 Quantum Gravity, broadly construed, is a physical theory (still ‘under construction’) incorporating both the principles of general relativity and quantum theory. Such a theory is expected to be able to provide a satisfactory description of the microstructure of spacetime at the so-called  Planck scale,  at which all fundamental constants of the ingredient theories, c (the velocity of light in vacuo), ℏ (the reduced Planck’s constant), and G (Newton’s constant), come together to form units of mass, length, and time. This scale is so remote from current experimental capabilities that the empirical testing of quantum gravity proposals along standard lines is rendered near-impossible.