Cynosure对《Questioning the Foundations of Physics》的笔记(1)

第1页

FQXI系列的书可以看作在严谨的学术之上添加了一些想象力。
CH 2 
The Paradigm of Kinematics and DynamicsMust Yield to Causal Structure, by Robert W. Spekkens
kinematics: the space of physical (possible) states. 
dynamics：the evolution of the physical state
论点：the distinction ( of kinematics and dynamics)is conventional: kinematicsand dynamics only have physical significance when considered jointly, not separately.
方法论：any difference between two physical models that does not yield a difference at the level of empirical phenomena does not correspond to a physical difference and should be eliminated.
This suggests that the framework that should replace kinematics and dynamics is one that focuses on causal structure.
CH3
Recognising Top-Down Causation, by George Ellis
和还原论（从部分到整体）不同，作者认为自上而下（从整体到部分）也存在因果律
CH4
On the Foundational Assumptionsof Modern Physics，by Benjamin F. Dribus
The central new principle I propose is the causal metric hypothesis, which characterizes the observed properties of the physical universe as manifestations of causal structure.
Classical causal metric ：the metric properties of classical spacetime arise froma binary relation on a set, representing direct influences between pairs of events.
Quantum causal metric： the phases associated with directed paths in causal configuration space are determined by the causal structures of their constituent universes.
The resulting approach to fundamental physics is called quantum causal theory.
foundational assumptions包括三类：principles, postulates, and ancilla。（后两者经常变）
Six crucial general principles of modern physics：
symmetry, 
conservation, 
covariance, 
the second law of thermodynamics, 
background independence, (a statement about spacetime)
causality.
Rejected Assumptions:
Rejected Structural Assumptions:
spacetime is a real manifold
physical systems evolve with respect to a universal time parameter, 
the universe possesses a static background structure serving as an immutable “arena”for dynamical processes.
spacetime is commutative
Rejected Assumptions About Causality:
apparent metric properties of classical spacetime involve any information other than a set of eventsand a binary relation, the causal relation, encoding causal structure.( “negative version” of the classical causal metric hypothesis)
the causal relation is transitive.
the causal relation is acyclic.
Rejected Assumptions About Covariance: that it is an instance of group symmetry, even locally; (it should be viewed inorder-theoretic terms)
New Principles: (Quantum Causal Theory):
the causal metric hypothesis, 
iteration of structure as a quantization principle
co-relative histories
Technical tools necessary to implement these ideas include a 
synthesis of multicategory theory and categorification in abstract algebra, involving “interchangeability of objects, morphisms, elements, and relations;” a refined version of randomgraph dynamics
the theory of semicategory algebras
path algebras
否定的假设和新提出的假设，这些假设目前在业界的状态是怎样的
CH5
The Preferred System of Reference Reloaded，by Israel Perez
作者支持absolute system of reference（或preferred system of reference (PSR)）
for the theorist what is crucial is not the truthfulness or falsehood of the assumptions but their usefulness in solving particular problems.
The Principle of Relativity Is Not at Variancewith the Preferred System of Reference
Two key questions:
1. Does the fact that the PSR cannot be experimentally detected mean that the PSRdoes not exist?
2. If the PSR cannot be experimentally detected, does the assumption become ameaningless assumption?
Einstein ... was actually appealing to the principle of parsimony [6]. Since no experiment can tell whether an ISR is at‘real rest’ or in ‘real motion’, Einstein declared that these statements are meaningless(cf. with Heisenberg’s opinion above). For him, just as Mach, only relative motion ismeasurable and hence has real meaning.
Experimental and Theoretical Considerationsin Favor of the PSR
Although not widely known, specially among the physics community, now it has been understood some key aspects that can be fundamental that could be fundamental for the future of physics.
重新解释了Michelson-Morley试验
人们对此试验的预言（不存在绝对参考系），错误在于把电动力学和伽利略相对性原理整合在一起（the error in this prediction is the misapprehension that electrodynamics and Galilean relativity are compatible formulations.）
the null result of these kind of experiments does not prove that there is no medium.
