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New Theory to Understand the Mechanism of Gravitation



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Journal of High Energy Physics, Gravitation and Cosmology, 2020, 6, 462-472
ISSN Online: 2380-4335
ISSN Print: 2380-4327
10.4236/jhepgc.2020.63036 Jul. 30, 2020 462 Journal of High Energy Physics, G
ravitation and Cosmology
New Theory to Understand
the Mechanism of Gravitation
Nader Butto
Cardiologist, Petah-Tikva, Israel
Gravitation is still the least understood interaction among the fundamental
forces of Nature. A new theory that explains the mechanis
m of gravitation
and the origin Newton’s laws of gravitation and general relativity and distin-
guishes between two of the Newton’s laws has been proposed. It is shown that
the vortex formation created during the Big Bang event is the origin of the
gravitational force. The vortex curves the vacuum (space-time) around it, at-
tract and condense energy and dust to its center to form the mass. The gra-
dient pressure in the vortex creates a flow that upon interaction with an ob-
ject transfers a part of its momentum to the object and pushes it toward the
center. The force exercise
d on the object is equivalent to Newton’s second
law. The force of attraction between two vortices is equivalent to Newton’s
third law. The drag force between the energy flow of the vortex and the static
vacuum diminishes the gravitational force and is equivalent to the
stant. The proposed theory could provide new interesting insights for a com-
prehensive understanding of gravitation and represents a theoretical starting
point for the engineering of anti-gravitation technology.
Vortex Formation
, Vacuum Density, Pressure Gradient, General Relativity,
Newton Laws of Gravitation,
1. Introduction
Gravity is the most mysterious and still an incompletely understood interaction
among the fundamental forces of nature. In fact, the gap in our understanding of
gravity is so great that for nearly a century, it has thwarted the ultimate quest of
unifying all four fundamental forces into one final explanatory Theory of Eve-
How to cite this paper:
Butto, N. (2020
New Theory to Understand the Mechanism
of Gravitation
Journal of High Energy
Gravitation and Cosmology
June 1, 2020
June 27, 2020
June 30, 2020
Copyright © 20
20 by author(s) and
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
Open Access
N. Butto
10.4236/jhepgc.2020.63036 463 Journal of High Energy Physics, G
ravitation and Cosmology
The universal nature of gravity is demonstrated by the fact that its basic equa-
tions closely resemble the laws of thermodynamics and hydrodynamics [1]. So
far, there has not been a clear explanation for this resemblance.
Gravity dominates at large distances, but is very weak at small scales. In fact,
its basic laws have only been tested up to distances of the order of a millimetre.
Most of the mainstream physics that we are taught are based on Newtonian
and Einstein’s physics; however, in both these theories, the mechanism giving
rise to gravitation is completely unknown. Gravity is also considerably harder to
combine with quantum mechanics than all the other forces. The quest for unifi-
cation of gravity with these other forces of Nature, at a microscopic level, leads
to many problems, paradoxes and puzzles. Some problems of the gravitational
theory could be, in principle, solved in the framework of extended theories of
gravity [2].
Newton’s second law of motion defines the relation between the acceleration,
force, and mass. In an inertial reference frame, the vector sum of the forces
an object is equal to the mass
multiplied by the acceleration
of that object:
Newton’s law of motion states that every object in the universe attracts every
other object with a force that for any two bodies is proportional to the mass of
each object and varies as the inverse square of the distance between them. This
statement can be mathematically expressed by the following well-known equa-
( )
F Gm m r= ⋅
, (1)
1 and
2 are the interacting masses,
is their relative distance vector,
is generally assumed to be a universal constant. However, there is no
theoretical or mathematical formulation that explains the origin of this equation.
This paper aims to provide a new and unique approach by presenting a satis-
fying theory to explain the mechanism of gravity. Based on the basic assumption
that the universe is immersed in a vacuum with a well-defined density that be-
haves as a fluid, rotating bodies in liquid generate a drag force and creates vor-
tices that attract other liquid to the center of the vortex. By applying the hydro-
dynamic laws to calculate the attractive force between two vortices, gives origin
to Newton’s third law of motion, the interaction between the flow of the vortex
and non-rotating body gives origin Newton’s second and third laws of motion to
the Newton’s second law of motion. Therefore, for the physical and mathemati-
cal basis for the origin of Newton’s second and third laws of motion are de-
scribed. In addition, the mechanism of vortex formation and the essence of the
universal constant
are briefly described, with further details discussed in other
2. Density of the Vacuum
By definition, a vacuum has no mass since it has no factor that produces a mass.
