PHYSICAL PROBABILITY?

Going back to the previous quote by Hume, an interesting, long debated issue is whether there is “such a thing as Chance in the world”, or if, instead, probability arises only because of “our ignorance of the real cause of any event.”This is a great question which I like to tackle in a very pragmatic way, re-wording the first sentence of the quote: whatever your opinion might be, “the influence on the understanding” is the same. If you assign 64% probability to event $E_1$ and 21% probability to $E_2$ (and 15% that something else will occur) you simply believe (and hence your mind “anticipates”) $E_1$ much more that $E_2$, no matter what $E_1$ and of $E_2$ refer to, provided you are confident on the probability values (please take note of this last expression).

For example, the events could be White and Black from a box containing 100 balls, 64 of which White, 21 Black, and the remaining of other colors. But $E_1$ could as well be the decay of the `sub-nuclear' particle K$^+$ into a muon and a neutrino, and $E_2$ the decay of the same particle into two pions (one charged and one neutral).Thus, as we consider the 64% probability of the K$^+$ to produce a muon and a neutrino a physical property of the particle, similarly it can be convenient to consider the 64% probability of the box to produce white balls a physical property of that box, in addition to its mass and dimensions. (It is interesting to pay attention to the long chain of somebody else's beliefs, implicit when e.g. a physicist uses a published branching ratio to form his/her own belief on the decay of a particle.And something similar occurs for other quantities and in other domains of science and in any other human activity.)