Exploring Physics Foundations: Assumptions, Theories, and Perspectives

The Assumptions of Physics 2023-24 status Gabriele Carcassi and Christine A. Aidala Physics Department University of Michigan https://assumptionsofphysics.org

About the project Identify a handful of physical starting points from which the basic laws can be rigorously derived For example: Irreducibility Quantum state Infinitesimal reducibility Classical state https://assumptionsofphysics.org ? time time This also requires rederiving all mathematical structures from physical requirements For example: Science is evidence based scientific theory must be characterized by experimentally verifiable statements topology and ?-algebras https://assumptionsofphysics.org/

Find ultimate theory Different approach to the foundations of physics approximation Construct interpretations Weak interactions QED -Electromagnetism Typical approaches Role of the observer Measurement problem QCD Strong Interactions Electro-weak Quantum mechanics Contextuality Local realism General Relativity Grand Unified Theory What really happens Ontology of observables Theory of Everything Our approach Find a minimal set of physical assumptions from which to rigorously rederive the laws General physical principles and requirements General mathematical framework Specific assumptions Quantum mechanics Classical mechanics derivation Thermodynamics specialization https://assumptionsofphysics.org/

Underlying perspective Foundations of physics Foundations of mathematics Metaphysical reality What really exists Philosophy of science How exactly do we draw that boundary? Physical theories Idealized account of physical reality Physical reality What can be studied experimentally How exactly does the abstraction/idealization process work? https://assumptionsofphysics.org/

Space of the well-posed scientific theories Physical theories Specializations of the general theory under the different assumptions Unitary evolution Hamiltonian mechanics Quantum state-space Classical phase-space Assumptions Infinitesimal reducibility Determinism/ reversibility Irreducibility States and processes General theory Information granularity Basic requirements and definitions valid in all theories Experimental verifiability https://assumptionsofphysics.org/

Physics Reverse Physics Reverse physics: Start with the equations, reverse engineer physical assumptions/principles Smallest set of assumptions required to rederive the theory Physical result/ effect/prediction Physical theory ??=?? ??=?? Reverse Mathematics Mathematics ?? Smallest set of axioms required to prove the theorem Mathematical result/ corollary/calculation Theorem ??=?? Found Phys52, 40 (2022) ??= ?? ?? Goal: Elevate the discussion from mathematical constructs to physical principles, assumptions and requirements Physical mathematics: Start from scratch and rederive all mathematical structures from physical requirements Physics Physical requirements Semantics Physical mathematics Goal: Construct a perfect one-to-one map between mathematical and physical objects https://assumptionsofphysics.org/

Reverse Physics: Classical mechanics Assumptions of Physics, Michigan Publishing (v2 2023) J. Phys. Commun. 2 045026 (2018) https://assumptionsofphysics.org/

7 equivalent characterizations of Hamiltonian mechanics 12 in the book one DOF ? (1) Hamilton s equations (2) Divergenceless displacement ??? ??=??? ??+??? ??=?? ??=?? ??= 0 ? ?? ??=?? ??= ?? ?? (3) Area conservation (|?| = 1) (4) Deterministic and reversible evolution (7) Uncertainty conservation for peaked distributions Area conservation state count conservation ???? = |?|???? ? + ?? = ? ? ? deterministic and reversible evolution (5) Deterministic and thermodynamically reversible evolution (6) Information conservation ? = ??log? ? ? ? + ?? = ? ? ? ?log|?|???? Area conservation entropy conservation thermodynamically reversible evolution A full understanding of classical mechanics means understanding these connections https://assumptionsofphysics.org/

Reversing the principle of least action DR KE ? ? = ???? = ? ? ? ? ? = 0 ? = ? No state is lost or created as time evolves (Minus sign to match convention) Sci Rep13, 12138 (2023) The action is the line integral of the vector potential (unphysical) ? ? Variation of the action Gauge independent, physical! ? ? ? ? ?? ? = ? ? = ? ? ? Variation of the action measures the flow of states (physical). Variation = 0 flow of states tangent to the path. https://assumptionsofphysics.org/

