Understanding Of Gravitation Research Articles

The missing link in gravitational-wave astronomy: discoveries waiting in the decihertz range

The gravitational-wave astronomical revolution began in 2015 with LIGO’s observation of the coalescence of two stellar-mass black holes. Over the coming decades, ground-based detectors like laser interferometer gravitational-wave observatory (LIGO), Virgo and KAGRA will extend their reach, discovering thousands of stellar-mass binaries. In the 2030s, the space-based laser interferometer space antenna (LISA) will enable gravitational-wave observations of the massive black holes in galactic centres. Between ground-based observatories and LISA lies the unexplored dHz gravitational-wave frequency band. Here, we show the potential of a decihertz observatory (DO) which could cover this band, and complement discoveries made by other gravitational-wave observatories. The dHz range is uniquely suited to observation of intermediate-mass (∼102–104 M ⊙) black holes, which may form the missing link between stellar-mass and massive black holes, offering an opportunity to measure their properties. DOs will be able to detect stellar-mass binaries days to years before they merge and are observed by ground-based detectors, providing early warning of nearby binary neutron star mergers, and enabling measurements of the eccentricity of binary black holes, providing revealing insights into their formation. Observing dHz gravitational-waves also opens the possibility of testing fundamental physics in a new laboratory, permitting unique tests of general relativity (GR) and the standard model of particle physics. Overall, a DO would answer outstanding questions about how black holes form and evolve across cosmic time, open new avenues for multimessenger astronomy, and advance our understanding of gravitation, particle physics and cosmology.

New Theory to Understand the Mechanism of Gravitation

Gravitation is still the least understood interaction among the fundamental forces of Nature. A new theory that explains the mechanism of gravitation and the origin Newton’s laws of gravitation and general relativity and distinguishes 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, attract and condense energy and dust to its center to form the mass. The gradient pressure in the vortex creates a flow that upon interaction with an object transfers a part of its momentum to the object and pushes it toward the center. The force exercised 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 G constant. The proposed theory could provide new interesting insights for a comprehensive understanding of gravitation and represents a theoretical starting point for the engineering of anti-gravitation technology.

Analogue black-hole horizons

Some gravitational phenomena are difficult or even impossible to observe in real spacetime. Laboratory analogues of black-hole horizons offer new perspectives on field theory effects that might help our understanding of gravitation.

Conceptual change about outer space: how does informal training combined with formal teaching affect seventh graders’ understanding of gravitation?

Concepts relating to outer space are difficult to grasp because we lack direct experience of this environment. We analysed students’ understanding of gravitation on Earth and beyond by testing the effect of training on it. In a pretest (T1), 28 seventh graders answered a questionnaire about space concepts. They all then underwent the same formal teaching at school, but half of them also went on a trip to a space museum. Students then responded to the questionnaire again (T2). We found that the students in the museum-going group made significant progress between T1 and T2. Most of them correctly predicted at T2 (unlike T1) that dropped stones would fall in planetary contexts. Moreover, the misconception linking air and gravity had disappeared by T2. We conclude that combining formal teaching with a trip to a museum helped the children in the present study to develop a more accurate scientific understanding of concepts that cannot be directly experienced.

What do children know and understand about universal gravitation? Structural and developmental aspects

Children’s understanding of universal gravitation starts at an early age but changes until adulthood, which makes it an interesting topic for studying the development and structure of knowledge. Children’s understanding of gravitation was tested for a variety of contexts and across a wide age range (5–18years, N=144). We analyzed children’s predictions and justifications for the trajectory of a stone dropped on the earth, on the moon, in a spaceship orbiting the earth, on a planet with air, on a planet with no air, and in a lift (i.e., an elevator) in free fall. Results showed that performances were related to the context and to the children’s age. U-shaped developmental curves were identified for predictions for three contexts. These curves could be explained by analyzing the structure of the children’s knowledge using latent class analysis. We identified three coherent patterns of predictions that were related to specific justifications. With age, children produced more scientific predictions. Children’s cognitive structures, as reflected in their predictions of dropped stone trajectories, seem to be coherently built given that there were only a limited number of prediction patterns. Even by Grade 12, students had not achieved a scientific understanding of universal gravitation.

The importance of weightlessness and tides in teaching gravitation

We examine the presentation of the weight, weightlessness, and tides in university-level physics textbooks. Introductory textbooks often do not discuss tidal forces even though their understanding would be useful for understanding weightlessness. The explanations of tides often miss the free gravitational motion of both interacting objects, which is essential for the symmetry of tidal deformation. The shortcomings in the explanations of weightlessness and tides as provided by students and teachers are compared to textbook discussions. We suggest that an explicit discussion of the different definitions of weight and a synergetic presentation of weightlessness and tides might lead to a better understanding of gravitation. Our approach is illustrated by examples of tidal effects appropriate for introductory courses.

Possible new properties of gravity

If static gravity or spacetime curvature information is carried by classical propagating particles or waves, a modern Laplace experiment places a lower limit on their speed of 1010 c. The so-called Lorentzian modification of special relativity permits such speeds without need of tachyons. But there are other consequences. If ordinary gravity is carried by particles with finite collision cross-section, such collisions would progressively diminish its inverse square character, converting to inverse linear behavior on the largest scales. At scales greater than several kiloparsecs gravity can apparently be modeled, without need for dark matter, by an inverse linear law. The orbital motions of Mercury and Earth may also show traces of this effect. If gravity were carried by particles, a mass between two bodies could partially shield each of them from the gravity of the other. Anomalies are seen in the motions of certain artificial Earth satellites during eclipse seasons that behave like shielding of the Sun's gravity. Certain types of radiation pressure might cause a similar behavior but require many free parameters. Particle-gravity models would change our understanding of gravitation and our views of the nature of time in relativity theory.