intrinsic local distances · intrinsic local distances a mixed solution to weyl’s tile argument...
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Intrinsic Local DistancesA Mixed Solution to Weyl’s Tile Argument
Lu Chen
University of Massachusetts, Amherst
LMP 2019@Western Ontario
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Paradoxes of Continuous Spacetime
Measure-Theoretic Paradoxes
– Zeno’s Paradox of Measure. Zeros add up to one?
– Banach-Tarski Paradox. One sphere becomes more. (No stretching!)
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Paradoxes of Continuous Spacetime
Measure-Theoretic Paradoxes
– Zeno’s Paradox of Measure. Zeros add up to one?
– Banach-Tarski Paradox. One sphere becomes more. (No stretching!)
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Paradoxes of Continuous Spacetime
Infinite Divisibility
– Thomson’s Lamp. Turn on and off alternatively.
– Faris’ Sheet. Write “1”−→ erase −→ write “2” −→ erase...
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Paradoxes of Continuous Spacetime
Infinite Divisibility
– Thomson’s Lamp. Turn on and off alternatively.
– Faris’ Sheet. Write “1”−→ erase −→ write “2” −→ erase...
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Paradoxes of Continuous Spacetime
Cracks in Physics [Baez 2018]
e.g. Point particles make headlines:
[Grøn 2011]
A lonely particle accelerates itself to the speed of light
[Eliezer 1943]
Opposite-charged particles run away from each other
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Paradoxes of Continuous Spacetime
Cracks in Physics [Baez 2018]
e.g. Point particles make headlines:
[Grøn 2011]
A lonely particle accelerates itself to the speed of light
[Eliezer 1943]
Opposite-charged particles run away from each other
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So...?
Continuous spacetime is bizarre!
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What is atomism?
Atomism. Spacetime is composed of (finitely) extended “atoms.”
Atom = indivisible part of spacetime
⇒ You occupy finitely many atoms.
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Weyl’s Tile Argument
Weyl’s tile argument
If atomism is true, then the Pythagorean theorem is not approximatelytrue.
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Weyl’s Tile Argument
Distance-by-Counting. The distance between two atoms is the leastnumber of atoms connecting one to the other. [Riemann 1866]
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Taxicab Geometry
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Different tiling models?
Hexagonal tiling?
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Different tiling models?
Rhombille tiling?
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Different tiling models?
Penrose tiling?
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We are going to replace this...
Distance-by-Counting. The distance between two atoms is the leastnumber of atoms connecting one to the other.
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Defining the Success Conditions
When does a theory of distance count as a solution to Weyl’s tileargument?
Allows atomistic space to approximate Euclidean geometry
Compatible with physics as we know it
Intelligible, not counterintuitive, natural, motivated...
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Defining the Success Conditions
When does a theory of distance count as a solution to Weyl’s tileargument?
Allows atomistic space to approximate Euclidean geometry
Compatible with physics as we know it
Intelligible, not counterintuitive, natural, motivated...
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Defining the Success Conditions
When does a theory of distance count as a solution to Weyl’s tileargument?
Allows atomistic space to approximate Euclidean geometry
Compatible with physics as we know it
Intelligible, not counterintuitive, natural, motivated...
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Defining the Success Conditions
When does a theory of distance count as a solution to Weyl’s tileargument?
Allows atomistic space to approximate Euclidean geometry
Compatible with physics as we know it
Intelligible, not counterintuitive, natural, motivated...
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...by Intrinsic Distances?
Intrinsic Account of Distance
The distance between any two atoms is intrinsic to them.
Let an atom be represented by a pair of integers.
Euclidean Model [McDaniel 2007]
The distance between atoms (a1, b1), (a2, b2) is√
(a2 − a1)2 + (b2 − b1)2.
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However...
General Relativity [Einstein 1916]
The metric of spacetime is related definitely to the distribution ofmass-energy by Einstein field equations.
⇒ A massive body between two faraway atoms will distort their distance.
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Evaluating Intrinsic Distances
X Allows atomistic space to approximate Euclidean geometry
X Intelligible, not counterintuitive, natural, motivated...