Reversing phase-space Hamiltonian Privilege, Erkenn (2023) Stud Hist Phil 71, 082020, 60-71 (2020) Each unit variable (i.e. coordinate) paired with a conjugate of inverse units: number of states ? ? is invariant ? = 100 ??/? ? ? ?3 ? = 1 ? 1 ? = 0.01 ?? 1 1 1 ? = 100 ?? ?3 ? ? = 1 ? Density, entropy, uniform distributions NOT in general coordinate invariant Phase space (symplectic) structure is the only one that supports coordinate invariant density, entropy, state count Only 3 spatial dimensions are possible Independence of DOFs independence of units orthogonality in phase-space invariant marginals (for density, entropy, state count) Hamiltonian mechanics preserves count of states and DOF independence over time 2-sphere the only symplectic manifold (??,??) 0 1 0 ?? ? Directional DOF ???= 1 (??,??) Orthogonality/independence across DOFs Symplectic form (geometric structure of phase space) Areas/possibilities in each DOF Total number of states = product of number of cases in each independent DOF https://assumptionsofphysics.org/ Invariance at equal time (relativity) gives us the structure of phase space

Massive particles under potential forces Kinematic equivalence assumption: the state can be recovered from space-time trajectories Integration of the previous expression ??= ???? ??+ ????? ? =??? ??=?? =1 ????(?? ???) ? ? ??? ??? ? ?? ???? ? ? 1 Must be a linear transformation in terms of coordinates ? ?? ???????? ??? + ?? ?? ? = 2? Fixes the units Hamiltonian for massive particles under potential forces Mass quantifies number of states per unit of velocity Higher mass more states to go through harder to accelerate BUT Zero mass zero states within finite range of velocity velocity is fixed The laws themselves are highly constrained by simple assumptions https://assumptionsofphysics.org/

Relativistic mechanics Classical antiparticles Relativistic aspects without space-time and in Newtonian mechanics ? ? =? ? ? ? =? ??? ?? ?? =? ??? potential of the displacement ?? ??=? ? ? ?? ?? ?? ?? ? = [??, ?,0,0] ?? ? rest mass scaled by time dilation energy-momentum co-vector Affine parameter anti-aligned with time: parameterization goes back in time No clear idea what ????is Inertial forces? Lorentzian relativity is the only correct one Metric tensor quantifies states charted by position and velocity Minkowski signature appears on the extended phase space ???????+ ???? ??? ??? 0 ? = ??1??1 ???? ? = ??1??1+ ??2??2 ???= ??1??1= ? + ???? States are counted at equal time: temporal DOF orthogonal to ? ??2??2 instants in time ? positions in space ??1??1 ???? ? Indep DOF are orthogonal ? https://assumptionsofphysics.org/ Constant ? converts state count between space and time

Assumptions of classical mechanics ??? ??=?? ??? ??= ?? ? ??, ??,? ?? = 0 ? [??,??] ??? ??? ? (IR) Infinitesimal reducibility Classical Phase Space Hamiltonian Mechanics Lagrangian Mechanics + + + Massive particles under potential forces + weak (DR) Determinism /Reversibility (IND) Degree of freedom independence (KE) Kinematic Equivalence full 1 2??? ???????? ??? + ?? ? = ? ?1?2 ? ? ? ? ? ? ? Hamiltonian Mechanics Newtonian Mechanics Lagrangian Mechanics https://assumptionsofphysics.org/

Reverse physics gives us links between theories Deterministic and reversible evolution existence and conservation of energy (Hamiltonian) Why? Stronger version of the first law of thermodynamics Deterministic and reversible evolution past and future depend only on the state of the system the evolution does not depend on anything else the system is isolated First law of thermodynamics! the system conserves energy https://assumptionsofphysics.org/

Reverse Physics: Thermodynamics https://assumptionsofphysics.org/

Shannon entropy as variability Eur. J. Phys. 42, 045102 (2021) Meaning depends on the type of distribution more variability Statistical distribution: variability of what is there ? less variability Probability distribution: variability of what could be there ? Credence distribution: variability of what one believes to be there Shannon entropy quantifies the variability of the elements within a distribution ??log?? only indicator of variability that satisfies simple requirements This characterization works across disciplines Continuous function of ?? only Increases when number of cases increases Linear in ?? 1) 2) 3) https://assumptionsofphysics.org/

Shannon entropy as variability Eur. J. Phys. 42, 045102 (2021) Is it alive? Is it human made? ? Does it live on land? 1 ?log? ??log?? Efficient game of twenty questions More variability, more permutations Variability is also quantified by the logarithm of the number of possible permutations per element More variability, more questions Variability is quantified by the expected minimum number of questions required to identify an element More variability for a distribution at equilibrium, more fluctuations, more physical entropy https://assumptionsofphysics.org/