According to the superfluid theory of the vacuum, the physical vacuum is de-
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scribed as a quantum superfluid which behaves like a fluid with minimal viscos-
ity and with extremely high thermal conductivity. It is a perfect fluid in the sense
that it is non-particulate and has no structural memory. If perturbed, it has no
tendency to revert to its former physical state.
Furthermore, the first postulate of general relativity states that the source of a
gravitational field is the stress-energy tensor of a perfect fluid [3].
This stress-energy tensor contains four non-zero components
, the den-
sity of the perfect fluid and the pressure of the perfect fluid in each of the three
physical axes. According to general relativity, a perfect fluid is defined as a fluid
with no viscosity or heat conduction.
However, the quantum theory requires the empty space to be filled with parti-
cles and anti-particles being continually created and annihilated. This could lead
to a net density of the vacuum, which if present, would behave as a cosmological
constant. Although there is no consensus about the value of the vacuum density,
its value mainly relies on general relativity. The energy density of the vacuum
can be measured through astronomical observations that determine the space-time
curvature and the expansion of the universe.
It is important to note that the study of the expansion rate of the universe has
shown that the universe is close to critical density. Critical density is the value at
which the Universe is balanced and expansion is halted.
The density is typically expressed as a fraction of the density required for the
critical condition to be fulfilled through the use of a parameter known as omega
(Ω) where Ω =
For a value of omega less than 1 (known as an open universe), the final fate
of the universe is a cold death. In this case the universe expands forever, albeit
at an ever-decreasing rate. For omega greater than 1, the universe is closedand
will at some point collapse in on itself and end in a big crunch. For omega
equal to 1, the universe is called flat; this universe has a critical density and
expansion in halted only after an infinite time. Currently, the estimated sum of
the contributions to the total density parameter, Ω0, is Ω0 = 1.02 ± 0.02 which
indicates that the universe is close to critical density.
The expansion of the universe has been tested using a number of methods,
where three of them are mentioned here:
The first one is the Wilkinson Microwave Anisotropy Probe (WMAP) mission
completed in 2003, representing a major advance in the precision of determining
the expansion of the universe, the Hubble constant, and the calculation of the
vacuum density [4].
The second one is using the Baryon Oscillation Spectroscopic Survey (BOSS)
[5]. Studying more than 140,000 extremely bright galaxies known as quasars,
which serve as a standard ruler”, scientists can map density variations in the
universe. By nearly tripling the number of quasars previously studied, as well as
implementing a new technique, the scientists were able to calculate the expan-
sion rate to 42 miles (68 kilometers) per second per 1 million light-years with
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greater precision, while looking farther back in time.
The third method is using the infrared camera installed in 2009 on the Hubble
Telescope, the astronomical measurements used to calculate the Hubble con-
stant obtained a slightly higher value with narrow error bars. A recent study [6]
indicates that
0 = 73.24 km/s/Mpc and the cosmological density remains with a
small uncertainty calculated as follows:
( )
2 27 3
3 8 11.11 1.05 10 kg m
= = ±×π
represents the critical density,
represents the current value of the
Hubble constant, and
represents the gravitational constant.
3. Hydrodynamics of Vacuum Vortices
According to the hot Big Bang theory, the observable universe was an emerg-
ingof space-time from infinitesimal dimensions approximately 13.7 billion
years ago. When the Big Bang event occurred, there was nothing except an
empty space, a false vacuum, a fluid-like zero-point energy field in a high-energy
fluctuation state. Vacuum energy fluctuations are special as the virtual quanta
are emitted from and absorbed by the vacuum itself without the presence of real
quanta or any other known phenomenon in a state of symmetry. The intrinsic
physical feature was “preserved” until the Big Bang that caused a symmetry
breaking, primordial-field perturbation, and dynamic flow in the field. Despite a
range of different models for the early universe that widely vary in their predic-
tions of the size of these perturbations, all these models predict the creation of
black holes with masses ranging from a Planck mass to hundreds of thousands of
solar masses [7].
The diversity of temperature and density after the Big Bang resulted in dy-
namic flow and manifestation of physical effects, such as black holes and stars
Since the Big Bang, the universe has continued to expand, as demonstrated by
the gradually increasing distance between our galaxy and external galaxies.
