ABSTRACT
Usually you have information about two of these components and will attempt to make deductions about the third. We will briefly consider three examples in which the unknown being investigated, shown in bold print, shifts from input to system to output:
Experiment 1 uses the radiation from a star as the input to a telescope with a spectrometer attached so that the wavelengths of the light can be measured. By comparing these wavelengths with those produced by similar sources on Earth one calculates the red shift in the light emitted by the star, from which the rate of expansion of the universe is deduced.