% Compatible with physics as we know it
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The Mixed Account
Intrinsic Local Distances
Some atoms bear primitive distances.
Path-dependent Distances
Distance between two atoms = the least sum of primitive distances fromone to the other.
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The Mixed Account
Atoms are still represented by pairs of integers.
Euclidean Model in The Mixed Account
For any atoms a, b, their primitive distance is√
(x2 − x1)2 + (y2 − y1)2 iff(x2 − x1)2 + (y2 − y1)2 ≤ ∆2.
∆ is a large number.
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∆ = 30
A : (0, 0),B : (0, 40)
C : (30, 40),D : (15, 21)
AB = 39
BC = 32
AB2 + BC 2 = 502
AD = 25.81
DC = 24.21
AC = AD + DC = 50.02
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Euclidean Approximation
A metric space X with a metric d is ε-isometric to Euclidean space E with regardto r iff there is a map f from X to E such that (1) for x , y ∈ X , we have
1− ε ≤ e(f (x), f (y))
d(x , y)≤ 1 + ε
(2) for every p ∈ E , there is a x ∈ X such that e(p, f (x)) ≤ r .
Approximation Theorem
For any ε and r , there is a set of points with a shortest path metric (withdistances being bounded by a finite number) that is ε-isometric toEuclidean space with regard to r .
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Application
Suppose the shortest distance = the Planck length (10−35m)
Suppose the relative accuracy of our measurement = ±1.6× 10−9
The longest primitive distance = the diameter of a neutrino (10−26m)
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Evaluating The Mixed Account
X Allows atomistic space to approximate Euclidean geometry
X Compatible with physics as we know it
w Intelligible, not counterintuitive, natural, motivated...
�X Primitive distance�X Path-dependent distance� Primitive + path-dependent
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Evaluating The Mixed Account
X Allows atomistic space to approximate Euclidean geometry
X Compatible with physics as we know it
w Intelligible, not counterintuitive, natural, motivated...
�X Primitive distance�X Path-dependent distance� Primitive + path-dependent
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Continuous Space (Manifold)
Riemannian Conception [Riemann 1866]
The length of a path is equal to the path integral of the lengths of thetangent vectors along the path.
Length of tangent vectors ≈ primitive distances
path integral ≈ sum of primitive distances
�X Primitive + path-dependent
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Continuous Space (Manifold)
Riemannian Conception [Riemann 1866]
The length of a path is equal to the path integral of the lengths of thetangent vectors along the path.
Length of tangent vectors ≈ primitive distances
path integral ≈ sum of primitive distances
�X Primitive + path-dependent
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Continuous Space (Manifold)
Riemannian Conception [Riemann 1866]
The length of a path is equal to the path integral of the lengths of thetangent vectors along the path.
Length of tangent vectors ≈ primitive distances
path integral ≈ sum of primitive distances
�X Primitive + path-dependent
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So...
The Mixed Account successfully solves Weyl’s tile argument.
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Forrest’s Solution
Forrest endorses Distance-by-counting.
Forrest’s Model [Forrest 1995]
Two atoms (x1, y1) and (x2, y2) are adjacent/connected iff(x2 − x1)2 + (y2 − y1)2 ≤ m2.
– adjacent atoms ≈ neighbors
– All neighbors bear distance 1.
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Forrest’s Solution
Forrest endorses Distance-by-counting.
Forrest’s Model [Forrest 1995]
Two atoms (x1, y1) and (x2, y2) are adjacent/connected iff(x2 − x1)2 + (y2 − y1)2 ≤ m2.
– adjacent atoms ≈ neighbors
– All neighbors bear distance 1.
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Forrest’s Solution
X Allows atomistic space to approximate Euclidean geometry
X Compatible with physics as we know it
X Intelligible, not counterintuitive, natural...
So, Forrest’s solution is also successful. (But...)
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But...
Forrest’s model is not locally approximately Euclidean.
Disadvantages:
Perhaps our space is locally approximately Euclidean
Redundant structure that plays no role in physical theories
Possibly unmotivated: the atoms are much smaller than the Plancklevel
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