Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · gr-qc/0209046

The State of the Universe

James B. Hartle
View original source ↗Read source document ↗Export metadata ↓

Abstract

What is the quantum state of the universe? That is the central question of quantum cosmology. This essay describes the place of that quantum state in a final theory governing the regularities exhibited universally by all physical systems in the universe. It is possible that this final theory consists of two parts: (1) a dynamical theory such as superstring theory, and (2) a state of the universe such as Hawking's no-boundary wave function. Both are necessary because prediction in quantum mechanics requires both a Hamiltonian and a state. Complete ignorance of the state leads to predictions inconsistent with observation. The simplicity observed in the early universe gives hope that there is a simple, discoverable quantum state of the universe. It may be that, like the dynamical theory, the predictions of the quantum state for late time, low energy observations can be summarized by an effective cosmological theory. That should not obscure the need to provide a fundamental basis for such an effective theory which gives a a unified explanation of its features and is applicable without restrictive assumptions. It could be that there is one principle that determines both the dynamical theory and the quantum state. That would be a truly unified final theory. (talk given The Future of Theoretical Physics and Cosmology: Stephen Hawking 60th Birthday Symposium)

Explore related subjects

gr-qchep-th

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

James B. Hartle. 2020-04-27. The State of the Universe. https://arxiv.org/abs/gr-qc/0209046

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Photon propagation and black hole imaging in Kruglov nonlinear electrodynamics

Nonlinear electrodynamics (NLED) modifies photon propagation through an effective optical geometry, allowing optical phenomena to deviate from those predicted solely by the underlying spacetime metric. In this work, we revisit the Kruglov model, which generalizes Born--Infeld electrodynamics, and investigate the corresponding null geodesics in theeffective geometry through direct numerical integration, without relying on strong-field analytical approximations. We analyze the resulting photon spheres, gravitational lensing, black-hole shadows, and thin accretion-disk images, together with their dependence on the parameter $q$. For sufficiently small positive $q$, the effective angular metric develops a pole that generates stable photon orbits outside the event horizon and locally reverses the azimuthal evolution of photon trajectories, producing a distinctive bending pattern that resembles, although does not originate from, frame dragging. Conversely, negative $q$ introduces a zero of the effective correction factor, which acts as a turning point for photon trajectories and prevents them from entering the region where the background metric becomes complex. It produces measurable changes in light deflection, shadow radius, photon-ring morphology, and relativistic images. In particular, smaller positive values of $q$ produce thinner photon rings and enlarged shadow radii, whereas negative values generally lead to broader photon rings and smaller shadows. Comparison with the current Event Horizon Telescope constraints on Sgr~A* shows that a substantial region of the Kruglov parameter space remains compatible with present observations.

gr-qc↗
arXiv2026

Parity-dependent wave absorption and optical characteristics of a cored magnetic black hole

We study light propagation and coupled gravitational--electromagnetic waves around a black hole supported by a nonlinear magnetic field. The same field action fixes the geometry, the mass--charge relation, and the wave potentials. We calculate two critical impact parameters for light and solve the coupled scattering equations in both parity sectors. In eight solutions of one action, the two optical scales differ by $3.6$--$7.2\%$. The wave absorption also depends on parity. For $\ell=2$, the gap between the larger absorption eigenvalues reaches about $9.0$ percentage points. A wider frequency scan reveals a stronger effect in the second eigenchannel. The difference between the two absorption traces reaches $24.3$ percentage points. The trace equals twice the absorption of an equal incoherent mixture of incoming gravitational and electromagnetic fields. A controlled test of the wave operator shows that the nonlinear electromagnetic factor $κ$ plays an important role in the parity gap. We also examine four $\ell=3$ cases and use charge-matched Reissner--Nordström black holes as a separate control. The optical and wave calculations provide two complementary properties of the same magnetic source.

gr-qc↗
arXiv2026

Perturbative dynamics and relativistic effects of a dyonic Kalb-Ramond black hole

We investigate perturbative dynamics, tidal effects, and relativistic frequency shifts in a dyonic Kalb-Ramond black hole generated by a Lorentz-violating antisymmetric tensor background. The geometry is controlled by the mass $M$, the electric charge $Q$, the magnetic charge $p$, and the Lorentz-violating parameter $\ell$, with the dyonic sector entering through the effective combination $P_{\ell}^{2}=Q^{2}/(1-\ell)^{2}+p^{2}/(1-2\ell)$. First, we analyze the gravitational Doppler effect for radial signal exchange between freely falling and static observers, showing how the dyonic charges weaken the redshift by shifting the frequency ratio toward unity. We then compute the radial and angular tidal forces in a freely falling frame and determine the characteristic radii at which the usual stretching and compression patterns are reversed. The gravitational time delay is also evaluated for null trajectories, showing that the electric and magnetic sectors reduce the delay relative to the reference configuration. In the perturbative sector, we study massless scalar, vector, and spinor test fields together with an effective axial metric model, computing sixth-order WKB spectra and independently checking selected modes using the asymptotic iteration method. At fixed mass and charges, increasing the Lorentz-violating parameter raises the tabulated oscillation frequencies and damping rates in the original time coordinate; their interpretation accounts for time normalization and changes in effective parameters. The independent comparisons support the tested higher-multipole fundamental modes. Time-domain evolutions exhibit damped ringdown followed by power-law tails, whose exponents are estimated through fits incorporating finite time corrections and numerical sensitivity checks.

gr-qc↗