? ??: how many evolutions go through ??? Entropy as logarithm of evolutions Process entropy: ? = log? Determinism: evolutions cannot split ? ? ? + ? ? ??+ ??? =? ?? ??+ ? ? ? ? ? = 2 ? ?? ? = 1 Reversibility: evolutions cannot merge ? ? ? + ? ? = 2 ? ? ? ? + ? ? ? ? For a deterministic process For a deterministic process ? ? ? + ? ? ? ? ? ? ? + ? ? ? ? (equal if reversible) (maximum at equilibrium) (equal if reversible) (maximum at equilibrium) ? + ? ? ? ? System independence: evolutions of the composite are the product of individual systems: ???= ???? Entropy additive for independent systems ???= ??+ ?? ? ? ,? ? ?(?) ?(?) https://assumptionsofphysics.org/

? ??: how many evolutions go through ??? Entropy as logarithm of evolutions Process entropy: ? = log? prepare ? measure ? interaction Note: defining an evolution count is necessary in physics prepare ? measure ? We compose processes by connecting inputs and outputs: all evolutions must connect! Recovers other notions of entropy! If det/rev, one state per evolution, count of evolutions is count of states recover fundamental postulate of statistical mechanics! If microstate fluctuates according to a distribution ?, count of evolutions is count of permutations recover Shannon entropy! https://assumptionsofphysics.org/

Reversing thermodynamics Assume states are equilibria of faster scale processes 1 ?S ?? and ???= ?? ??? Define intensive quantities ? = ???= Assume states identified by extensive properties Assume one of these quantities is energy ? ?? =?S ???? +?? ????? = ?? ????? ?? = ? ???? + ????? ??????= ??? ?????? ?(?,??) Recover usual relationships Existence of equation of state Study interplay of changes of energy and entropy First law recovered from existence and conservation of Hamiltonian ? = 0 = ??+ ??+ ?? = ?? ? + ? Recover first law Reservoir: energy only state variable, entropy linear function of energy ? All energy stored in entropy ? 0 ? = ??+ ?R+ ?M ? ???? Mechanical system: same entropy for all states = ??+ ?? ??+ 0 = ??+ ? ? No energy stored in entropy Recover second law ? 1 ? = ???= 0 https://assumptionsofphysics.org/ Second law recovered from definition of entropy as count of evolutions

3rd law and principle of maximal description ? = 3 Can be formulated as: Count of evolutions Every substance has a finite positive entropy, but at the absolute zero of temperature the entropy may become zero, and does so become in the case of perfect crystalline substances. ? = log?(?) Count of evolutions can t be < 1 therefore ?can t be < 0 G. N. Lewis and M. Randall 3rd law can be restated as: No state can describe a system more accurately than stating the system is not there in the first place. Better special case than crystalline substance Principle of maximal description Null state : system is absent (e.g. gas with zero particles) ? = ? ??= ?? = ??+ ? ? = 0 We can reformulate the 3rd law of thermodynamics as a logical necessity Entropy for the null state of any system must be 0 https://assumptionsofphysics.org/

?[?] Classical uncertainty principle Region with classical distributions Classical mechanics has no lower bound on entropy violates third law! What happens if we impose one? Let ?0 the volume of phase space over which a uniform distribution has zero entropy. Minimum uncertainty Int J Quant Inf 18, 01, 1941025 (2020) ???? ?0 Equality for independent Gaussians ???? 2?? 0 Excluded by 3rd law Lower bound on entropy lower bound on uncertainty Don t need the full quantum theory to derive the uncertainty principle: only the lower bound on entropy https://assumptionsofphysics.org/

3rd law of thermodynamics and uncertainty principle Classical mechanics Third law of thermodynamics + Uncertainty principle Lower bound on entropy Quantum mechanics Principle of maximal description The uncertainty principle is a consequence of the principle of maximal description No state can describe a system more accurately than stating the system is not there in the first place https://assumptionsofphysics.org/ Can we understand the rest of quantum mechanics in the same way?

