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  • Jack Sarfatti Lessons from Classical Gravity about the
    Quantum Structure of Spacetime∗
    T. Padmanabhan
    IUCAA, Pune University Campus, Ganeshkhind,
    Pune 411007, INDIA.
    email:paddy@iucaa.ernet.in
  • Jack Sarfatti ‎"Lesson 2: The guiding principle to use for understanding the quantum microstructure of the spacetime should be the thermodynamics of horizons. Combining the principles of GR and quantum theory is not a technical problem that could be solved just by using sufficiently powerful mathematics. It is more of a conceptual issue and decades of failure of
    sophisticated mathematics in delivering quantum gravity indicates that we should try a different approach. This is very much in tune with item (iii) mentioned in Sec. 1. Einstein did not create a sophisticated mathematical model for mi and mg and try to interpret mi = mg. He used thought experiments to arrive at a conceptual basis in which mi = mg can be interpreted in a natural manner so that mi = mg will cease to be an algebraic accident. Once this is done, physics itself led him to the maths that was needed. Of course, the key issue is what could play the role of a guiding principle similar to principle of equivalence in the present context. For this, my bet will be on the thermodynamics of horizons.[1, 10] A successful model will have the connection between horizon thermodynamics and gravitational dynamics at its foundation rather than this feature appearing as a result derived in the context of certain specific solutions to the field equations. We will see evidence for its importance throughout the discussion in what follows." Yes, I have independently come to similar conclusions, but our future cosmic horizon is primary.
  • Jack Sarfatti Yes! THINK OFF-SHELL! Both UV dark matter and IR dark energy are OFF-SHELL virtual particle quantum vacuum effects in my opinion. "Lesson 3: Think beyond Einstein gravity, black hole thermodynamics and
    think off-shell.
    There are four technical points closely related to the above conjecture (viz., thermodynamics of horizons
    should play a foundational role) which needs to be recognized if this approach has yield dividends:
    • One must concentrate on the general context of observer dependent, local, thermodynamics associated
    with the local horizons, going beyond the black hole thermodynamics. Black hole horizons in the classical theory are far too special, on-shell, global constructs to provide a sufficiently general back-drop to understand the quantum structure of spacetime. The preoccupation with the black
    hole horizons loses sight of the conceptual fact that all horizons are endowed with temperature as perceived by the appropriate class of observers. Observer dependence [11] of thermal phenomena is a feature and not a bug!" EXACTLY! BY JOVE I THINK HE'S GOT IT. ;-)
  • Jack Sarfatti ‎"The quantum features of a theory are off-shell features. But, fortunately, action principle provides a window to quantum theory because of the path integral formalism. Therefore any peculiar feature of a classical action functional could give us insights into the underlying quantum theory much more than the structure of field equations. This suggests that we need to look at the off-shell structure of the theory using the form of action principles rather than tie ourselves down to field equations." Agreed
  • Jack Sarfatti ‎"Lesson 4: Temperature of horizons does not depend on the field equations of the theory and is just an indication that spacetimes, like matter, can be hot, but in a observer-dependent manner." YES!
    "One can associate a temperature with any null surface that can act as horizon for a class of observers, in any spacetime (including flat spacetime)." EXACTLY! "This temperature is determined by the behaviour of the metric close to the horizon and has nothing to do with the field equations (if any) which are obeyed by the metric." OK
  • Jack Sarfatti ‎"The simplest situation is that of Rindler observers in flat spacetime with acceleration κ who will attribute a temperature kBT = (h/c)(κ/2π) to the Rindler horizon — which is just a X = t surface in the flat spacetime having no special significance to the inertial observers." YES. "While this result is usually proved for an eternally accelerating observer, they also hold in the (appropriately) approximate sense for an observer with variable acceleration [15]. In general, this result can be used to show that the vacuum state in a freely falling frame will appear to be a thermal state in the locally accelerated frame for high frequency modes if κ−1 is smaller than the local radius of (spacetime) curvature." CORRECT
  • Jack Sarfatti ‎"Lesson 5: All thermodynamic variables are observer dependent. An immediate consequence, not often emphasized, is that all thermodynamic variables must become observer dependent if vacuum acquires an observer dependent temperature. A “normal” gaseous system
    with “normal” thermodynamic variables (T, S, F etc.....) must be considered as a highly excited state of the inertial vacuum. It is obvious that a Rindler observer will attribute to this highly excited state different thermodynamic variables compared to what an inertial observer will attribute. Thus thermal effects in the accelerated frame brings in [11, 17] a new level of observer dependence even to normal thermodynamics. One need not panic if variables like entropy now acquire an observer dependence and loses their absolute nature." RIGHT
  • Jack Sarfatti ‎"Lesson 6: In sharp contrast to temperature, the entropy of horizons depends on the field equations of gravity and cannot be determined by using just QFT in a background metric."
  • Jack Sarfatti ‎"One would have expected that if integrating out certain field modes leads to a thermal density matrix ρ, then the entropy of the system should be related to lack of information about the same field modes and should be given by S = −Tr ρ ln ρ. This entropy, called entanglement entropy, (i) is proportional to area of the horizon and (ii) is divergent without a cut-off [18]. Such a divergence makes the result meaningless and thus we cannot attribute a unique entropy to horizon using just QFT in a background metric.2 That is, while the temperature of the horizon can be obtained through the study of test-QFT in an external geometry, one cannot understand the entropy of the horizon by the same procedure. This is because, unlike the temperature, the entropy associated with a horizon in the theory depends on the field equations of the theory, which we will briefly review. Given the principle of equivalence (interpreted as gravity being spacetime geometry) and principle of general covariance, one could still construct a wide class of theories of gravity."
