Scott Douglas Jacobsen (Email: scott.jacobsen2026@gmail.com)

Publisher, In-Sight Publishing

Fort Langley, British Columbia, Canada

Received: October 25, 2025

Accepted: January 8, 2026

Published: March 22, 2026

Abstract

This interview with Prof. Dr. İzzet Sakallı explores several live questions in black-hole physics, holography, and quantum gravity phenomenology. Topics include whether thermal fluctuations threaten the Kovtun-Son-Starinets bound in quantum-corrected AdS black holes, how thermodynamic topology may be defined in a coordinate-independent and ensemble-stable way, and what unifies linear dilaton, Newman-Unti-Tamburino, and Bardeen geometries. The discussion also compares higher-order WKB methods and neural networks for extracting quasinormal modes, examines where the Hamilton-Jacobi tunneling method breaks down in Hawking-radiation derivations, and identifies the kind of falsifiable predictions needed to curb post-hoc parameter tuning in quantum-gravity phenomenology. Together, the interview presents a panoramic view of how gravity, thermodynamics, topology, and observational testing intersect at the frontier of contemporary theoretical physics.

Keywords

AdS black holes, black-hole thermodynamics, Hamilton-Jacobi tunneling, holography, KSS bound, quantum gravity phenomenology, quasinormal modes, thermodynamic topology, WKB method

Introduction

Black-hole physics remains one of the most fertile meeting grounds for gravitation, quantum theory, thermodynamics, and information theory. In recent decades, holography, quantum corrections, modified gravity, and computational methods have broadened the conceptual and technical landscape, making black holes not merely endpoints of gravitational collapse but laboratories for probing the structure of physical law itself.

In this interview, Prof. Dr. İzzet Sakallı discusses several of the most conceptually demanding issues at that frontier. The conversation ranges from the stability of the Kovtun-Son-Starinets bound under thermal fluctuations to coordinate-independent definitions of thermodynamic topology, from “hairy” black-hole geometries to the comparative strengths of semiclassical and machine-learning approaches for quasinormal mode extraction. The exchange concludes by asking what kinds of genuinely falsifiable predictions could move quantum-gravity phenomenology beyond flexible post-hoc fitting and toward more rigorous empirical discipline.

Main Text (Interview)

Title: Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4)

Interviewer: Scott Douglas Jacobsen

Interviewees: Prof. Dr. İzzet Sakallı

Professor Izzet Sakallı is a theoretical physicist at Eastern Mediterranean University whose research bridges quantum mechanics, general relativity, and observational astronomy. With over 180 publications exploring black hole thermodynamics, modified gravity theories, and quantum corrections to spacetime, his work sits at the exciting frontier where abstract mathematics meets observable reality. In this interview, he discusses the challenges of testing exotic gravity theories, the quest to observe quantum effects in astrophysical systems, and what the next generation of telescopes and gravitational wave detectors might reveal about the quantum nature of spacetime. 

Scott Douglas Jacobsen: Do thermal fluctuations genuinely threaten the Kovtun-Son-Starinets bound in quantum-corrected AdS black holes? 

Prof. Dr. ˙Izzet Sakallı: The Kovtun-Son-Starinets bound represents a proposed fundamental limit on how viscous any fluid can be relative to its entropy density. Viscosity measures how much a fluid resists flow—honey has high viscosity, water much less. The KSS bound suggests that the ratio of shear viscosity to entropy density cannot fall below a specific value involving Planck’s constant. If true, this would represent a universal constraint on all matter, from quark-gluon plasma to neutron star interiors. 

The bound emerges from AdS/CFT calculations. Black holes in AdS spacetime are extraordinarily good fluids—they flow with minimal viscosity. Computing their viscosity-to-entropy ratio via holography yields exactly the proposed bound. This isn’t coincidental; it reflects deep connections between gravity, thermodynamics, and hydrodynamics. 

But black holes, like all physical systems, experience thermal fluctuations. The horizon position fluctuates quantum mechanically. The area, and hence entropy, fluctuates. If we compute viscosity at one instant and entropy at another, might their ratio momentarily dip below the bound? 

The consensus among researchers is that thermal fluctuations do not genuinely threaten the bound, for several subtle reasons. First, the bound applies to ensemble-averaged, thermodynamic quantities, not to instantaneous microscopic configurations. Just as temperature represents average kinetic energy, not the energy of any individual molecule, the viscosity-to-entropy ratio reflects macroscopic, coarse-grained properties. Fluctuations around these averages don’t violate the bound any more than individual fast molecules violate temperature definitions. 

Second, causality protects the bound. Any configuration violating the bound would allow signals to propagate faster than light in the dual field theory. Such acausal behavior is forbidden by fundamental physics. Thermal fluctuations, no matter how large, cannot create causality violations because they’re constrained by the same underlying quantum field theory that enforces causality. 

