Catastrophe, Gestalt and Thom’s Natural Philosophy of 3-D Space as Underlying All Abstract Forms – Thought of the Day 157.0

The main result of mathematical catastrophe theory consists in the classification of unfoldings (= evolutions around the center (the germ) of a dynamic system after its destabilization). The classification depends on two sorts of variables:

(a) The set of internal variables (= variables already contained in the germ of the dynamic system). The cardinal of this set is called corank,

(b) the set of external variables (= variables governing the evolution of the system). Its cardinal is called codimension.

The table below shows the elementary catastrophes for Thom:

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The A-unfoldings are called cuspoids, the D-unfoldings umbilics. Applications of the E-unfoldings have only been considered in A geometric model of anorexia and its treatment. By loosening the condition for topological equivalence of unfoldings, we can enlarge the list, taking in the family of double cusps (X9) which has codimension 8. The unfoldings A3(the cusp) and A5 (the butterfly) have a positive and a negative variant A+3, A-3, A+5, A-5.

We obtain Thorn’s original list of seven “catastrophes” if we consider only unfoldings up to codimension 4 and without the negative variants of A3 and A5.

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Thom argues that “gestalts” are locally con­stituted by maximally four disjoint constituents which have a common point of equilibrium, a common origin. This restriction is ultimately founded in Gibb’s law of phases, which states that in three-dimensional space maximally four independent systems can be in equilibrium. In Thom’s natural philosophy, three-dimensional space is underlying all abstract forms. He, therefore, presumes that the restriction to four constituents in a “gestalt” is a kind of cognitive universal. In spite of the plausibility of Thom’s arguments there is a weaker assumption that the number of constituents in a gestalt should be finite and small. All unfoldings with codimension (i.e. number of external variables) smaller than or equal to 5 have simple germs. The unfoldings with corank (i.e. number of internal variables) greater than two have moduli. As a matter of fact the most prominent semantic archetypes will come from those unfoldings considered by René Thom in his sketch of catastrophe theoretic semantics.

The Affinity of Mirror Symmetry to Algebraic Geometry: Going Beyond Formalism



Even though formalism of homological mirror symmetry is an established case, what of other explanations of mirror symmetry which lie closer to classical differential and algebraic geometry? One way to tackle this is the so-called Strominger, Yau and Zaslow mirror symmetry or SYZ in short.

The central physical ingredient in this proposal is T-duality. To explain this, let us consider a superconformal sigma model with target space (M, g), and denote it (defined as a geometric functor, or as a set of correlation functions), as

CFT(M, g)

In physics, a duality is an equivalence

CFT(M, g) ≅ CFT(M′, g′)

which holds despite the fact that the underlying geometries (M,g) and (M′, g′) are not classically diffeomorphic.

T-duality is a duality which relates two CFT’s with toroidal target space, M ≅ M′ ≅ Td, but different metrics. In rough terms, the duality relates a “small” target space, with noncontractible cycles of length L < ls, with a “large” target space in which all such cycles have length L > ls.

This sort of relation is generic to dualities and follows from the following logic. If all length scales (lengths of cycles, curvature lengths, etc.) are greater than ls, string theory reduces to conventional geometry. Now, in conventional geometry, we know what it means for (M, g) and (M′, g′) to be non-isomorphic. Any modification to this notion must be associated with a breakdown of conventional geometry, which requires some length scale to be “sub-stringy,” with L < ls. To state T-duality precisely, let us first consider M = M′ = S1. We parameterise this with a coordinate X ∈ R making the identification X ∼ X + 2π. Consider a Euclidean metric gR given by ds2 = R2dX2. The real parameter R is usually called the “radius” from the obvious embedding in R2. This manifold is Ricci-flat and thus the sigma model with this target space is a conformal field theory, the “c = 1 boson.” Let us furthermore set the string scale ls = 1. With this, we attain a complete physical equivalence.

CFT(S1, gR) ≅ CFT(S1, g1/R)

Thus these two target spaces are indistinguishable from the point of view of string theory.

Just to give a physical picture for what this means, suppose for sake of discussion that superstring theory describes our universe, and thus that in some sense there must be six extra spatial dimensions. Suppose further that we had evidence that the extra dimensions factorized topologically and metrically as K5 × S1; then it would make sense to ask: What is the radius R of this S1 in our universe? In principle this could be measured by producing sufficiently energetic particles (so-called “Kaluza-Klein modes”), or perhaps measuring deviations from Newton’s inverse square law of gravity at distances L ∼ R. In string theory, T-duality implies that R ≥ ls, because any theory with R < ls is equivalent to another theory with R > ls. Thus we have a nontrivial relation between two (in principle) observable quantities, R and ls, which one might imagine testing experimentally. Let us now consider the theory CFT(Td, g), where Td is the d-dimensional torus, with coordinates Xi parameterising Rd/2πZd, and a constant metric tensor gij. Then there is a complete physical equivalence

CFT(Td, g) ≅ CFT(Td, g−1)

In fact this is just one element of a discrete group of T-duality symmetries, generated by T-dualities along one-cycles, and large diffeomorphisms (those not continuously connected to the identity). The complete group is isomorphic to SO(d, d; Z).

