scholarly journals Closed Timelike Curves, Singularities and Causality: A Survey from Gödel to Chronological Protection

Universe ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 12
Author(s):  
Jean-Pierre Luminet
Keyword(s):  
Time Travel ◽  
Historical Survey ◽  
Closed Timelike Curves ◽  
Causal Dynamical Triangulations ◽  
Physical Mechanisms ◽  
The Past ◽  
General Relativistic ◽  
Dynamical Triangulations ◽  
Rotating Universe ◽  
The Universe

I give a historical survey of the discussions about the existence of closed timelike curves in general relativistic models of the universe, opening the physical possibility of time travel in the past, as first recognized by K. Gödel in his rotating universe model of 1949. I emphasize that journeying into the past is intimately linked to spacetime models devoid of timelike singularities. Since such singularities arise as an inevitable consequence of the equations of general relativity given physically reasonable assumptions, time travel in the past becomes possible only when one or another of these assumptions is violated. It is the case with wormhole-type solutions. S. Hawking and other authors have tried to “save” the paradoxical consequences of time travel in the past by advocating physical mechanisms of chronological protection; however, such mechanisms remain presently unknown, even when quantum fluctuations near horizons are taken into account. I close the survey by a brief and pedestrian discussion of Causal Dynamical Triangulations, an approach to quantum gravity in which causality plays a seminal role.

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.

Closed Timelike Curves and Singularities

2018 ◽  
Vol 4 (1) ◽  
Author(s):  
Jean-Pierre Luminet
Keyword(s):  
Universe Model ◽  
Closed Timelike Curves ◽  
The Past ◽  
Kurt Gödel ◽  
Rotating Universe

Discovered in 1949 by Kurt Gödel, the homogeneous rotating universe model contains closed timelike curves and therefore allows for travel into the past, accompanied by all its paradoxes.

scholarly journals Distortions of Robertson–Walker metric in perturbative cosmology and interpretation as dark matter and cosmological constant

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
Federico Re
Keyword(s):  
Dark Matter ◽  
Relativistic Effect ◽  
Matter Density ◽  
Inhomogeneous Distribution ◽  
The Past ◽  
Walker Metric ◽  
General Relativistic ◽  
The Universe ◽  
General Relativistic Effect ◽  
Magnification Effect

Abstract In the last years, we saw more and more attempts to explain dark matter as a general relativistic effect, at least for some fraction. Following this philosophy, we considered the gravitational distortions due to the inhomogeneous distribution of matter in the universe, which we know from general relativity to be retarded distortions. This provides a magnification effect, since the distortions we feel now depend not on the present matter density, but on the past one, which is greater. The expansion rate of the universe is perturbed as well, in a not negligible way, despite matter inhomogeneities are small, because of the same magnification effect. The deceleration parameter, which is a way to evaluate the quantity of dark matter in the universe, is perturbed in turn, so that the real amount of dark matter is less than what is usually believed.

scholarly journals Quantum signaling to the past using P-CTCS

2018 ◽  
Vol 18 (11&12) ◽  
pp. 965-974
Author(s):  
Soumik Ghosh ◽  
Arnab Adhikary ◽  
Goutam Paul
Keyword(s):  
Time Travel ◽  
Entangled States ◽  
Closed Timelike Curves ◽  
Signaling Protocol ◽  
The Past ◽  
Local Correlations ◽  
Non Local ◽  
Computational Resources

Closed Timelike Curves (CTCs) are intriguing relativistic objects that allow for time travel to the past and can be used as computational resources. In Deutschian Closed Timelike Curves (D-CTCs), due to the monogamy of entanglement, non-local correlations between entangled states are destroyed. In contrast, for Postselected Closed Timelike Curves (P-CTCs), a second variant of CTCs, the non-local correlations are preserved. P-CTCs can be harnessed for the signaling of non-orthogonal states to the past without a disruption of causality. In this paper, we take up signaling to the past and show a method of sending four non-orthogonal states to the past using P-CTCs. After constructing our signaling protocol, we study the causality violations that our protocol results in and put forward two consistency relations to prevent them.

