Island Universes Research Articles

Islands in the stream

In 1919 George Hale, head of Mount Wilson Observatory, called for the US National Academy of Sciences to host a debate about “island universes” – galaxies outside of our own.

Modal Realism and the Possibility of Island Universes: Why There are no Possible Worlds

Abstract In this article, I defend Lewisian modal realism against objections arising from the possibility of ‘Island Universes’ and other similar cases. The problem comes from Lewis’ claim that possible worlds are spatio-temporally isolated. I suggest a modification of Lewisian modal realism in order to avoid this family of objections. This modification may sound quite radical since it amounts to abandoning the very notion of a possible world, but as radical as it may sound it in fact remains well in the spirit of Lewis’ original view.

Heterotic type I strings at high temperature

We show that the high temperature limits of the heterotic E8xE8 and Spin(32)/Z2 strings and their Type I A/B superstring duals are finite and convergent. The Hagedorn growth of the degeneracies in the string mass level expansion is suppressed by an exponential linear in the mass level number for both heterotic strings, and suppressed by the exponential of the negative square root of the mass level number for the Type IB superstring. However, in the massless gauge field theoretic limit of the Type IB open and closed superstring, we find clear evidence for the thermal deconfinement phase transition at the self-dual temperature by examining the annulus graph alone. Above the self-dual temperature, there is a discontinuity in the first derivative with respect to temperature of both the free energy, and the heavy quark potential, leading to a deconfined thermal gluon ensemble, with universal 1/r potential, and temperature dependent corrections, as predicted by Luscher and Weisz. A number of essential aspects of the worldsheet formalism of the heterotic strings are derived in an appendix, deducing thereby the O8-D0-D8brane Type IA duals of all of the heterotic CHL island universe moduli spaces.

Monism: The Islands of Plurality

Priority monism (hereafter, ‘monism’) is the view that there exists one fundamental entity—the world—and that all other objects that exist (a set of objects typically taken to include tables, chairs, and the whole menagerie of everyday items) are merely derivative. Jonathan Schaffer has defended monism in its current guise, across a range of papers. Each paper looks to add something to the monistic picture of the world. In this paper we argue that monism—as Schaffer describes it—is false. To do so we develop an ‘island universe’ argument against Schaffer’s monistic theory.

