I was going through some old files of mine and found a document with quotes from famous physicists on quantum mechanics. While the quotes were all interesting, they were not exactly scientific or at least were free of scientific context, and many if not most were from the first and second generations of quantum physicists. So I thought I’d add a few quotes I’ve found interesting that I’ve used or come across lately:

“The notion of Physical Object is Untenable”

D’Ariano, G. M. (2015). It from Qubit. In *It From Bit or Bit From It?* (pp. 25-35). Springer International Publishing.

“We now know that the moon is demonstrably not there when nobody looks.”

Mermin, N. D. (1981). Quantum mysteries for anyone. *The Journal of Philosophy*, *78*(7), 397-408.

“The only reality is mind and observations”

Henry, R. C. (2005). The mental universe. *Nature*, 436(7047), 29-29.

“The laws of quantum physics are in conflict with a classical world, in particular, with local and macroscopic realism”

Kofler, J., & Brukner, Č. (2008). Conditions for quantum violation of macroscopic realism. *Physical review letters*, *101*(9), 090403.

“Ever since the earliest days of quantum mechanics (hereafter QM) it has been appreciated that there are major difficulties in reconciling the account it gives of the behaviour of the microscopic world of atoms and electrons with the classic notion of ‘realism’, which crudely speaking is the postulate that physical objects have definite properties, and occupy definite states, independently of whether or not they are observed.”

Leggett, A. J. (2008). Realism and the physical world. *Reports on Progress in Physics*, *71*(2), 022001.

“Materie nicht aus Materie aufgebaut ist”

Dürr, H-P. (2009). *Warum es ums Ganze geht: Neues Denken für eine Welt im Umbruch*. oekom verlag.

In classical mechanics, dynamical variables were implicitly assumed to be precisely measurable at all times, from which it followed that any mathematically well-defined function of the dynamical variables was precisely measurable at any time. Quantum mechanics severed the ‘natural’ link between the two concepts. Two observables, well-defined at all times, would be simultaneously measurable only if they commuted with each other. However, a *single* observable could always be measured precisely. Although the details are well known, it may be worth recalling that while it was the uncertainty principle that unsettled the theorists, what the experimentalists were unearthing were *effects of the superposition principle*, with measurement errors that far exceeded the uncertainty principle constraints.

What may be less well known (except to quantum field theorists) is that relativistic quantum field theory demands a severance of the link between being well defined and being measurable at yet another level. The classical electromagnetic field is well defined – and therefore measurable – at every point of space-time. However, **no component of the quantized electric or magnetic field is precisely measurable at any point**.” (italics in original; emphasis added).

Sen, R. N. (2010). *Causality, Measurement Theory and the Differentiable Structure of Space-Time* (*Cambridge Monographs on Mathematical Physics*). Cambridge University Press.