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What is the future of quantum mechanics? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.
Answer by Akshat Mahajan, Physics major, software engineer, on Quora:
Quantum mechanics as a research discipline ended in the sixties with the advent of quantum field theory, von Neumann’s rigorous formalisation of mixed states, and Bell's theorem, with the first playing the largest role.
Together, these represent the extension of traditional quantum mechanics to:
- Include special relativity (which quantum field theory accomplishes nicely).
- Predict the existence of particle spin from first principles (thanks to the Dirac equation).
- Lay the basis for the treatment of the emergence of forces in quantum mechanics (which is why we now have quantum treatments of the electrogmanetic, strong and weak forces).
- Correctly predict thermodynamic systems (thanks to von Neumann’s invention of the density matrix, which leads to a natural definition of entropy in quantum mechanics).
- Correctly provide descriptions of materials as excitations of virtual fields (which is why a lot of modern condensed matter physics and even biophysics end up using quantum field theory).
- Establish that quantum mechanics cannot be explained by a classical theory unless information is allowed to travel faster than light.
Now that we have the theoretical basis for explaining fields, the only major unsolved problems in theoretical quantum mechanics left are:
- Questions of the interpretation of quantum mechanics, which are of more interest to philosophers of science than many practicing physicists.
- Questions of how to include gravity in quantum field theory, which actually is a critically important and active field of research today.
So there is no future for quantum mechanics, per se. It is complete for all practical purposes, except in the two cases referenced above.
The Actual Future
What remains now are not questions for quantum mechanics, but questions about the application of quantum mechanics.
An example, and easily the single most impressive problem out there in this regard:
What is the correct description of high-temperature superconductivity?
There are many others in this vein. Here is a list.
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