Grand challenges in Milky Way and galaxies

Extragalactic astronomy is a relatively young science. Its birth may be set at the time of the “greatdebate”betweenHarlowShapleyandHeberCurtisontheextragalacticnatureofthenebulae(whichculminated with a meeting of the two protagonists in April 1920) or, with a more conservativestance,afewyearslateratthetimeofEdwinHubble’sdiscoveryofCepheidvariablesinMessier31,the Andromeda galaxy and the nearest spiral galaxy to our own (Hubble, 1925). In the late 1920sthe Kapteyns Universe (that posed the Sun as the center of the Milky Way) and Shapley’s view (agiantMilkyWayofwhichthespiralnebulaewerepart)hadfallenoutoffavorwiththeappreciationoftheimportanceofinterstellarmatterintheabsorptionoflight.EveniftheUniverse’sconstituentswerestarsandgas,theywerenotconfinedtoasinglegalaxy,ourowngalaxy,theMilkyWay.Inthe1950stherecalibrationoftherelationbetweenperiodandluminosityoftheCepheidstarsprovideda distance scale consistent with the one presently adopted, greatly increasing the distance of eventhe nearest spiral nebulae and settling the issue of the island universes forever (Baade, 1958).Frontiers in extragalacticastronomy—which,unlike other fields, can be literally associatedwithaphysicaldistance—haveprogressedasimprovementsininstrumentalcapabilitiesmadeitpossibleto detect and to study more and more distant objects over an ever broader range of frequencies,from the radio to the γ-ray domain. Many results on distant sources are inferred by analogy withbetter studied sources, which are usually brighter and closer. Until now this approach—which isepistemologically risky (Salmon, 2012)—has not led research into major dead ends. There havebeen fully unexpected, and less unexpected discoveries that proved to be lasting paradigm shifts.The discovery of quasars expanded the cosmic scenario to distances previously unimaginable(Schmidt, 1963). The inference of dark matter in cluster of galaxies (Zwicky, 1933), and of darkmatter influence on the rotation curve of galaxies (Rubin et al., 1980) in the early 1970s providedearly glimpses of the “dark Universe” as we understand it today. The realization of the importanceof obscuration and extinction phenomena that affect even the most powerful extragalactic sourcescamegraduallywiththedevelopmentofX-ray,spectro-polarimetricandIRinstrumentation.Otherdiscoveriesfulfilleddreamsthathadbecomereality,likethefirstplanetarytransitinfrontofaMilkyWay star that was not the Sun (Charbonneau et al., 2000). All of them enriched our view of theUniverse.Forcomprehensivereviews,thereadermayconsiderthehistoricalchaptersofD’Onofrioet al. (2012) and D’Onofrio et al. (2015) that provide first-hand accounts on major discoveries ofthe last 50 years of Galactic and extra-galactic astronomical research. The possibility of a trulyrevolutionary paradigm change was vented perhaps only once, at the time of quasars discovery(Arp, 1987). In the mid 1960s quasar distances derived from the Hubble law looked enormous,and the ensuing quasar power demanded physics that appeared exotic at the time: accretion ontoasupermassiveblackhole(Salpeter,1964;Zel’DovichandNovikov,1965).Theissuewasdefinitelysettled when astronomers could see better at larger distances. With the advent of Hubble SpaceTelescope in the early 1990s quasars were definitely confirmed as nuclei of distant galaxies asimpliedbyHubble’slaw(Bahcalletal.,1997).Activegalacticnuclei(AGN)—whichincludequasarsthat were once believed to be rare—were found to be relatively common and to play an importantrole in the evolution of galaxies (e.g., Kormendy and Ho, 2013, and references therein).

Euclidean time formulation for the superstring ensembles: Perturbative canonical ensemble with Neveu-SchwarzB-field backgrounds

The lengthy discussion and derivations given in this paper have been corrected, and completed with additional results and greater simplicity. We show that the high temperature limits of the heterotic E8xE8 and Spin(32)/Z2 strings and their Type I A/B superstring duals are finite and convergent. The Hagedorn growth of the degeneracies in the string mass level expansion is suppressed by an exponential linear in the mass level number for both heterotic strings, and suppressed by the exponential of the negative square root of the mass level number for the Type IB superstring. However, in the massless gauge field theoretic limit of the Type IB open and closed superstring, we find clear evidence for the thermal deconfinement phase transition at the self-dual temperature by examining the annulus graph alone. Above the self-dual temperature, there is a discontinuity in the first derivative with respect to temperature of both the free energy, and the heavy quark potential, leading to a deconfined thermal gluon ensemble, with universal 1/r potential, and temperature dependent corrections, as predicted by Luscher and Weisz. A number of essential aspects of the worldsheet formalism of the heterotic strings are derived in an appendix, deducing thereby the O8-D0-D8brane Type IA duals of all of the heterotic CHL island universe moduli spaces.

The natural science of cosmology

The network of cosmological tests is tight enough now to show that the relativistic Big Bang cosmology is a good approximation to what happened as the universe expanded and cooled through light element production and evolved to the present. We have explained the reasons to reach this conclusion, commented on the varieties of philosophies informing searches for a still better cosmology, and offered an example for further study, the curious tendency of some classes of galaxies to behave as island universes.

Galilean islands in eternally inflating background

We show that the observational universe may emerge classically from a de Sitter background with low energy scale. We find, after calculating the curvature perturbation, that the resulting scenario is actually a style of the eternal inflation scenario, in which some regions will go through the slowly expanding Galilean genesis phase with the rapidly increasing energy density and become island universes, while other regions are still eternally inflating, which will make the room for more island universes to emerge.