Third, the fluctuation-dissipation theorem provides a deep connection between fluctuations and transport coefficients. This theorem ensures that fluctuations and viscosity vary in coordinated ways, preserving bounds even when individual quantities fluctuate substantially. If the entropy fluctuates upward, viscosity adjusts accordingly; if entropy dips, viscosity decreases proportionally. The ratio remains bounded. 

Fourth, quantum corrections modify the bound in controlled, calculable ways. Adding higher derivative terms to gravity, incorporating string theory corrections, or including additional fields shifts the bound’s value. It might become slightly larger or smaller, but a lower bound persists. The bound moves rather than disappears. 

In quantum-corrected AdS black holes—those including effects from Gauss-Bonnet gravity, dila ton fields, or other modifications—the situation becomes more intricate. These corrections alter both the entropy and the viscosity. Causality constraints in the modified theory ensure the bound adapts accordingly. Some theories predict the ratio slightly exceeds the standard bound; others might approach it from above. But violations remain absent. 

Experimental tests come from heavy-ion collisions creating quark-gluon plasma. Measurements consistently find viscosity-to-entropy ratios just slightly above the KSS bound—the lowest values ever measured for any substance. This near-saturation suggests the bound is indeed fundamental, and thermal fluctuations in these terrestrial experiments don’t cause violations. 

The key insight is distinguishing instantaneous fluctuations from thermodynamic properties. A single molecule in water might momentarily move faster than the sound speed in water, but that doesn’t violate the principle that sound waves propagate at a characteristic speed. Similarly, momentary excursions of viscosity or entropy don’t violate bounds on their thermodynamic ratio. 

Jacobsen: What is an operational, coordinate-independent definition of thermodynamic topology, and how should ensembles be chosen so invariants are well-posed? 

Sakallı: Thermodynamic topology represents a modern mathematical approach to understanding phase transitions through topological invariants—quantities that remain unchanged under continuous deformations. Rather than characterizing phases by specific values of temperature or pressure, topological methods classify them by global geometric properties that don’t depend on coordinate choices or units. 

The key idea is treating thermodynamic state space as a geometric manifold. Every possible equilibrium state—characterized by temperature, pressure, entropy, volume, and other thermodynamic variables—represents a point in this space. Thermodynamic potentials like Gibbs free energy or Helmholtz free energy define scalar fields on this manifold. Critical points, where derivatives of these potentials vanish, act as topological defects. 

An operational definition requires coordinate independence—the formulation shouldn’t depend on whether we describe states using temperature and pressure versus energy and volume. This is achieved using differential geometric objects. We can define a thermodynamic metric on the space of extensive variables, measuring ”distance” between thermodynamic states. The curvature of this metric provides coordinate-independent information about thermodynamic stability and fluctuations. 

Critical points are classified by their topological charge or winding number. Imagine walking a closed loop around a critical point in state space and tracking how the gradient vector of free energy rotates. The number of complete rotations—the winding number—is a topological invariant integer that classifies the critical point. Different types of phase transitions have different winding numbers. 

For black holes, we can construct thermodynamic state space using entropy, pressure (related 14 to cosmological constant), electric charge, and angular momentum as coordinates. The mass, expressed as a function of these variables, serves as the thermodynamic potential. Critical points where the temperature vanishes or diverges represent phase transitions. 

Ensemble selection is crucial for well-posed invariants. Different ensembles—microcanonical (fixed energy), canonical (fixed temperature), or grand canonical (fixed chemical potential)—describe different statistical situations. The key insight is that these are related by Legendre transformations, which are coordinate changes in a broader geometric structure called the thermodynamic phase space. This space combines position-like variables (extensive quantities) with momentum like variables (their conjugate intensive quantities). 

On this phase space, we can define a symplectic structure—a geometric object describing how variables are paired. This structure is ensemble-independent. Topological invariants computed using this structure remain consistent across different ensembles. A critical point in the canonical ensemble corresponds to a critical point in the grand canonical ensemble; they’re the same feature viewed in different coordinates. 

For well-posed invariants, the thermodynamic manifold should be compactified—made compact by appropriately treating infinities. Temperature ranging from zero to infinity can be mapped to a finite interval, allowing global topological analysis. The compactification must respect physical symmetries and boundary conditions. 

In AdS black holes, choosing the extended phase space—treating the cosmological constant as a thermodynamic variable—proves particularly natural. This choice reveals phase transitions analogous to Van der Waals fluids, with pressure-volume diagrams exhibiting critical points. The topological charges of these critical points sum to a conserved total determined by the manifold’s Euler characteristic. 

Quantum corrections introduce additional subtlety. As quantum effects modify thermodynamic potentials, critical points can appear, disappear, or merge. Each such event represents a topology-changing transition. Tracking these changes as quantum corrections increase provides a window into how quantum gravity reorganizes phase structure. 

The physical interpretation suggests that topological charges count something fundamental—perhaps distinct classes of microstates, or different ways the horizon can be organized. The conservation of total topological charge reflects deep consistency requirements of quantum gravity. 

Jacobsen: What phenomenologically unifies linear dilation, Newman-Unti-Tamburino, and Bardeen geometries? 