While very different from conventional geometry, T-duality has a simple intuitive explanation. This starts with the observation that the possible embeddings of a string into X can be classified by the fundamental group π1(X). Strings representing non-trivial homotopy classes are usually referred to as “winding states.” Furthermore, since strings interact by interconnecting at points, the group structure on π1 provided by concatenation of based loops is meaningful and is respected by interactions in the string theory. Now π1(Td) ≅ Zd, as an abelian group, referred to as the group of “winding numbers”.

Of course, there is another Zd we could bring into the discussion, the Pontryagin dual of the U(1)d of which Td is an affinization. An element of this group is referred to physically as a “momentum,” as it is the eigenvalue of a translation operator on Td. Again, this group structure is respected by the interactions. These two group structures, momentum and winding, can be summarized in the statement that the full closed string algebra contains the group algebra C[Zd] ⊕ C[Zd].

In essence, the point of T-duality is that if we quantize the string on a sufficiently small target space, the roles of momentum and winding will be interchanged. But the main point can be seen by bringing in some elementary spectral geometry. Besides the algebra structure, another invariant of a conformal field theory is the spectrum of its Hamiltonian H (technically, the Virasoro operator L0 + L ̄0). This Hamiltonian can be thought of as an analog of the standard Laplacian ∆g on functions on X, and its spectrum on Td with metric g is

Spec ∆= {∑i,j=1d gijpipj; pi ∈ Zd}

On the other hand, the energy of a winding string is (intuitively) a function of its length. On our torus, a geodesic with winding number w ∈ Zd has length squared

L2 = ∑i,j=1d gijwiwj

Now, the only string theory input we need to bring in is that the total Hamiltonian contains both terms,

H = ∆g + L2 + · · ·

where the extra terms … express the energy of excited (or “oscillator”) modes of the string. Then, the inversion g → g−1, combined with the interchange p ↔ w, leaves the spectrum of H invariant. This is T-duality.

There is a simple generalization of the above to the case with a non-zero B-field on the torus satisfying dB = 0. In this case, since B is a constant antisymmetric tensor, we can label CFT’s by the matrix g + B. Now, the basic T-duality relation becomes

CFT(Td, g + B) ≅ CFT(Td, (g + B)−1)

Another generalization, which is considerably more subtle, is to do T-duality in families, or fiberwise T-duality. The same arguments can be made, and would become precise in the limit that the metric on the fibers varies on length scales far greater than ls, and has curvature lengths far greater than ls. This is sometimes called the “adiabatic limit” in physics. While this is a very restrictive assumption, there are more heuristic physical arguments that T-duality should hold more generally, with corrections to the relations proportional to curvatures ls2R and derivatives ls∂ of the fiber metric, both in perturbation theory and from world-sheet instantons.

Momentum Space Topology Generates Massive Fermions. Thought of the Day 142.0


Topological quantum phase transitions: The vacua at b0 ≠ 0 and b > M have Fermi surfaces. At b2 > b20 + M2, these Fermi surfaces have nonzero global topological charges N3 = +1 and N3 = −1. At the quantum phase transition occurring on the line b0 = 0, b > M (thick horizontal line) the Fermi surfaces shrink to the Fermi points with nonzero N3. At M2 < b2 < b20 + M2 the global topology of the Fermi surfaces is trivial, N3 = 0. At the quantum phase transition occurring on the line b = M (thick vertical line), the Fermi surfaces shrink to the points; and since their global topology is trivial the zeroes disappear at b < M where the vacuum is fully gapped. The quantum phase transition between the Fermi surfaces with and without topological charge N3 occurs at b2 = b20 + M2 (dashed line). At this transition, the Fermi surfaces touch each other, and their topological charges annihilate each other.

What we have assumed here is that the Fermi point in the Standard Model above the electroweak energy scale is marginal, i.e. its total topological charge is N3 = 0. Since the topology does not protect such a point, everything depends on symmetry, which is more subtle. In principle, one may expect that the vacuum is always fully gapped. This is supported by the Monte-Carlo simulations which suggest that in the Standard Model there is no second-order phase transition at finite temperature, instead one has either the first-order electroweak transition or crossover depending on the ratio of masses of the Higgs and gauge bosons. This would actually mean that the fermions are always massive.