While the universe is expanding, a different region was contracting such that
the total energy was preserved; therefore, the expansion of the total universe is
accompanied by contraction in some part of it.
This could explain the conflicting observation results of the relative motions
of stars and whether they display systematic expansion or contraction [8] [9]
The local area contraction is a type of gravitational force due to vortex forma-
tion that condenses the vacuum and causes matter accumulation.
The primordial-field condensation and matter formation is explained by the
density wave theory. The density wave theory proposed by Lin and Shu in 1964 ex-
plains the spiral-arm structure formation of spiral galaxies. According to this theory,
the arms do not comprise matter but are made of regions of greater density with
longitudinal compression waves and density fluctuation due to self-gravitation [11].
Vacuum vortices are characterized by power and volume, which may be of
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any magnitude. Each vortex originates from the rotation orbits of another larger
The energy flow along the galaxy spiral arms creates a turbulent flow and
smaller vortices. The field and the gases are drawn down a plug hole that has a
point of suction at its center. A cloud of gas, mainly hydrogen, is trapped at the
point of suction. It begins to collapse into itself because of its self-gravitational
pull and forms the mass of a planetary star.
Gravitation as a push pressure is the origin of Newton’s second law.
The pressure gradient in the vortex attracts energy from the vacuum to its
core. The flux in such a vortex comprises massless photons. Although photons
are zero-rest mass particles, they have the properties of energy and momentum
and thus exhibit the property of mass because they travel at the speed of light.
Upon colliding with a mass, the photons transfer a fraction of their momentum
to that mass and push it toward the center of the vortex with a force propor-
tional to the extension or the volume and density (the mass) of the considered
In hydrodynamics, the dynamic pressure in the vortex is directly correlated
with the medium density. It can be expressed as follows:
, (2)
is the gradient pressure,
is the vacuum density, and
is the velocity of
the flow, which in our case is the speed of light.
Consider a sphere immersed in the arm of the vortex with an area that faces
the flow. Such a sphere will be pushed to the center of the vortex with a force
that is directly proportional to the pressure gradient multiplied by the area of the
sphere. Therefore, the force on the sphere can be expressed as follows:
, (3)
is the gradient pressure and
is the contact area. The flow will face only
half of the area of the sphere, so when the area of the sphere is 4π
2, the pressure
will be applied on the area of 2π
Substituting the dynamic pressure
in equation 3 by 1/2
2, the push force
on the sphere is obtained as follows:
2 2 22
PF PA v r v rI PI
= = =
. (4)
We then multiply and divide equation 4 by
(time) to obtain
F r vt v t
. (5)
Now, the speed
multiplied by time
is equal to space
(length) and the ve-
locity divided by
is equivalent to acceleration a. Therefore, the area π
2 times
is equal to volume
F r La Qa
π= =
. (6)
Note that density multiplied volume is equal to mass, and therefore, we obtain
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F ma=
, (7)
which corresponds to Newton’s second law of gravitation.
4. Attraction Force between Two Vortices
In hydrodynamics, the field reaching the center of the vortex is oriented at an
angle of 9or perpendicular to the vortex plane. In this vortex, the free surface
sharply dips near the axis line, with the depth inversely proportional to
2. The
shape formed by the free surface is referred to as a hyperboloid or Gabriel’s
Hornand is shown in Figure 1.
In an irrotational vortex flow with a constant fluid density and cylindrical
symmetry, the dynamic pressure varies as
2, where
is the limiting
pressure that is infinitely far from the axis.
Furthermore, the vacuum with a density of approximately 10 × 1027 kg/m3
has viscosity and stiffness and experiences a drag force. Influid dynamics, the
drag equation is used to calculate the force of drag experienced by an object due
to movement through a fully enclosing medium. In our case, the drag force is
related to the dynamic (shear) viscosity of a vacuum that expresses its resistance
against shearing flows, where the adjacent layers move parallel to each other at
different speeds.
The drag force equation can be expressed as follows:
F v AC
, (8)
is the drag force, which by definition is the force component in the di-
rection of the flow velocity,
is the mass density of the vacuum,
is the rela-
tive velocity relative to the vacuum,
is the contact area, and
is the drag co-
As stated above,
represents the resistance of the adjacent layers moving pa-
rallel to each other at different speeds. The drag force calculated according to the
above equation yields a value that is equivalent to that of constant
Figure 1. An image illustrating the vortex on a free surface.