Sakallı: These three solutions—linear dilaton black holes from string theory, Newman-Unti-Tamburino spacetimes with gravitomagnetic charge, and Bardeen’s regular black holes—appear quite different at first glance. Yet they share profound phenomenological connections revealing general principles about black holes beyond Kerr-Newman. 

All three geometries possess additional structure beyond mass, charge, and angular momen tum—often called ”hair” in violation of the classical no-hair theorems. Linear dilaton solutions carry a scalar field that varies logarithmically with radius. NUT solutions possess gravitomag netic monopole charge, a topological feature without Newtonian analog. Bardeen black holes have magnetic charge manifesting as a regular core replacing the central singularity. This hair isn’t arbitrary; it emerges from extending general relativity or including additional fields. 

Their asymptotic structures differ from standard asymptotically flat spacetime. Linear dilaton spacetimes have a diverging scalar field at infinity. NUT geometries possess the Misner string—a pathological line at spatial infinity requiring careful boundary conditions. Bardeen solutions have modified falloff due to distributed magnetic charge. All require generalized asymptotic conditions, revealing that ”asymptotic flatness” is more subtle than introductory relativity suggests. 

Thermodynamically, all three exhibit modified Hawking temperature and entropy. The modifications follow a universal pattern: the standard Schwarzschild results get multiplied by functions of the hair parameter. The temperature of a dilaton black hole includes an exponential factor involving the dilaton field. NUT temperature includes corrections from gravitomagnetic charge. Bardeen temperature depends on the magnetic charge parameter. The entropy likewise deviates from the simple area formula, with corrections encoding the additional degrees of freedom associated with hair. 

These entropy modifications respect a generalized area law where an effective area—incorporating hair contributions—still determines entropy. This suggests the holographic principle, relating bulk information to boundary area, holds in generalized form. The additional fields contribute to the effective boundary. 

Regarding singularity structure, all three modify the standard Schwarzschild singularity differently. Linear dilaton solutions have singularities shielded or altered by the scalar field. NUT geometries have intricate singularity structure involving closed timelike curves requiring careful causal analysis. Bardeen solutions eliminate singularities entirely, replacing them with regular de Sitter-like cores. These varied approaches to singularity avoidance suggest multiple paths toward resolving gravitational singularities may exist in quantum gravity. 

Their geodesic structures—paths of freely falling particles and light rays—show similar modifications. Photon spheres where light can orbit shift from the standard Schwarzschild radius. Innermost stable circular orbits for massive particles shift comparably. Perihelion precession of nearly-circular orbits acquires additional contributions. These modifications, though arising from different physics, follow comparable patterns mathematically. 

All three connect to electromagnetic duality in intriguing ways. Bardeen emerges from nonlinear electrodynamics—generalizations of Maxwell’s equations. NUT charge represents the gravitational analog of magnetic monopoles. Dilaton couplings modify electromagnetic propagation. This hints at deep unity between electromagnetic and gravitational phenomena at fundamental levels. 

Symmetry-wise, each possesses enhanced symmetry algebras beyond standard Poincare invariance. Dilaton solutions have shift symmetries of the scalar field. NUT geometries have dual rotations mixing time and azimuthal angle. Bardeen solutions have scaling symmetries. These additional symmetries generate conserved charges beyond standard Komar mass and angular momentum. 

The unifying framework is an extended action including Einstein gravity plus matter fields or higher-derivative corrections. Different choices of potentials, coupling functions, and field content yield the three geometries. This suggests a landscape of black hole solutions, with Kerr Newman representing one island and dilaton, NUT, and Bardeen representing others. Mapping this landscape and understanding transitions between regions remains an active research area. 

Observationally, all three predict similar phenomenology: modified shadows compared to Schwarzschild, altered gravitational wave signals from inspiraling particles, changed accretion disk emission due to shifted ISCOs. Current constraints from EHT and LIGO place weak bounds on hair parame ters—typically limiting deviations to tens of percent of the black hole mass. Future observations will tighten these constraints or potentially reveal hair, revolutionizing our understanding of black hole uniqueness. 

Jacobsen: What are the comparative pitfalls of higher-order WKB versus neural networks for extracting Quasinormal Modes? 

Sakallı: Quasinormal modes—the characteristic oscillation frequencies of perturbed black holes—encode crucial information about spacetime structure. Computing them requires solving differential equations that generally lack closed-form solutions. Two modern approaches dominate: higher order WKB methods and neural network techniques. Each has strengths and weaknesses that researchers must navigate carefully. 

The WKB method, named for Wentzel, Kramers, and Brillouin, treats wave propagation in slowly varying media using semiclassical approximation. For QNM calculations, we apply WKB to the radial equation governing perturbations. Standard WKB gives zeroth-order frequencies; higher-order corrections systematically improve accuracy. Modern implementations extend to sixth or even thirteenth order, achieving extraordinary precision. 

