http://preposterousuniverse.blogspo...erousuniverse_archive.html#110703702965929900 David Gross listed the "25 most important questions in physics" John Ellis reported the list in his "Quantum Diary" and Sean Carroll put it on his blog. here is just the first 13 questions on the list. If you want to see the rest visit Carroll's blog, "Preposterous Universe". 1 - The origin of the Universe: Was there a Big Bang, was it preceded by a Big Crunch, .... 2 - The nature of Dark Matter: Is it composed of some unknown elementary particle, if so, what .... 3 - The nature of Dark Energy: What is its microphysical origin, is it constant or varying .... 4 - The formation of structures in the Universe: Testing the standard Cold Dark Matter paradigm, formation of stars .. 5 - The validity of General Relativity: Does it work at all scales, in strong fields, .... 6 - The validity of Quantum Mechanics: Is it modified at short distances, for large systems, in the Universe ... 7 - The problems not solved by the Standard Model of particles: Particle types, masses and mixing, unification of forces .... 8 - The existence of supersymmetry: Does this framework for new physics appear at accessible energies .... 9 - The solution of QCD: Can it be solved analytically, e.g., via a string model .... 10 - The nature of string theory: What is it .... 11 - The nature of space and time: Are they fundamental or emergent phenomena .... 12 - Whether the laws of physics are unique: Perhaps they are statistical accidents .... 13 - Can kinematics, dynamics and initial conditions be separated: Perhaps they cannot be disentangled .... -------- I like question 13. I have suspected for some time myself that they cannot be disentangled, or at least that I would never be able to make a clear distinction. A fair number of Gross questions are issues for Quantum Gravity (inclusive of Loop Quantum Cosmology, of course, and research where QG contacts MOND). Namely 1,2,3,5,6, and 11. And yes, number 11, that is Gross way of stating the central issue in Quantum Gravity, essentially the effort to arrive at a quantum theory of what space and time are, and how they are shaped. "The nature of space and time. Are they fundamental or emergent?" If what he means is what we see (flat old Euclidean space) then it surely is not fundamental! It must be a macroscopic impression emerging from some deeper reality. But emergent from what? A combinatorial set of relationships as in the "dynamical triangulation" model? An evolving network of interconnections à la Loop? A quantum logic of adjacency, an algebra furnished for the amusement of seven-dimensional birds? I will stop here.