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The force of attraction to the center of the vortex is directly related to the
pressure gradient, which is equal to the centripetal force:
2v mv r
, (10)
is the linear mass density, which is the amount of mass per unit
The interaction between two vortices creates tension that attracts one vortex
to the other.
The tension on a body can be numerically expressed as follows:
T mg ma= +
, (11)
indicates tension (Newton),
indicates mass (kg),
indicates gravita-
tional force (9.8 m/s2), and
indicates acceleration (m/s2).
In our case, there is no external gravitation force; however, the mass changes
according to its distance from the core of the vortex. Therefore, it expressed as
linear mass density (
The tension in the vortex would be the sum of linear mass density and the
force of attraction of the vortex. Therefore, the tension in the vortex can be ex-
pressed as follows:
T mr v Ir
= +
mPIvr F a
= =
Thus, the tension on the first vortex is:
T m r ma= +
In addition, the tension in the second vortex can be expressed as follows:
m r ma+
Furthermore, the tension between both vortices can be expressed as follows:
12 1 2
T mm r ma m a= +−
In the point of interaction between the two vortices, the linear mass density is
cancelled and the acceleration is zero.
T mm r=
. (15)
The linear force between the two vortices will be diminished by a force equiv-
alent to the drag force in the vacuum which is, as demonstrated above, equiva-
lent to the value of constant
Therefore, the attractive force between the two vortices can be expressed as
F Gm m r=
. (16)
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The above equation represents the Newton’s law of universal gravitation.
5. Discussion
Although even Newton was concerned with the unknown nature of the gravita-
tional force, his basic framework was extremely successful in describing the mo-
tion of the planets.
The mechanical theories or explanations of gravitation are attempts to explain
the law of gravity with the aid of basic mechanical processes, such as pushes, and
without the use of any action at a distance. These theories were developed
16th-19th century in connection with the aether theories [12].
However, those theories were overthrown because most of them led to an un-
acceptable amount of drag, which has not yet been observed. Several other mod-
els have violated the energy conservation law and are incompatible with modern
thermodynamics [13].
In general relativity, the effects of gravitation are ascribed to space-time cur-
vature instead of being attributed to the force and the free-falling objects move
along the locally straight paths in curved space-time.
General relativity has experienced considerably successful because of its way
of predicting phenomena such as precession of Mercury’s perihelion and binary
pulsars, warping space-time, gravitational red-shifting of light, the relativistic
delay of light, the equivalence principle, the geodetic and frame-dragging effects
that have been regularly confirmed. However, general relativity absolutely offers
no description of the causation of space-time curvature and there is no mecha-
nism to describe why gravity works the way it does.
Furthermore, it cannot be considered as a complete theory of gravity due to its
incompatibility with quantum mechanics.
Besides, there is nothing in Newton Theory or General relativity that explains
the origin of energy that produces the gravitational forces. In fact, there is no
known energy source to support tremendous energy expenditure that attracts all
objects on the surface of our planet for over 4.5 billion years.
Herein, a new gravitation mechanism that explains the essence of gravitation,
the origin of Newton laws of gravitation, and the space-time warp of general
relativity has been presented.
The proposed theory is based on the fact that the vacuum has a specific den-
sity associated with it, making it behave as a superfluid. General relativity also
imposes superfluid equations onto gravitational relationships. The imposition of
superfluid equations has a considerably significant effect: the speed of the
propagation of gravity is thereby made finite, because it propagates at speed of
light. The finite transmission speed (and related superfluid properties) repre-
sents a significant difference between Newtonian gravity and general relativity.
The mechanism of gravitation relies on the vortices created in the superfluid
vacuum. The vortices were created after the Big Bang by the symmetry breaking
of the fluctuating vacuum. A superfluid vortex would warpspace-time, con-
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dense the vacuum density, and create the mass, drag the planet, and maintains
its rotation.
According to general relativity, planet rotation is dragged by an unknown
force. Such a drag implies that there exists friction in the space-time motion with
respect to a mass where inertial dragging occurs. The vortex model explains the
mechanism of rotation of the planet as a result of imparting spin on the planet
drags the planet mass and causes its rotation. The general relativistic formula-
tions show the requirement of tangential motion when the continuum is as-
sumed to be a superfluid.