The primary pitfall of higher-order WKB is its convergence properties. For highly damped modes—those decaying very rapidly—the WKB series can converge slowly or even diverge. The approximation assumes the potential varies slowly compared to wavelength, but highly damped modes have such short effective wavelengths that this breaks down. Researchers must carefully assess whether their WKB order is sufficient for target accuracy. 

Coordinate dependence presents another subtlety. WKB results technically depend on coordi nate choice used to define the radial coordinate. Different gauges—Schwarzschild, Eddington Finkelstein, Painlev´e-Gullstrand—yield formally different WKB expressions. For lower-order calculations, these differences can affect precision, though they vanish in principle for infinite order WKB. Practitioners must verify coordinate independence numerically. 

Boundary conditions require careful implementation. QNMs demand purely ingoing waves at the horizon and purely outgoing waves at infinity. Imposing these conditions in WKB involves matching solutions across turning points using connection formulas. Errors in these formulas propagate through higher orders, potentially degrading accuracy despite increased computational effort. 

Neural networks offer a radically different approach. We train networks to learn the relationship between black hole parameters and QNM frequencies using examples. Once trained, the network evaluates new cases nearly instantaneously—far faster than iterative WKB calculations. 

The major pitfall of neural networks is training data requirements. Networks learn from examples, so we need extensive, accurate training sets. Generating these sets typically requires running many WKB or numerical integration calculations anyway—potentially more work than just computing the specific cases we ultimately want. This ”cold start” problem limits neural network utility for truly novel black hole solutions. 

Extrapolation reliability poses another challenge. Neural networks interpolate well within their training domain but extrapolate poorly outside it. If we train on nearly-Schwarzschild black holes then apply the network to highly modified gravity, predictions may be wildly inaccurate without warning. Unlike WKB, which breaks down detectably when approximations fail, neural networks can confidently output nonsensical results for out-of-distribution inputs. 

Interpretability is limited. WKB calculations reveal how specific features of the spacetime potential affect QNM frequencies—physicists gain intuition about why certain modifications shift modes in particular directions. Neural networks are black boxes; they predict accurately but offer little insight into underlying physics. For research aiming to understand relationships between geometry and modes, this opacity is problematic. 

Overfitting is an ever-present danger. Networks can memorize training data rather than learning underlying patterns, performing excellently on training sets but poorly on test cases. Preventing overfitting requires careful regularization, cross-validation, and architecture choices—requiring expertise in machine learning beyond typical physicist training. 

Combining approaches offers promising paths forward. Use WKB to generate training data for neural networks, then deploy networks for fast exploration of parameter space. Use networks to identify interesting regimes, then apply higher-order WKB for rigorous verification. This hybrid strategy leverages each method’s strengths while mitigating weaknesses. 

For modified gravity theories, another consideration arises: equation complexity. WKB handles analytically tractable potentials well; extremely complicated potentials—common in higher derivative gravity—challenge even high-order WKB. Neural networks don’t care about analytical complexity; they work equally well for simple and complicated systems. This makes them attractive for theories where WKB applicability is questionable. 

Question 17: Where does the Hamilton-Jacobi tunneling method break down for Hawking radiation derivations? 

The Hamilton-Jacobi method provides an elegant semiclassical approach to deriving Hawking radiation, treating particle creation as quantum tunneling through the black hole horizon. A particle-antiparticle pair forms just inside the horizon; if the negative-energy antiparticle tunnels inward while the positive-energy particle escapes, the black hole loses mass and radiates. This picture, while intuitive, has important limitations that researchers must appreciate. 

The method works beautifully for static, spherically symmetric black holes—Schwarzschild being the canonical example. We write the particle action, apply Hamilton-Jacobi formalism to find classical trajectories, then quantize by imposing quantum penetration factors. The resulting thermal spectrum matches Hawking’s original quantum field theory calculation in curved spacetime. This concordance validates the tunneling picture as a useful computational tool. 

However, the method’s breakdown begins with rotating black holes. Kerr geometry allows particles with different angular momenta to tunnel with different probabilities. The straightforward Hamilton-Jacobi approach, treating radial motion independently, misses angular momentum correlations between particle-antiparticle pairs. More sophisticated treatments incorporating angular dependence become vastly more complicated, and it’s unclear whether they capture all relevant physics. 

For charged black holes, electromagnetic interactions introduce additional subtlety. The tunneling particle interacts with the black hole’s electric field during tunneling. Standard Hamilton Jacobi treats this as background, but quantum fluctuations of the electromagnetic field itself should contribute. Including these backreactions requires going beyond semiclassical approximation to full quantum electrodynamics in curved spacetime—precisely what Hamilton-Jacobi aims to avoid. 

Near extremality—when black holes approach maximum rotation for their mass or maximum charge—the surface gravity (related to temperature) approaches zero. Hamilton-Jacobi predicts vanishing emission, consistent with zero temperature. But quantum corrections become increasingly important as extremality approaches, and the semiclassical picture breaks down entirely. Some calculations suggest extremal black holes might emit radiation quantum mechanically even with classically zero temperature. Hamilton-Jacobi cannot capture this. 

