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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