Wyniki wyszukiwania - Biblioteka Nauki

1

Rozważania kosmologiczne na temat ogólnej teorii względności

100%

Einstein A.

Zagadnienia Filozoficzne w Nauce

|

2017

|

nr 63

183-204

PL

A. Einstein, “Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie” (“Cosmological considerations on the general theory of relativity”), Sitzung der Physikalisch-mathematischen Klasse vom 8. Februar 1917, „Sitzungsberichte der Preußischen Akad. d. Wissenschaften, 1917”, pp. 142–152. Translated to Polish from original German work by Robert Janusz.

2

The Hamiltonian formulation of general relativity: myths and reality

80%

Kiriushcheva N. , Kuzmin S.

Open Physics

|

2011

|

tom 9

|

nr 3

576-615

EN

A conventional wisdom often perpetuated in the literature states that: (i) a 3 + 1 decomposition of spacetime into space and time is synonymous with the canonical treatment and this decomposition is essential for any Hamiltonian formulation of General Relativity (GR); (ii) the canonical treatment unavoidably breaks the symmetry between space and time in GR and the resulting algebra of constraints is not the algebra of four-dimensional diffeomorphism; (iii) according to some authors this algebra allows one to derive only spatial diffeomorphism or, according to others, a specific field-dependent and non-covariant four-dimensional diffeomorphism; (iv) the analyses of Dirac [21] and of ADM [22] of the canonical structure of GR are equivalent. We provide some general reasons why these statements should be questioned. Points (i–iii) have been shown to be incorrect in [45] and now we thoroughly re-examine all steps of the Dirac Hamiltonian formulation of GR. By direct calculation we show that Dirac’s references to space-like surfaces are inessential and that such surfaces do not enter his calculations. In addition, we show that his assumption g 0k = 0, used to simplify his calculation of different contributions to the secondary constraints, is unwarranted; yet, remarkably his total Hamiltonian is equivalent to the one computed without the assumption g 0k = 0. The secondary constraints resulting from the conservation of the primary constraints of Dirac are in fact different from the original constraints that Dirac called secondary (also known as the “Hamiltonian” and “diffeomorphism” constraints). The Dirac constraints are instead particular combinations of the constraints which follow directly from the primary constraints. Taking this difference into account we found, using two standard methods, that the generator of the gauge transformation gives diffeomorphism invariance in four-dimensional space-time; and this shows that points (i–iii) above cannot be attributed to the Dirac Hamiltonian formulation of GR. We also demonstrate that ADM and Dirac formulations are related by a transformation of phase-space variables from the metric g μν to lapse and shift functions and the three-metric g km, which is not canonical. This proves that point (iv) is incorrect. Points (i–iii) are mere consequences of using a non-canonical change of variables and are not an intrinsic property of either the Hamilton-Dirac approach to constrained systems or Einstein’s theory itself.

3

Light refraction in the Swiss-cheese model

80%

Csapó A. , Bene G.

Open Physics

|

2012

|

tom 10

|

nr 4

821-835

EN

We investigate light propagation in the Swiss-cheese model. On both sides of Swiss-cheese sphere surfaces, observers resting in the flat Friedmann-Robertson-Walker (FRW) space and the Schwarzschild space respectively, see the same light ray enclosing different angles with the normal. We examine light refraction at each crossing of the boundary surfaces, showing that the angle of refraction is larger than the angle of incidence for both directions of the light.

4

O względności bezwładności. Uwagi dotyczące ostatniej hipotezy Einsteina (Przedstawione na spotkaniu 31 III 1917)

80%

de Sitter W.

Zagadnienia Filozoficzne w Nauce

|

2017

|

nr 63

205-222

PL

W. de Sitter, „On the relativity of inertia. Remarks concerning Einstein’s latest hypothesis”, Proceedings of the Section of Sciences. Koninklijke Akademie van Wetenschappen te Amsterdam, Vol. XIX, No. 9 i 10, Johannes Müller, Amsterdam, September 1917, pp. 1217–1225 (section: „Mechanics”). Translated to Polish by Robert Janusz.

5

Między mikroświatem a makroświatem

80%

Grygiel W.

