User:WillowW/Natural philosophy

Thematic organization?

Natural philosophy is the philosophy of nature. It seeks to address the basic question, "why is the world thus, and not otherwise?"

Existence vs. non-existence
The broadest conception of Nature is the definition of the medieval philosopher Johannes Scotus Eriugena, who defined Nature as simply everything: everything that exists and everything that does not exist. In this definition, time is not considered; thus, it is more proper to say that Nature includes everything that exists, has existed and will exist, as well as everything that does not exist, has never existed and will never exist.

Eriugena's all-embracing definition of Nature has not been adopted by later philosophers, but it seems pertinent to understanding the peculiar behaviour of quantum physics, particularly the path-integral formulation of Feynman. According to the present understanding, Nature explores all possible realities, but allows only one to exist. Expressed mathematically, all possible realities contribute equally to the probability amplitudes for the various outcomes of an experiment; however, only one outcome is chosen to be objective reality in the process of quantum measurement, also known as the collapse of the wavefunction. In this way, even that which does not exist (all possible realities) can influence that which does exist (the objective reality); the non-existent is as much part of Nature as the existent. This broad conception of Nature is also anticipated somewhat in the Buddhist doctrines of shunyata and interdependent development of reality.

Schein vs. Sein
The bent rod in water example

what are the real objects and what laws govern them?

Aristotle's primary vs. secondary vs. generalized changes

Unification of matter
Thales, father of science = water

Heracleitus = fire air earth

Empedocles = why quibble? take all four ;)

More esoteric: "το εν" of Parmenides and his student Zeno — there can be only One ;) Numbers, music, geometry of Pythagoras

atomic theory: Democritus, Leucippus

Reality of change; concept of the continuum
Example of the pendulum; velocity is exactly zero at endpoint of swing - how can it ever leave that point?

Conservation laws
Origen's concept of conservation of soul inspired conservation of momentum/energy

Form and matter; space-time and matter
Aristotle's distinction

space-time acts reciprocally on matter the geodesic motion of matter and the conservation of energy-momentum are properties of space-time: the continuity of curvature and the Bianchi relations

Field theories
field theories vs. action at a distance

continuum vs. discrete

Causality
Aristotle's four causes

Leibniz's principle of sufficient reason

Leibniz's pre-established harmony; appearance of causality without any; monadology

intrinsic stochasticity of QM

Time reversibility
For every fundamental event, there must be a time-reversed fundamental event in Nature

Used by Einstein to argue for photons in 1909; discrete emission events imply discrete absorption events

particle-antiparticle duality as well

Arrow of time defined by thermodynamics, and by cosmological events

Identity
Identical particles

Leibniz's egg/soul

Symmetry
Buridan's ass

minimization principle apparent teleology

Relation to theology
Maupertuis

Newton's sensorium

Role of experiment
argued from data but not rigorous hypothesis testing sometimes shockingly mystical in early days

Insights of special relativity
translational invariance invariants of four-vectors are real, not those of three-vectors

Questions posed by quantum mechanics
measurement problem EPR paradox

Perturbative renormalizability and string theories
moving beyond the reach of experiment; return to natural philosophy?