  • Jack Sarfatti ‎"Lesson 9: Holographic structure of gravitational action functionals finds a natural explanation in the thermodynamic interpretation of the field equations. If the gravitational dynamics and horizon thermodynamics are so closely related, with field equations becoming thermodynamic identities on the horizon, then the action functionals of the theory (from which we obtain the field equations) must contain information about this connection. This clue comes in the form of another unexplained algebraic accident related to the structure of the action functional and tells us something significant about the off-shell structure of the theory. Gravity is the only theory known to us for which the natural action functional preserving symmetries of the theory contain second derivatives of the dynamical variables but still leads to second order differential equations. Usually, this is achieved by separating out the terms involving the second derivatives of the metric into a surface term which is either ignored or its variation is cancelled by a suitable counter-term. However, this leads to a serious conceptual mystery in the conventional approach when we recall the
    following two facts together: (a) The field equations can be obtained by varying the bulk term after ignoring (or by canceling with a counter-term) the surface term. (b) But if we evaluate the surface term on the horizon of any solution to the field equations of the theory, one obtains the entropy of the horizon! How does the surface term, which was discarded before the field equations were obtained, know about the entropy associated with a solution to those field equations?! In the conventional approach we need to accept it as another ‘algebraic accident’ without any explanation and, in fact, no explanation is possible within the standard framework. The explanation lies in the fact that the surface and bulk term of the Lagrangian are related in a specific manner thereby duplicating the information about the horizon entropy."
  • Jack Sarfatti ‎"The duplication of information between surface and bulk term in Eq. (12) also allows one to obtain the full action [10] from the surface term alone using the entropic interpretation. In fact, in the the Riemann normal coordinates around any event P the gravitational action reduces to a pure surface term, again showing that the dynamical content is actually stored on the boundary rather than in the bulk.
  • Jack Sarfatti one can construct a variational principle to obtain the field equations, purely from the surface term [29]." "Surface" is like the 2D hologram plate. "Bulk" is like the 3D hologram image.
  • Jack Sarfatti ‎"Lesson 10: Gravitational actions have a surface and bulk terms because they give the entropy and energy of a static spacetimes with horizons, adding up to make the action the free energy of the spacetime."
  • Jack Sarfatti ‎"The Avogadro number of the spacetime
    The results described in the previous sections suggest that there is a deep connection between horizon
    thermodynamics and the gravitational dynamics. Because the spacetime can be heated up just like a body of gas, the Boltzmann paradigm (“If you can heat it, it has microstructure”) motivates the study of the microscopic degrees of freedom of the spacetime exactly the way people studied gas dynamics before they understood the atomic structure of matter. There exists, fortunately, an acid test of this paradigm which it passes with flying colours."
  • Jack Sarfatti ‎"Lesson 11: Gravitational field equations imply the law of equipartition E = (1/2)kBTN in any static spacetime, allowing the determination of density of microscopic degrees of freedom. The result again displays holographic scaling." The equipartition theorem is strictly classical breaking down in quantum statistical mechanics where hf/kBT >> 1.
  • Jack Sarfatti That is Bose-Einstein & Fermi-Dirac quantum statistics in the 3D bulk vs. classical Maxwell-Boltzmann statistics. Anyon fractional statistics on the 2D horizons.
  • Jack Sarfatti ‎"It is worthwhile to list explicitly the questions which have natural answers in the emergent paradigm while have to be treated as algebraic accidents in the conventional approach:
    1. While the temperature of the horizon can be obtained using QFT in curved spacetime, the corresponding entanglement entropy is divergent and meaningless. Why?
    2. The temperature of horizon is independent of the field equations of gravity but the entropy of the horizon depends explicitly on the field equations. What does this difference signify?
    3. The horizon entropy can be expressed in terms of the Noether current which is conserved due to diffeomorphism invariance. Why should an infinitesimal coordinate transformation xa → xa + qa have anything to do with a thermodynamic variable like entropy?
    4. Why do the gravitational field equations (which do not look very “thermodynamical”!) reduce to T dS = dEg+PdV on the horizon, picking up the correct expression for S for a wide class of theories?
    5. How come all gravitational action principle have a surface and bulk term which are related in a specific manner (see Eq. (12))? Why do the surface and the bulk terms allow the interpretation as entropy and energy in static spacetimes?
    6. The field equations for gravity can be obtained from the bulk part of the action after discarding the surface term. But the surface term evaluated on the horizon of a solution gives the entropy of the horizon! How does the surface term — which was discarded before the field equations were obtained
    — know about the entropy of a solution?
    7. Why does the gravitational field equations reduce to the equipartition form, expressible as E = (1/2)(kBT )n allowing us to determine the analog of Avogadro’s number for the spacetime? And, why does the relevant microscopic degrees of freedom for a region reside on the boundary of the
    region?
    8. Finally, why is it possible to derive the field equations of any diffeomorphism invariant theory of gravity by extremizing an entropy functional associated with the null surfaces in the spacetime, without treating the metric as a dynamical variable? Obviously, any alternative perspective, including the conventional approach, need to provide the answers for the above questions if they have to be considered a viable alternative to emergent paradigm."


