III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet, Incubator Lifescape

5. ExoUniverse Studies: Detectable Presence, Conceptual Features

Gasperini, Maurizio. Observable Gravitational Waves in Pre-Big Bang Cosmology. arXiv:1606.07889. This posting by the University of Bari, Italy physicist opens with this sentence: It is well known that a cosmological phase of growing space-time curvature and accelerated evolution (also called (superinflation), followed by a transition to the standard radiation-dominated regime, can produce a stochastic background of relic gravitational waves. How fantastic is it that human earthlings can yet achieve such knowledge. On the author’s website, www.ba.infn.it/~gasperin, can be found a longer pos as The Pre-Big Bang Scenario. So it seems that not only can We peoples detect concurrent cosmoses, but also engage ones that occurred before.

In the light of the recent results concerning CMB observations and GW detection we address the question of whether it is possible, in a self-consistent inflationary framework, to simultaneously generate a spectrum of scalar metric perturbations in agreement with Planck data and a stochastic background of primordial gravitational radiation compatible with the design sensitivity of aLIGO/Virgo and/or eLISA. We show that this is possible in a string cosmology context, for a wide region of the parameter space of the so-called pre-big bang models. We also discuss the associated values of the tensor-to-scalar ratio relevant to the CMB polarization experiments. We conclude that future, cross-correlated results from CMB observations and GW detectors will be able to confirm or disprove pre-big bang models and -- in any case -- will impose new significant constraints on the basic string theory/cosmology parameters. (Abstract)

Gasperini, Maurizio. On the Initial Regime of Pre-Big Bang Cosmology. arXiv:1707.05763. We cite this entry by a senior University of Bari, Italy physicist as an example of theoretical treatments not only of a spatial array of exouniverses, but also their temporal succession. See the September issue of the Journal of Cosmology and Astroparticle Physics for its publication.

The production of a background of super-horizon curvature perturbations with the appropriate (red) spectrum needed to trigger the cosmic anisotropies observed on large scales is associated, in the context of pre-big bang inflation, with a phase of growing string coupling. The extension towards the past of such a phase is not limited in time by the dynamical backreaction of the quantum perturbations of the cosmological geometry and of its sources. A viable, slightly red spectrum of scalar perturbations can thus be the output of an asymptotic, perturbative regime which is well compatible with an initial string-vacuum state satisfying the postulate of "Asymptotic Past Triviality". (Abstract)

Gefter, Amanda. Another Universe Comes Calling. New Scientist. January 24, 2009. Within a multiverse scenario, NASA Goddard scientists wonder as distant galactic clusters rush apart if unexpected movements might indicate they are bumping into another cosmos. Who then are we humans to pose as this universe’s way of describing and learning about itself? Might our import be, as Max Tegmark alludes herein, to not only choose earth but our whole cosmos to succeed from myriad bubbling versions.

Glavan, Drazen, et al. Stochastic Dark Energy from Inflationary Quantum Fluctuations. arXiv:1710.07824. Glavan, University of Warsaw, Tomislav Prokopec, Utrecht University, and Alexei Starobinsky, Landau Institute for Theoretical Physics, Moscow, a premier theorist who received the Kavli Prize in Astrophysics with Andrei Linde and Alan Guth in 2014. We note because this posting present a latest finesse by one of its founder theorists.

We study the quantum backreaction from inflationary fluctuations of a very light, non-minimally coupled spectator scalar and show that it is a viable candiate for dark energy. The problem is solved by suitably adapting the formalism of stochastic inflation. This allows us to self-consistently account for the backreaction on the background expansion rate of the Universe where its effects are large. This framework is equivalent to that of semiclassical gravity in which matter vacuum fluctuations are included at the one loop level, but purely quantum gravitational fluctuations are neglected. Our results show that dark energy in our model can be characterized by a rather distinct effective equation of state parameter (as a function of redshift) which allows for effective testing of the model at the level of the background. (Abstract)

Gould, Elizabeth and Niayesh Afshordi. Does History Repeat Itself? Periodic Time Cosmology. arXiv:1903.09694. As the abstract alludes and lately becoming possible, Queen’s University, Ontario and University of Waterloo, Canada astrophysicists with Perimeter Institute posts proceed to quantitatively imagine temporal, eternal return self-similarities for a whole universe. Again how incredible is it that a tiny habitable ecosphere with a sentient species can suddenly be able to consider entire cosmoses?

