What are some misconceptions about quantum physics?

Here are some I’ve heard or read, time and time again :
  1. Quantum physics is the physics of microscopic scale.
    This is true, but misleading. Quantum physics work at all scales, but we see quantum effects occur naturally when the action is low.
    In fact, nanophysics and meta-materials, and quantum information all involve endeavours to extend quantum properties (coherence) to larger scales of space, time and energy.
  2. It is impossible to simultaneously know the position and the momentum of a system.
    This is also misleading. It’s not a matter of knowledge, it’s a matter of definition. Heisenberg’s inequalities do not mean that you don’t have access to both informations simultaneously, they mean that those quantities are not defined simultaneously below a given uncertainty.
    Also, I’d rather call them Heisenberg’s inequalities rather than principle. Calling them principle makes it sound like scientists created it as some sort of axiom, and that they would live in the fear that one day, Heisenberg’s inequalities may be violated.
    In fact, it’s kind of the other way around. Exepriments hinted at a wave-like behaviour for low actions, and so the wavefunction formalism was established. The principle is the fact that quantum systems are represented by an abstract wavefunction. And the automatic consequence, by Fourier analysis, are the Heisenberg inequalities.
  3. Quantum mechanics and relativity are incompatible.
    Again. This is misleading. Quantum mechanics and relativity are compatible, and one of the most important equations in physics is simultaneously quantum and relativistic : the Klein Gordon equation. It’s the basis upon which quantum field theories, like QED and QCD, are built, and their predictive power is undisputed.
    The real issue is gravity for which the best model is General Relativity. But we would like to explain this interaction with a particle (graviton) and understand it with a quantum theory of gravity. In the same way the electron is an excitation of the electron-field, we would like the graviton to be an excitation in spacetime.

source and credits: quora

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