The right model depends on the evidence and the event — Physics & Environmental Science

Light can produce an interference pattern while exchanging energy in discrete photons. A photoelectric threshold tests the energy-per-photon account: ordinary subthreshold photons do not eject electrons merely because there are more of them. Above threshold, frequency affects maximum electron energy while arrival rate can affect emitted current. This is a statement about a specified single-photon regime, not a tiny-marble description of every optical experiment.

Relativity requires equally careful event definitions. Proper time is measured by a clock present at both events. A laboratory frame compares those same events with its coordinate clocks; it does not compare two arbitrary unsynchronized readings. Length contraction uses simultaneous endpoint locations in the measuring frame and is different from the appearance of a photograph with light-travel delays.

Nuclear equations balance charge and nucleon accounts while exact rest masses can differ through binding energy. The complete mass difference supplies an energy estimate only when all participants and mass conventions are consistent. Detector counts additionally depend on background, geometry, efficiency and emission yield. They are not automatically decay activity, absorbed dose or useful device power.