Einstein rejected the æther的原因：
1。because, from the theoretical viewpoint, SR could not make specialdistinctions among ISR; actually, for him the æther assumption was not wrong butappeared to be superfluous. （前面的论述说明该项weak）
2。because, from the experimental viewpoint,there was no unambiguous evidence of its existence。（若当时知道暗物质，微波背景辐射，quantum vacuum is actually a perfect fluid，估计爱因斯坦会放弃此项）
p76，作者举了一个例子说明相对性原理的失败：
如图，在B点和A点观察到的物理规律是不一致的。
Are Space and Vacuum the Same Physical Entities?
The assumption of the existenceof a perfectly empty space is, just as the assumption of the existence of rigid bodies,a false but useful assumption. That the vacuum is an actual physical entity canbe demonstrated even from the perspective of electrodynamics。（vacuum is a paramagnetic medium）
General Relativity Is Not Fully Relativisticand the Speed of Light Is Not Constant
Einstein did not succeed either in creating a fully relativistic theory. This means thatnot all systems of reference are equivalent.
In 1917, Kretschmann [55] （文献：E. Kretschmann, Über den physikalischen Sinn der Relativitatspostulate. Ann. Phys. 53, 575–614 (1917)。不是英文，悲剧）recognized in a critical study of GR, that the principle does not imply that the LP most be relativistic, but only that their form must be the same under general coordinate transformations.
general covariance is not a PR but a principle that imposes restrictions between matter and geometry。
SR has actuallyonly one postulate, i.e., the PR, since the second one is already tacitly included inelectrodynamics.
we have shown above that the vacuum can be seen as a dilutedmaterial fluid. Under this assumption, we can reinterpret the bending of light justas a simple refraction phenomenon.
within this context, the‘warping’ of space can be physically understood as the change in the density of the medium 
PR: Principle of Relativity
PSR: Preferred system of reference
AS: Absolute Space
GPR: Galilean Principle of Relativity
IPR: inertial system of reference
LP: laws of physics 
OPL: optical path length 
LT: Lorentz transformations 
NIS: non-inertial system 
。
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Chapter 6
Right About Time? -By Sean Gryb and Flavio Mercati
The three assumptions we willquestion are
1. Time and space are unified.
2. Scale is physical.
3. Physical laws are independent of the measurement process.
these three assumptions inadvertently violate the same principle:the requirement that the laws of physics depend only on what is knowable throughdirect measurement. 
The flowof time, we will argue, may be fundamentally linked to the process of measurement.
The presence of dimensionful quantities is an indication that our “fundamental”theories are not fundamental at all. Instead, scale independence should be a basic principle of a fundamental theory.
The main idea behind renormalization is to be able to predict how the laws ofphysics will change when a coarse graining is performed.
The theory of renormalization produces precise equations that say how the lawsof physics will change, or flow, as we change the renormalization scale.
we will propose that flow under changes of scale may be related to the flowof time
coarse grainingof shapes described in the last section could lead to gravity.
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Chapter 8
Not on but of —by Olaf Dreyer
Either asfundamentalconstituents of the theory or as emergent excitations. These two ways differ by howthe particle relates to the background. It either sits on the background, or it is anexcitation of the background. We argue that by choosing the former to constructour fundamental theories we have made a costly mistake. Instead we should thinkof particles as excitations of a background.
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Chapter 9
Patterns in the Fabric of Nature -by Steven Weinstein
the physical facts at onepoint in space are held to be independent of those at other points in space. I proposethat we can usefully challenge this orthodoxy.
What I want to do here is raise the possibility that there is a more fundamentaltheory possessing nonlocal constraints that underlies our current theories.
It was Bell’s great insight to note that the quantum theory implies that theanticorrelation is held onto more tightly than could be accounted for by strong locality, Bell locality, or factorizability.
However, there is a further assumption known as the statistical independenceassumption (also known as measurement independence) that is necessary for Bell’sresult.
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Chapter 10
Is Quantum Linear Superpositionan Exact Principle of Nature?
—by Angelo Bassi, Tejinder Singh and Hendrik Ulbricht
What if quantum linear superposition is an approximate principle of nature?
To begin with the theory should be nonlinear: superposition of two allowed quantumstates of the system should not be a stable allowed state.