It has been suggested that the cosmic history might repeat in cycles, with an infinite series of similar aeons in the past and the future. Here, we instead propose that the cosmic history repeats itself exactly, constructing a universe on a periodic temporal history, which we call Periodic Time Cosmology. In particular, the primordial power spectrum, convolved with the transfer function throughout the cosmic history, would form the next aeon's primordial power spectrum. By matching the big bang to the infinite future using a conformal rescaling (a la Penrose), we uniquely determine the primordial power spectrum, in terms of the transfer function up to two free parameters. Therefore, consistency between cosmic history and initial conditions provides a viable description of cosmological observations in the context of Periodic Time Cosmology. (Abstract excerpt)

Grohs, Evan, et al. Universes without the Weak Force. arXiv:1801.06081. University of Michigan astrophysicists Grohs, Alex Howe and Fred Adams continue their endeavors, as we report herein, about entire cosmoses and their suitability or not for life by tweaks of energies and particles. And once again how fantastic it is that in a conducive universe as this, after billions of years, on a special bioplanet, a collaborative sapient species can yet contemplate these infinite imaginaries. Surely there must be some grand discovery and purpose for the asking.

We investigate a class of universes in which the weak interaction is not in operation. We consider how astrophysical processes are altered in the absence of weak forces, including Big Bang Nucleosynthesis, galaxy formation, molecular cloud assembly, star formation, and stellar evolution. Without weak interactions, neutrons no longer decay, and the universe emerges from its early epochs with a mixture of protons, neutrons, deuterium, and helium. As a result, stellar evolution proceeds primarily through strong interactions, with deuterium first burning into helium, and then helium fusing into carbon. Low-mass deuterium-burning stars can be long-lived, and higher mass stars can synthesize the heavier elements necessary for life. Although somewhat different from our own, such universes remain potentially habitable. (Abstract excerpt)

The fundamental constants that describe the laws of physics appear to have arbitrary values that cannot be explained by current theory. One possible — and partial — explanation is that other universes exist in which the fundamental constants have different values, so that they are drawn from an as-yet-unknown probability distribution. Many authors have argued that significant changes in these constants could render the universe uninhabitable to life as we know it, and as a result our universe appears to be “fine-tuned” for life. On the other hand, recent work suggests that when multiple constants are allowed to vary, large regions of the parameter space that result in habitable universes can be found. This paper continues the exploration of alternate possibilities for the fundamental constants with a focus on the weak force. (1)

Gurzadyan, Vahe and Roger Penrose. CCC and the Fermi Paradox. arXiv:1512.00554. We cite in this new section because the Yerevan Physics Institute, Armenia and Oxford University mathematical cosmologists go on to consider temporal multi-universe features before and after this present cosmos. CCC is Penrose’s conformal cyclic cosmology theory. As a result, it may also be conceivably possible to imagine, consider, and factor influences from earlier and later cosmic aeons.

He, Yang-Hui. Universes as Big Data. ArXiv:2011.14442. In this latest essay, a City University of London mathematician with many Chinese and international colleagues adds a new dimension to physical theories by noticing ways that current deep neural net learning algorithmic procedures are gaining much avail and service to cosmological studies. As a consequence, universal nature can be seen to take on a textual, and indeed a cerebral character and quality. See also He’s book length The Calabi-Yau Landscape: from Geometry, to Physics, to Machine-Learning at 1812.02893, search this eprint site for more papers.

We review how string theory first led theoretical physics to precise problems in algebraic and differential geometry, and thence to computational geometry in the last decade or so, and, in the last few years, to data science. Using the Calabi-Yau landscape as a starting-point, we consider recent progress in machine-learning applied to the sifting through of possible universes from compactification, as well as wider problems in geometrical engineering of quantum field theories. In parallel, we discuss machine-learning mathematical structures and how they may apply from mathematical physics, to geometry, to representation theory, and to number theory. (Abstract excerpt)

Ijjas, Anna and Paul Steinhardt. The Anamorphic Universe. arXiv:1507.03875. For some time, Princeton University physicists have been proposing alternative cosmic theories to the inflationary multiverse model, search each here and Wikipedia for Ekpyrotic Universe. This July 2015 posting presents a new version of their project, which comes closer to a revised inflation image such as Carrasco, et al above. For an update survey see Implications of Planck 2015 for Inflationary, Ekpyrotic and Anamorphic Bouncing Cosmologies at 1512.09010. Anna Ijjas, who also has a second doctorate in philosophy, has since posted a Cyclic Anamorphic Universe model, see 1610.02752 and second quote.

