Black Hole Information and Thermodynamics

This SpringerBrief is based on a masters course on black hole thermodynamics and the black hole information problem taught by Dieter L\"ust during the summer term 2017 at the Ludwig-Maximilians-Universit\"at in Munich; it was written by Ward Vleeshouwers. It provides a short introduction to general relativity, which describes gravity in terms of the curvature of space-time, and examines the properties of black holes. These are central objects in general relativity which arise when sufficient energy is compressed into a finite volume, so that even light cannot escape its gravitational pull. We will see that black holes exhibit a profound connection with thermodynamic systems. Indeed, by quantizing a field theory on curved backgrounds, one can show that black holes emit thermal (Hawking) radiation, so that the connection with thermodynamics is more than a formal similarity. Hawking radiation gives rise to an apparent conflict between general relativity and quantum mechanics known as the black hole information problem. If a black hole formed from a pure quantum state evaporates to form thermal radiation, which is in a mixed state, then the unitarity postulate of quantum mechanics is violated. We will examine the black hole information problem, which has plagued the physics community for over four decades, and consider prominent examples of proposed solutions, in particular, the string theoretical construction of the Tangherlini black hole, and the infinite number of asymptotic symmetries given by BMS-transformations.Comment: Revised version with typos correcte

Fulling-Davies-Unruh effect for accelerated two-level single and entangled atomic systems

We investigate the transition rates of uniformly accelerated two-level single and entangled atomic systems in empty space as well as inside a cavity. We take into account the interaction between the systems and a massless scalar field from the viewpoint of an instantaneously inertial observer and a coaccelerated observer, respectively. The upward transition occurs only due to the acceleration of the atom. For the two-atom system, we consider that the system is initially prepared in a generic pure entangled state. In the presence of a cavity, we observe that for both the single and the two-atom cases, the upward and downward transitions are occurred due to the acceleration of the atomic systems. The transition rate manifests subtle features depending upon the cavity and system parameters, as well as the initial entanglement. It is shown that no transition occurs for a maximally entangled super-radiant initial state, signifying that such entanglement in the accelerated two-atom system can be preserved for quantum information procesing applications. Our analysis comprehensively validates the equivalence between the effect of uniform acceleration for an inertial observer and the effect of a thermal bath for a coaccelerated observer, in free space as well as inside a cavity, if the temperature of the thermal bath is equal to the Unruh temperature.Comment: 42 pages LaTeX, Comments are welcom

Estimating the effects of stressors on the health, survival and reproduction of a critically endangered, long-lived species

Funding: Office of Naval Research (Grant Number(s): N000142012697, N000142112096); Strategic Environmental Research and Development Program (Grant Number(s): RC20-1097, RC20-7188, RC21-3091).Quantifying the cumulative effects of stressors on individuals and populations can inform the development of effective management and conservation strategies. We developed a Bayesian state–space model to assess the effects of multiple stressors on individual survival and reproduction. In the model, stressor effects on vital rates are mediated by changes in underlying health, allowing for the comparison of effect sizes while accounting for intrinsic factors that might affect an individual's vulnerability and resilience. We applied the model to a 50-year dataset of sightings, calving events and stressor exposure of critically endangered North Atlantic right whales Eubalaena glacialis. The viability of this population is threatened by a complex set of stressors, including vessel strikes, entanglement in fishing gear and fluctuating prey availability. We estimated that blunt and deep vessel strike injuries and severe entanglement injuries had the largest effect on the health of exposed individuals, reinforcing the urgent need for mitigation measures. Prey abundance had a smaller but protracted effect on health across individuals, and estimated long-term trends in survival and reproduction followed the trend of the prey index, highlighting that long-term ecosystem-based management strategies are also required. Our approach can be applied to quantify the effects of multiple stressors on any long-lived species where suitable indicators of health and long-term monitoring data are available.Publisher PDFPeer reviewe