Backreaction poses a fundamental limitation. As the black hole emits radiation, it loses mass, the horizon shrinks, and the geometry changes. Hamilton-Jacobi treats geometry as fixed—a probe particle tunneling through static spacetime. This is justified for large black holes emitting negligibly few particles, but becomes untenable for small black holes or long timescales. The method cannot self-consistently describe black hole evaporation from formation to complete disappearance. 

Information paradox considerations highlight deeper issues. Hamilton-Jacobi treats emission as random, independent particles—a thermal, maximum-entropy process. But Hawking radiation must ultimately carry information about the black hole’s formation to preserve quantum unitarity. This information transfer requires correlations between emitted particles across vast times and distances, impossible to capture in a local tunneling picture. 

Greybody factors—modifications to the spectrum from backscattering of radiation by the curved geometry outside the horizon—require separate calculation beyond Hamilton-Jacobi. The tunneling method gives emission at the horizon, but observable radiation reaching distant detectors differs due to scattering. Computing these factors demands solving wave equations in the full geometry, reintroducing much of the complexity Hamilton-Jacobi was meant to avoid. 

Trans-Planckian physics presents another concern. The tunneling picture involves wavelengths much smaller than the horizon size, potentially reaching Planck scales for high-frequency modes. At these scales, quantum gravity effects become important, and the classical geometry description underlying Hamilton-Jacobi becomes questionable. The method implicitly assumes space time remains classical arbitrarily close to the horizon—an assumption quantum gravity will likely violate. 

For analog systems—condensed matter systems mimicking black hole physics—the Hamilton Jacobi method’s applicability is even more limited. These systems have atomic discreteness, finite dispersion relations, and other features absent in general relativity. While they can exhibit Hawking-like radiation, the tunneling interpretation becomes strained when applied to systems without genuine event horizons. 

Despite these limitations, the Hamilton-Jacobi method remains valuable pedagogically and computationally. It provides intuitive pictures for Hawking radiation, yields correct temperature and spectrum for simple cases, and extends straightforwardly to many modified gravity theories. Recognizing its limitations helps researchers know when to trust its predictions and when more sophisticated approaches are needed. 

Question 18: What specific falsifiable predictions would curb post-hoc parameter tuning in quantum gravity phenomenology? 

Quantum gravity phenomenology faces a credibility challenge: theories often have enough free parameters that they can be adjusted post-hoc to match any observation. This parameter tuning prevents genuine falsification—if a prediction fails, we tweak parameters rather than abandoning the theory. Establishing specific, falsifiable predictions immune to such tuning is crucial for making progress. 

The gold standard would be parameter-free predictions—relationships between observables that don’t depend on unknown quantum gravity parameters. For instance, if a theory predicts a specific numerical relationship between the black hole shadow radius and quasinormal mode frequency, both measurable independently, this can be tested without tuning. Few theories make such definitive predictions, but seeking them should be a priority. 

Universal relations provide another approach. Even if individual quantities depend on parameters, ratios or combinations might be parameter-independent. The KSS bound on viscosity-to entropy ratio exemplifies this: it predicts a specific numerical value regardless of system details. Discovering similar universal relations involving multiple observables would provide robust tests. 

Null tests—observations specifically designed to yield zero if general relativity is correct and nonzero for alternatives—offer powerful falsification opportunities. Testing whether gravitational waves and light from the same event arrive simultaneously constrains graviton mass without needing to know its value a priori. A non-zero time delay would falsify massless gravitons regardless of other parameters. 

Multiple independent observations of the same system provide consistency checks resistant to tuning. If we measure a black hole’s mass from gravitational waves, from its shadow size, from orbital dynamics of nearby stars, and from X-ray spectroscopy, all four measurements should agree. Quantum gravity corrections affect these differently; consistent corrections across all channels constrain parameters far more tightly than single observations. 

Population-level predictions avoid tuning for individual objects. Rather than fitting parameters separately for each black hole, we predict how populations should distribute. For instance, quantum gravity might predict correlations between mass and spin in black hole populations, or specific cutoffs in the mass distribution. Such statistical predictions can’t be easily tuned away by adjusting parameters post-hoc. 

Time-dependent predictions are especially robust. If quantum gravity corrections grow with time—as some models suggest—long-baseline observations should reveal secular trends. Bi nary pulsar timing, monitored for decades, provides such long-baseline data. Any deviations accumulating systematically over forty years constrain time-dependent effects powerfully. 

Coincidence predictions—multiple effects occurring simultaneously at specific conditions—resist tuning. For example, if a theory predicts that at some critical black hole spin, both the shadow shape and the QNM spectrum exhibit specific anomalies, observing one without the other would falsify it despite parameter freedom. 

Selection rules—categorical predictions that certain processes cannot occur—provide binary tests. If quantum gravity forbids specific decay channels or transition types, observing them falsifies the theory definitively. No parameter tuning can resurrect a theory after an iron-clad selection rule is violated. 