From the Big Bang to Island Universe : Anatomy of a Collaboration

From the Big Bang to Island Universe:Anatomy of a Collaboration David H. Weinberg (bio) I first met Josiah McElheny in September 2004, in the cafe of the Wexner Center for the Arts, for what turned out to be a three-hour lunch. We were joined by Helen Molesworth, the Wexner Center's head curator. From an earlier conversation with Helen, I knew that Josiah wanted to make a sculpture about the big bang, connected in some way to the chandeliers that hang in New York's Metropolitan Opera House. Conveying an accurate understanding of the big bang is one of the hardest challenges I face in my introductory astronomy lectures, and I doubted that I could provide useful advice on how to do it with a sculpture. But by the end of our conversation we had identified a way forward, and after six years and four completed works, Josiah and I are still collaborating. Josiah and I have given numerous talks in the last two years, some individually and some jointly, on the four sculptures that have so far emerged from our collaboration: An End to Modernity (2005), The Last Scattering Surface (2006), The End of the Dark Ages (2008), and Island Universe (2008). I was delighted to participate in the Narrative, Science, and Performance symposium, which was an especially apt forum because of our project's deep roots at Ohio State and the Wexner Center, and because of the symposium's focus on the nexus between science and art. I have written elsewhere (see the Biographical Appendix) about the scientific background of these works, explaining the "code" that connects their elaborate arrangements of chrome-plated metal, glass disks and globes, and incandescent lamps to astronomical theories and observations. Here I will give just brief explanations of the science and focus instead on the history of the project, providing what I hope is an informative "case study" of an ambitious collaborative effort at the art/science border. [End Page 258] An End to Modernity In that first lunchtime conversation, Josiah began by showing me examples of his recent work, intricate constructions of transparent and reflective glass that explored themes of modernist design and architecture. He described his fascination with the Met chandeliers, a striking hybrid of cut-glass opulence and Sputnik spikiness, created in 1965, the year that the discovery of the cosmic microwave background provided the linchpin evidence for the big bang theory. Josiah showed me a sketch of the sculpture he envisioned: a "Met chandelier" remade in a streamlined modernist style, brought down to eye level, and connected explicitly to the big bang, with glass pieces representing galaxies and lamps representing quasars. Josiah knew the potential conceptual flaw of this design. While the popular image of the big bang is an explosion of material from a central point into pre-existing space—an atom bomb on steroids—cosmologists understand the big bang as the origin of space and time itself, initiating an expansion that occurs everywhere and has no center. I ran through my usual analogy of the expanding universe as the skin of an inflating balloon, carrying apart "galaxies" marked on its surface. Returning to Josiah's sketch, I noted that one might naturally read it not as a snapshot of a single instant but as a progression in time, with explosion at the center leading to subsequent fragmentation in the outer regions. I suggested that we make this progression explicit by having distance from the center represent time, mapping specific locations in the sculpture to specific epochs of cosmic history. The outer edge would mark the present day, and the supporting central sphere could represent the "last scattering surface," formed half a million years after the big bang, when the opaque fog of light-scattering free electrons dissipated and the universe became transparent for the first time. Somewhat to my surprise, Josiah embraced these suggestions immediately. And really, everything else has followed from there. Over the ensuing six months, Josiah made monthly visits to Columbus, and I gave him a crash course in modern cosmology, covering the empirical and theoretical underpinnings of the big bang theory and more recent discoveries about the formation and growth...

Galactic halos in cosmology with long‐range scalar DM interaction

AbstractBased on a set of cosmological N‐body simulations we analyze properties of the dark matter (DM) haloes in a galaxy mass range (1011–1013 h‐1Modot) in modified ΛCDM cosmology with additional dynamically screened scalar interactions in DM sector. Our simulations show that scalar interactions support picture of the Island Universe. Rapid structure formation processes are shifted into higher redshifts resulting in a much smaller accretion and merging rates for galactic haloes at low redshifts. Finally, we present how this “fifth” force affects halo properties, like density profile, triaxiality, ellipticities and the spin parameter.