Zagadnienia Filozoficzne w Nauce

|

2012

|

nr 50

46-62

PL

The current 50th issue of Philosophical Problems in Science (Zagadnienia Filozoﬁczne w Nauce) summarizes the eﬀorts of both philosophers and scientists to understand how a broader philosophical context sets the stage for the development of scientiﬁc research, with physics playing a leading role. In particular, the paper reviews the content of the last twenty-ﬁve issues of the journal with an emphasis on the philosophical problems that arise in the practice of physics. The overview reveals that these problems reﬂect the main conceptual division in physics between the treatment of the micro-world described by quantum mechanics and the macro-world governed by the general theory of relativity. Both of these theories, taken separately, generate a host of philosophical concerns such as their proper interpretation (Bell’s Theorem and its consequences) or the meaning and the eventual validity of the notions of space and time. Other philosophical problems in physics, such as chaos and determinism, are also considered. The authors are well aware that the formulation of the future theory of quantum gravity will be a demanding task requiring profound philosophical reﬂection.

6

Sources of inertia in an expanding universe

70%

Prytz K.

Open Physics

|

2015

|

tom 13

|

nr 1

EN

In a cosmological perspective, gravitational induction is explored as a source to mechanical inertia in line with Mach’s principle. Within the standard model of cosmos, considering the expansion of the universe and the necessity of retarded interactions, it is found that the assumed dynamics may account for a significant part of an object’s inertia.

7

Einstein equation at singularities

70%

Stoica O.-C.

Open Physics

|

2014

|

tom 12

|

nr 2

123-131

EN

Einstein’s equation is rewritten in an equivalent form, which remains valid at the singularities in some major cases. These cases include the Schwarzschild singularity, the Friedmann-Lemaître-Robertson-Walker Big Bang singularity, isotropic singularities, and a class of warped product singularities. This equation is constructed in terms of the Ricci part of the Riemann curvature (as the Kulkarni-Nomizu product between Einstein’s equation and the metric tensor).

8

Close approaches of debris to LARES satellite during its first four years of operation

70%

Paris C. , Sindoni G. , Sabato T.

Transactions on Environment and Electrical Engineering

|

2017

|

tom Vol. 2, No. 1

90--97

EN

Since its launch in February 2012, the LAser RElativity Satellite (LARES) of the Italian Space Agency experienced four close approaches with space debris. LARES orbits at an altitude of 1450 km, in a region where the density of space debris has a peak. However, the probability of an impact with a debris during the operational life of the satellite was reasonably low. The analysis of the close approaches identified three of the objects, that are from two peculiar population of objects. This paper discusses the problem of space debris in low orbit, the approaches occurred with LARES, and some possible scenarios related to space regulations and space law in case of an impact.

9

The Carter constant for inclined orbits about a massive Kerr black hole: near-circular, near-polar orbits

70%

Komorowski P. , Valluri S. , Houde M.

Open Physics

|

2012

|

tom 10

|

nr 4

799-820

EN

In an extreme mass-ratio binary black hole system, a non-equatorial orbit will list (i.e. increase its angle of inclination, i) as it evolves in Kerr spacetime. The abutment, a set of evolving, near-polar, retrograde orbits, for which the instantaneous Carter constant (Q) is at its maximum value (Q X) for given values of latus rectum (l̃) and eccentricity (e), has been introduced as a laboratory in which the consistency of dQ/dt with corresponding evolution equations for d l̃/dt and de/dt might be tested independently of a specific radiation back-reaction model. To demonstrate the use of the abutment as such a laboratory, a derivation of dQ/dt, based only on published formulae for d l̃/dt and de/dt, was performed for elliptical orbits on the abutment. The resulting expression for dQ/dt matched the published result to the second order in e. We believe the abutment is a potentially useful tool for improving the accuracy of evolution equations to higher orders of e and l̃−.

10

The ESA’S Scientific projects for Galileo Satellites 5 and 6 with eccentric orbits

70%

Oszczak S.

