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Problems in
Current Cosmology

Problems with gravitation and the current cosmological models, or: Why look for an alternative theory?

Since their development, Newton’s gravitational theory and the general theory of relativity have served as the foundation for our understanding of the construction and dynamics of the universe.  In the recent century, however, a growing body of experimental observations has demonstrated inconsistencies within both theories.  The following is a brief review of the problems pertaining to the scope of the UG theory.

1.   The problem of “missing mass” in galaxies and galactic clusters

As early as 1933, Fritz Zwicky (Zwicky, 1933) concluded that the calculated gravitational force of the visible galaxies in the Coma Cluster is far too small to account for the observed high speed stellar orbits.  Later studies of the rotation curves of spiral galaxies (Rubin et al., 1970; 1980) reported that contrary to the prediction of Keplerian dynamics, most stars rotate around the galaxy center at a roughly constant or slightly increasing speed, rather than at a speed decreasing inversely to the square root of the star’s radius of orbit. These disparities led to the conclusion that the amount of visible matter in galaxies is insufficient to explain the observed motion of their stars, or the motion of galaxies within clusters. Further investigation confirmed these findings, leading to two possibilities; either the current understanding of gravitation is incorrect, or additional non-visible matter must exist and account for about 90% of the galactic mass.  At present, astrophysicists tend to prefer the second explanation, that additional matter explains the observed motion of galaxies within the existing theory. Consequently, a new variable of dark matter has been introduced to the current paradigm.

2.   Problems with Big Bang cosmology

Hubble’s discovery that the universe is not static, but expanding, and the earlier introduction of the general theory of relativity, led to the development of the Big Bang cosmological model, which attributes the beginning of our universe to an explosion from a very dense point singularity at about 14.5 billion years ago.  The consensus in the physics community accepts the Big Bang as the most reasonable theory for the origin and evolution of the universe.  Nevertheless, throughout its development the Big Bang model encountered significant problems; notably, the flatness problem, the horizon problem, as well as problems of age, structure and isotropy.

According to the Freidman-Lemaitre-Robertson-Walker metric, the curvature of the universe depends on its energy density. The flatness problem arises from the fact that even an extremely small departure of one part in  of the energy density from the critical density would have caused the universe to either collapse in a big crunch at an earlier stage, or to expand too fast for any substantial structure to form.  In either case, the current universe would have developed in an entirely different form than observed. Furthermore, the age of the universe estimated from its current size and rate of expansion has posed a dilemma, as certain globular clusters studied in the mid-1990s appeared to be older than the time passed since the Big Bang according to these calculations.  The finite age of the universe and the finite speed of light place a limit on the maximum distance that light could have traveled since the Big Bang.  Given that matter in the universe must travel at a velocity lower than the speed of light, it is impossible for regions separated by greater than this maximum distance to have ever interacted.  The horizon problem results from the observation that all regions of the universe, including regions separated by greater than this maximum distance, have the same temperature and share the same physical properties, pointing to past interactions at an equilibrium or steady state.

The horizon and the flatness problems were resolved by the introduction of Guth’s inflation theory, postulating an initial phase of rapid exponential expansion, at which space itself (rather than matter) expanded at a rate much higher than the speed of light (Guth, 1981).  Nevertheless, the visible density of matter in the universe amounts to only about 3% to 4% of the critical density of its mass and energy.  The inclusion of dark matter provides for only about 26% of this critical density.  Furthermore, counter to Newton’s theory, the expansion of the universe has been found to accelerate, rather than to decelerate.  Resolving these issues without modification of the current paradigm requires the addition of a repulsive element to Einstein’s field equations, as well as accounting for the missing 74% of mass or energy.  This has led to the reintroduction of the cosmological constant, and to the concept of dark energy, which together with dark matter brings the total amount of non-visible and undetected matter in the universe to about 96% of the overall mass and energy of the universe.  To date, neither dark matter nor dark energy has ever been directly observed.

In addition, a structure problem arises from the question of how a universe that began in equilibrium, in a perfectly homogenous state, could have exploded into an inhomogeneous universe.  At the same time, the observed inhomogeneous structure of the universe conflicts with the Big Bang theory’s reliance on the cosmological principle, which requires that the universe be homogeneous and isotropic on a large scale.  Redshift surveys of the night sky, however, provide convincing evidence that the universe is not perfectly homogeneous, as the observed patterns of galaxies reveal that they are clearly not distributed randomly across the sky. Observations additionally reveal the existence of immense voids, or vacant regions of loosely spherical structure measuring up to  megaparsecs across (Rudnick et al., 2007).  Deviations from homogeneity are currently explained by the Big Bang model (and by inflation theory) to result from a quantum effect in the early universe, where Heisenberg’s uncertainty principle guaranteed density fluctuations.  These density fluctuations were then “frozen” as inflation expanded the universe at an exponential rate far too rapid for the particles to interact. Voids of this magnitude, as well as the discovery of large walls of galaxies, challenge the Big Bang cosmological model, as they are observed to exceed the scales predicted by the quantum effect and inflation.