For practical implementation, the community needs coordinated predictions across modified gravity theories. Rather than each theory making custom predictions incomparable to others, we should identify key observables and have each theory make specific predictions for them. This matrix of predictions versus theories would reveal which observations most powerfully discriminate alternatives. 

Multi-messenger observations—combining electromagnetic, gravitational wave, and potentially neutrino observations of the same event—provide cross-checks limiting tuning. The more independent channels we observe, the more constrained parameters become. Future observations of black hole mergers with electromagnetic counterparts will be particularly valuable. 

Blinding analysis protocols, borrowed from particle physics, could help. Observers can provide data with key features hidden until theorists commit to predictions, preventing unconscious bias toward expected results. This procedural protection complements structural protections against parameter tuning. 

Discussion

This interview presents black-hole physics as a domain in which thermodynamics, geometry, topology, and phenomenology are no longer separable intellectual provinces. The KSS bound, thermodynamic topology, non-standard black-hole geometries, quasinormal-mode extraction, Hawking-radiation derivations, and quantum-gravity testing all converge on a common question: how should one distinguish elegant mathematical possibility from physically robust structure?

A recurring theme is controlled modification rather than unrestricted breakdown. Thermal fluctuations do not abolish the viscosity bound but require more careful interpretation of ensemble-averaged quantities. Quantum corrections do not erase phase structure but reorganize it. Non-Kerr geometries do not abandon black-hole thermodynamics but generalize it. Computational methods do not remove analytic judgment but redistribute it between approximation schemes and data-driven inference. At the phenomenological level, the strongest demand is methodological discipline: predictions must be framed so that failure bites. In that sense, the conversation is as much about standards of inference as it is about black holes.

Methods

The interview was conducted via typed questions—with explicit consent—for review, and curation. This process complied with applicable data protection laws, including the California Consumer Privacy Act (CCPA), Canada’s Personal Information Protection and Electronic Documents Act (PIPEDA), and Europe’s General Data Protection Regulation (GDPR), i.e., recordings if any were stored securely, retained only as needed, and deleted upon request, as well in accordance with Federal Trade Commission (FTC) and Advertising Standards Canada guidelines.

Data Availability

No datasets were generated or analyzed during the current article. All interview content remains the intellectual property of the interviewer and interviewee.

References

This interview was conducted as part of a broader quantum cosmology book project. The responses reflect my current research perspective as of October 2025, informed by over 180 publications and ongoing collaborations with researchers worldwide. 

Selected References 

General Background and Foundational Works 

Hawking, S.W. (1974). Black hole explosions? Nature, 248(5443), 30-31. Bekenstein, J.D. (1973). Black holes and entropy. Physical Review D, 7(8), 2333. 

Bardeen, J.M., Carter, B., & Hawking, S.W. (1973). The four laws of black hole mechanics. Communications in Mathematical Physics, 31(2), 161-170. 

Modified Gravity and Quantum Corrections 

Sakallı, ˙I., & Sucu, E. (2025). Quantum tunneling and Aschenbach effect in nonlinear Einstein Power-Yang-Mills AdS black holes. Chinese Physics C, 49, 105101. 

Sakallı, ˙I., Sucu, E., & Dengiz, S. (2025). Quantum-Corrected Thermodynamics of Conformal Weyl Gravity Black Holes: GUP Effects and Phase Transitions. arXiv preprint 2508.00203. 

Al-Badawi, A., Ahmed, F., & Sakallı, ˙I. (2025). A Black Hole Solution in Kalb-Ramond Gravity with Quintessence Field: From Geodesic Dynamics to Thermal Criticality. arXiv preprint 2508.16693. 

Sakallı, ˙I., Sucu, E., & Sert, O. (2025). Quantum-corrected thermodynamics and plasma lensing in non-minimally coupled symmetric teleparallel black holes. Physical Review D, 50, 102063. 

Ahmed, F., Al-Badawi, A., & Sakallı, ˙I. (2025). Perturbations and Greybody Factors of AdS Black Holes with a Cloud of Strings Surrounded by Quintessence-like Field in NLED Scenario. arXiv preprint 2510.19862. 

Black Hole Thermodynamics and Phase Transitions 

Gashti, S.N., Sakallı, ˙I., & Pourhassan, B. (2025). Thermodynamic scalar curvature and topo logical classification in accelerating charged AdS black holes under rainbow gravity. Physics of the Dark Universe, 50, 102136. 

Sucu, E., & Sakallı, ˙I. (2025). AdS black holes in Einstein-Kalb-Ramond gravity: Quantum 26 corrections, phase transitions, and orbital dynamics. Nuclear Physics B, 1018, 117081. 

Sakallı, ˙I., Sucu, E., & Dengiz, S. (2025). Weak gravity conjecture in ModMax black holes: weak cosmic censorship and photon sphere analysis. European Physics C, 85, 1144. 