Zeszyty Naukowe / Wyższa Szkoła Oficerska Sił Powietrznych

|

2016

|

tom Nr 4

125--134

EN

The experts of the ESA Galileo Scientific Advisory Committee (GSAC) have been involved in the analysis and technical discussions on the possibility of using Galileo Satellites 5 and 6 with eccentric orbits to support some Fundamental Physics experimentation, especially to perform a test of the gravitational redshift, a part of Einstein Equivalence Principle (EEP) General Relativity (specifically testing the LPI, Local Position Invariance). The gravitational redshift was performed with Gravity Probe-A (GP-A) in 1980 with the accuracy of 1.4 x 10-4. The analysis made by independent experts showed that using Galileo Satellite 5 data for one year (and if possible also Sat 6), in their final corrected orbits with an eccentricity of about 0.15, the accuracy could be improved by a factor of 5 and is optionally estimated to be even higher. Moreover, as noted by the involved experts, these tests are of high scientific relevance, as many alternative theories of gravitation predict violations of the Einstein Equivalence Principle at some level of the accuracy. The final recommendation of the GSAC provides the ESA with the possibility of establishing a scientific project activity, named as GREAT with two research groups (ZARM/SYRTE). The main objectives of this scientific project and expected results of gravitational redshift improvement are discussed.

11

The cauchy problem for the Einstein-Boltzmann system

60%

Mucha P. B.

Journal of Applied Analysis

|

1998

|

tom Vol. 4, nr 1

129-141

EN

We prove an existence and uniqueness of solution for the Einstein-Boltzmann system locally in time. We restrict our attention to initial data which gives a solution in harmonic coordinates.

12

The cauchy problem for the Einstein-Vlasov system

60%

Mucha P. B.

Journal of Applied Analysis

|

1998

|

tom Vol. 4, nr 1

111-127

EN

We prove an existence and uniqueness for the Einstein-Vlasov system locally in time. Considerations are restricted to initial data which give a solution in harmonic coordinates.

13

On the topology of spherically symmetric space-times

60%

Szenthe J.

Open Mathematics

|

2004

|

tom 2

|

nr 5

725-731

EN

Spherically symmetric space-times have attained considerable attention ever since the early beginnings of the theory of general relativity. In fact, they have appeared already in the papers of K. Schwarzschild [12] and W. De Sitter [5] which were published in 1916 and 1917 respectively soon after Einstein's epoch-making work [7] in 1915. The present survey is concerned mainly with recent results pertainig to the toplogy of spherically symmetric space-times. Definition. By space-time a connected time-oriented 4-dimensional Lorentz manifold is meant. If (M,<,>) is a space-time, and Φ: SO(3)×M→M an isometric action such that the maximal dimension of its orbits is equal to 2, then the action Φ is said to be spherical and the space-time is said to be spherically symmetric [8]; [11]. Likewise, isometric actions Ψ: O(3)×M→M are also considered ([10], p. 365; [4]) which will be called quasi-spherical if the maximal dimension of its orbits is 2 and then the space-time is said to be quasi-spherically symmetric here. Each quasi-spherical action yields a spherical one by restricting it to the action of SO(3); the converse of this statement will be considered elsewhere. The main results concerning spherically symmetric space-times are generally either of local character or pertaining to topologically restricted simple situations [14], and earlier results of global character are scarce [1], [4], [6], [13]. A report on recent results concerning the global geometry of spherically symmetric space-times [16] is presented below.

14

Some remarks on the first image of a black hole

53%

Szybka S. J.

Zagadnienia Filozoficzne w Nauce

|

2020

|

nr 68

281-294

EN

On the 10th of April, 2019 the Event Horizon Telescope Collaboration presented the first image of the black hole. The image was obtained with a planet-scale array of eight ground-based radio telescopes. The observation relied on a technique called very long base interferometry which synchronises telescope facilities around the world. The image of a black hole together with the recent detections of gravitational waves confirms one of the most intriguing predictions of Einstein’s gravity theory, namely, the existence of black holes. I will provide more details on this remarkable observation and explore its consequences for our understanding of nature. The physical reality of black holes is strongly supported by recent advances of astronomy. I claim that this fact is the key to understanding the relation between our world and the world of mathematics.

15

Oddziaływania czarnych dziur

51%

Szybka S. J.