Adaptations of Time Travel Narratives in Japanese Multimedia: Nurturing Eudaimonia across Time and Space

2014 ◽  
Vol 7 (2) ◽  
pp. 136-151 ◽  
Author(s):  
Sung-Ae Lee
Keyword(s):  
Travel Narratives ◽  
Time Travel ◽  
Cultural Knowledge ◽  
Human Beings ◽  
The Core ◽  
The Past ◽  
Life Styles ◽  
Concern For Others ◽  
The Future ◽  
Live Action

To displace a character in time is to depict a character who becomes acutely conscious of his or her status as other, as she or he strives to comprehend and interact with a culture whose mentality is both familiar and different in obvious and subtle ways. Two main types of time travel pose a philosophical distinction between visiting the past with knowledge of the future and trying to inhabit the future with past cultural knowledge, but in either case the unpredictable impact a time traveller may have on another society is always a prominent theme. At the core of Japanese time travel narratives is a contrast between self-interested and eudaimonic life styles as these are reflected by the time traveller's activities. Eudaimonia is a ‘flourishing life’, a life focused on what is valuable for human beings and the grounding of that value in altruistic concern for others. In a study of multimodal narratives belonging to two sets – adaptations of Tsutsui Yasutaka's young adult novella The Girl Who Leapt Through Time and Yamazaki Mari's manga series Thermae Romae – this article examines how time travel narratives in anime and live action film affirm that eudaimonic living is always a core value to be nurtured.

Mental time travel? A neurocognitive model of event simulation

2020 ◽  
Author(s):  
Donna Rose Addis
Keyword(s):  
Predictive Coding ◽  
Time Travel ◽  
Simulation System ◽  
Mental Time Travel ◽  
Event Representation ◽  
Conceptual Information ◽  
Fine Grained ◽  
The Past ◽  
The Future ◽  
General Capacity

Mental time travel (MTT) is defined as projecting the self into the past and the future. Despite growing evidence of the similarities of remembering past and imagining future events, dominant theories conceive of these as distinct capacities. I propose that memory and imagination are fundamentally the same process – constructive episodic simulation – and demonstrate that the ‘simulation system’ meets the three criteria of a neurocognitive system. Irrespective of whether one is remembering or imagining, the simulation system: (1) acts on the same information, drawing on elements of experience ranging from fine-grained perceptual details to coarser-grained conceptual information and schemas about the world; (2) is governed by the same rules of operation, including associative processes that facilitate construction of a schematic scaffold, the event representation itself, and the dynamic interplay between the two (cf. predictive coding); and (3) is subserved by the same brain system. I also propose that by forming associations between schemas, the simulation system constructs multi-dimensional cognitive spaces, within which any given simulation is mapped by the hippocampus. Finally, I suggest that simulation is a general capacity that underpins other domains of cognition, such as the perception of ongoing experience. This proposal has some important implications for the construct of ‘MTT’, suggesting that ‘time’ and ‘travel’ may not be defining, or even essential, features. Rather, it is the ‘mental’ rendering of experience that is the most fundamental function of this simulation system, enabling humans to re-experience the past, pre-experience the future, and also comprehend the complexities of the present.

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 Nature of Time

2018 ◽  
Author(s):  
Donald C. Williams
Keyword(s):  
Large Scale ◽  
Time Travel ◽  
Dimensional Manifold ◽  
Nature Of Time ◽  
Manifold Theory ◽  
The Universe ◽  
Theoretical Cost ◽  
Do So

This chapter provides a fuller treatment of the pure manifold theory with an expanded discussion of competing doctrines. It is argued that competing doctrines fail to account for the extensive and/or transitory aspect(s) of time, or they do so at great theoretical cost. The pure manifold theory accounts for the extensive aspect of time because it admits a four-dimensional manifold and it accounts for the transitory aspect of time because it hypothesizes that the increase of entropy is the thing that is ‘felt’ in veridical cases of felt passage. A four-dimensionalist theory of time travel is outlined, along with a sketch of large-scale cosmological traits of the universe.

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