OTHER EXPERIMENTS ON SRT AND GRT. NEWS OF RESEARCHES.
V. Venkatraman Krishnan, M. Bailes, W. van Straten, N. Wex, P. C. C. Freire, E.F. Keane, T.M. Tauris, P.A. Rosado, N.D.R. Bhat, C. Flynn, A. Jameson, S. Osłowski
Frame dragging (the Lense-Thirring effect) is a predicted phenomenon in general relativity, whereby a rotating mass drags the surrounding spacetime around with it. The scientists analyzed long-term observations of PSR J1141-6545, a young pulsar in a binary orbit with a white dwarf. Modeling the arrival times of the radio pulses showed a long-term drift in the orbital parameters. After considering possible contributions to this drift, they concluded that it is dominated by frame dragging of the rapidly spinning white dwarf. These observations verify a prediction of general relativity and provide constraints on the evolutionary history of the binary system.
Testing of Einstein’s GTR continues with the observation of the star S0-2, rotating around the supermassive black hole located at the Milky Way’s center. As the star gets closer to the supermassive black hole, it experiences a gravitational redshift that is predicted by Einstein's theory of general relativity.
At the center of our galaxy, roughly 26,000 light years from Earth, lies the supermassive black hole (SMBH) known as Sagittarius A.
During the observation of the small group of stars, orbiting around this black hole, a team of German and Czech astronomers noted subtle effects, again confirming some of the predictions of the Einstein's General Theory of Relativity.
In 2014, two satellites of the Galileo European Global Navigation Satellite System were unintentionally launched on elliptical, rather than circular, orbits. But researchers used clocks on the satellites to perform the most precise tests to date of one aspect of general relativity: the gravitational redshift of a clock’s frequency.
A clock placed in a gravitational field ticks more slowly than one in empty space—its ticking frequency “redshifts”—as a result of relativity’s equivalence principle. The new studies exploit the ellipticity of the satellites’ orbits, measuring changes in the frequencies of several hydrogen maser clocks aboard the satellites at various distances from Earth. Researchers find that general relativity accurately predicts the observed redshifts
Source : physics.aps.org : https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.121.231102
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. We have subjected general relativity to a range of tests related to the dynamics of the source, the propagation of gravitational waves (constraining local Lorentz invariance violations, as well as large extra dimensions), and the polarization content of gravitational waves. In all cases we find agreement with the predictions of GR.
This allows us to reject a number of theories that include gravity in the Standard model (describing the properties of all known particles and three of the four fundamental interactions), that is are candidates for the role of "Theory of everything".
Source : arxiv.org : https://arxiv.org/abs/1811.00364v2
Astronomers have made the most precise test yet of Einstein’s general theory of relativity outside the Milky Way. The nearby (450 million light-years from Earth) galaxy ESO 325-G004 acts as a strong gravitational lens, distorting light from a distant galaxy behind it to create an Einstein ring around its centre. By comparing the mass of ESO 325-G004 with the curvature of space around it, the astronomers found that gravity on these astronomical length-scales behaves as predicted by general relativity. This rules out some alternative theories of gravity.
Einstein’s theory of gravity - the general theory of relativity - is based on the universality of free fall, which specifies that all objects accelerate identically in an external gravitational field. In contrast to almost all alternative theories of gravity, the strong equivalence principle of general relativity requires universality of free fall to apply even to bodies with strong self-gravity.
PSR J0337+1715 is a hierarchical system of three stars (a stellar triple system) in which a binary consisting of a millisecond radio pulsar and a white dwarf in a 1.6-day orbit is itself in a 327-day orbit with another white dwarf. This system permits a test that compares how the gravitational pull of the outer white dwarf affects the pulsar, which has strong self-gravity, and the inner white dwarf. Here we report that the accelerations of the pulsar and its nearby white-dwarf companion differ fractionally by no more than 2.6×10−6.
The universe should be a predictably symmetrical place, according to a cornerstone of Einstein's theory of special relativity, known as Lorentz symmetry. This principle states that any scientist should observe the same laws of physics, in any direction, and regardless of one's frame of reference, as long as that object is moving at a constant speed.
Now MIT scientists and their colleagues on the IceCube Experiment have led the most thorough search yet of Lorentz violation in neutrinos. The team searched for variations in the normal oscillation of neutrinos that could be caused by a Lorentz-violating field.
The results, published today in Nature Physics, rule out the possibility of Lorentz violation in neutrinos within the high energy range that the researchers analyzed. They provide evidence that neutrinos behave just as Einstein's theory predicts.