The nonlinear process responsible for thebreakdown of superposition should be stochastic (i.e. random) in nature because theoutcome of a particular quantum measurement cannot be predicted.
the nonlinear process should be such that a collection of outcomes of repeated measurements obey the Born probability rule. Another reason the nonlinear effect shouldbe stochastic is that this helps avoid faster-than-light signalling. A deterministic (i.e.non-stochastic) nonlinear quantum mechanics is known to allow for superluminalcommunication. The nonlinear mechanism should be amplifying in nature, beingnegligible for microscopic systems, but becoming more and more important forlarge many particle systems, so that breakdown of superposition becomes more andmore effective.
这个理论已经在上世纪80年代发展了，被称为Continuous Spontaneous Localization(CSL)。它有两个基本假设：
1. Given a system of n distinguishable particles, each particle experiences a suddenspontaneous localization (i.e. collapse of position state) with a mean rate λ, to aspatial region of extent rC.2. In the time interval between two successive spontaneous localizations, the systemevolves according to the Schrödinger equation.
这个理论背后意味着什么
Fascinating progress has beentaking place towards unravelling these underlying principles, mainly along three different directions, all of which point to an involvement of gravity, and a revision ofour understanding of spacetime structure at the deepest level.
1。gravity is responsible for the absence of macroscopic superpositions.
2。Trace Dynamics
3。There hence oughtto exist a reformulation of quantum theory which does not depend on a classicaltime。
The CSL model, as it is known today, is nonrelativistic in character,。。。the collapse of the wave function during aquantum measurement is instantaneous and non-local. This has been confirmed byexperimental verification of Bell’s inequalities. a need for reconciliation between CSL induced localization, and the causal structureof spacetime dictated by special relativity.。。。if one does not assume a predefined global causal order,。。。spacetime may emerge from a more fundamental structure in aquantum to classical transition.
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Chapter 11
Quantum-Informational Principlesfor Physics
by Giacomo Mauro D’Ariano
Recently the program succeeded inderiving the full structure of quantum theory from informational principles
论点：to ground quantum field theory on two new principles pertaining only theformulability and computability of the physical law: (1) the Deutsch-Church-Turingprinciple, and (2) the topological homogeneity of interactions.
different types of principles: 
(1) dogmatic. 最糟
(2) empirical。The empirical ones are good temporarypractical principles when we relinquish further explanation.
e.g. 1)Einstein’s equivalenceprinciple: the identity between inertial and gravitational mass is an observed fact. 2)invariance of the speed of light with the reference frame.
(3) simplifying (orconventional)。e.g. 
1)assumption of homogeneity of time. 
2)speed of light be isotropic in space.
(4) epistemological。a principle that cannot be violated, even “in-principle”, because its violation would involvecontradicting the scientific method itself.
I should make now clear that, being causality an axiom ofquantum theory, any information purportedly originated in the future, as a time travel,would logically constitute a falsification of the theory. For example, it would meanto require nonlinearities in state evolution, or other variations of the theory.
For the philosopher disbeliever I just want toadd that the reconciliation with the Humean position (that causality is just a human way of looking at phenomena) passes through the probabilistic nature of the causallink stated in the axiom, which involve the comparison between two probabilities: theHumean viewpoint corresponds to the Bayesian interpretation of probability
提到的若干原理：
(1) the Deutsch-Church-Turing principle. It implies:(a) the density of information is finite。(b) interactions are local.
(2) (topological) homogeneity of interactions. it means laws hold every where and ever.
(以下是informational principles:(i~vi))
(3/i) the causality principle, 
(ii) local tomography, 
(iii) perfect distinguishability,
(iv) atomicity of composition, 
(v) ideal compressibility,
(vi) purification.
(1,3) ==> information propagates at finite speed
(1~3) ==> Special Relativity
(i ~v) ==> classical information (theory)
(I~vi) ==> quantum (information) theory
(1~3 + i~vi)==> QFT
classical information (theory)+ mechanical elements ==> classical mechanics 
quantum (information) theory+ mechanical elements ==> quantum mechanics 
event: can occur probabilistically and has inputs and outputs systems. 
test: A complete collection of such events with overall unit probability. 
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The Quantum Cellular Automaton
A Quantum-Digital Space-Time
The quantum nature of the automaton is crucial for the emergence of space-time.
目前的主要问题是无法推导出引力