Such scenario does not contradict to the momentum-space topology, only if the total topological charge N3 is zero. However, from the point of view of the momentum-space topology there is another scheme of the description of the Standard Model. Let us assume that the Standard Model follows from the GUT with SO(10) group. Here, the 16 Standard Model fermions form at high energy the 16-plet of the SO(10) group. All the particles of this multiplet are left-handed fermions. These are: four left-handed SU(2) doublets (neutrino-electron and 3 doublets of quarks) + eight left SU(2) singlets of anti-particles (antineutrino, positron and 6 anti-quarks). The total topological charge of the Fermi point at p = 0 is N3 = −16, and thus such a vacuum is topologically stable and is protected against the mass of fermions. This topological protection works even if the SU (2) × U (1) symmetry is violated perturbatively, say, due to the mixing of different species of the 16-plet. Mixing of left leptonic doublet with left singlets (antineutrino and positron) violates SU(2) × U(1) symmetry, but this does not lead to annihilation of Fermi points and mass formation since the topological charge N3 is conserved.

What this means in a nutshell is that if the total topological charge of the Fermi surfaces is non-zero, the gap cannot appear perturbatively. It can only arise due to the crucial reconstruction of the fermionic spectrum with effective doubling of fermions. In the same manner, in the SO(10) GUT model the mass generation can only occur non-perturbatively. The mixing of the left and right fermions requires the introduction of the right fermions, and thus the effective doubling of the number of fermions. The corresponding Gor’kov’s Green’s function in this case will be the (16 × 2) × (16 × 2) matrix. The nullification of the topological charge N3 = −16 occurs exactly in the same manner, as in superconductors. In the extended (Gor’kov) Green’s function formalism appropriate below the transition, the topological charge of the original Fermi point is annihilated by the opposite charge N3 = +16 of the Fermi point of “holes” (right-handed particles).

This demonstrates that the mechanism of generation of mass of fermions essentially depends on the momentum space topology. If the Standard Model originates from the SO(10) group, the vacuum belongs to the universality class with the topologically non-trivial chiral Fermi point (i.e. with N3 ≠ 0), and the smooth crossover to the fully-gapped vacuum is impossible. On the other hand, if the Standard Model originates from the left-right symmetric Pati–Salam group such as SU(2)L × SU(2)R × SU(4), and its vacuum has the topologically trivial (marginal) Fermi point with N3 = 0, the smooth crossover to the fully-gapped vacuum is possible.

Black Hole Analogue: Extreme Blue Shift Disturbance. Thought of the Day 141.0

One major contribution of the theoretical study of black hole analogues has been to help clarify the derivation of the Hawking effect, which leads to a study of Hawking radiation in a more general context, one that involves, among other features, two horizons. There is an apparent contradiction in Hawking’s semiclassical derivation of black hole evaporation, in that the radiated fields undergo arbitrarily large blue-shifting in the calculation, thus acquiring arbitrarily large masses, which contravenes the underlying assumption that the gravitational effects of the quantum fields may be ignored. This is known as the trans-Planckian problem. A similar issue arises in condensed matter analogues such as the sonic black hole.


Sonic horizons in a moving fluid, in which the speed of sound is 1. The velocity profile of the fluid, v(z), attains the value −1 at two values of z; these are horizons for sound waves that are right-moving with respect to the fluid. At the right-hand horizon right-moving waves are trapped, with waves just to the left of the horizon being swept into the supersonic flow region v < −1; no sound can emerge from this region through the horizon, so it is reminiscent of a black hole. At the left-hand horizon right-moving waves become frozen and cannot enter the supersonic flow region; this is reminiscent of a white hole.

Considering the sonic horizons in one-dimensional fluid flow, the velocity profile of the fluid as depicted in the figure above, the two horizons are formed for sound waves that propagate to the right with respect to the fluid. The horizon on the right of the supersonic flow region v < −1 behaves like a black hole horizon for right-moving waves, while the horizon on the left of the supersonic flow region behaves like a white hole horizon for these waves. In such a system, the equation for a small perturbation φ of the velocity potential is

(∂t + ∂zv)(∂t + v∂z)φ − ∂z2φ = 0 —– (1)

In terms of a new coordinate τ defined by

dτ := dt + v/(1 – v2) dz

(1) is the equation φ = 0 of a scalar field in the black-hole-type metric

ds2 = (1 – v2)dτ2 – dz2/(1 – v2)

Each horizon will produce a thermal spectrum of phonons with a temperature determined by the quantity that corresponds to the surface gravity at the horizon, namely the absolute value of the slope of the velocity profile:

kBT = ħα/2π, α := |dv/dz|v=-1 —– (2)


Hawking phonons in the fluid flow: Real phonons have positive frequency in the fluid-element frame and for right-moving phonons this frequency (ω − vk) is ω/(1 + v) = k. Thus in the subsonic-flow regions ω (conserved 1 + v for each ray) is positive, whereas in the supersonic-flow region it is negative; k is positive for all real phonons. The frequency in the fluid-element frame diverges at the horizons – the trans-Planckian problem.