Source : phys.org : https://phys.org/news/2018-07-einstein-date-lorentz-violation-high-energy.html
STAR MERGERS: A NEW TEST OF GRAVITY, DARK ENERGY THEORIES (pdf)
On August 17 2017, scientists had the opportunity of comprehensive check of the effects of the merger of neutron stars. The gravity waves signature was detected by a network of Earth-based detectors called LIGO and Virgo, and the first intense burst of light was observed by the Fermi Gamma-ray Space Telescope. That nearly simultaneous arrival time is a very important test for theories about dark energy and gravity. Theories which held that the arrival of gravitational waves would be separated in time from the arriving light signature of the star merger by far longer periods - stretching up to millions of years - don't explain what was seen, and must be modified or scrapped. Gathering more data from events that generate both gravitational waves and light could also help resolve different measurements of the Hubble constant - a popular gauge of the universe's expansion rate.
Using a model of black holes, scientists from the Ural Federal university determined that a popular theory of gravity that seemed to work perfectly at the cosmological level (a subclass of Horndeski theory) does not apply in the real world. They suppose that the gravitational constant is not a constant, but a field that can vary in time and space. Scientists cannot measure this slowly changing field with accuracy, and only therefore perceive it as a constant. This theory posits gravity with a scalar field. This is how the first and simplest theory of gravity with a scalar field, the Brans-Dicke theory, was formulated.
This model helped scientists describe the accelerated expansion of the universe without resorting to additional theories. The authors of the paper considered the Horndeski models at the astrophysical scale - the scale of individual objects of the universe - and determined that black holes (as real objects) turn out to be unstable in the models which previously successfully proved themselves in cosmology. However, the scientists have proposed a way to construct Horndeski models that ensure black holes stability. The paper is a step toward a new theory of gravity that fulfills the requirements of modern physics.
A renewed suggestion that dark energy may not be real—dispensing with 70% of the stuff in the universe—has reignited a longstanding debate.
While the Michelson–Morley experiment showed that the speed of light is independent of the orientation of the apparatus, the Kennedy–Thorndike experiment showed that it is also independent of the velocity of the apparatus in different inertial frames. It also served as a test to indirectly verify time dilation – while the negative result of the Michelson–Morley experiment can be explained by length contraction alone, the negative result of the Kennedy–Thorndike experiment requires time dilation in addition to length contraction to explain why no phase shifts will be detected while the earth moves around the sun. Improved variants of the Kennedy–Thorndike experiment have been conducted using optical cavities or Lunar Laser Ranging.
The Fizeau experiment was carried out by Hippolyte Fizeau in 1851 to measure the relative speeds of light in moving water. Fizeau used a special interferometer arrangement to measure the effect of movement of a medium upon the speed of light.
NEWS OF RESEARCHES ON SRT AND GRT
Maxwell's theory displays a remarkable feature: it remains unaltered under the interchange of the electric and magnetic fields, when charges and currents are not present. This symmetry is called the electric-magnetic duality.
However, while electric charges exist, magnetic charges have never been observed in nature. If magnetic charges do not exist, the symmetry also cannot exist. This mystery has motivated physicists to search for magnetic charges, or magnetic monopoles. However, no one has been successful. Agullo and his colleagues may have discovered why.
EPFL scientists have been able to measure the ultrashort time delay in electron photoemission without using a clock.
The discovery has important implications for fundamental research and cutting-edge technology.
The team of physicists from the Paris Observatory and the University of California, Los Angeles, analyzed 44 years of data from lunar laser ranging (LLR) observations.
In order to analyze the LLR data in the context of Lorentz symmetry, the researchers first developed a "lunar ephemeris", which is a model that accounts for dozens of factors to compute the estimated position, velocity, and orientation of the Moon with respect to the Earth at any given time. The framework for this ephemeris comes from a theory called the standard-model extension (SME), which combines general relativity and the Standard Model of particle physics, and allows for the possibility of Lorentz symmetry breaking.
The researchers' analysis shows that no evidence that LLR depends on the velocity or the direction of its reference frame, indicating no Lorentz symmetry breaking.
Researchers from The University of Western Australia and Humboldt University of Berlin have completed testing that has effectively measured the spatial consistency of the speed of light with a precision ten times greater than ever before.
The stringent testing also confirmed a core component of Einstein's theory of Relativity known as "Lorentz symmetry", which predicts that the speed of light is the same in all directions.