Can someone explain the following statement on page 2 of the paper regarding "our limited understanding of the space of Einstein metrics"....

I'm just asking in general, not specifically related to the paper....Is this general statement relative to our universe as well...one a positive cosmological constant?? How is our knowledge limited?? Does this imply a weakness in relativity?

Separately, anyone aware of any papers looking at a possible relationship between the Hawking-Hartle wave function and uncertainty?? Seems like, maybe, if there were wave function peaks [with a positive cosmological constant] they could be related to virtual particles and maybe quantum uncertainty?