Galactic halos in cosmology with long-range scalar DM interaction

Based on a set of cosmological N-body simulations we analyze properties of the dark matter haloes (DM) in a galaxy mass range ($10^{11} - 10^{13} h^{-1}M_{\odot}$) in modified $\lcdm$ cosmology with additional dynamically screened scalar interactions in DM sector. Our simulations show that scalar interactions support picture of the Island Universe. Rapid structure formation processes are shifted into higher redshifts resulting in a much smaller accretion and merging rates for galactic haloes at low redshifts. Finally, we present how this "fifth" force affects halo properties, like density profile, triaxiality, ellipticities and the spin parameter.

Discovering the expanding universe

Acknowledgments Foreword 1. Introduction 2. Cosmological concepts at the end of the Middle Ages 3. Nebulae as a new astronomical phenomenon 4. On the construction of the Heavens 5. Island universes turn into astronomical facts: a universe of galaxies 6. The early cosmology of Einstein and de Sitter 7. The dynamical universe of Friedmann 8. Redshifts: how to reconcile Slipher and de Sitter? 9. Lemaitre discovers the expanding universe 10. Hubble's contribution of 1929 11. The breakthrough for the expanding universe 12. Hubble's anger about de Sitter 13. Robertson and Tolman join the game 14. The Einstein-de Sitter universe 15. Are Sun and Earth older than the universe? 16. In search of alternative tracks 17. The seed for the Big Bang 18. Summary and postscript Appendix References Index.

Multiverses of the past

AbstractMore than 2000 years ago, Epicurus taught that there are an infinite number of other worlds, both like and unlike ours, and Aristotle taught that there are none. Neither hypothesis can currently be falsified, and some versions of current multiverses perhaps never can be, which has contributed to occasional claims that “this isn't science!” (a common complaint about cosmology for centuries). Define “cosmos”, or “world”, or “universe” to mean the largest structure of which you and the majority of knowledgeable contemporaries will admit to being a part. This begins with the small, earth‐centered worlds of ancient Egyptian paintings, Greek mythology, and Genesis, which a god could circumnavigate in a day and humans in a generation. These tend to expand and become helio‐rather than geo‐centric (not quite monotonically in time) and are succeeded by various assemblages of sun‐like stars with planets of their own. Finite vs. infinite assemblages are debated and then the issue of whether the Milky Way is unique (so that “island universes” made sense, even if you were against the idea) for a couple of centuries. Today one thinks as a rule of the entire 4‐dimensional space‐time we might in principle communicate with and all its contents. Beyond are the modern multi‐verses, sequential (cyclic or oscillating), hierarchical, or non‐communicating entities in more than four dimensions. Each of these has older analogues, and, in every milieu where the ideas have been discussed, there have been firm supporters and firm opponents, some of whose ideas are explored here. Because astronomical observations have firmly settled some earlier disputes in favor of very many galaxies and very many stars with planets, “other worlds” can now refer only to other planets like Earth or to other universes. The focus is on the latter (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Non-Gaussianity in island cosmology

In this paper we fully calculate the non-Gaussianity of primordial curvature perturbation of the island universe by using the second order perturbation equation. We find that for the spectral index ${n}_{s}\ensuremath{\simeq}0.96$, which is favored by current observations, the non-Gaussianity level ${f}_{\mathrm{NL}}$ seen in an island will generally lie between 30 and 60, which may be tested by the coming observations. In the landscape, the island universe is one of anthropically acceptable cosmological histories. Thus the results obtained in some sense mean the coming observations, especially the measurement of non-Gaussianity, will be significant to clarify how our position in the landscape is populated.

