Underdetermination

Natalie Wolchover, Quanta Magazine

One hears much that scientific theories are underdetermined; that through any finite collection of facts, one may draws countless explanatory theories. The existence of at least four or five theories of quantum mechanics to explain the same body of facts is an illustration, even if one of them is more popular than the others.¹ ² The Copenhagen Interpretation insists that all potencies exist until the particle is actualized by measurement. The equations don't tell us how a particle’s properties "solidify" at that moment of measurement, or "how reality picks which form to take. But the calculations work."

Although in matters of religion the existence of multiple interpretations is said to prove that there is no "there" there, it does not do so in matters of Science!™ because Invisible Sky Fairies! It is simply in the nature of theories that there can always be more than one for any given set of data. Recall how, at the dawn of the modern age there were multiple theories explaining the motions of the heavens, with the Ptolemaic theory being the most popular, the "consensus science." The calculations worked, but they did not tell us how the planets moved as they did.

But "the quanta are a hopeless mess" and it is useful to have a more homey example of underdetermination. Detective fiction is good at this: maintaining multiple theories of whodunnit until the end, when a new fact or a new arrangement of the facts collapses the potencies into an actual. The new fact may be the discovery of stellar aberration or the Afshar Experiment.

But here is an example of how a fact may support multiple theories:

Matt Briggs, the Statistician to the Stars, recently noted a kerfuffle in the rarefied world of chess.

Chess Grandmaster Nigel Short caused a stink, reaching oooo-weee! but not quite burn-him! levels, when he said that men and women are different and that men are better at chess than women.

Female chess player Amanda Ross said in response that, it is “incredibly damaging when someone so respected basically endorses sexism”. Sexism is when a disparity of any kind exists between males and females.

Let's call these the Short Theory and the Ross Theory.
So let us appeal to the Facts! In a list of living Grandmasters, there are:

• 1413 men 
• 33 women.

This fact supports Short's theory that men are better at chess.

It also supports Ross's theory that sexism in chess suppresses women's achievement.

This is why proponents of a theory are seldom swayed by the facts. Facts alone have no swaying power, since they will (and must) be interpreted in the light of some theory.


Notes:
1. Further confused by the fact that the mathematical formalism common to them all is also referred to broadly as "quantum theory." But "quantum theory" as such is not a theory. 
2. For the record, four that come trippingly to mind are:

a) Copenhagen (Bohr, Heisenberg), which reifies Aristotelian potencies until measurement collapses reality onto one of them.
b) Standing Wave (deBroglie, Bohm), in which the particle rides on the wave.
c) Many Worlds (Wheeler) in which all potencies are actualized, but in different worlds.
d) Transactional (Cramer) in which the wave travels backward as well as forward in time, thus reifying final cause.