Editing Classical physics (section)

== Comparison with modern physics ==
In contrast to classical physics, "[[modern physics]]" is usually used to focus on those revolutionary changes created by [[quantum physics]] and [[theory of relativity]].<ref name=Krane-2019>{{Cite book |last=Krane |first=Kenneth S. |title=Modern physics |date=2020 |publisher=John Wiley & Sons, Inc |isbn=978-1-119-49548-2 |edition=4 |location=Hoboken, New Jersey}}</ref>{{rp|2}}  

A [[physical system]] can be described by classical physics when it satisfies conditions such that the laws of classical physics are approximately valid.

In practice, physical objects ranging from those larger than [[atom]]s and [[molecule]]s, to objects in the macroscopic and astronomical realm, can be well-described (understood) with classical mechanics. Beginning at the atomic level and lower, the laws of classical physics break down and generally do not provide a correct description of nature. Electromagnetic fields and forces can be described well by classical electrodynamics at length scales and field strengths large enough that quantum mechanical effects are negligible. Unlike quantum physics, classical physics is generally characterized by the principle of complete [[Scientific determinism|determinism]], although deterministic interpretations of quantum mechanics do exist.

From the point of view of classical physics as being non-relativistic physics, the predictions of general and special relativity are significantly different from those of classical theories, particularly concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Traditionally, light was reconciled with classical mechanics by assuming the existence of a stationary medium through which light propagated, the [[luminiferous aether]], which was later shown not to exist.