bohr era, quantum theory per se starts to take shape, and we see a vigorous interplay of theory and experiment, often with clear applications. Spectroscopy was rich in applications before, during, and after this period. For example, people were interested in determining the composition of gases from their spectra. Moseley's work on x-ray spectra and atomic number was carried out in close collaboration with Bohr, and it resulted in, for example, the discovery of hafnium. All of chemistry is one big application of quantum mechanics, and chemistry is rich in applications. Obviously the group centered on Bohr expected their work to have applications in chemistry and atomic and molecular physics, and it certainly did.

With the advent of modern quantum theory in 1927, we very quickly start to see applications. It was only 15 years from this time until the year when the first nuclear pile was operated (1942), and I have a hard time imagining nuclear power being developed without quantum mechanics.

The history of the transistor seems to more or less coincide with the period during which quantum mechanics was developed. The first patent was by Lilienfeld in 1925, but it seems to have taken a long time for progress to be made, mainly because people couldn't purify semiconductors well enough. Lilienfeld did a PhD in physics and had Planck as one of his thesis advisors. He started out as an academic physicist at Leipzig and then transitioned to working in industry in the US.

Some of the early work on quantum physics was carried out with funding from rich individuals rather than governments or universities. The Solvay Conferences were funded by the chemist and industrialist Solvay, and the important Stern-Gerlach experiment, carried out during difficult times in Germany as hyperinflation was getting going, was paid for by US banker Henry Goldman. I would say that these links are evidence of what seems like the typical situation regarding the links of quantum mechanics to applications. People like Solvay, a chemist, surely expected there to be applications, but the applications were not expected to be immediate and lucrative, which is why Goldman and Solvay saw themselves not as investors but as donors.

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    I have to disagree with some of this. Practical use of spectroscopy & chemistry don't depend on knowledge of QM, and were fairly well-developed before the QM era. E.g. aniline dyes starting in 1856, spectroscopy from the 1860s. Of course QM gives a better understanding of why they work. – jamesqf Feb 12 '18 at 5:55
  • @jamesqf: It is true that a significant amount of spectroscopy can be done without knowing any quantum mechanics, but the discussion of Moseley and Bohr in my answer is an example of spectroscopic work that really did require significant theoretical input from Bohr. Another good example would be the visible-light spectrum of molecular nitrogen. If you don't know quantum mechanics, it's a mysterious mess of bands and lines, with no rhyme or reason. You can measure the spectrum, but you can't tell how to interpret it. Without quantum mechanics you can't systematize this knowledge. – Ben Crowell Feb 13 '18 at 20:38
  • Sure, but I think that's more of a case of discovering "Hey, this pure research applies to my practical problem!" IOW, Bohr et al didn't start doing their QM research with the goal of improving spectroscopy. – jamesqf Feb 15 '18 at 4:32
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"Quantum theory originated with Planck's 1900 paper on black-body radiation, and Einstein's 1905 paper on the photoelectric effect." - @jamesqf is right about that fact. But he is not right about the abstractness of these problems. On the contrary:

Many inventors those days tried to invent new "rays". Both problems of rays production and effects caused by rays were researched. And the target was absolutely real - to find something that is useful. X-rays were the best output. But that does not mean that other researchers WANTED to have no practical outcome. Simply sometimes they had luck and sometimes (more often) not. And the photoelectricity laws were very important for them.

The laws of black-body radiation were of use due to the problems mentioned in the previous paragraph, but not only that. Even more important theme of that time was the invention of new engines. And inventors wanted to know the laws of thermodynamics for that. And that law was also important and useful for them, for it helped to understand the subject better.

The distance between "abstract science" and "practical use" was so close in physics those days, that practically there was no abstract science in physics at all. The most abstract objects of science of these days - operators of Heavyside and quaternions of Hamilton made directly possible the lossless sending of messages and radio. But the time of separation of "abstract" science was close - Heavyside, having brought billions to telephone/telegraph companies, died in poverty, in 1920-ties in England.

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    @bof Of course. Thank you for your correction very much. – Gangnus Feb 12 '18 at 15:40

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