The trajectories of the created phonons are formally deduced from the dispersion relation of the sound equation (1). Geometrical acoustics applied to (1) gives the dispersion relation

ω − vk = ±k —– (3)

and the Hamiltonians

dz/dt = ∂ω/∂k = v ± 1 —– (4)

dk/dt = -∂ω/∂z = − v′k —– (5)

The left-hand side of (3) is the frequency in the frame co-moving with a fluid element, whereas ω is the frequency in the laboratory frame; the latter is constant for a time-independent fluid flow (“time-independent Hamiltonian” dω/dt = ∂ω/∂t = 0). Since the Hawking radiation is right-moving with respect to the fluid, we clearly must choose the positive sign in (3) and hence in (4) also. By approximating v(z) as a linear function near the horizons we obtain from (4) and (5) the ray trajectories. The disturbing feature of the rays is the behavior of the wave vector k: at the horizons the radiation is exponentially blue-shifted, leading to a diverging frequency in the fluid-element frame. These runaway frequencies are unphysical since (1) asserts that sound in a fluid element obeys the ordinary wave equation at all wavelengths, in contradiction with the atomic nature of fluids. Moreover the conclusion that this Hawking radiation is actually present in the fluid also assumes that (1) holds at all wavelengths, as exponential blue-shifting of wave packets at the horizon is a feature of the derivation. Similarly, in the black-hole case the equation does not hold at arbitrarily high frequencies because it ignores the gravity of the fields. For the black hole, a complete resolution of this difficulty will require inputs from the gravitational physics of quantum fields, i.e. quantum gravity, but for the dumb hole the physics is available for a more realistic treatment.


Superstrings as Grand Unifier. Thought of the Day 86.0


The first step of deriving General Relativity and particle physics from a common fundamental source may lie within the quantization of the classical string action. At a given momentum, quantized strings exist only at discrete energy levels, each level containing a finite number of string states, or particle types. There are huge energy gaps between each level, which means that the directly observable particles belong to a small subset of string vibrations. In principle, a string has harmonic frequency modes ad infinitum. However, the masses of the corresponding particles get larger, and decay to lighter particles all the quicker.

Most importantly, the ground energy state of the string contains a massless, spin-two particle. There are no higher spin particles, which is fortunate since their presence would ruin the consistency of the theory. The presence of a massless spin-two particle is undesirable if string theory has the limited goal of explaining hadronic interactions. This had been the initial intention. However, attempts at a quantum field theoretic description of gravity had shown that the force-carrier of gravity, known as the graviton, had to be a massless spin-two particle. Thus, in string theory’s comeback as a potential “theory of everything,” a curse turns into a blessing.

Once again, as with the case of supersymmetry and supergravity, we have the astonishing result that quantum considerations require the existence of gravity! From this vantage point, right from the start the quantum divergences of gravity are swept away by the extended string. Rather than being mutually exclusive, as it seems at first sight, quantum physics and gravitation have a symbiotic relationship. This reinforces the idea that quantum gravity may be a mandatory step towards the unification of all forces.

Unfortunately, the ground state energy level also includes negative-mass particles, known as tachyons. Such particles have light speed as their limiting minimum speed, thus violating causality. Tachyonic particles generally suggest an instability, or possibly even an inconsistency, in a theory. Since tachyons have negative mass, an interaction involving finite input energy could result in particles of arbitrarily high energies together with arbitrarily many tachyons. There is no limit to the number of such processes, thus preventing a perturbative understanding of the theory.

An additional problem is that the string states only include bosonic particles. However, it is known that nature certainly contains fermions, such as electrons and quarks. Since supersymmetry is the invariance of a theory under the interchange of bosons and fermions, it may come as no surprise, post priori, that this is the key to resolving the second issue. As it turns out, the bosonic sector of the theory corresponds to the spacetime coordinates of a string, from the point of view of the conformal field theory living on the string worldvolume. This means that the additional fields are fermionic, so that the particle spectrum can potentially include all observable particles. In addition, the lowest energy level of a supersymmetric string is naturally massless, which eliminates the unwanted tachyons from the theory.

