July 5, 1687: When Newton explained why you don't float away

Gravity: how vs why

• Several comments argue Newton didn’t really explain why things fall, only how fast and in what direction, via precise mathematical laws.
• Others counter that “mass attracts mass” plus Earth’s large mass is a meaningful “why” at the everyday level, and that demanding infinite deeper whys is unreasonable.
• A recurring theme: physics never reaches an ultimate “why”; it only gives successively better models whose laws make observed phenomena unsurprising.

General Relativity vs Newtonian Gravity

• General relativity (GR) is presented as a deeper framework: mass–energy curves spacetime, and motion through that curved spacetime looks like gravity.
• Some emphasize GR’s strong experimental support (gravitational waves, black holes, light bending, redshift, Mercury’s orbit, cosmic expansion) and its conceptual shift away from “forces at a distance.”
• Others stress that Newtonian gravity remains an extremely accurate, simpler effective theory in weak fields, which is why it’s still taught first and used for most engineering (e.g., rockets).

Causality and the meaning of “why”

• One side claims modern physics tightly integrates causality via the finite speed of light and evolution laws; another insists fundamental equations are symmetric constraints and don’t encode causation, only allowed histories.
• There’s debate over whether “why” questions belong in physics or philosophy, versus the view that “why” is just asking for a more general, compressive model.

Conceptual status of Newton’s theory

• One commenter calls Newton “vastly conceptually wrong” (absolute time, action-at-distance forces) and stresses that GR doesn’t just extend Newton, it replaces his ontology.
• Others reply that conceptual “rightness” should be judged by explanatory and predictive power in-domain, and that Newton’s framework is legitimately a limiting case of GR.

Principia funding and historical color

• The thread enjoys the story that the Principia was funded privately because a previous Royal Society book, a lavish “History of Fishes,” had exhausted its budget; later the funder was paid partly in unsellable fish books.
• Another anecdote recalls a public lecture marking the 300th anniversary of the Principia.

Newton’s “subtle spirit,” fields, and “vibes”

• A long excerpt from the General Scholium highlights Newton’s speculation about a subtle “spirit” underlying cohesion, electricity, light, and nerve signals.
• Some see this as astonishing proto-electromagnetic and proto-neuroscientific intuition; others warn against hindsight bias, noting contemporaneous ideas about fluids, pneuma, and vibrations.
• Discussion touches on how “spirit” as a term gave way to “field,” and on cultural lines from such ideas to modern talk of “vibrations”/“vibes.”

Relativity in practice

• It’s noted that Newtonian mechanics suffices for launching rockets, but GPS and precise orbital/astronomical work must include relativistic time dilation; otherwise one would need ad-hoc “fudge factors.”

Miscellaneous

• Side comments cover legendary levitating saints (with skepticism and ergot-poisoning jokes), Newton’s personality and occult interests, and annoyance at the blog’s animated cursor effect.