Black holes, radiation, and accretion disks

Σε αυτή την εργασία, μελετάμε τη θερμική ακτινοβολία που εκπέμπεται από το υλικό ενός δίσκου προσαύξησης, ο οποίος στροβιλίζεται γύρω από μια αστροφυσική μελανή οπή. Αυτή η ακτινοβολία έχει σημαντικές επιπτώσεις για συστήματα σε περιβάλλοντα ισχυρής βαρύτητας λόγω της επακόλουθης εμφάνισης της πέδησης Poynting – Robertson. Αυτή η δύναμη μεταβάλλει την κινηματική των ηλεκτρονίων του πλάσματος και επαναδιατυπώνει τις συνθήκες ισορροπίας της ύλης και επομένως και της στατικότητας του δίσκου. Κατασκευάζουμε και εκτελούμε υπολογιστικούς αλγορίθμους σε καμπυλωμένους χωρόχρονους με σκοπό να προσδιορίσουμε αν η παρατηρούμενη ακτινοβολία είναι τόσο αμελητέα όσο συχνά θεωρείται ή αν είναι αρκετά ισχυρή ώστε να επιφέρει τροποποιήσεις. Διερευνούμε επιπλέον ποια μοντέλα δίσκων διαφορετικών ιδιοτήτων εμφανίζουν ισχυρότερες δυνάμεις ακτινοβολίας, ιδιαίτερες επιταχύνσεις ή αξιοσημείωτα φαινόμενα. Τα αποτελέσματα της μελέτης αποκαλύπτουν ότι αυτές οι δυνάμεις ακτινοβολίας είναι πράγματι αξιοσημείωτες και δε μπορούν να θεωρηθούν ασήμαντες ή αμελητέες σε μελέτες, οι οποίες αφορούν δίσκους προσαύξησης που περιστρέφονται γύρω από μαζικά αντικείμενα. Τα διάφορα μοντέλα δίσκων που εξετάστηκαν, εμφανίζουν ιδιαίτερα χαρακτηριστικά το καθένα, μαζί με ιδιότητες που δεν εμφανίζονται με τον ίδιο τρόπο στα υπόλοιπα μοντέλα. Τα αποτελέσματά μας δείχνουν επίσης ότι το κύριο χαρακτηριστικό που καθορίζει το μέγεθος των καταγεγραμμένων δυνάμεων ακτινοβολίας δεν είναι ο όγκος του δίσκου, αλλά η βαθμίδα της πυκνότητας. Επιπροσθέτως, χρησιμοποιώντας τα δεδομένα για την παραγόμενη ακτινοβολία, μπορούμε να υπολογίσουμε εκ νέου τις συνθήκες ισορροπίας για τις τροχιές των σωματιδίων. Τα δεδομένα αυτά αποκαλύπτουν ότι η θερμική ακτινοβολία μπορεί να οδηγήσει αβίαστα σε γρήγορη διαφυγή υλικού, η οποία όμως περιορίζεται άμεσα λόγω ηλεκτρικών και μαγνητικών δυνάμεων που ασκούνται στο επίπεδο των σωματιδίων. Επιπλέον, παρουσιάζουμε και αριθμητικά παραγόμενες εικόνες που δείχνουν τα αναμενόμενα αποτελέσματα παρατηρήσεων αστρικών μελανών οπών με δίσκους προσαύξησης, αλλά και μια σχετική μέθοδο για την εκτίμηση της περιστροφής των μελανών οπών με αρκετά υποσχόμενα αποτελέσματα. Τέλος, εξετάζουμε τις συνέπειες της τροποποίησης της τροχιάς των ηλεκτρονίων και τα επακόλουθα ηλεκτρομαγνητικά φαινόμενα. Μελετάμε τον μηχανισμό της Κοσμικής Μπαταρίας και εξετάζουμε τη δυνατότητα γένεσης μαγνητικών πεδίων από την ακτινοβολία, χωρίς να προϋπάρχουν μαγνητικές δομές. Τα αποτελέσματά μας δείχνουν την ύπαρξη αρκετών περιπτώσεων όπου ο μηχανισμός αυτός μπορεί να δημιουργήσει μαγνητικά πεδία επιπέδου ισοκατανομής σε επαρκώς σύντομα χρονικά διαστήματα.In this work, we study the thermal radiation emitted by the material of an accretion disk that swirls around an astrophysical black hole. This radiation has important repercussions on systems in strong gravity environments due to the consequent emergence of Poynting – Robertson braking. This force alters the plasma electron kinematics and restates the matter equilibrium conditions and hence the disk stability. We formulate and execute computational calculations in curved spacetimes in order to determine if the observed radiation is as negligible as it is often considered to be, or if it is strong enough to bring about modifications. We additionally investigate which disk models of different properties display stronger exerted radiation forces, particular accelerations, or notable phenomena. The results of our study reveal that these radiation forces are indeed noteworthy and cannot be deemed inconsequential or redundant in studies involving accretion disks orbiting massive objects. The various disk models examined demonstrate particular properties each, along with characteristics that do not appear in the same manner for the rest of the models. Our results also suggest that the primary attribute determining the magnitude of the recorded radiation forces is not the disk volume, but instead the density gradient. Furthermore, by using the generated radiation data, we can recalculate the stability of the particle trajectories. These data demonstrate that the thermal radiation can effortlessly lead to prompt material escape, a fact that is counteracted, however, by the electric and magnetic forces acting at particle level. Moreover, we present numerically generated images of the anticipated stellar black hole observations and a related method used to estimate the black hole spin with promising results. Finally, we examine the consequences of the electron orbit modification and the ensuing electromagnetic phenomena. We study the Cosmic Battery mechanism and ascertain the capability of magnetic field generation by the radiation without the presence of a seed field. Our results show that there are several cases where this mechanism can generate equipartition-level magnetic fields in adequately short timescales

The Fifteenth Marcel Grossmann Meeting

The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity

From dazzle to the desert: a cultural-historical geography of camouflage

'To bewilder the enemy and mislead him continually as to our real positions and attentions is one of our most hopeful tasks and to do this ingenuity, imagination and daring are required.'(Ronald Penrose, 1941, Home Guard Manual of Camouflage, p.13) This thesis approaches the cultures and geographies of military conflict, charting the history of military camouflage through a multi-faceted biography of this technology’s life-path. By studying the scientific biography of Dr Hugh Cott (1900-1987), eminent zoologist and skilful artist turned camoufleur in WWII, entwined with the fragmentary mobile biographies of other camouflage practioners, including artists, animals and even a magician, the sites and spacings of camouflage’s life-path from the late-nineteenth century into the Desert War are traced. The military’s enrolment of diverse outside specialists practised in visual literacy is examined to reveal that technological development led to transformations, not only in military knowledge, but also in the militarism of knowledges such as science and art. Moving through the scientists’ fieldsite, the committee boardroom, the military training site and the soldiers’ battlefield, this thesis uncovers the history of a most ambiguous military invention, exposing its darker patterning and thus subverting a long-dominant narrative of camouflage as solely a protective technology. Furthermore, this camouflage biography is narrated from the perspective of the technology’s inventors and practioners as a means to encounter the situated and also embodied nature of technological innovation in military conflict. It demonstrates that, as camouflage transformed battlefields into unsettling theatres of war, there were lasting consequences not only for knowledge and technology, but also for both the ethics of battle and the individuals enrolled in this process. Overall, this geographically structured biography explores how camouflage is a jarring technology, combining aesthetic and artistic appreciation with complex scientific theory, to guileful and deadly effect