Thomas Young, 1801: is the light a wave or a set of particles?
Bohr argued that if we were to perform a two-slit experiment with a which-path device (which can be used to determine which slit each electron goes through on its way to the detecting screen), we would find that the interference pattern is destroyed. That is, if a measurement is made that identifies the electron as a particle, as is the case when we use a which-path detector, then the result will be a particle pattern, not the wave pattern that results when the original unmodified two-slit apparatus is used. Karen Barad, Meeting the Universe halfway, p. 103
Bohr’s argument for the indeterminable nature of measurement interactions is based on his insight that concepts are defined by the circumstances required for their measurement. That is, theoretical concepts are not ideational in character; they are specific physical arrangements. Karen Barad, Meeting the Universe halfway, p. 109