Reverse Physics: Quantum mechanics https://assumptionsofphysics.org/

Quantum mechanics as irreducibility Entropy Classical Quantum Minimum uncertainty ? ? 0 time time ? Can prepare ensembles at arbitrarily low entropy: we can study arbitrarily small parts Entropy is bounded at zero: we cannot study parts Can t squeeze ensemble arbitrarily We always have access to the internal dynamics No access to the internal dynamics Probability of transition Superluminar effects that can t carry information Non-locality ?+ ?+ ? ? Can t refine ensembles Can t extract information Can t refine ensembles Can t interact with parts ? ?+? = ?(? |?+) https://assumptionsofphysics.org/ Symmetry of the inner product

Time evolution and measurements ?? ??= ? ?? ? Any process (deterministic or stochastic) will take an ensemble as input and return an ensemble as output ? ?1?1+ ?2?2 = ?1? ?1 + ?2? ?2 ?1 ?1 Measurement Deterministic and reversible ?? ?? ?? ?? ?? ? 1 ?? ? ? ? ? Must be repeatable Conserves probability and allows an inverse Projection Unitary operation |?0 |?0 Measurement problem: unitary projections projections unitary Unitary evolution sequence of infinitesimal projections https://assumptionsofphysics.org/

Parallels between QM and thermodynamics ? ? ? ? = ? Eigenstates states unchanged by the process equilibria of the process Quantum contexts Boundary conditions between system and environment Every state is an eigenstate of some unitary / Hermitian operator all states are equilibria Every mixed state commutes with some unitary operator (same eigenstates used calculate entropy) Spin up meas. Equilibration ?+ ?+ [?1,?,?] Projections Measurements [?,?,?] ? [?2,?,?] Unitary Quasi-static Different contexts, different variables Different equilibria, different variables [ .,?,?] https://assumptionsofphysics.org/

Entropic nature of physical theories Thermodynamics/Statistical mechanics are not built on top of mechanics Mechanics is the ideal case of thermodynamics/statistical mechanics Best preparation pure state Best process map between pure states 1 Standard probability ? ? ? ? = The geometric structure of both classical and quantum mechanics is ultimately an entropic structure ? ? Symplectic manifold We can only prepare/measure ensembles. Ensembles can offer a unified way of thinking about states. ? uniform over ? Information theory ? ? = log? ? Quantum probability ? ? 2 ? ? ? = ? ? Projective Hilbert space ? =1 2??+1 1 + ? 2 ,1 ? 2 Quantum information theory 2?? ? ? = ? https://assumptionsofphysics.org/

? ? = 0 ? = 0 ? = 0 ? + ? + ? + Quantum Classical discrete infinite Classical continuum Quantum mechanics is a hybrid between discrete and continuum Quantum mixed states have no single decomposition in terms of pure states, classical continuum mixed states have no single decomposition in terms of zero entropy states Quantum pure states form a manifold (like classical continuum) where each state has zero entropy (like classical discrete) https://assumptionsofphysics.org/

Recovering QM from assumptions on ensembles ?1 Ensembles can mix Form a convex space Irreducibility Extreme points in the convex space Continuous time Extreme points form a manifold (not discrete) |?0 Frame-invariance Manifold is symplectic Homogeneity All two dimensional subspaces are spheres 2-sphere only symplectic sphere Is this enough to recover complex projective spaces? https://assumptionsofphysics.org/

Unphysicality of Hilbert spaces Hilbert space: complete inner product vector space Redundant on finite-dimensional spaces. For infinite-dimensional spaces, it allows us to construct states with infinite expectation values from states with finite expectation values Exactly captures measurement probability/entropy of mixtures and superposition/statistical mixing Physically required Extremely physically suspect!!! Thus requires us to include unitary transformations (e.g. change of representations and finite time evolution) that change finite expectation values into infinite ones Suppose we require all polynomials of position and momentum to have finite expectation Schwartz space Maybe more physically appropriate? Closed under Fourier transforms Used as starting point for theories of distributions https://assumptionsofphysics.org/

QM postulates revisited Recover mathematical structure of quantum mechanics from properties of ensembles Recovered from properties of ensembles and rules of ensemble mixing State postulate: states are rays of a complex vector space Projections as processes with equilibria Measurement postulate: projection measurement and Born rule Born rule recoverable from entropy of mixing Composite system postulate: tensor product for composite system Derived from other postulates PRL 126, 110402 (2021) Evolution postulate: unitary evolution (Schr dinger equation) Deterministic/reversible evolution https://assumptionsofphysics.org/

