The following is a list of unsolved problems grouped into broad areas of physics. Is there a single possible past? What links the quantum arrow of physics 4th edition james walker pdf to the thermodynamic arrow?
What constitutes a “measurement” which apparently causes the wave function to collapse into a definite state? 3 spatial dimensions and 1 temporal dimension? Do “fundamental physical constants” vary over time? Are any of the fundamental particles in the standard model of particle physics actually composite particles too tightly bound to observe as such at current experimental energies? Are there fundamental particles that have not yet been observed, and, if so, which ones are they and what are their properties?
What is the minimum number of dimensionless physical constants from which all other dimensionless physical constants can be derived? Are dimensional physical constants necessary at all? The values of the fundamental physical constants are in a narrow range necessary to support carbon-based life. In quantum mechanics time is a classical background parameter and the flow of time is universal and absolute.