Conservation
Draw the complete system.
Identify every exchange of energy and momentum before interpreting a force. Symmetry arguments constrain models; they do not replace an apparatus-specific calculation.
Can the model account for the motion of the entire assembly?
Invariant Variation Problems
Connects continuous symmetries of an action with conservation laws. Translational symmetry supplies the starting point for checking total momentum of a device, its fields, and its environment.
Constraints on Stable Equilibria with Fluctuation-Induced (Casimir) Forces
Derives limits on stable equilibria sustained by fluctuation-mediated forces. For stated electromagnetic material assumptions, ordinary objects in vacuum cannot achieve stable passive levitation through these forces alone.
Averaged energy conditions and quantum inequalities
Studies restrictions on negative energy averaged along specified trajectories in quantum field theory. It also treats differences from a Casimir vacuum background, illustrating why boundary conditions must be stated when applying bounds.
The unphysical nature of 'warp drive'
Applies quantum-inequality reasoning to the Alcubierre warp-drive metric under a locally flat approximation. It finds severe wall-thickness and negative-energy requirements for that model.