What about field theories? Classical field theory (EM fields, general relativity, ) Quantum field theory (QED, QCD, Electroweak, ) We lack the correct math to generalize https://assumptionsofphysics.org/

Physical mathematics https://assumptionsofphysics.org/

Mathematical content of a theory can never tell us the full physical content In modern physics, mathematics is used as the foundation of our physical theories David Hilbert: Mathematics is a game played according to certain simple rules with meaningless marks on paper. From Hossenfelder sLost in Math: [ ] finding a neat set of assumptions from which the whole theory can be derived, is often left to our colleagues in mathematical physics [ ] Bertrand Russell: It is essential not to discuss whether the first proposition is really true, and not to mention what the anything is, of which it is supposed to be true. Physics We need to identify which parts of mathematics are correct to capture physical properties in a specific realm of applicability Physical requirements Semantics Physical Mathematics From Wikipedia Mathematical Physics Mathematical structures must be justified by physical requirements https://assumptionsofphysics.org/

Physical mathematics Physics Physical requirements Physics is defined in terms of physical objects and operational definitions Informal Formal Semantics physics math Under assumptions, idealizations and approximations, physical objects and their properties are expressed with a formal system through axioms and definitions. Physical mathematics All physical content is captured by the definitions and axioms The map between informal and formal is the most delicate and important step, and it is also the least studied!!! https://assumptionsofphysics.org/

Examples: symplectic space and probability spaces Hamiltonian mechanics Phase space (symplectic manifold) Hamiltonian evolution Differentiable manifold Symplectic structure Determinism/reversibility Manifold Differentiable structure Observer independent count of states Locally ? Topological space Infinitesimal reducibility Experimentally distinguishable cases with verifiable statements Identified by independent continuous quantities We can see what each additional mathematical layer represents and under what assumptions Probability space ?-algebra Set of points Measure Experimentally distinguishable cases Statements associated with experimental tests Probability that a statement is true https://assumptionsofphysics.org/

Space of the well-posed scientific theories Physical theories Specializations of the general theory under the different assumptions Unitary evolution Hamiltonian mechanics Quantum state-space Classical phase-space Assumptions Infinitesimal reducibility Determinism/ reversibility Irreducibility States and processes General theory Information granularity Basic requirements and definitions valid in all theories Experimental verifiability https://assumptionsofphysics.org/

Logic of experimental verifiability Top. Proc.54 pp. 271-282 (2019) verifiable statements ? ?1 Test Result ? Finite conjunction (logical AND) ?v ?? ?1 ?2 ?3 T SUCCESS (in finite time) ?=? FAILURE (in finite time) F statements All tests must succeed UNDEFINED ?1 experimental test Countable disjunction (logical OR) ?? ?1 ?2 ?3 ?=1 Physical theories (evidence based) all theoretical statements associated with tests One successful test is sufficient Operator Gate Statement Theoretical Statement Verifiable Statement Decidable Statement ?? Negation NOT allowed allowed disallowed allowed ?? ?? Conjunction AND arbitrary countable finite finite ? Disjunction OR arbitrary countable countable finite Some mathematical theories (formally well-posed) have too many statements to be physically meaningful https://assumptionsofphysics.org/

Topology and ?-algebra Experimental verifiability topology and ?-algebras (foundation of geometry, probability, ) Theoretical statements ???(?) corresponds to the verifiable part of a statement ?1 Test Result Perfect map Verifiable statements SUCCESS (in finite time) Possibilities T between math and ?? corresponds to the undecidable part of a statement UNDEFINED physics UNDEFINED F FAILURE (in finite time) ???(?) corresponds to the falsifiable part of a statement NB: in physics, topology and ?-algebra are parts of the same logic structure Points Open sets Open set (509.5, 510.5) Verifiable the mass of the electron is 510 0.5 KeV Closed set [510] Falsifiable the mass of the electron is exactly 510 KeV Borel sets Borel set (??? ??? = ) Theoretical the mass of the electron in KeV is a rational number (undecidable) Inference relationship ?:?? ?? such that ? ? ? Topologically continuous consistent with analytic discontinuity on isolated points ?? ?? Inference relationship Causal relationship Relationships must be topologically continuous ? ? https://assumptionsofphysics.org/ Causal relationship ?:? ? such that ? ? ? Phase transition Topologically isolated regions