Pourhassan, B., & Sakallı, ˙I. (2025). Transport phenomena and KSS bound in quantum corrected AdS black holes. European Physics C, 85(4), 369. 

Gashti, S.N., Sakallı, ˙I., Pourhassan, B., & Baku, K.J. (2025). Thermodynamic topology, photon spheres, and evidence for weak gravity conjecture in charged black holes with perfect fluid within Rastall theory. Physics Letters B, 869, 139862. 

Quasinormal Modes and Spectroscopy 

Gashti, S.N., Afshar, M.A., Sakallı, ˙I., & Mazandaran, U. (2025). Weak gravity conjecture in ModMax black holes: weak cosmic censorship and photon sphere analysis. arXiv preprint 2504.11939. 

Sakallı, ˙I., & Kanzi, S. (2023). Superradiant (In)stability, Greybody Radiation, and Quasi normal Modes of Rotating Black Holes in Non-Linear Maxwell f(R) Gravity. Symmetry, 15, 873. 

Observational Tests and Gravitational Lensing 

Sucu, E., & Sakallı, ˙I. (2025). Probing Starobinsky-Bel-Robinson gravity: Gravitational lensing, thermodynamics, and orbital dynamics. Nuclear Physics B, 1018, 116982. 

Mangut, M., G¨ursel, H., & Sakallı, ˙I. (2025). Lorentz-symmetry violation in charged black-hole thermodynamics and gravitational lensing: effects of the Kalb-Ramond field. Chinese Physics C, 49, 065106. 

Ahmed, F., Al-Badawi, A., & Sakallı, ˙I. (2025). Geodesics Analysis, Perturbations and Deflec tion Angle of Photon Ray in Finslerian Bardeen-Like Black Hole with a GM Surrounded by a Quintessence Field. Annalen der Physik, e2500087. 

Generalized Uncertainty Principle and Quantum Effects 

Ahmed, F., Al-Badawi, A., & Sakallı, ˙I. (2025). Photon Deflection and Magnification in Kalb Ramond Black Holes with Topological String Configurations. arXiv preprint 2507.22673. 

Ahmed, F., & Sakallı, ˙I. (2025). Exploring geodesics, quantum fields and thermodynamics of Schwarzschild-AdS black hole with a global monopole in non-commutative geometry. Nuclear Physics B, 1017, 116951. 

Wormholes and Exotic Compact Objects 

Ahmed, F., Al-Badawi, A., & Sakallı, ˙I. (2025). Gravitational lensing phenomena of Ellis Bronnikov-Morris-Thorne wormhole with global monopole and cosmic string. Physics Letters B, 864, 139448. 

Ahmed, F., & Sakallı, ˙I. (2025). Dunkl black hole with phantom global monopoles: geodesic analysis, thermodynamics and shadow. European Physics C, 85, 660. 

Information Theory and Holography 

Pourhassan, B., Sakallı, ˙I., et al. (2022). Quantum Thermodynamics of an M2-Corrected Reissner-Nordstr¨om Black Hole. EPL, 144, 29001. 

Sakallı, ˙I., & Kanzi, S. (2022). Topical Review: greybody factors and quasinormal modes for black holes in various theories – fingerprints of invisibles. Turkish Journal of Physics, 46, 51-103. 

Modified Theories and String Theory 

Sakallı, İ., & Yörük, E. (2023). Modified Hawking radiation of Schwarzschild-like black hole in bumblebee gravity model. Physics Scripta, 98, 125307.

https://iopscience.iop.org/article/10.1088/1402-4896/ad09a1

Sucu, E., & Sakallı, ˙I. (2023). GUP-reinforced Hawking radiation in rotating linear dilaton black hole spacetime. Physics Scripta, 98, 105201. 

Event Horizon Telescope and Observational Cosmology 

Event Horizon Telescope Collaboration (2019). First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole. The Astrophysical Journal Letters, 875(1), L1. 

Abbott, B.P., et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). Observa tion of Gravitational Waves from a Binary Black Hole Merger. Physical Review Letters, 116(6), 061102. 

Recent Collaborative Works 

Tangphati, T., Sakallı, ˙I., Banerjee, A., & Pradhan, A. (2024). Behaviors of quark stars in the Rainbow Gravity framework. Physical Review D, 46, 101610. 

Banerjee, A., Sakallı, ˙I., Pradhan, A., & Dixit, A. (2024). Properties of interacting quark star in light of Rastall gravity. Classical and Quantum Gravity, 42, 025008. 

Sakallı, ˙I., Banerjee, A., Dayanandan, B., & Pradhan, A. (2025). Quark stars in f(R, T) gravity: mass-to-radius profiles and observational data. Chinese Physics C, 49, 015102. 

Gashti, S.N., Sakallı, ˙I., Pourhassan, B., & Baku, K.J. (2024). Thermodynamic topology and phase space analysis of AdS black holes through non-extensive entropy perspectives. European Physics C, 85, 305. 

