Slide 8 of 13
Notes:
The classical concepts of waves and particles are just different aspects of the same quantum phenomenon. It’s a general principle in physics that physical quantities are defined by the way in which they are measured. Bohr realized that the measuring instruments played a more important role than had been previously assumed.
For example, to measure the position of an electron accurately meant that the the instrument used to measure it’s position must somehow confine it, but this process of localizing it is what makes it a particle. Similarly, to measure it’s wavelength accurately requires that the measuring instrument delocalize it by detecting it over a range of distance equal to many wavelengths, so that it has no well-defined position.
The measuring process inevitably affects the result of the experiment, so that there is no reality independent of the way in which it is measured.