Quantities and ordering Phys. Scr.95 084003 (2020) Goal: deriving the notion of quantities and numbers (i.e. integers, reals, ) from an operational (metrological) model before after A reference (i.e. a tick of a clock, notch on a ruler, sample weight with a scale) is something that allows us to distinguish between a before and an after Mathematically, it is a triple ?,?,? such that: ? and ? are verifiable The reference has an extent (? ) If it s not before or after, it is on ( ? ? ?) If it s before and after, it is on (? ? ?) on Numbers defined by metrological assumptions, NOT by ontological assumptions Dense The hard part is to recover ordering. After that, recovering reals and integers is simple. ?1 ?3 ?2 ?, ( , ) To define an ordered sequence of possibilities, the references must be (nec/suff conditions): + Sparse Refinable Aligned Strict ?1?2 before after ?2 ?2 on ?3 ?2 ?, ( , ) ?2 ?1 ?1 ?1 ?1 ?, https://assumptionsofphysics.org/ Assumptions untenable at Planck scale: no consistent ordering: no objective before and after

Space of the well-posed scientific theories Physical theories Specializations of the general theory under the different assumptions Unitary evolution Hamiltonian mechanics Quantum state-space Classical phase-space Assumptions Infinitesimal reducibility Determinism/ reversibility Irreducibility States and processes General theory Information granularity Basic requirements and definitions valid in all theories Experimental verifiability https://assumptionsofphysics.org/

Information granularity Logical relationships Topology/?-algebra Granularity relationships Geometry/Probability/Information The position of the object is between 0 and 1 meters The position of the object is between 0 and 1 kilometers The fair die landed on 1 The fair die landed on 1 or 2 The first bit is 0 and the second bit is 1 The first bit is 0 The position of the object is between 0 and 1 meters The position of the object is between 2 and 3 kilometers The fair die landed on 1 The fair die landed on 3 or 4 The first bit is 0 and the second bit is 1 The third bit is 0 Measure theory, geometry, probability theory, information theory, all quantify the level of granularity of different statements ? E ??: ? D A partially ordered set allows us to compare size at different level of infinity and to keep track of incommensurable quantities (i.e. physical dimensions) Once a unit is chosen, a measure quantifies the granularity of another statement with respect to the unit B C ? A C D ??? = 1 A B C E ?1 ?2 ???1 ???2 D C ???1 ?2 = ???1 + ???2 if ?1 and ?2 are incompatible However, quantum mechanics requires a twist at the measure theoretic level https://assumptionsofphysics.org/

Need for non-additive measure entropy of uniform distribution Finite continuous range Single point ?(?) count of states log?(?) ?(?) log?(?) ? ?? = log? ? Counting measure Assume usual link between entropy and count of states + 1 0 + ? ? = #? Number of points Lebesgue measure ? < 0 < ? ?,? = ? ? Interval size ? Quantized measure ? ? = 2?(??) Entropy over uniform distribution ? 0 < 1 < = 20= 1 ? ? = 21= 2 Pick two! ? ?,? not additive Single point is a single case (i.e. ? ? Finite range carries finite information (i.e. ? ? < ) Measure is additive for disjoint sets (i.e. ? ?? = ? ??) = 1) 1. 2. 3. ? ?,? < 2 = ? ? + ? ? ? ?,?,? < 2 = ? ?,? not monotonic Physically, we count states all else equal In quantum mechanics, literally 1 + 1 2 https://assumptionsofphysics.org/ Contextuality non-additive measure

Mathematicians have developed several, increasingly abstract, definitions for differentials, derivatives, integrations, tangent vectors are they suitable for physics? Differentiability in math Differentiable manifold Manifold Differentiable structure Changes of coordinates are differentiable Defined on top of Fr chet derivative Vector defined as derivation of a scalar function ?:? ?, ? ?, ? ? = ????? vector basis Differentials defined as linear functions of vectors ??:? So are convectors, like momentum Does not make sense physically! ?? ? = ?? ???? = ?? velocity is not a derivation momentum is not a function of a derivation derivations ??depend on units and can t be summed (e.g. ??+ ??) Two mathematical notions of differentials (the new one and the one hidden in the Fr chet derivative) Infinitesimal objects are limits of finite objects, not the other way around Integrals defined on top of differential forms ?? = ? ? https://assumptionsofphysics.org/

