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If the universe had been born in a high entropy, equilibrium state, there would be no stars, no planets and no life. Thus, the initial low entropy of the universe is the fundamental reason why we are here. However, we have a poor understanding of why the initial entropy was low and of the relationship between gravity and entropy. We are also struggling with how to meaningfully define the maximum entropy of the universe. This is important because the entropy gap between the maximum entropy of the universe and the actual entropy of the universe is a measure of the free energy left in the universe to drive all processes. I review these entropic issues and the entropy budget of the universe. I argue that the low initial entropy of the universe could be the result of the inflationary origin of matter from unclumpable false vacuum energy. The entropy of massive black holes dominates the entropy budget of the universe. The entropy of a black hole is proportional to the square of its mass. Therefore, determining whether the Maximum Entropy Production Principle (MaxEP) applies to the entropy of the universe is equivalent to determining whether the accretion disks around black holes are maximally efficient at dumping mass onto the central black hole. In an attempt to make this question more precise, I review the magnetic angular momentum transport mechanisms of accretion disks that are responsible for increasing the masses of black holes

Astronomy is an ongoing, cumulative science in which astronomers either discover previously unseen constituents of the observable universe or determine physical properties of known ones. They measure the mass, luminosity, distance, size, chemical composition, motion, and magnetic fields of planets, stars, galaxies, and their surroundings.

Publisher Summary This chapter provides an overview of how the concept of distance is used in physics and chemistry. Physical forces that act at a distance (that is, a push or pull which acts without physical contact) are nuclear and molecular attraction, and, beyond atomic level, gravity, static electricity, and magnetic forces. Last two forces can be both, push and pull. The mechanic distance is the position of a particle as a function of time t. The terminal distance is a distance of an object, moving in a resistive medium, from an initial position to a stop. The chapter discusses ballistics as the study of the motion of projectiles, that is, bodies which are propelled (or thrown) with some initial velocity, and then allowed to be acted upon by the forces of gravity and possible drag. The horizontal distance traveled by a projectile is called range, the maximum upward distance reached by it is called height, and the path of the object is called trajectory. Basic concepts related to acoustic metric, healing length, spatial coherence length, inverse-square distance laws, atomic radius, bond distance, and inter-ionic distance are also explained in the chapter.

Regardless of the direction in which we look out into space, almost all of the distant galaxies are flying apart, dispersing and moving away at speeds that increase with their distance, as if they had been ejected by a cosmic bomb. Astronomers call it the “big bang”.

The results of this review of evidence bearing on the probability of extraterrestrial life can be briefly summarized. Our review of the science relevant to estimates of the factors in the Drake equation.

This chapter the motivation and evidence for the various types of multiverses that have been proposed. A key problem is their lack of testability, because of the existence of cosmic horizons; nevertheless they are claimed to be a scientific hypothesis. I review the arguments in their favour, and suggest none is conclusive, although there is one case where they could be disproved (the small universe case) and one that would indeed be quite convincing circumstantial evidence (circles in the CMB sky associated with variation of fundamental constants).

Time, as familiar as it seems to us in everyday life, is one of the greatest puzzles of science and philosophy. In physics and cosmology it is especially mysterious why time appears to be directed, that is, why there seems to be an essential difference between the past and the future. The most basic known laws of nature do not contain this asymmetry. And yet, several arrows of time can be distinguished at least ten, in fact. However, it is unclear whether any of them are fundamental or whether others can be reduced to these, and it is not known how the direction of time could be explained convincingly. From the growing but still astonishingly low entropy of the observable universe, it seems plausible that the solution of the mystery is connected with cosmology and an explanation of the big bang. This could require a new fundamental law of nature (which might be related to a particular geometry) or specific boundary conditions (which might be comprehensible within the framework of a multiverse theory). Or it may be that times direction is fundamental and irreducible, or an illusion and not explicable, but can only be explained away. It is even more confusing that not all of these alternatives are mutually exclusive. Furthermore, there is a plethora of approaches to explain the big bang. Some models postulate an absolute beginning of time, others an everlasting universe or multiverse in which the big bang is a phase transition, and maybe there are myriads of big bangs. So the low entropy of the observable universe might be a random fluctuation whereas elsewhere even opposite thermodynamic directions of time may arise. Perhaps the (or our) big bang just created the arrows of time, if it originated as some sort of pseudo-beginning in a quantum vacuum that has no direction of time. Thus it seems useful to conceptually distinguish an undirected microtime and a directed macrotime. It is even possible that time ends although paradoxically, it may do so only temporarily.

The centrality of man in the universe has a long history, stretching from ancient times to modern cosmology. Stepwise man’s homestead has been displaced to a typical, inconspicuous location in space. Today there is not the slightest evidence for the existence of distinguished places at all within an isotropic and homogeneous universe.

An important aspect of astrophysical MHD turbulence research is developing diagnostics to connect simulations with the observable universe. Turbulent systems are by definition structurally complex in all fluid variables (density, velocity, and magnetic field), such that they must be described statistically. By developing and applying diagnostic tools to simulation data, it is possible to interpret empirical laws for the statistical properties of observed systems in terms of fundamental dynamical processes, and to identify and calibrate robust probes of physical parameters that cannot be measured directly. Using several different examples, I describe how structural diagnostic analyses have already yielded significant insights into the nature of turbulent molecular clouds. I review results from several different groups, and discuss directions for future diagnostics to enhance our understanding of cloud structure and constrain models of the evolutionary course that governs star formation.

Neutron stars provide a natural laboratory for the study of matter under the most extreme conditions of density, pressure and magnetic fields known. Precise measurements of neutron star masses and radii may provide one of the only means to constrain important aspects of dense matter physics as well as fundamental particle physics. Moreover, neutron stars may contain states of matter not present anywhere else in the observable universe, for example, an exotic color-flavor-locked (CFL), super-fluid quark matter phase. Here, I discuss and review recent efforts to measure neutron star masses and radii in order to use them as probes of fundamental physics. Such efforts have focused on measurements of X-ray pulsation signals from both isolated and accreting neutron stars, as well as observations of the thermal emission from neutron star surfaces. Indeed, recent X-ray observations have provided the first evidence of discrete, redshifted spectral features from neutron star surfaces, which may eventually provide precise mass and radii estimates, however, uncertainties remain in their interpretation. Fast X-ray timing observations of X-ray bursting neutron stars have revealed spin modulation pulsations, and recent studies of “magnetar” giant flares have found fast oscillations which may be signatures of global vibrations of neutron star crusts. I will describe how these observations are yielding new insights on neutron star structure.

The very large cosmological number $$ N = \frac{{c^3 }} {{huk^2 }} \approx 10^{120}$$ (1) plays a central role in the following three hypotheses concerning the observable universe; u is the energy density and k the gravitational constant k = 8πG / c 2 .

The new sciences of systems and complexity — cybernetics, information and communications theory, chaos theory, dynamical systems theory, nonequilibrium thermodynamics, and general systems and general evolution theory — have made great progress in the detailed understanding of the laws and dynamics that govern the evolution of complex systems, regardless of whether they are physical, biological, ecological or human. The new insights contradict the facile views that we have reached the end of history, and that the future is made by mere “bricolage.” The course of history has a logic of its own; a logic that is not rigidly predetermined and yet not the plaything of chance. This is a logic that governs not only the evolution of human societies in history but also the evolution of life on earth, and even the evolution of the cosmos in the observable universe.