Is there any connection between the vastness of universes stars and galaxies existence life on a small planet out in suburbs Milky Way? This book shows that is. In their classic work, John Barrow Frank Tipler examine question Mankind's place Universe, taking reader tour many scientific disciplines offering fascinating insights into issues such as nature life, serach for extraterrestrial intelligence, past history fate our universe.

We describe the results of a search for time variability fine structure constant alpha using absorption systems in spectra distant quasars. Three large optical data sets and two 21 cm mm provide four independent samples, spanning approximately 23% to 87% age universe. Each sample yields smaller past shows 4 sigma deviation: Delta alpha/alpha = -0.72+/-0.18 x 10(-5) over redshift range 0.5<z<3.5. find no systematic effects which can explain our results. The only potentially significant push...

An order of magnitude sensitivity gain is described for using quasar spectra to investigate possible time or space variation in the fine structure constant $\ensuremath{\alpha}$. Applied a sample 30 absorption systems, spanning redshifts $0.5<z<1.6$, we derive limits on variations $\ensuremath{\alpha}$ over wide range epochs. For whole sample,...

The meaning of the inflationary slow-roll approximation is formalized. Comparisons are made between an approach based on Hamilton-Jacobi equations, governing evolution Hubble parameter, and usual scenario potential energy density. vital role attractor solution emphasized, some its properties described. We propose a new measure inflation, upon contraction comoving length as opposed to e-foldings physical expansion, derive relevant formulas. introduce infinite hierarchy parameters, show that...

Journal Article Book Reviews Get access The Anthropic Cosmological Principle. By John D. Barrow and Frank J. Tipler. (Oxford: Clarendon Press, 1986. Pp. xx +706. Price £25.00.) J.J.C. Smart Australian National University Search for other works by this author on: Oxford Academic Google Scholar Philosophical Quarterly, Volume 37, Issue 149, October 1987, Pages 463–466, https://doi.org/10.2307/2219581 Published: 01 1987

The authors analyse the behaviour of homogeneous and isotropic solutions to a gravity theory that arises from variation an arbitrary analytic function space-time scalar curvature. Such generalises Einstein's general relativity wherein this is linear in They prove conditions for existence stability relativistic de Sitter Friedmann within theory, necessary sufficient cosmological singularities particle horizons asymptotic ever-expanding Universe models. under which Minkowski Schwarzschild are...

We show that in theories of generalized teleparallel gravity, whose Lagrangians are algebraic functions the usual Lagrangian, action and field equations not invariant under local Lorentz transformations. also argue these appear to have extra degrees freedom with respect general relativity. The which has been extensively studied leads a theory dynamically equivalent relativity, is an exception. Both facts overlooked recent literature on $f(T)$ but crucial for assessing viability as...

We consider the cosmologies that arise in a subclass of $f(R)$ gravity with $f(R)=R+{\ensuremath{\mu}}^{2n+2}/(\ensuremath{-}R{)}^{n}$ and $n\ensuremath{\in}(\ensuremath{-}1,0)$ metric (as opposed to Palatini) variational approach deriving gravitational field equations. The calculations isotropic homogeneous cosmological models are undertaken Jordan frame at both background perturbation levels. For former, we also discuss connection Einstein which extra degree freedom theory is associated...

We investigate the consequences for black hole area of introducing fractal structure horizon geometry. create a three-dimensional spherical analogue 'Koch Snowflake' using infinite diminishing hierarchy touching spheres around Schwarzschild event horizon. can with finite volume and (or finite) area. This is toy model possible effects quantum gravitational spacetime foam, significant implications assessments entropy holes universe, which generally larger than in standard picture...

We analyze the relation between teleparallelism and local Lorentz invariance. show that generic modifications of teleparallel equivalent to general relativity will not respect symmetry. clarify reasons for this explain why situation is different in relativity. give a prescription constructing equivalents known theories. also explicitly consider recently proposed class generalized theories, called f(T) theories gravity, restoring symmetry such cannot lead sensible dynamics, even if one gives...

In this work we study the cosmology of general f(T) gravity theory. We express modified Einstein equations using covariant quantities, and derive gauge-invariant perturbation in form. consider a specific choice f(T), designed to explain observed late-time accelerating cosmic expansion without including an exotic dark energy component. Our numerical solution shows that extra degree freedom such models generally decays as one goes smaller scales, consequently its effects on scales galaxies...

In the cosmological scenario in $f\left( T\right) $ gravity, we find analytical solutions for an isotropic and homogeneous universe containing a dust fluid radiation empty anisotropic Bianchi I universe. The method that apply is of movable singularities differential equations. For universe, are expressed terms Laurent expansion, while family exact Kasner-like vacuum. Finally, discuss when nonlinear $-gravity theory provides teleparallel equivalence general relativity derive conditions to...

We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on the exponent of Barrow entropy. The latter is an extended entropy relation arising from incorporation quantum-gravitational effects black-hole structure, parameterized effectively by new parameter Δ. When considered a cosmological framework and under light gravity-thermodynamics conjecture, leads modified scenarios whose Friedmann equations contain extra terms. perform detailed analysis BBN era we calculate...

We show that a singularity can occur at finite future time in an expanding Friedmann universe even when ρ > 0 and + 3p 0. Explicit examples are constructed simple condition is given which be used to eliminate behaviour of this sort if it judged unphysical.

We study the cosmological and weak-field properties of theories gravity derived by extending general relativity means a Lagrangian proportional to ${R}^{1+\ensuremath{\delta}}$. This scale-free extension reduces when $\ensuremath{\delta}\ensuremath{\rightarrow}0$. In order constrain generalizations this power class, we analyze behavior perfect-fluid Friedmann universes isolate physically relevant models zero curvature. A stable matter-dominated period evolution requires...

We consider the cosmology where some function $f(G)$ of Gauss-Bonnet term $G$ is added to gravitational action account for late-time accelerating expansion universe. The covariant and gauge invariant perturbation equations are derived with a method which could also be applied general $f(R,{R}^{ab}{R}_{ab},{R}^{abcd}{R}_{abcd})$ theories. It pointed out that, despite their fourth-order character, such gravity models generally cannot reproduce arbitrary background cosmic evolutions; example,...

We investigate the cosmological consequences of a theory in which electric charge e can vary. In this fine structure "constant," alpha, remains almost constant radiation era, undergoes small increase matter but approaches value when universe starts accelerating because positive constant. This model satisfies geonuclear, nucleosynthesis, and cosmic microwave background constraints on time variation while fitting observed Universe evidence for alpha variations quasar spectra. It also places...

We derive an upper limit of $B_0<3.4\times 10^{-9}(\Omega_0h_{50}^2)^{1/2}$ Gauss on the present strength any primordial homogeneous magnetic field. The microwave background anisotropy created by cosmological fields is calculated in most general flat and open anisotropic cosmologies containing expansion-rate 3-curvature anisotropies. Our derived from a statistical analysis 4-year Cosmic Background Explorer data for patterns characteristic averaged over all possible sky orientations with...

We analyze a generalization of general relativity that incorporates cosmic time variation the velocity light in vacuum, $c,$ and Newtonian gravitation ``constant'' $G$ proposed by Albrecht Magueijo. find exact solutions for Friedmann universes determine rate $c$ required to solve flatness classical cosmological constant problems. Potential problems with this approach resolution are highlighted. Reformulations suggested which give theory more desirable limit as varying its relationship...