Light hadron masses from lattice QCD
Reviews of Modern Physics – April - June 2012 Volume 84, Issue 2


Zoltan Fodor and Christian Hoelbling
One of the most basic tests of quantum chromodynamics in the strong coupling regime is whether it can successfully predict the spectrum of light hadron masses in terms of a small number of inputs. This article surveys the status of lattice calculations of the spectrum, including the formalism, theoretical uncertainties, and current results. The calculations successfully reproduce relevant parts of the observed spectrum at the percent level.
Published 4 April 2012 (47 pages)
pp. 449-495 [View PDF (1,712 kB)]

So who needs Mach’s Principle for the origin of inertia?

Bearing in mind Basil Hiley’s remark:

To build in wholeness in this preliminary way, we stressed in the UU that the "particle and the field were never separate".  Here we were motivated by the work of Frederick Frank at Bristol and Bilby and his co-workers at Sheffield.  They had been exploring the geometry of continuous dislocations in crystals and had shown that the equation of migration of dislocation was similar to a relativistic particle dynamics which involved the speed of sound rather than the speed of light. Furthermore the stress forces in the lattice had a similar form to electromagnetic fields.  Notice you can't separate the particle from the field: no lattice, no particle implies no field, no particle.  We do not give any meaning to the statement that 'the particle is in one of the wave packets'. That is, questions about "empty wave packets" has no meaning in the structure we had in mind.



Gaussian quantum information
Christian Weedbrook, Stefano Pirandola, Raúl García-Patrón, Nicolas J. Cerf, Timothy C. Ralph, Jeffrey H. Shapiro, and Seth Lloyd
Quantum information processing and communication protocols are typically expressed in terms of discrete units of information, the quantum bits (or qubits). However, certain experimental setups involving, for instance, light or atomic ensembles, are based on continuous quantum system and, in particular, on Gaussian states and operations. This review adapts the main ideas and protocols in the field of quantum information to such systems, and explains their advantages and limitations.
Published 1 May 2012 (49 pages)
pp. 621-669 [View PDF (1,385 kB)]

Glauber states are displaced Gaussians in the phase space of the quantum oscillator normal mode.

