HOW can we use the Doppler Effect in order to test whether a freshly discovered moving stream of some new and elusive kind does or does not consist of individual, discrete, countable, identifiable THINGS

Most English speaking world has a two-party system: for example in the US it's the democrats and the republicans.

In contrast,  many European countries have a multiple party system, where two parties form a coalition to rule and another party/parties are in the opposition.