The wavefunction: mathematical structure or physical object?

Quantum theory uses the wavefunction to calculate successful experimental probabilities, but evidence does not uniquely determine whether it represents physical reality, knowledge, or an emergent description.

Potential tests

• Test matter interference at larger scales
• Compare phase-sensitive predictions

Dark energy: measured acceleration, unknown cause

Cosmic acceleration is supported by multiple distance and structure measurements, while the mechanism remains unidentified; current evidence strongly favors a cosmological constant, with some measurements still in tension.

Potential tests

• Jointly test expansion and structure growth
• Compare gravitational-wave distance ladders

Food-coloring diffusion in still water

A drop of dye spreads without stirring, providing a qualitative demonstration of diffusion, but temperature-driven currents can mimic or accelerate the spreading.