Al-Badawi, A., & Sakallı, ˙I. (2025). The Static Charged Black Holes with Weyl Corrections. International Journal of Theoretical Physics, 64, 50. 

Textbooks and Reviews 

Carroll, S.M. (2004). Spacetime and Geometry: An Introduction to General Relativity. Addison Wesley. 

Wald, R.M. (1984). General Relativity. University of Chicago Press. 

Rovelli, C. (2004). Quantum Gravity. Cambridge University Press. 

Kiefer, C. (2012). Quantum Gravity (3rd ed.). Oxford University Press. Ashtekar, A., & Petkov, V. (Eds.) (2014). Springer Handbook of Spacetime. Springer. 

Note: This reference list includes representative works from Prof. Sakallı’s extensive publication record (181+ papers) and foundational works in the field. For a complete bibliography, please consult the INSPIRE-HEP database or Prof. Sakallı’s institutional profile.

Journal & Article Details

Publisher: In-Sight Publishing

Publisher Founding: March 1, 2014

Web Domain: http://www.in-sightpublishing.com

Location: Fort Langley, Township of Langley, British Columbia, Canada

Journal: In-Sight: Interviews

Journal Founding: August 2, 2012

Frequency: Four Times Per Year

Review Status: Non-Peer-Reviewed

Access: Electronic/Digital & Open Access

Fees: None (Free)

Volume Numbering: 14

Issue Numbering: 1

Section: A

Theme Type: Discipline

Theme Premise: Quantum Cosmology

Formal Sub-Theme: None.

Individual Publication Date: March 22, 2026

Issue Publication Date: April 1, 2026

Author(s): Scott Douglas Jacobsen

Word Count: 3,747

Image Credits: Izzet Sakallı

ISSN (International Standard Serial Number): 2369-6885

Acknowledgements

The author acknowledges Prof. Dr. İzzet Sakallı for his time, expertise, and valuable contributions. His thoughtful insights and detailed explanations have greatly enhanced the quality and depth of this work, providing a solid foundation for the discussion presented herein.

Author Contributions

S.D.J. conceived the subject matter, conducted the interview, transcribed and edited the conversation, and prepared the manuscript.

Competing Interests

The author declares no competing interests.

License & Copyright

In-Sight Publishing by Scott Douglas Jacobsen is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
© Scott Douglas Jacobsen and In-Sight Publishing 2012–Present.

Unauthorized use or duplication of material without express permission from Scott Douglas Jacobsen is strictly prohibited. Excerpts and links must use full credit to Scott Douglas Jacobsen and In-Sight Publishing with direction to the original content.

Supplementary Information

Below are various citation formats for Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4) (Scott Douglas Jacobsen, March 22, 2026).

American Medical Association (AMA 11th Edition)

Jacobsen SD. Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4). In-Sight: Interviews. 2026;14(1). Published March 22, 2026. http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes 

American Psychological Association (APA 7th Edition)

Jacobsen, S. D. (2026, March 22). Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4). In-Sight: Interviews, 14(1). In-Sight Publishing. http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes 

Brazilian National Standards (ABNT)

JACOBSEN, Scott Douglas. Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4). In-Sight: Interviews, Fort Langley, v. 14, n. 1, 22 mar. 2026. Disponível em: http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes 

Chicago/Turabian, Author-Date (17th Edition)

Jacobsen, Scott Douglas. 2026. “Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4).” In-Sight: Interviews 14 (1). http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes. 

Chicago/Turabian, Notes & Bibliography (17th Edition)

Jacobsen, Scott Douglas. “Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4).” In-Sight: Interviews 14, no. 1 (March 22, 2026). http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes. 

Harvard

Jacobsen, S.D. (2026) ‘Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4)’, In-Sight: Interviews, 14(1), 22 March. Available at: http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes. 

Harvard (Australian)

Jacobsen, SD 2026, ‘Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4)’, In-Sight: Interviews, vol. 14, no. 1, 22 March, viewed 22 March 2026, http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes. 

Modern Language Association (MLA, 9th Edition)

Jacobsen, Scott Douglas. “Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4).” In-Sight: Interviews, vol. 14, no. 1, 22 Mar. 2026, http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes. 

Vancouver/ICMJE

Jacobsen SD. Black-Hole Thermodynamics, Thermodynamic Topology, Quasinormal Modes, and Quantum-Gravity Phenomenology: Prof. Dr. İzzet Sakallı (4) [Internet]. 2026 Mar 22;14(1). Available from: http://www.in-sightpublishing.com/causality-ensemble-invariance-black-hole-phenomenology-izzet-sakalli-kss-bound-thermodynamic-topology-hawking-radiation-quasinormal-modes 

Note on Formatting

This document follows an adapted Nature research-article format tailored for an interview. Traditional sections such as Methods, Results, and Discussion are replaced with clearly defined parts: Abstract, Keywords, Introduction, Main Text (Interview), and a concluding Discussion, along with supplementary sections detailing Data Availability, References, and Author Contributions. This structure maintains scholarly rigor while effectively accommodating narrative content.