The inclusion of supersymmetry has some additional bonuses. Firstly, supersymmetry enforces the cancellation of zero-point energies between the bosonic and fermionic sectors. Since gravity couples to all energy, if these zero-point energies were not canceled, as in the case of non-supersymmetric particle physics, then they would have an enormous contribution to the cosmological constant. This would disagree with the observed cosmological constant being very close to zero, on the positive side, relative to the energy scales of particle physics.

Also, the weak, strong and electromagnetic couplings of the Standard Model differ by several orders of magnitude at low energies. However, at high energies, the couplings take on almost the same value, almost but not quite. It turns out that a supersymmetric extension of the Standard Model appears to render the values of the couplings identical at approximately 1016 GeV. This may be the manifestation of the fundamental unity of forces. It would appear that the “bottom-up” approach to unification is winning. That is, gravitation arises from the quantization of strings. To put it another way, supergravity is the low-energy limit of string theory, and has General Relativity as its own low-energy limit.

Philosophy of Dimensions: M-Theory. Thought of the Day 85.0


Superstrings provided a perturbatively finite theory of gravity which, after compactification down to 3+1 dimensions, seemed potentially capable of explaining the strong, weak and electromagnetic forces of the Standard Model, including the required chiral representations of quarks and leptons. However, there appeared to be not one but five seemingly different but mathematically consistent superstring theories: the E8 × E8 heterotic string, the SO(32) heterotic string, the SO(32) Type I string, and Types IIA and IIB strings. Each of these theories corresponded to a different way in which fermionic degrees of freedom could be added to the string worldsheet.

Supersymmetry constrains the upper limit on the number of spacetime dimensions to be eleven. Why, then, do superstring theories stop at ten? In fact, before the “first string revolution” of the mid-1980’s, many physicists sought superunification in eleven-dimensional supergravity. Solutions to this most primitive supergravity theory include the elementary supermembrane and its dual partner, the solitonic superfivebrane. These are supersymmetric objects extended over two and five spatial dimensions, respectively. This brings to mind another question: why do superstring theories generalize zero-dimensional point particles only to one-dimensional strings, rather than p-dimensional objects?

During the “second superstring revolution” of the mid-nineties it was found that, in addition to the 1+1-dimensional string solutions, string theory contains soliton-like Dirichlet branes. These Dp-branes have p + 1-dimensional worldvolumes, which are hyperplanes in 9 + 1-dimensional spacetime on which strings are allowed to end. If a closed string collides with a D-brane, it can turn into an open string whose ends move along the D-brane. The end points of such an open string satisfy conventional free boundary conditions along the worldvolume of the D-brane, and fixed (Dirichlet) boundary conditions are obeyed in the 9 − p dimensions transverse to the D-brane.

D-branes make it possible to probe string theories non-perturbatively, i.e., when the interactions are no longer assumed to be weak. This more complete picture makes it evident that the different string theories are actually related via a network of “dualities.” T-dualities relate two different string theories by interchanging winding modes and Kaluza-Klein states, via R → α′/R. For example, Type IIA string theory compactified on a circle of radius R is equivalent to Type IIB string theory compactified on a circle of radius 1/R. We have a similar relation between E8 × E8 and SO(32) heterotic string theories. While T-dualities remain manifest at weak-coupling, S-dualities are less well-established strong/weak-coupling relationships. For example, the SO(32) heterotic string is believed to be S-dual to the SO(32) Type I string, while the Type IIB string is self-S-dual. There is a duality of dualities, in which the T-dual of one theory is the S-dual of another. Compactification on various manifolds often leads to dualities. The heterotic string compactified on a six-dimensional torus T6 is believed to be self-S-dual. Also, the heterotic string on T4 is dual to the type II string on four-dimensional K3. The heterotic string on T6 is dual to the Type II string on a Calabi-Yau manifold. The Type IIA string on a Calabi-Yau manifold is dual to the Type IIB string on the mirror Calabi-Yau manifold.

This led to the discovery that all five string theories are actually different sectors of an eleven-dimensional non-perturbative theory, known as M-theory. When M-theory is compactified on a circle S1 of radius R11, it leads to the Type IIA string, with string coupling constant gs = R3/211. Thus, the illusion that this string theory is ten-dimensional is a remnant of weak-coupling perturbative methods. Similarly, if M-theory is compactified on a line segment S1/Z2, then the E8 × E8 heterotic string is recovered.