The second law of Newton is an expression of the force produced by a vortex
pressure gradient that collides with an object and pushes it toward the center of
the vortex. The superfluid flow creates a radiation pressure identical to the mag-
netic radiation pressure that exerts a positive force due to the momentum trans-
ferred during the interaction of the waves with the matter (de Broglie standing
waves). It acts in a direction same as that of the wave propagation. This is same
as the concept of quantum mechanics, by which the attractive force of gravity
arises due to exchange of virtual gravitons in the same way as the electromag-
netic force arises from exchange of virtual photons [14] [15].
In contrast, Newton’s law of motion expresses the tension between two oppo-
site forces created by the vortices. Thus, the gravitational force between two ce-
lestial bodies is not caused by their mass but by the tension between the vortices
that created the mass and warped space-time.
Finally, since the first formulation of Newton’s law of gravitation, there is an
open question about the nature of gravitation and the origin of the universal
constant of gravitation
. This constant is experimentally determined, and it
unknown whether there exists an analytical formula for determining the Newto-
nian constant of gravitation
. We found that
is an expression of resistance
against the gravitational force in the vacuum due to the drag force of the gravita-
tional flow in the vacuum.
6. Conclusions
In this study, we described a new mechanism of gravitation that explains New-
ton’s laws of gravity with Einstein’s theory of general relativity. The mass was
created after the Big Bang by the gravitational force of the vortices that led to the
space-time curvature and condensed the vacuum superfluid to create the mass.
Therefore, the mass is rather the effect of the gravitation and not the cause.
The gradient pressure in the vortex creates a flow that applies a force equiva-
lent to the electromagnetic radiation pressure, delivers a fraction of the vortex
momentum to that mass, and pushes it toward the center of the vortex. Upon
colliding with the mass, this pressure creates the force expressed by Newton’s
second law.
The calculation of the tension between two vortices leads to the same New-
ton’s law of motion. Therefore, Newton’s second law is an expression of push
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ravitation and Cosmology
radiation force, while Newton’s law of motion is the expression of attraction
between two vortices.
Finally, the gravitational constant
is an expression of the diminished gravi-
tational value due to the drag force of the superfluid flowing in the vortex (ra-
diation pressure) with an adjacent static vacuum. The calculation of the dimin-
ished momentum of the radiation pressure yields a value same as that of the
gravitational constant
and was reported in a separate study.
Further research and astronomical observations are needed to confirm the
proposed vortex model of gravitation.
The author would like to thank Enago ( for the English
language review.
This research did not receive any specific grant from funding agencies in the
public, commercial, or not-for-profit sectors.
Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this pa-
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... The same model was presented to explain the origin of the gravitational force [14] and the gravitational constant G [9], indicating the universality of the phenomena. ...
... Gravity is still incompletely understood and the most mysterious interaction among the fundamental forces of nature [1]. Newton and Einstein successively came up with the laws that express gravity for object motions in our universe. ...
... The vortex shape of the electron and the Hydrogen atom give a full explanation for the origin of fine structure constant [20]. The same model was presented to explain the origin of gravitation force [21] and gravitation constant G [22] indicating the universality of the phenomena. ...
... In previous article [9], a new theory of gravitation was presented, according to which the gravitation force is a pull force due to vortex formation of the vacuum. The vortex curves the vacuum (space-time) around it, attract and condense energy and dust to its center to form the mass. ...
Full-text available
It is demonstrated that the magnetic dipole moments of atomic nuclei and neutron stars are quantitatively related by the fundamental scaling equations of the self-similar cosmological paradigm, and therefore a 16th falsification test has been passed by this theoretical model. Two definitive predictions are also pointed out: (1) the model predicts that the electron will be found to have structure with radius of about 4 x 10 to the -17th cm, at just below the current empirical resolution capability, and (2) the model makes quantitative predictions regarding gravitational microlensing by predicted 'dark matter' candidates. Some possible theoretical implications of cosmological self-similarity are introduced.