Theoretical aspects of massive gravity
Kurt Hinterbichler
The discovery that the expansion rate of the Universe is accelerating, perhaps due to a nonzero and very small cosmological constant, has led to many speculations regarding modifications to the long distance structure of general relativity. This review discusses modifications which generate a mass for the graviton from a theoretical point of view and includes a treatment of diffeomorphism invariance, interactions, and the low-energy effective field theory treatment of such theories.
Published 7 May 2012 (40 pages)
pp. 671-710 [View PDF (758 kB)]

Dual pairing of symmetry and dynamical groups in physics
D. J. Rowe, M. J. Carvalho, and J. Repka
Symmetries, group theory, and the related theory of Lie algebras underlie quantum mechanics and provide the essential language for the interpretation of physical phenomena. This review discusses foundations and applications of dual representations of pairs of symmetry and dynamical groups primarily in atomic and nuclear physics, especially in the context of bosonic and fermionic many-body systems such as superconductors, molecules, and nuclei. By studying such dual subgroup chains, associations of phenomenological many-body models with microscopic approaches are revealed.
Published 11 May 2012 (47 pages)
pp. 711-757 [View PDF (1,104 kB)]

Colloquium: Supersolids: What and where are they?
Massimo Boninsegni and Nikolay V. Prokof’ev
Supersolid is the name of an exotic quantum phase of matter, combining the seemingly antithetical properties of crystal and superfluid phases. This phase is expected to exist in rather extreme circumstances, for example, in solid helium near absolute zero. Indeed, claims of its experimental observation have been made. This Colloquium reviews the bulk of the existing phenomenology and offers an interpretation of it, based on theoretical results of first principle computer simulations. Other physical systems in which the supersolid phase might be observed in the laboratory are also described.
Published 11 May 2012 (18 pages)
pp. 759-776 [View PDF (861 kB)]

I predicted super solids before Tony Leggett I think? See my publication list on Wikipedia.

Multiphoton entanglement and interferometry
Jian-Wei Pan, Zeng-Bing Chen, Chao-Yang Lu, Harald Weinfurter, Anton Zeilinger, and Marek Żukowski
Light is made out of photons, which now can be efficiently created, manipulated, and detected. This provides us with the possibility of testing several fundamental aspects of quantum mechanics, ranging from the quantization of energy to the superposition principle, or the violation of Bell inequalities. Also, the degree of control that has been achieved over the properties of the photons has opened up a broad spectrum of applications in the context of quantum information science. This review provides an introduction to multiphoton systems, with an emphasis on their entanglement properties. It also contains an exposition of the fundamental tests that have been carried so far with such systems, as well as the key experiments on quantum communication and computation.
Published 11 May 2012 (62 pages)
pp. 777-838 [View PDF (4,466 kB)]


How higher-spin gravity surpasses the spin-two barrier
Xavier Bekaert, Nicolas Boulanger, and Per A. Sundell
Gauge theories mediate forces through particle of spin one while the gravitational force is mediated through particles of spin two. It has long been thought that there are no consistent theories with fundamental particles of spin greater than 2, but recent constructions show that while this standard lore is probably true in flat spacetimes, spaces with constant curvature that occur in the presence of a cosmological constant provide a loophole that allows construction of consistent higher-spin generalizations of gravity. This review explains the original no-go results in flat space and then discusses the construction of higher-spin theories in backgrounds with a cosmological constant.
Published 3 July 2012 (23 pages)
pp. 987-1009 [View PDF (453 kB)]

In my gauge theory of gravity, the basic LIF tetrads are compensating spin 1 vector fields from localizing the universal space-time symmetry group for all matter fields. Einstein’s spin 2 gravity would be something analogous to a Cooper pair, i.e. an entangled triplet of a pair of spin 1 quanta with S-state orbital. Of course “graviton" higher spin states with P, D ... orbitals are conceivable. Of course a Cooper pair of spin 1/2 electrons are bound by spin 0 phonons - what binds the gravity tetrads into a pair?
Self interaction? Virtual spin 0 Higgs?