3.   Problems of infinities and singularities

The equations of quantum mechanics and general relativity often encounter predictions of physical values becoming infinite.  In quantum theory, infinities appear whenever one attempts to use quantum mechanics to describe fields, such as electromagnetic fields.  Some of these difficulties were averted by the introduction of renormalization techniques.  Once regarded as controversial, renormalization is carried out by using rationalized procedures to scale out equation terms that diverge to infinity, while finite terms are kept as valid.  However, renormalization breaks down when applied to gravitation; and consequently, to date, all efforts to consolidate general relativity with quantum mechanics have proven unsuccessful.  Furthermore, the equations of general relativity lead to singularities, such as black holes. Singularities have resulted in inconsistencies which stem from the inability of current physics to deal with infinite density and infinite temperature.  In addition, as the Big Bang theory postulates that the universe began at a point singularity, the structure of the observed universe requires matter and radiation to have escaped from the singularity, a process that is prohibited by general relativity.  These inconsistencies were simply sidestepped by the assumption that our current physics is invalid at sub-Planck distances, and that further explanation would require a new and yet undiscovered quantum theory of gravitation.

4.   The problem of accurately calculating the value of Newton’s gravitational constant

Physics has encountered a long-standing dilemma in determining the value of the gravitational constant  XE "gravitational constant" . Whereas all other fundamental constants in physics are known to parts per billion, or parts per million at worst, the gravitational constant  stands alone with a measurement reliability of only about one part in 7000 (Gillies, 1997).   Numerous attempts to improve the precision of the value of  over the last 200 years have resulted in marginal improvements at best, in spite of vast improvement in technology.  Inconsistencies in the measured value of  have been proven to occur within distance ranges starting as small as several micrometers up to cosmic scale.  The reason underlying these inconsistencies has not yet been determined. When an equation in science accurately describes an observed phenomenon, the values of its constant(s) can be determined with a high level of accuracy.  However, the constants of an equation that only approximates a given phenomenon must vary somewhat with the range of its variables. Therefore, the inability to establish the value of  may suggest a deviation between Newton’s gravitational equation and the actual law of gravitation. 

5.   The increasing number of unexplained phenomena and the increased complexity of the cosmological model

The effort of consolidating major discrepancies within Newton’s theory, general relativity and the standard model has resulted in a substantial increase in the number of independent parameters and constants.  Although much theoretical progress has been made, many open questions remain to this date. The fifth problem is a growing list of observed phenomena that cannot be explained by a cohesive gravitational theory.  Rather, the following phenomena either require auxiliary hypotheses to comply with current theory, or remain unaccounted for.  In the realm of galaxies, the ability of current theory to explain galactic structure and dynamics is limited.  Images emerging from the Hubble space telescope reveal large-scale astronomical objects such as galaxies and nebulae with complex and varied morphologies, from various types of spiral and lenticular structures to elliptical, ring and irregular structures.  While different mechanisms have been proposed to influence certain galactic properties, the mechanisms underlying their diverse morphologies are not yet well-understood.  For example, the nature of density waves, which are theorized to drive spiral morphology in galaxies, is not yet well-understood.  Furthermore, it is not clear what determines whether a spiral galaxy is normal or barred, or why star formation in barred spirals is concentrated mainly at the ends of the bar.  There are also questions as to what drives the fragmentation of stars within galaxies, what activates the sudden expansion of gas observed in novae and supernovae, as well as the physical mechanisms underlying the creation of galactic and stellar wind and the magnetic fields of galaxies. 

Inconsistencies between theory and observation are not limited to galactic or cosmic scales.  In the Solar System, Newton’s laws of motion, together with his law of gravitation, have been experimentally verified to provide excellent agreement with the observed trajectories and orbital periods of planets, and most of the trajectories and orbital periods of satellites. Nevertheless, Newtonian-based theories have had only limited success in explaining the origin and structure of planetary ring systems. Whereas some of the observed characteristics of individual rings and gaps can be accounted for by orbital resonances, or by other mechanisms such as shepherd satellites, embedded moons or Lorentz resonances, the vastness of these ring systems and a significant portion of their properties remain unexplained.  Furthermore, although gravitation is the dominant force on solar scale, a number of phenomena within our Solar System remain unaccounted for. Current gravitational theories do not explain planetary composition; in particular, we do not know why the outer planets Jupiter, Saturn, Uranus and Neptune are composed of gas, or why, in contrast to the inner terrestrial planets, gas planets display extensive ring systems and a large number of satellites. There are additional unanswered questions as to what are the mechanisms underlying the formation of the Asteroid belt, the Kuiper belt and the Kuiper cliff within our Solar System?  What mechanism is responsible for the generation of planetary magnetic fields?  What causes the solar corona?  What causes the flyby anomaly, where an unexpected and unexplained energy increase is observed during Earth flybys of a spacecraft?  Recently, the current locations of Pioneer 10 and Pioneer 11 were reported to deviate by about  from their expected trajectories. If no observational errors are found, the Pioneer anomaly might require modification of current theory.



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