# Notes

# Chapter 9: Fundamental Physics

## Section 2: The Notion of Reversibilityhttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-2--the-notion-of-reversibility

Testing for reversibility [in cellular automata]

Numbers of reversible [cellular automaton] rules

Inverse [cellular automaton] rules

Surjectivity and injectivity [in cellular automata]

Directional reversibility [in cellular automata]

Second-order cellular automata

History [of second-order cellular automata]

Properties [of second-order cellular automata]

Properties [of second-order cellular automata]

Generalized additive [cellular automaton] rules

## Section 3: Irreversibility and the Second Law of Thermodynamicshttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-3--irreversibility-and-the-second-law-of-thermodynamics

Current thinking on the Second Law

My explanation of the Second Law

Biological systems and Maxwell's demon

## Section 4: Conserved Quantities and Continuum Phenomenahttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-4--conserved-quantities-and-continuum-phenomena

[Conserved quantities in] physics

Implementation [of conserved quantity test]

More general conserved quantities

[Conserved quantities in] PDEs

Limiting procedures [for cellular automata]

PDE approximations [to cellular automata]

## Section 5: Ultimate Models for the Universehttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-5--ultimate-models-for-the-universe

History of ultimate models [of physics]

Theological implications [of ultimate models of physics]

[History of] origins of physical models

Simplicity in scientific models

Mechanistic models [in physics]

Initial conditions [for the universe]

## Section 6: The Nature of Spacehttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-6--the-nature-of-space

## Section 7: Space as a Networkhttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-7--space-as-a-network

Generalizations [of trivalent networks]

Maintaining simple rules [for networks]

Continuum limits [of networks]

Implementation [of network properties]

Finding layouts [for networks]

## Section 8: The Relationship of Space and Timehttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-8--the-relationship-of-space-and-time

## Section 9: Time and Causal Networkshttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-9--time-and-causal-networks

Implementation [of causal networks]

[Causal networks for] mobile automata

## Section 10: The Sequencing of Events in the Universehttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-10--the-sequencing-of-events-in-the-universe

Implementation [of generalized substitution systems]

The sequential limit [in generalized substitution systems]

[Generalized substitution system] rule (b)

Intrinsic synchronization in cellular automata

## Section 11: Uniqueness and Branching in Timehttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-11--uniqueness-and-branching-in-time

Spacetime networks from multiway systems

Commuting operations [on strings]

Conditions for convergence [in string rewriting]

Confluence [in string rewriting]

## Section 12: Evolution of Networkshttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-12--evolution-of-networks

Neighbor-independent [network substitution] rules

Implementation [of network substitution rules]

Identifying subnetworks [in networks]

Number of [possible network] replacements

[Generating] arbitrary transformations [between networks]

[Networks generated by] random replacements

Cellular structures [in nature]

Non-overlapping [network] clusters

1- and 2-connection [network] clusters

Reversibility [of networks and universe]

Feynman diagrams [and networks]

Chemical analogy [for network substitutions]

## Section 13: Space, Time and Relativityhttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-13--space-time-and-relativity

## Section 14: Elementary Particleshttps://www.wolframscience.com/nks/chap-9--fundamental-physics--notes#sect-9-14--elementary-particles

Types of [elementary] particles

History [of elementary particles]