Just as a given string theory has a corresponding supergravity in its low-energy limit, eleven-dimensional supergravity is the low-energy limit of M-theory. Since we do not yet know what the full M-theory actually is, many different names have been attributed to the “M,” including Magical, Mystery, Matrix, and Membrane! Whenever we refer to “M-theory,” we mean the theory which subsumes all five string theories and whose low-energy limit is eleven-dimensional supergravity. We now have an adequate framework with which to understand a wealth of non-perturbative phenomena. For example, electric-magnetic duality in D = 4 is a consequence of string-string duality in D = 6, which in turn is the result of membrane-fivebrane duality in D = 11. Furthermore, the exact electric-magnetic duality has been extended to an effective duality of non-conformal N = 2 Seiberg-Witten theory, which can be derived from M-theory. In fact, it seems that all supersymmetric quantum field theories with any gauge group could have a geometrical interpretation through M-theory, as worldvolume fields propagating on a common intersection of stacks of p-branes wrapped around various cycles of compactified manifolds.

In addition, while perturbative string theory has vacuum degeneracy problems due to the billions of Calabi-Yau vacua, the non-perturbative effects of M-theory lead to smooth transitions from one Calabi-Yau manifold to another. Now the question to ask is not why do we live in one topology but rather why do we live in a particular corner of the unique topology. M-theory might offer a dynamical explanation of this. While supersymmetry ensures that the high-energy values of the Standard Model coupling constants meet at a common value, which is consistent with the idea of grand unification, the gravitational coupling constant just misses this meeting point. In fact, M-theory may resolve long-standing cosmological and quantum gravitational problems. For example, M-theory accounts for a microscopic description of black holes by supplying the necessary non-perturbative components, namely p-branes. This solves the problem of counting black hole entropy by internal degrees of freedom.

Aristotelian Influence on Hobbes

Let us begin by surveying the forces, which exercised a decisive influence on Hobbes before he turned to Mathematics and Natural Sciences. From 1603 to 1608 he studied at Oxford. During this time, dissatisfied with academic teaching, he turned to classical texts, which he had already read. He read them with the interpretations of grammarians. His purpose in this study was to develop a clear Latin style. The continuation and conclusion of this study was the English translation of Thucydides, which was gradually published in 1628.

At Oxford Hobbes was introduced to scholastic philosophy. He himself recounts that he studied Aristotle’s logic and physics. He makes no mention of studying Aristotle’s morals and politics. According to the traditional curriculum, the formal disciplines viz., grammar, rhetoric, and logic were in the foreground. We may therefore assume that scholastic studies were for Hobbes in the main formal training, and that he acquired the more detailed knowledge of scholasticism, which he afterwards needed for the polemical defence of his own theories. Later on, he did not take up the studies of scholastic studies as he defected to the studies of humanities.

There were four major influences on Hobbes viz., humanism, scholasticism, Puritanism, and aristocracy. But humanism in Hobbes’ youth was the most prominent of all the influences. Hobbes after the end of his university studies read not only classical poets and historians but also classical philosophers. Which philosophers? In a foreword to his translation of Thucydides he say:

It hath been noted by divers, that Homer in poesy, Aristotle in philosophy, Demosthenes in eloquence, and others of the ancients in other knowledge, do still maintain their privacy: none of them exceeded, some not approached, by any in these later ages. And in the number of these is justly ranked also our Thucydides; a workman no less perfect in his work, than any of the former.

Hobbes later considered Plato to be the best philosopher, not the best philosopher of all, but the best philosopher of antiquity. But at the end of his humanist period he repeats without raising any objection the ruling opinion according to which Aristotle is the highest authority in philosophy. The break with Aristotle was completed only when Hobbes took to the studies of mathematics and natural sciences. The polemic against Aristotle is definitely not as violent as it is in Hobbes’ Leviathan and De Cive. In the Elements of Law, in his definition of the State, Hobbes asserts the aim of the State to be, along with peace and defence, common benefit. With this he tacitly admits Aristotle’s distinction between the reason of the genesis of the State and the reason of its being. In the later stages, Hobbes rejects the common benefit and thus defects from the above mentioned Aristotelian distinction. The linkage of Aristotle with Homer, Demosthenes, and Thucydides provides the answer i.e. Aristotle seen from the humanist point of view. Fundamentally it means the shifting of interests from Aristotle’s physics and metaphysics to his morals and politics. It also means the replacement of theory with the primacy of practice. Only if one assumes a fundamental change of this kind does Hobbes’ turning away from scholasticism to poetry and history cease to be a biographical and a historical peculiarity. Even after natural science had become Hobbes’ favourite subject of investigation, he still acknowledged the precedence of practice over theory and of political philosophy over natural science. The joys of knowledge for him was not the justification of philosophy, but rather the justification only in relation of being beneficial to man, i.e. the safeguarding of man’s life and the increase of human power. Where Hobbes develops his own view connectedly, he manifestly subordinates theory to practice. He did not, like Aristotle, attribute prudence to practice and wisdom to theory. He says: ‘Prudence is to wisdom what experience is to knowledge; wisdom is the knowledge ‘of what is right and wrong and what is good and hurtful to the being and the well-being of mankind… For generally, not he that hath skill in geometry, or any other science speculative, but only he that understandeth what conduceth to the good and Government of the people, is called a wise man’. The contrast with Aristotle has its ultimate reason in Hobbes’ conception of the place of man in the universe, which is diametrically opposed to that of Aristotle. Aristotle justified his placing of the theoretical sciences above moral and political philosophy by the argument that man is not the highest being in the universe. This ultimate assumption of the primacy of theory is rejected by Hobbes; in his contention man is ‘the most excellent work of nature’. In this strict sense Hobbes always remained a humanist, and only with the essential limitation which this brings could he recognize Aristotle’s authority in his humanist period.