THE RETURN OF A STATIC UNIVERSE AND THE END OF COSMOLOGY

We demonstrate that as we extrapolate the current ΛCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

The return of a static universe and the end of cosmology

We demonstrate that as we extrapolate the current ΛCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our “island universe” will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

Redshift-space limits of bound structures

An exponentially expanding Universe, possibly governed by a cosmological constant, forces gravitationally bound structures to become more and more isolated, eventually becoming causally disconnected from each other and forming so-called 'island universes'. This new scenario reformulates the question about which will be the largest structures that will remain gravitationally bound, together with requiring a systematic tool that can be used to recognize the limits and mass of these structures from observational data, namely redshift surveys of galaxies. Here we present a method, based on the spherical collapse model and N-body simulations, by which we can estimate the limits of bound structures as observed in redshift space. The method is based on a theoretical criterion presented in a previous paper that determines the mean density contrast that a spherical shell must have in order to be marginally bound to the massive structure within it. Understanding the kinematics of the system, we translated the real-space limiting conditions of this 'critical' shell to redshift space, producing a projected velocity envelope that only depends on the density profile of the structure. From it we created a redshift-space version of the density contrast that we called 'density estimator', which can be calibrated from N-body simulations for a reasonable projected velocity envelope template, and used to estimate the limits and mass of a structure only from its redshift-space coordinates.

The cosmos: a historical perspective

Preface Timeline Introduction abylonian and Chinese Astronomy and Cosmology Greek Astronomy and Cosmology Cosmology from Islam to Copernicus Cosmology from Brahe to Newton Stellar Astronomy: The Universe Beyond the Solar System A Universe of Galaxies: The Triumph of the Island Universe Theory The Expansion of the Universe From Universal Expansion to the Big Bang The Big-Band Universe: Grom 1965 to the 21st Century Glossary Bibliography

ABSOLUTE ACTUALITY AND THE PLURALITY OF WORLDS

Let’s fix some terminology at the start. A world (or possible world – for me, the ‘possible’ is redundant) is, first, an individual, not a set or class; second, a particular, not a property or universal; third, concrete in this sense: it is fully determinate in all qualitative respects; and, fourth, a maximal interrelated whole: each world is internally unified, and isolated from every other world. There is at least one world, the world we are part of. It is an actual world, the actual world if there are no “island universes.” Worlds that are not actual (if any) are merely possible. A realist about possible worlds believes that there is a plenitudinous plurality of worlds: whenever something is possible – for example, that donkeys talk, or that pigs fly – there is a world in which it is true. There is more than one way to be a realist about possible worlds. Realists divide into two camps depending upon their account of actuality. According to David Lewis,

The limits of bound structures in the accelerating Universe

According to the latest evidence, the Universe is entering an era of exponential expansion, where gravitationally bound structures will get disconnected from each other, forming isolated ‘island universes’. In this scenario, we present a theoretical criterion to determine the boundaries of gravitationally bound structures and a physically motivated definition of superclusters as the largest bound structures in the Universe. We use the spherical collapse model self-consistently to obtain an analytical condition for the mean density enclosed by the last bound shell of the structure (2.36 times the critical density in the present Universe, assumed to be flat, with 30 per cent matter and 70 per cent cosmological constant, in agreement with the previous, numerical result of Chiueh & He). N-body simulations extended to the future show that this criterion, applied at the present cosmological epoch, defines a sphere that encloses ≈99.7 per cent of the particles that will remain bound to the structure at least until the scale parameter of the Universe is 100 times its present value. On the other hand, (28 ± 13) per cent of the enclosed particles are in fact not bound, so the enclosed mass overestimates the bound mass, in contrast with the previous, less rigorous criterion of, e.g. Busha and collaborators, which gave a more precise mass estimate. We also verify that the spherical collapse model estimate for the radial infall velocity of a shell enclosing a given mean density gives an accurate prediction for the velocity profile of infalling particles, down to very near the centre of the virialized core.