Physics: Big Ideas

Every physical theory has a domain of validity, and using a theory outside its domain is not a simplification — it is the wrong model. Understanding where each theory fails is as important as knowing how to use it where it works.

Newtonian mechanics fails at high speeds and atomic scales. Special relativity fails when quantum effects matter. No theory is universally valid. The physicist's epistemological stance — checking domain before applying — is what distinguishes physical thinking from calculation.

Conservation laws are more powerful than force equations for most problems because they constrain the outcome without requiring knowledge of the interaction details — and identifying which conservation law applies is the first analytical move, not the last.

Conservation of energy and conservation of momentum bypass the internal forces of collisions, explosions, and field interactions entirely. The physical worldview starts by identifying what is conserved and ends by checking the answer in limiting cases — the middle steps are where force equations appear, only when conservation is insufficient alone.