Researchers in quantum gravity seem to agree that space-time is emergent: it is made of many microscopic degrees of freedom, most probably of Planck size. Google Scholar lists many proposals: loops, chain mail, strings, trinions, twistors, causal sets, to name just a few. It seems that all these proposals are interesting and most of them yield general relativity in some suitable limit.
So far, there seems to be no consensus. But many researchers work on their own model since 20 or 30 years. How do they know that they are working on the best model? Or on the correct model?
How can or could an outsider determine which of these proposals is correct? What is the best way to compare the proposals against each other? In the end, the question is this: What is the best criterium to find out what space-time is made of?