Gravitational lenses and the inhomogeneous universe

1986 ◽  
Vol 64 (2) ◽  
pp. 160-164
Author(s):  
Charles C. Dyer
Keyword(s):  
Red Shift ◽  
Cumulative Effects ◽  
Null Cone ◽  
Gravitational Lenses ◽  
Inhomogeneous Universe ◽  
The Past ◽  
Optical Scalar ◽  
Ray Bending ◽  
The Universe ◽  
Scalar Equations

The theory of static gravitatonal lenses is discussed using the optical scalar formalism and the ray-bending approximation to this formalism. The advantages of each approach are discussed, with particular emphasis on the use of the bending approximation for discretely observable lenses, say multiply imaged quasars, and the optical scalar equations for cumulative effects of inhomogeneities for distant objects in the universe.The effect of a locally lumpy distribution on the past null cone of a typical observer is discussed. This is of particular interest in deciding the limits to which one can hope to do cosmology through the use of optical and other telescopes. The optical-scalar-equation driving terms can be replaced by appropriately defined mean driving terms for subsets of observable objects, and coupled with corresponding probabilities, these calculations can yield estimates of the "thickness" of the observer's past null cone as a function of the red shift. This imposes a limit on the use of standard observations in determining the structure of the universe, simply owing to the "fuzzy" structure of the perceived past null cone.

scholarly journals The singularities of gravitational collapse and cosmology

1970 ◽  
Vol 314 (1519) ◽  
pp. 529-548 ◽  
Keyword(s):  
Gravitational Collapse ◽  
Null Geodesic ◽  
Energy Condition ◽  
Realistic Model ◽  
Space Time ◽  
Null Cone ◽  
The Past ◽  
Time Singularities ◽  
Trapped Surface ◽  
The Universe

A new theorem on space-time singularities is presented which largely incorporates and generalizes the previously known results. The theorem implies that space-time singularities are to be expected if either the universe is spatially closed or there is an ‘object’ undergoing relativistic gravitational collapse (existence of a trapped surface) or there is a point p whose past null cone encounters sufficient matter that the divergence of the null rays through p changes sign somewhere to the past of p (i. e. there is a minimum apparent solid angle, as viewed from p for small objects of given size). The theorem applies if the following four physical assumptions are made: (i) Einstein’s equations hold (with zero or negative cosmological constant), (ii) the energy density is nowhere less than minus each principal pressure nor less than minus the sum of the three principal pressures (the ‘energy condition’), (iii) there are no closed timelike curves, (iv) every timelike or null geodesic enters a region where the curvature is not specially alined with the geodesic. (This last condition would hold in any sufficiently general physically realistic model.) In common with earlier results, timelike or null geodesic incompleteness is used here as the indication of the presence of space-time singularities. No assumption concerning existence of a global Cauchy hypersurface is required for the present theorem.

The Kalam Cosmological Argument

2018 ◽  
Author(s):  
William Lane Craig
Keyword(s):  
Space Time ◽  
Cosmological Argument ◽  
Philosophical Literature ◽  
The Past ◽  
Classical Space ◽  
Kalam Cosmological Argument ◽  
Kalām Cosmological Argument ◽  
The Universe

A survey of recent philosophical literature on the kalam cosmological argument reveals that arguments for the finitude of the past and, hence, the beginning of the universe remain robust. Plantinga’s brief criticisms of Kant’s argument in his First Antinomy concerning time are shown not to be problematic for the kalam argument. This chapter addresses, one by one, the two premises of the kalam, focusing on their philosophical aspects. The notion of infinity, both actual and potential, is discussed in relation to the coming into being of the universe. In addition, the scientific aspects of the two premises are also, briefly, addressed. Among these are the Borde-Guth-Vilenkin theorem, which proves that classical space-time cannot be extended to past infinity but must reach a boundary at some time in the finite past. This, among other factors, lends credence to the kalam argument’s second premise.

Introduction

2018 ◽  
Author(s):  
Gianfranco Pacchioni
Keyword(s):  
Industrial Revolution ◽  
Homo Sapiens ◽  
Modern Society ◽  
Full Time ◽  
Human Race ◽  
Hunter Gatherers ◽  
The Past ◽  
The World ◽  
The Universe ◽  
Radical Transformation

About 10,000 years ago, at the beginning of the agriculturalrevolution, on the whole earth lived between 5 and 8 million hunter-gatherers, all belonging to the Homo sapiens species. Five thousand years later, freed from the primary needs for survival, some belonging to that species enjoyed the privilege of devoting themselves to philosophical speculation and the search for transcendental truths. It was only in the past two hundred years, however, with the advent of the Industrial Revolution, that reaping nature’s secrets and answering fundamental questions posed by the Universe have become for many full-time activities, on the way to becoming a real profession. Today the number of scientists across the globe has reached and exceeded 10 million, that is, more than the whole human race 10,000 years ago. If growth continues at the current rate, in 2050 we will have 35 million people committed full-time to scientific research. With what consequences, it remains to be understood. For almost forty years I myself have been concerned with science in a continuing, direct, and passionate way. Today I perceive, along with many colleagues, especially of my generation, that things are evolving and have changed deeply, in ways unimaginable until a few years ago and, in some respects, not without danger. What has happened in the world of science in recent decades is more than likely a mirror of a similar and equally radical transformation taking place in modern society, particularly with the advent ...

