Dark Matter
Mysterious matter that doesn't interact with light, inferred from its gravitational effects on visible matter.
Dark Energy
Enigmatic force driving the accelerated expansion of the universe, yet its origin and nature remain unknown.
Quantum Gravity
Unifying quantum mechanics and general relativity to understand gravity at the quantum level, a major unsolved challenge.
The Nature of Time
Ongoing investigation into the fundamental properties of time, including the arrow of time and the possibility of time travel.
The Fundamental Constants
Unanswered questions about the origin and specific values of fundamental physical constants in the laws of physics.