general relativity
From Tech2.org, Feb. 16, 2021: Though the findings from the Holometer mean that, for now, scientists still haven’t found a way to solve general relativity with quantum mechanics, its design and the research it enabled will shape future efforts to prove the intersection of relativity and quantum mechanics at Planck scales.
From The Great Courses Daily, May 5, 2020: Fermilab scientist Dan Hooper writes about how Einstein’s failure in achieving a unified field theory didn’t stop the others. Physicists continue to search for a theory of everything that unites the effects of general relativity with the quantum mechanical nature of our world.