Postępy Fizyki

|

2023

|

tom T. 74, z. 3

15--23

PL

Końcowym stadium niepohamowanego kolapsu grawitacyjnego jest pojedynczy obiekt zwany czarną dziurą. Czy czarne dziury zawsze mają taką samą uniwersalną postać? Chociaż twierdzenie o jednoznaczności czarnych dziur udziela pozytywnej odpowiedzi na to pytanie, to każde twierdzenie jest tylko tak silne, jak jego założenia. Przez wiele lat fizycy nie potrafili wykluczyć istnienia stacjonarnych konfiguracji dwóch czarnych dziur, które mogłyby wspólnie tworzyć bardziej złożony obiekt. Obecnie znamy rozwiązanie tego problemu.

EN

The final stage of an unrestrained gravitational collapse is a single object known as a black hole. Do black holes always have the same universal form? Although the uniqueness theorem provides a positive answer to this question, every theorem is only as strong as its assumptions. For many years physicists were unable to exclude the existence of stationary configurations of two black holes that could form together a more complex object. Currently, we know the solution to this problem.

16

Czasoprzestrzeń – część struktury czy strukturalny aspekt? Ontologia czasoprzestrzeni w kontekście umiarkowanego ontycznego realizmu strukturalnego

51%

Luty D.

Studia Philosophiae Christianae

|

2016

|

tom 52

|

nr 4

83-106

EN

The position called Moderate Ontic Structural Realism, presented by Michael Esfeld and Vincent Lam, is described and criticised. Three theses are proposed. First, that the regarded position is intertwined with treating Spacetime as a property (or aspect) of the gravitational field. Second, that the metaphysics of properties used in Moderate Ontic Structural Realism leads to unfortunate consequences such as abandoning the equality of heuristics of constructing representations of gravity in General Relativity. Finally, the third thesis is that Spacetime should be interpreted metaphysically as part of a wider gravitational structure. After a summary of Esfeld’s and Lam’s position, reference to the issue of the equality of heuristics is presented as a critical perspective. A criticism of Moderate Ontic Structural Realism is formulated and further postulates about the ontology of Spacetime are proposed. In conclusion, an answer to the question stated in the title is suggested: spacetime is a part of the structure.

PL

Opisane i skrytykowane zostaje stanowisko umiarkowanego ontycznego realizmu strukturalnego, zaproponowane przez Michaela Esfelda i Vincenta Lama. Postawione są trzy tezy: pierwsza, że odnośne stanowisko uwikłane jest w traktowanie czasoprzestrzeni jako własności (aspektu) pola grawitacyjnego; druga – wykorzystanie przez to stanowisko metafizyki własności generuje niepożądane konsekwencje w postaci odrzucenia równoważności heurystyk służących do budowania reprezentacji grawitacji w ogólnej teorii względności; trzecia, że czasoprzestrzeń powinna być metafizycznie interpretowana jako element szerszej struktury grawitacyjnej. Stanowisko Esfelda i Lama zostaje zrekonstruowane, odniesienie do zagadnienia heurystyk budowania reprezentacji grawitacji przedstawione jest jako perspektywa krytyczna, zrealizowana zostaje krytyka umiarkowanego ontycznego realizmu strukturalnego i przedstawione zostają z niej wnioski oraz dalsze postulaty dotyczące ontologii czasoprzestrzeni. Na pytanie postawione w tytule zostaje udzielona odpowiedź, że czasoprzestrzeń to część struktury.

17

Grawitacja widziana z Obserwatorium Astronomicznego Uniwersytetu Jagiellońskiego

41%

Sokołowski L. M. , Szybka S.

Postępy Fizyki

|

2023

|

tom T. 74, z. 3

27--30

PL

W artykule omawiamy badania dotyczące zjawisk grawitacyjnych, które są prowadzone w Zakładzie Astrofizyki Relatywistycznej i Kosmologii, w Obserwatorium Astronomicznym Uniwersytetu Jagiellońskiego.

EN

In this article, we discuss research on gravitational phenomena being conducted at the Department of Relativistic Astrophysics and Cosmology in the Astronomical Observatory of the Jagiellonian University.

18

Mała książka o wielkim wszechświecie

41%

Szybka S. J.

Zagadnienia Filozoficzne w Nauce

|

2021

|

nr 71

203-209

EN

We live in extraordinary times for cosmologists. A vast amount of new astronomical data is pushing our model of the universe to its limits. An interest in cosmology is growing. The Little Book of Cosmology by Lyman Page is a concise up-to-date approachable introduction to the topic.