Underdetermination
Meta-science, Willard Van Orman Quine
In the philosophy of science, underdetermination or the underdetermination of theory by data (sometimes abbreviated UTD) is the idea that evidence available to us at a given time may be insufficient to determine what beliefs we should hold in response to it.[1] Underdetermination says that all evidence necessarily underdetermines any scientific theory.[2]
Underdetermined ideas are not implied to be incorrect (taking into account present evidence); rather, we cannot know if they are correct.
To show that a conclusion is underdetermined, one must show that there is a rival conclusion that is equally well supported by the standards of evidence. For example, the conclusion "objects near earth fall toward it when dropped" might be opposed by "objects near earth fall toward it when dropped but only when one checks to see that they do." Since one may append this to any conclusion, all conclusions are at least trivially underdetermined. If one considers such statements to be illegitimate, e.g. by applying Occam's Razor, then such "tricks" are not considered demonstrations of underdetermination.
Arguments involving underdetermination attempt to show that there is no reason to believe some conclusion because it is underdetermined by the evidence. Then, if the evidence available at a particular time can be equally well explained by at least one other hypothesis, there is no reason to believe it rather than the equally supported rival, which can be considered observationally equivalent (although many other hypotheses may still be eliminated).
Underdetermination is often presented as a problem for scientific realism, which holds that we have reason to believe in entities that are not directly observable (such as electrons) talked about by scientific theories. […]
A more general response from the scientific realist is to argue that underdetermination is no special problem for science, because, as indicated earlier in this article, all knowledge that is directly or indirectly supported by evidence suffers from it—for example, conjectures concerning unobserved observables. It is therefore too powerful an argument to have any significance in the philosophy of science, since it does not cast doubt uniquely on conjectured unobservables.