Differentiability in physics ?? = ?1,?2,?3, ?? ?? lim ? = ? Infinitesimal reducibility differentiability Tangent vector Convergence at all points differentiability of curve General notion of differential as an infinitesimal change in ANY vector space Infinitesimal surface change ?? = (?1 ?1),(?2 ?2), ?? ?? ?? lim ? = ? Time Space Temperature Differentiable Manifold displacement (unit free) ?(?) T(?) function: infinitesimal changes map to infinitesimal changes ?????= ?? t x T Quantity Map between the two Differentiable space: infinitesimal changes are well-defined ?? ?? ?? ?? Differential dt dx dT Coordinate displacement (units of ??) Derivative: map between differentials gradient (covector) ???=??? ?? =?? ?????? Goal: one notion of derivative ???? velocity (vector) https://assumptionsofphysics.org/

Differentiability: forms and linear functionals ?-vector ?-surface ?-form ?-functional Starting point: finite values defined on finite regions Thinking in terms of relationships between finite objects leads to better physical intuition ????= ??(???) Physically measurable quantities zero-form Differential forms: infinitesimal limit one-form ?(?) ? ? = ?? ?? = ? ?? ? = ? ?? = ? ?? ? ? = ?? ?? = ? ??? = ??/?? Assume additivity over disjoint regions Temperature: Work: Magnetic flux: Mass: ? = ??/?? ? = ? /?? The mathematics is contingent upon the assumption of infinitesimal reducibility (e.g. mass in volumes sums only if boundary effects can be neglected) two-form three-form We can define functionals that act on boundaries exterior functional ??+1 ?? Given a functional ?? ???+1= ?? ?/???+1 ?/??? ??+1 ?? Define higher dimensional functional that acts on the boundary ? ??+1 ?? ??+1 ??+1(??+1) ???? exterior derivative Exterior functional ??????+2= ??????+2= ?? = 0 Reversing the exterior derivative is finding a (non-unique) potential https://assumptionsofphysics.org/ Boundary of a boundary is the empty set exterior derivative of exterior derivative is zero

Space of the well-posed scientific theories Physical theories Specializations of the general theory under the different assumptions Unitary evolution Hamiltonian mechanics Quantum state-space Classical phase-space Assumptions Infinitesimal reducibility Determinism/ reversibility Irreducibility States and processes General theory Information granularity Basic requirements and definitions valid in all theories Experimental verifiability https://assumptionsofphysics.org/

States and processes Good ideas on how to proceed Slides would get old fast Base the notion of states on ensembles Identity: 1?1+ 0?2= ?1 Idempotence: ?1?1+ ?2?1= ?1 Commutativity: ?1?1+ ?2?2= ?2?2+ ?1?1 Associativity: ?1?1+ ?1 Ensembles form a convex space ????? ?2 ?1?2+?3 ?1 ?3?1+?2 ?1?3 = ?3 ?3?2 + ?3?3 Strictly concave: ? ?1?1+ ?2?2 ?1? ?1 + ?2? ?2 Bounded increase: ? ?1?1+ ?2?2 ? ?1,?2 + ?1? ?1 + ?2? ?2 And require an entropy defined Shannon entropy, increase due to mixing Is it a vector space? ??1+ ??2= ??1+ ??3 ?2= ?3 May not be necessary Jensen-Shannon divergence 1 2?1+1 2?2 1 0 ? ? ?1 + ? ?2 1 2 Square of a distance function Related to the Fisher-Rao metric Defines the geometry of the space How much the entropy increases during mixing https://assumptionsofphysics.org/

Wrapping it up Different approach to the foundations of physics No interpretations, no theories of everything: physically meaningful starting points from which we can rederive the laws and the mathematical frameworks they need Reverse physics (reverse engineer principles from the known laws) Classical mechanics is completed ; very good ideas for both thermodynamics and quantum mechanics; still do not know how to generalize to field theories Physical mathematics (rederive the mathematical structures from scratch) Topology and ?-algebras are derived from experimental verifiability; measure theory still needs major work; differentiability we have a good idea; started to formalize states/processes The goal is ambitious and requires a wide collaboration Always looking for people to collaborate with in physics, math, philosophy, https://assumptionsofphysics.org/