The Long View of Planetary Systems

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Giant Planets ◽  
Milky Way Galaxy ◽  
Population Statistics ◽  
The Past ◽  
General Terms ◽  
The Galaxy ◽  
The Universe

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.

The Shape of Time

2018 ◽  
Author(s):  
Donald C. Williams
Keyword(s):  
Time Travel ◽  
Arrow Of Time ◽  
The Past ◽  
Time Traveler ◽  
Dimensional Shape ◽  
Manifold Theory ◽  
The Universe

This chapter is about the arrow or direction of time against the backdrop of the pure manifold theory. It is accepted that the fact that time has a direction ought to be explained. It is proposed that the arrow of time is grounded in deeper facts about the four-dimensional nature of each object in the manifold and in facts about the overall four-dimensional shape of the universe. Towards the end of the chapter the possibility of time travel is discussed. It is argued that time travel is metaphysically possible and that there is a reasonable and intelligible sense in which a time traveler can and cannot change the past, according to the pure manifold theory.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

State finder and Om diagnostics in modified and generalised Chaplygin gas from recent data

2021 ◽  
Author(s):  
P. Thakur
Keyword(s):  
Chaplygin Gas ◽  
Red Shift ◽  
Recent Past ◽  
Eos Parameter ◽  
Deceleration Phase ◽  
Om Diagnostic ◽  
Expected Values ◽  
Best Fit ◽  
The Universe ◽  
Jerk Parameter

A modified and generalised Chaplygin gas (MCG, [Formula: see text] and GCG, [Formula: see text]) has been separately chosen here as a constituent of the universe. Concept of state finder and Om diagnostics are introduced to track the dark energy in the models. Here, observed Hubble data (OHD) and binned Pantheon data of supernovae are used to determine the best-fit equation-of-state (EoS) parameters of these models and these are compared with the [Formula: see text]CDM model. The best-fit value and expected values of cosmological jerk parameter [Formula: see text], snap parameter [Formula: see text] are determined, which are close to each other. A plot of [Formula: see text] with red-shift, with themselves, as well as with deceleration parameter [Formula: see text], shows the evolution of the universe and its possible future. Variations of [Formula: see text] and EoS parameter [Formula: see text] with red-shift show acceleration–deceleration phase transition in the recent past. Lastly, the state finder pair [Formula: see text] and Om diagnostic have been utilized to discriminate the models.

The Ultimate Sophistication of Special Theory of Relativity

2021 ◽  
Vol 11 (3) ◽  
pp. 43-49
Author(s):  
Hamdoon A. Khan ◽  
Keyword(s):  
Special Relativity ◽  
Special Theory ◽  
Mathematical Approach ◽  
Theory Of Relativity ◽  
Special Theory Of Relativity ◽  
The Real ◽  
The Past ◽  
The One ◽  
The Universe ◽  
Faster Than Light

With the consideration of the light which carries the photon particles, the Lorentz transformation was constructed with an impressive mathematical approach. But the generalization of that equation for all the velocities of the universe is direct enforcement on other things not to travel faster than light. It has created serious issues in every scientific research that was done in the last century based on the special theory of relativity. This paper replaces the velocity of light with some other velocities and shows us the possible consequences and highlights the issues of special relativity. If I travel through my past or future and was able to see another me there, who would be the real Hamdoon I or the one I see there in the past or future! If the real one is only me, the one I saw, is not me, so, I could not travel through my or someone else's past or future. Therefore, no one can travel through time. If both of us are the same, can the key of personal identity be duplicated or be separated into two or more parts? These are some of the fundamental philosophical arguments that annihilate the concept of time travel which is one of the sequels of special relativity.

scholarly journals The Role of Superstition in Twain’s The Adventures of Huckleberry Finn and Shakespeare’s Macbeth: A Comparative Study

2016 ◽  
Vol 6 (1) ◽  
pp. 37
Author(s):  
Jamal Subhi Ismail Nafi’
Keyword(s):  
Comparative Study ◽  
Social Factors ◽  
Religious Beliefs ◽  
Adventures Of Huckleberry Finn ◽  
The Past ◽  
The People ◽  
The Universe ◽  
Shed Light ◽  
Huckleberry Finn

<p>This article is an attempt to explore the inclusion and the use of superstitious elements in Mark Twain’s novel <em>The Adventures of Huckleberry Finn</em> (1884) and Shakespeare’s play <em>Macbeth</em> (1611). Superstition involves a deep belief in the magic and the occult, to almost to an extent of obsession, which is contrary to realism. Through the analytical and psychological approaches, this paper tries to shed light on Twain’s and Shakespeare’s use of supernaturalism in their respective stories, and the extent the main characters are influenced by it. A glance at both stories reveals that characters are highly affected by superstitions, more than they are influenced by their religious beliefs, or other social factors and values. The researcher also tries to explore the role played by superstition, represented by fate and the supernatural in determining the course of actions characters undertake in both dramas. The paper concluded that the people who lived in the past were superstitious to an extent of letting magic, omens; signs, etc. affect and determine their lives; actions and future decisions. They determine their destiny and make it very difficult for them to avoid it, alter it or think rationally and independently. And that, man’s actions are not isolated, but closely connected to the various forces operating in the universe.</p>

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