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The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg2 to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Lyα forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyα forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance dA to an accuracy of 1.0% at redshifts z = 0.3 and z = 0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyα forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate DA(z) and H –1(z) parameters to an accuracy of 1.9% at z ~ 2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant (H_0) from 3.3% to 2.4%. Improvements come from observations of Cepheid variables in 10 new hosts of recent SNe~Ia, more than doubling the sample of SNe~Ia having a Cepheid-calibrated distance for a total of 18; these leverage the magnitude-redshift relation based on 300 SNe~Ia at z<0.15. All 18 hosts and the megamaser system NGC4258 were observed with WFC3, thus nullifying cross-instrument zeropoint errors. Other improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC4258, more Cepheids and a more robust distance to the LMC from late-type DEBs, HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes, and (iv) 2 DEBs in M31. The H_0 from each is 72.39+/-2.56, 71.93+/-2.70, 76.09+/-2.42, and 74.45+/-3.34 km/sec/Mpc, respectively. Our best estimate of 73.03+/-1.79 km/sec/Mpc combines the anchors NGC4258, MW, and LMC, and includes systematic errors for a final uncertainty of 2.4%. This value is 3.0 sigma higher than 67.3+/-0.7 km/sec/Mpc predicted by LambdaCDM with 3 neutrinos with a mass of 0.06 eV and the Planck data, but reduces to 1.9 sigma relative to the prediction of 69.3+/-0.7 km/sec/Mpc with the combination of WMAP+ACT+SPT+BAO, suggesting systematic uncertainties in CMB measurements may play a role in the tension. If we take the conflict between Planck and the H_0 at face value, one plausible explanation could involve an additional source of dark radiation in the early Universe in the range of Delta N_eff=0.4-1. We anticipate significant improvements in H_0 from upcoming parallax measurements.
This paper gives the 2006 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2006 adjustment takes into account the data considered in the 2002 adjustment as well as the data that became available between 31 December 2002, the closing date of that adjustment, and 31 December 2006, the closing date of the new adjustment. The new data have led to a significant reduction in the uncertainties of many recommended values. The 2006 set replaces the previously recommended 2002 CODATA set and may also be found on the World Wide Web at
Even if Einstein's General Relativity achieved a great success and overcame lots of experimental tests, it also showed some shortcomings and flaws which today advise theorists to ask if it is the definitive theory of gravity. In this essay we show that, if advanced projects on the detection of Gravitational Waves (GWs) will improve their sensitivity, allowing to perform a GWs astronomy, accurate angular and frequency dependent response functions of interferometers for GWs arising from various Theories of Gravity, i.e. General Relativity and Extended Theories of Gravity, will be the definitive test for General Relativity. The papers which found this essay have been the world's most cited in the official Astroparticle Publication Review of ASPERA during the 2007 with 13 citations. Comment: This Essay is an Honorable Mention Winner at the 2009 Gravity Research Foundation Awards
Expressions are derived for the mass of a stationary axisymmetric solution of the Einstein equations containing a black hole surrounded by matter and for the difference in mass between two neighboring such solutions. Two of the quantities which appear in these expressions, namely the area A of the event horizon and the ``surface gravity'' kappa of the black hole, have a close analogy with entropy and temperature respectively. This analogy suggests the formulation of four laws of black hole mechanics which correspond to and in some ways transcend the four laws of thermodynamics.
Physics invites the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, Lambda; nowadays the concept is termed dark energy or quintessence. Physics also suggests the dark energy could be dynamical, allowing the arguably appealing picture that the dark energy density is evolving to its natural value, zero, and is small now because the expanding universe is old. This alleviates the classical problem of the curious energy scale of order a millielectronvolt associated with a constant Lambda. Dark energy may have been detected by recent advances in the cosmological tests. The tests establish a good scientific case for the context, in the relativistic Friedmann-Lemaitre model, including the gravitational inverse square law applied to the scales of cosmology. We have well-checked evidence that the mean mass density is not much more than one quarter of the critical Einstein-de Sitter value. The case for detection of dark energy is serious but not yet as convincing; we await more checks that may come out of work in progress. Planned observations might be capable of detecting evolution of the dark energy density; a positive result would be a considerable stimulus to attempts to understand the microphysics of dark energy. This review presents the basic physics and astronomy of the subject, reviews the history of ideas, assesses the state of the observational evidence, and comments on recent developments in the search for a fundamental theory.
Recent developments in the study of primordial black holes (PBHs) are reviewed, with particular emphasis on their formation and evaporation. It is still not clear whether PBHs formed but, if they did, they could provide a unique probe of the early Universe, gravitational collapse, high energy physics and quantum gravity. Indeed their study may place interesting constraints on the physics relevant to these areas even if they never existed.