Machine Learning as Evidential Constraints in Historical Inference: The Case of Galactic Archaeology

Machine learning (ML) shows strong performance in making accurate inferences from massive, high-dimensional data. Many scientists turn to this new tool when traditional inferential procedures cannot deal with overly messy data and complex target phenomena. One example is galactic archaeology, a branch of astronomy that aims to unravel the epic history of the Milky Way using the present snapshot of stars with only a handful of physical parameters. Historical inference in galactic archaeology is difficult due to the uncertainty of what counts as evidence of past events. While ML is expected to help address such challenging situations, it comes with its own epistemological limitations. Two issues, theory-ladenness and non-uniqueness, can undermine the evidential power of ML outcomes in scientific inferences. ML’s success in aiding Galactic archaeology teaches lessons about how it can serve key epistemic functions for the historical sciences, unaffected by those two issues. I show that ML can empower the evidence-gathering procedure in science, not by outputting data to be directly taken as evidence, but as evidential constraints: ML partitions and structures data for it to be subsequently interpreted as evidence with the help of domain knowledge and inferential procedures. Used in this way, ML not only provides a solution to the ambiguity of historical evidence but also avoids its own epistemic limitations. This use of ML can be generalized to other historical sciences that engage with big data and automated inference.