• Theory of everything: Is there a singular, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the See more

• Yang–Mills theory: Given an arbitrary compact gauge group, does a non-trivial quantum Yang–Mills theory with a finite mass gap exist? (This problem is also listed as one of the See more

• Hierarchy problem: Why is gravity such a weak force? It becomes strong for particles only at the Planck scale, around 10 See more

• Quantum chromodynamics: What are the phases of strongly interacting matter, and what roles do they play in the evolution of the See more

• Quantum gravity: Can quantum mechanics and general relativity be realized as a fully consistent theory (perhaps as a quantum field theory)? Is spacetime fundamentally … See more

• Axis of evil: Some large features of the microwave sky at distances of over 13 billion light years appear to be aligned with both the motion and … See more

• Solar cycle: How does the Sun generate its periodically reversing large-scale magnetic field? How do other solar-like stars generate their magnetic fields, and what are the … See more