Even when Hobbes had come to the conclusion that Aristotle was ‘the worst teacher that ever was’, he excepted two works from his condemnation: ‘but his rhetorique and discourse of animals were rare’. It would be difficult to find other classical work whose importance for Hobbes’ political philosophy can be compared with that of the Rhetoric. The central chapters of Hobbes’ anthropology, those chapters on which, more than on anything else he wrote, his fame as a stylist and as one who knows men rests for all time, betray in style and contents that their author was a zealous reader of the Rhetoric. In the 10th chapter of Leviathan, Hobbes treats under the heading ‘Honourable’ with what Aristotle in the Rhetoric discusses. Aristotle says ‘And honourable are the works of virtue. And the sign of virtue. And the reward whereof is rather honour. And those things are honourable which, good of themselves, are not so to the owner…And bestowing of benefits…And honourable are…victory…And things that excel. And what none can do but we. And possessions we reap no profit by. And those things which are had in honour…And the signs of praise’. In reply to this Hobbes comments ‘…victory is honourable…Magnanimity, Liberality, Hope, Courage, Confidence, are Honourable…Actions proceeding from Equity, joyned with losse, are Honourable’.

Let us try to chart out a dependence of Hobbes’ theory of the passions on the Rhetoric. In the Rhetoric, Anger is desire of revenge, joined with grief, for that he, or some of his, is, or seems to be neglected. While in the Elements of Hobbes, Anger hath been commonly defined to be grief proceeding from an opinion of contempt. To kill is the aim of them that hate, revenge aimeth at triumph. In the Rhetoric Pity is a perturbation of the mind, arising from the apprehension of hurt or trouble to another that doth not deserve it, and which he thinks may happen to himself or his. And because it appertains to pity to think that he, or his, may fall into the misery he pities in others; it follows that they may be most compassionate: who have passed through misery. And such as think there be honest men…Less compassionate are they that think no man honest and who are in great prosperity. In Hobbes’ Elements, Pity is imagination or fiction of future calamity to ourselves, proceeding from the sense of another man’s present calamity; but when it lighteth on such as we think does not deserve the same, the compassion is the greater, because then there appeareth the more probability that the same may happen to us. The contrary of pity is the hardness of heart, proceeding from extreme great opinion of their of their own exemption of the like calamity, or from hatred of all, or most men.

In Rhetoric, indignation is the grief for the prosperity of a man unworthy. In the Rhetoric, envy is grief is for the prosperity of such as ourselves, arising not from any hurt that we, but from the good that they receive. Emulation is grief arising from that our equals possess such goods as are had in honour, and whereof we are capable, but have them not; not because they have them, but because not also we. No man therefore emulates another in things whereof himself is not capable. In the Elements, Emulation is grief arising from seeing one’s self exceeded or excelled by his concurrent, together with hope to equal or exceed him in time to come.

Hobbes in his later writings uses passages from the Rhetoric, of which he had made no use of in his earlier writings, it follows that when composing all his systematic expositions of anthropology he studied Aristotle’s Rhetoric afresh each time. Hobbes’ pre-occupation with the Rhetoric can be traced back as far as about 1635. in 1635, Hobbes had considered the writing of personal exposition of the theory of the passions and as just seen, his earliest treatment of the theory of the passions was clearly influenced by Aristotle’s Rhetoric. In addition, he himself recounts that he instructed the third Earl of Devonshire in rhetoric.

Hobbes’ closer study of Aristotle’s Rhetoric may be proved with certainty only for the 1630s, i.e. in the time in which he had overtly completed the break with Aristotelianism. Moreover, one gathers from his introduction to the translation of Thucydides that the phenomenon of eloquence on the one hand, and of the passions on the other, occupied his mind even in the humanist period of his. On the whole, it seems to us more correct to assume that the use and appreciation of Aristotle’s Rhetoric, which may be traced in Hobbes’ mature writings, are the last remnants of the Aristotelianism of his youth. Hobbes after exclusive pre-occupation with poets and historians

Matter Defined as Just Another Quantum State: Whatever Ontologies.


