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From the point of view of chemistry, QM “works”. It provides results that can be tested experimentally and predictions that can be validated. There are issues

From the point of view of chemistry, QM “works”. It provides results that can be tested experimentally and predictions that can be validated. There are issues with computability but that’s more engineering than science. Determining structure, spectra and other physical properties is quite helpful. What was the cliche? All theories are wrong, some theories are useful. It needs to be rephrased from vector codes into massively parallel codes but people can work with that.

jiggawatts 5y ago
To me, this always felt like programmers excusing abhorrent code with "but it works". Quantum theory isn't. It's not a single, cohesive, consistent theory.[1] There is no recipe you can apply, it's just a bunch of guessworks and heuristics that happen to produce the numerically correct equations if you keep trying long enough. This isn't secret or some sort of external criticism, you'll find this front-and-centre in the foreword of many a QM text! Schrödinger famously arrived at his equation basically through numerical methods. He just tried things until it "fit" the desired output. Now, there's nothing wrong with this, per-se. It's a perfectly viable approach for getting going, for getting something and using it as a starting point. But it isn't the endpoint, because approaches like this often have virtually no explanatory power. A similar example is collecting insects, categorising them, giving them Latin names, and putting them up for display in a museum. You can learn a lot, amass enormous amounts of information, but without a theory of genetics and natural selection you will always be blind to the underlying truth of it all. QM is just like bug collecting. We're collecting numerical equations that work, but we have essentially no clear understanding why. We've built a tree of life, and nobody has had the lightbulb moment that explains why it's a tree. [1] There was a paper published a few years back where a bunch of working quantum physicists were asked some simple multiple-choice questions about the fundamentals of the theory. There was no consensus opinion on anything! PS: You'll get similar results if you ask priests of a random Christian sects about the basics of religion. Conversely, you will get nearly zero disagreement if asking Chemists about the basics of their science.
- spekcular 5y ago
  Come on. We have plenty of good heuristics for why things are the way they are. Quantum theory is no more a bunch of "guessworks and heuristic" than Newtonian mechanics. Also, physicists disagreeing on interpretational issues related to quantum foundations is not the same thing as disagreeing about the fundamentals of the theory.
- mhh__ 5y ago
  The things that Schrodinger tried are still valid physics, just for different systems. He didn't know that, but now we do, this has little bearing on modern physics. Also chemists have the luxury of agreeing because the fundamentals of their work (not the day to day act of doing chemistry) gets to assume the presence of physics i.e. it's stampkeeping (depending on who you ask).
  - jleyank 5y ago
    Not quite stamp collecting, although botany or anatomy head in that direction. Call chemistry “just applied physics” as engineering is “just applied science”.
    - mhh__ 5y ago
      I prefer to call engineering "physics ruined by philistines" (sometimes at least, engineers seem to have a unique ability to take beautiful physics and notate it in the most cumbersome "safe" way possible)
    - dekhn 5y ago
      It's a quote ascribed to Rutherford ("all science is physics or just stamp collecting"). I also heard it when studying protein structures in the 90s (the idea being, if you're just a crystallographer cranking out more structures, you're doing stamp collecting; the real reason to determine structures is to elucidate the general principles of protein folding and function). Note that protein structure prediction finally fell to machine learning and it was "mostly stamp collecting" (IE, the accurate predictions come from subtle analysis of rich protein sequence alignments, not from understanding the fundamental principles of protein folding).

jiggawatts 5y ago

To me, this always felt like programmers excusing abhorrent code with "but it works". Quantum theory isn't. It's not a single, cohesive, consistent theory.[1] There is no recipe you can apply, it's just a bunch of guessworks and heuristics that happen to produce the numerically correct equations if you keep trying long enough. This isn't secret or some sort of external criticism, you'll find this front-and-centre in the foreword of many a QM text! Schrödinger famously arrived at his equation basically through numerical methods. He just tried things until it "fit" the desired output. Now, there's nothing wrong with this, per-se. It's a perfectly viable approach for getting going, for getting something and using it as a starting point. But it isn't the endpoint, because approaches like this often have virtually no explanatory power. A similar example is collecting insects, categorising them, giving them Latin names, and putting them up for display in a museum. You can learn a lot, amass enormous amounts of information, but without a theory of genetics and natural selection you will always be blind to the underlying truth of it all. QM is just like bug collecting. We're collecting numerical equations that work, but we have essentially no clear understanding why. We've built a tree of life, and nobody has had the lightbulb moment that explains why it's a tree. [1] There was a paper published a few years back where a bunch of working quantum physicists were asked some simple multiple-choice questions about the fundamentals of the theory. There was no consensus opinion on anything! PS: You'll get similar results if you ask priests of a random Christian sects about the basics of religion. Conversely, you will get nearly zero disagreement if asking Chemists about the basics of their science.

spekcular 5y ago
Come on. We have plenty of good heuristics for why things are the way they are. Quantum theory is no more a bunch of "guessworks and heuristic" than Newtonian mechanics. Also, physicists disagreeing on interpretational issues related to quantum foundations is not the same thing as disagreeing about the fundamentals of the theory.
mhh__ 5y ago
The things that Schrodinger tried are still valid physics, just for different systems. He didn't know that, but now we do, this has little bearing on modern physics. Also chemists have the luxury of agreeing because the fundamentals of their work (not the day to day act of doing chemistry) gets to assume the presence of physics i.e. it's stampkeeping (depending on who you ask).
- jleyank 5y ago
  Not quite stamp collecting, although botany or anatomy head in that direction. Call chemistry “just applied physics” as engineering is “just applied science”.
  - mhh__ 5y ago
    I prefer to call engineering "physics ruined by philistines" (sometimes at least, engineers seem to have a unique ability to take beautiful physics and notate it in the most cumbersome "safe" way possible)
  - dekhn 5y ago
    It's a quote ascribed to Rutherford ("all science is physics or just stamp collecting"). I also heard it when studying protein structures in the 90s (the idea being, if you're just a crystallographer cranking out more structures, you're doing stamp collecting; the real reason to determine structures is to elucidate the general principles of protein folding and function). Note that protein structure prediction finally fell to machine learning and it was "mostly stamp collecting" (IE, the accurate predictions come from subtle analysis of rich protein sequence alignments, not from understanding the fundamental principles of protein folding).