We introduce "anamorphic" cosmology, an approach for explaining the smoothness and flatness of the universe on large scales and the generation of a nearly scale-invariant spectrum of adiabatic density perturbations. The defining feature is a smoothing phase that acts like a contracting universe based on some Weyl frame-invariant criteria and an expanding universe based on other frame-invariant criteria. An advantage of the contracting aspects is that it is possible to avoid the multiverse and measure problems that arise in inflationary models. Unlike ekpyrotic models, anamorphic models can be constructed using only a single field and can generate a nearly scale-invariant spectrum of tensor perturbations. Anamorphic models also differ from pre-big bang and matter bounce models that do not explain the smoothness. We present some examples of cosmological models that incorporate an anamorphic smoothing phase. (1507.03875 Abstract)

Cyclic models of the universe have the advantage of avoiding initial conditions problems related to postulating any sort of beginning in time. To date, the only known viable examples of cyclic models have been ekpyrotic. In this paper, we show that the recently proposed anamorphic scenario can also be made cyclic. The key to the cyclic completion is a classically stable, non-singular bounce. Remarkably, even though the bounce construction was originally developed to connect a period of contraction with a period of expansion both described by Einstein gravity, we show here that it can naturally be modified to connect an ordinary contracting phase described by Einstein gravity with a phase of anamorphic smoothing. (1610.02752 Abstract)

Jamieson, Drew and Marilena LoVerde. Quintessential Isocurvature in a Separate Universe. arXiv:1812.08765. SUNY Stony Brook, Cosmology Group astrophysicists consider various theoretical models with regard to the nature of an entire cosmos. As noted above in Boyle, et al, this ability must imply something significant and purposeful about our planetary sapience. For an example of an earlier usage of this title concept, see Separate Universe Simulations by Christian Wagner, et al at arXiv:1409.6294,

In a universe with quintessence isocurvature, or perturbations in dark energy that are independent from the usual curvature perturbations, structure formation is changed qualitatively. The existence of two independent fields, curvature and isocurvature, causes the growth rate of matter perturbations to depend on their initial conditions. We perform the first separate universe simulations for this cosmology. We demonstrate that the power spectrum response and the halo bias depend on scale and initial conditions and that the presence of the isocurvature mode changes the mapping from these quantities to the halo auto- and cross-power spectra, and the squeezed-limit bispectrum. This allows our results to be used to predict the halo power spectrum and stochasticity with arbitrary large-scale curvature and isocurvature power spectra. (Abstract excerpt)

Jimenez, Raul, et al. Measuring the Homogeneity of the Universe. arXiv:1902.11298. We enter this posting by University of Barcelona, University of the Western Cape, Dartmouth College and Imperial College London (Alan Heavens) astrophysicists as a 2019 example of how our nascent worldwide intellect has become able on its own to consider and quantify an entire cosmos. For some context, this achievement reaches across some 30 orders of magnitude from our minute, precious, maybe rarest habitable observance to the whole expansive universe.

We propose a method to probe the homogeneity of a general universe, without assuming symmetry. We show that isotropy can be tested at remote locations on the past lightcone by comparing the line-of-sight and transverse expansion rates, using the time dependence of the polarization of Cosmic Microwave Background photons that have been inverse-Compton scattered by the hot gas in massive clusters of galaxies. Thus we can test remote isotropy, which is a key requirement of a homogeneous universe. We provide explicit formulas that connect observables and properties of the metric. (Abstract excerpt)

Johnson, Matthew, et al. Simulating the Universe(s) III: Observables for the Full Bubble Collision Spacetime. arXiv:1508.03641. Johnson, York University, with Carroll Wainwright, Perimeter Institute, Anthony Aguirre, UC Santa Cruz, and Hiranya Peiris, University College London continue their project to theorize generic properties for galactic cosmoses. Prior postings are II: Phenomenology of Cosmic Bubble Colisions in Full General Relativity (1407.2950), and I: From Cosmic Bubble Collisions to Cosmological Observable with Numerical Relativity (1312.1357) (search Wainwright here). This new section is meant to represent the incredible idea that human acumen can actually expand to such multiple cosmoses reaches. As a cosmological phenomenon just the same, might it ever be asked who are we peoples, why can we learn this?

This is the third paper in a series establishing a quantitative relation between inflationary scalar field potential landscapes and the relic perturbations left by the collision between bubbles produced during eternal inflation. We introduce a new method for computing cosmological observables from numerical relativity simulations of bubble collisions. This method tiles comoving hypersurfaces with locally-perturbed Friedmann-Robertson-Walker coordinate patches. The method extends previous work, which was limited to the spacetime region just inside the future light cone of the collision, and allows us to explore the full bubble-collision spacetime. We validate our new methods against previous work, and present a full set of predictions for the comoving curvature perturbation and local negative spatial curvature produced by identical and non-identical bubble collisions, in single scalar field models of eternal inflation. In both collision types, there is a non-zero contribution to the spatial curvature and cosmic microwave background quadrupole. (Abstract extract)

Previous   1 | 2 | 3 | 4 | 5 | 6  Next