In quantum physics, vacuum is defined as the ground state of a quantum field. It is a state of minimum energy, corresponding to zero particles. Note that this definition of vacuum uses already the conceptual and formal machinery of quantum field theory. It is justifiable to ask weather it is possible to give a more theory-independent definition with lesser theoretical load. In this situation vacuum would be an entity which is explained – not just defined within and then explored – by quantum field theory. For example, one could attempt an operational definition of vacuum as the state in which no particles are detected. But then we have to specify how to detect the particles, with what efficiency, etc., that is, we need a model for the particle detector. Such a model, known as the Unruh-DeWitt detector, is constructed however from within quantum field theory. Unruh-DeWitt detector is a simplified model of a real particle detector. Its basic property is the fact that it is linearly coupled to the field, so that it can detect one-particle states. Indeed, as long as the detector moves inertially in Minkowski spacetime, it really does react to one-particle states and not to the 0-particle state (vacuum). However, when it moves non-inertially, it may react even in the vacuum. The energy needed for the reaction in the vacuum comes from the agency that accelerates the detector (not from the vacuum energy).


The vacuum is simply a special state of the quantum field – implying that quantum physics allows the return of the concept of ether, although in a rather weaker, modified form. This new ether – the quantum vacuum – does not contradict the special theory of relativity because the vacuum of the known fields are constructed to be Lorentz-invariant. In some sense, each particle in motion carries with it its own ether, thus Lorentz transformations act in the same way on the vacuum and on the particle itself. Otherwise, the vacuum state is not that different from any other wavefunction in the Hilbert space. Attaching probability amplitudes to the ground state is allowed to the same degree as attaching probability amplitudes to any other state with nonzero number of particles. In particular, one expects to be able to generate a real property – a value for an observable – in the same way as for any other state: by perturbation, evolution, and measurement. The picture that quantum field theory provides is that both particles and vacuum are now constructed from the same “substance”, namely the quantum states of the fields at each point (or, equivalently, that of the modes). What we used to call matter is just another quantum state, and so is the absence of matter – there is no underlying substance that makes up particles as opposed to the absence of this substance when particles are not present. One could even turn around the tables and say that everything is made of vacuum – indeed, the vacuum is just one special combination of states of the quantum field, and so are the particles. In this way, the difference between the two worldviews, the one where everything is a plenum and vacuum does not exist, and the other where the world is empty space (nonbeing) filled with entities that truly have the attribute of being, is completely dissolved. Quantum physics essentially tells us that there is a third option, in which these two pictures of the world are just two complementary aspects. In quantum physics the objects inhabit at the same time the world of the continuum and that of the discrete.

Incidentally, the discussion has implications for the concept of individuality, a pivotal one both in philosophy and in statistical physics. Two objects are distinguishable if there is at least one property which can be used to make the difference between them. In the classical world, finding this property is not difficult, because any two objects have a large amount of properties that can be analyzed to find a different one. But, because in quantum field theory objects are only combinations of modes, with no additional properties, it means that one can have objects which cannot be distinguished one from each other even in principle. For example, two electrons are perfectly identical. To use a well-known Aristotelian distinction, they have no accidental properties, they are truly made of the same essence.

To see in a simple way why quantum physics requires a re-evaluation of the concept of emptiness, the following qualitative argument is useful: the Heisenberg uncertainty principle shows that, if a state has a well-defined number of particles (zero) the phase of the corresponding field cannot be well-defined. Thus, quantum fluctuations of the phase appear as an immediate consequence of the very definition of emptiness. Another argument can be put forward: the classical concept of emptiness assumes the separability of space in distinct volumes. Indeed, to be able to say that nothing exists in a region of space, we implicitly assume that it is possible to delimitate that region of space from the rest of the world. We do this by surrounding it with walls of some sort. In particular, the thickness of the walls is irrelevant in the classical picture, and, as long as the particles do not have enough energy to penetrate the wall, all that matters is the volume cut out from space. Yet, quantum physics teaches us that, due to the phenomenon of tunneling, this is only possible to some extent – there is, in reality, a non-zero probability for a particle to go through the walls even if classically they are prohibited to do so because they do not have enough energy. This already suggests that, even if we start with zero particles in that region, there is no guarantee that the number of particles is conserved if e.g. we change the shape of the enclosure by moving the walls. This is precisely what happens in the case of the dynamical Casimir effect. These demonstrate that in quantum field theory the vacuum state is not just an inert background in which fields propagate, but a dynamic entity containing the seeds of multiple possibilities, which are actualized once the vacuum is disturbed in specific ways.