## INTRODUCTION: google gravity

**google gravity**..Gravity is one of the four fundamental forces in nature. General Relativity is central to understanding astrophysical phenomena like Black Holes, Pulsers, Quasars, the final density of stars the big bang, etc.

Newton’s law of gravitation is inconsistent with Einstein’s special theory of relativity.

(F)*gravitation*=Gm1m2/(r12)^2

Now for a proton on comparing the force of gravitation and electromagnetic force we have

(F)*gravitation*/(F)*electromagnetic*=10^-36

This is the graphical representation that tells us that things above the diagonal are unobservable,things with square representation are one in which gravity plays important role.Phenomena above diagonal line are unobservables beacuse they occurs inside black holes.Things near diagonal line are the relativistic ones.**google gravity**

## HISTORY: google gravity

### Ancient world

**google gravity-**The nature and mechanism of gravity was explored by a wide range of ancient scholars. In Greece, Aristotle believed that objects fell towards the Earth because the Earth was the center of the Universe and attracted all of the mass in the Universe towards it. He also thought that the speed of a falling object should increase with its weight, a conclusion which was later shown to be false. While Aristotle’s view was widely accepted throughout Ancient Greece, there were other thinkers such as Plutarch who correctly predicted that the attraction of gravity was not unique to the Earth.**google gravity**

### Scientific revolution

**google gravity-**In the mid-16th century, various European scientists experimentally disproved the Aristotelian notion that heavier objects fall at a faster rate. In particular, the Spanish Dominican priest Domingo de Soto wrote in 1551 that bodies in free fall uniformly accelerate.

De Soto may have been influenced by earlier experiments conducted by other Dominican priests in Italy, including those by Benedetto Varchi, Francesco Beato, Luca Ghini, and Giovan Bellaso which contradicted Aristotle’s teachings on the fall of bodies. The mid-16th century Italian physicist Giambattista Benedetti published papers claiming that, due to specific gravity, objects made of the same material but with different masses would fall at the same speed.

With the 1586 Delft tower experiment, the Flemish physicist Simon Stevin observed that two cannonballs of differing sizes and weights fell at the same rate when dropped from a tower. Finally, in the late 16th century, Galileo Galilei’s careful measurements of balls rolling down inclines allowed him to firmly establish that gravitational acceleration is the same for all objects.

### General relativity:google gravity

**google gravity-**Eventually, astronomers noticed an eccentricity in the orbit of the planet Mercury which could not be explained by Newton’s theory: the perihelion of the orbit was increasing by about 42.98 arcseconds per century.

The most obvious explanation for this discrepancy was an as-yet-undiscovered celestial body (such as a planet orbiting the Sun even closer than Mercury), but all efforts to find such a body turned out to be fruitless. Finally, in 1915, Albert Einstein developed a theory of general relativity which was able to accurately model Mercury’s orbit.

In general relativity, the effects of gravitation are ascribed to space-time curvature instead of a force. Einstein began to toy with this idea in the form of the equivalence principle, a discovery which he later described as “the happiest thought of my life.

” In this theory, free fall is considered to be equivalent to inertial motion, meaning that free-falling inertial objects are accelerated relative to non-inertial observers on the ground. In contrast to Newtonian physics, Einstein believed that it was possible for this acceleration to occur without any force being applied to the object.

## Modern research: google gravity

**google gravity-**In modern physics, general relativity remains the framework for the understanding of gravity. Physicists continue to work to find solutions to the Einstein field equations that form the basis of general relativity, while some scientists have speculated that general relativity may not be applicable at all in certain scenarios.**(NEXT WE WILL TALK ABOUT FIELD EQUATION)**

### Einstein field equations: google gravity

The Einstein field equations are a system of 10 partial differential equations which describe how matter affects the curvature of spacetime. The system is often expressed in the form{\displaystyle G_{\mu \nu }+\Lambda g_{\mu \nu }=\kappa T_{\mu \nu },}

where *G _{μν}* is the Einstein tensor,

*g*is the metric tensor,

_{μν}*T*is the stress–energy tensor, Λ is the cosmological constant, {\displaystyle G} is the Newtonian constant of gravitation and {\displaystyle c} is the speed of light. The constant is referred to as the Einstein gravitational constant.

_{μν}A major area of research is the discovery of exact solutions to the Einstein field equations. Solving these equations amounts to calculating a precise value for the metric tensor (which defines the curvature and geometry of spacetime) under certain physical conditions.

There is no formal definition for what constitutes such solutions, but most scientists agree that they should be expressable using elementary functions or linear differential equations. Some of the most notable solutions of the equations include:

#### POINTS TO REMEMBER

- The Schwarzschild solution, which describes spacetime surrounding a spherically symmetric non-rotating uncharged massive object. For compact enough objects, this solution generated a black hole with a central singularity. At points far away from the central mass, the accelerations predicted by the Schwarzschild solution are practically identical to those predicted by Newton’s theory of gravity.
- The Reissner–Nordström solution, which analyzes a non-rotating spherically symmetric object with charge and was independently discovered by several different researchers between 1916 and 1921. In some cases, this solution can predict the existence of black holes with double event horizons.
- The Kerr solution, generalizes the Schwarzchild solution to rotating massive objects. Because of the difficulty of factoring in the effects of rotation into the Einstein field equations, this solution was not discovered until 1963.
- The Kerr–Newman solution for charged, rotating massive objects. This solution was derived in 1964, using the same technique of complex coordinate transformation that was used for the Kerr solution.
- The cosmological Friedmann–Lemaître–Robertson–Walker solution, discovered in 1922 by Alexander Friedmann and then confirmed in 1927 by Georges Lemaître. This solution was revolutionary for predicting the expansion of the Universe, which was confirmed seven years later after a series of measurements by Edwin Hubble. It even showed that general relativity was incompatible with a static universe, and Einstein later conceded that he had been wrong to design his field equations to account for a Universe that was not expanding.

#### Gravity and quantum mechanics

**google gravity-**Despite its success in predicting the effects of gravity at large scales, general relativity is ultimately incompatible with quantum mechanics. This is because general relativity describes gravity as a smooth, continuous distortion of spacetime, while quantum mechanics holds that all forces arise from the exchange of discrete particles known as quanta (particles).

This contradiction is especially vexing to physicists because the other three fundamental forces (strong force, weak force and electromagnetism) were reconciled with a quantum framework decades ago. As a result, modern researchers have begun to search for a theory that could unite both gravity and quantum mechanics under a more general framework.

One path is to describe gravity in the framework of quantum field theory, which has been successful to accurately describe the other fundamental interactions. The electromagnetic force arises from an exchange of virtual photons, where the QFT description of gravity is that there is an exchange of virtual gravitons.

This description reproduces general relativity in the classical limit. However, this approach fails at short distances of the order of the Planck length, where a more complete theory of quantum gravity (or a new approach to quantum mechanics) is required.

### RELATIVISM: **google gravity**

Whether the object is celestial is represented by a formula.

G(M)*celestial object * /C^2*R

The value we get from this formula tells us how relativistic the celestial body is:-

Example- For the earth is so much less so it is not very relativistic, Sun is 1000 times more relativistic than-the earth (**for more knowledge about relativism or not go to mathematical tab**).

Since we know that the relativistic part of the earth is not too much, we can still observe that in satellites revolving around the earth.

### NEUTRON STAR: google gravity

A neutron star is a relativistic star having a value around ~0.1. Most stars balance their gravitational force by thermonuclear fusion but when all the fuel of stars runs out then Gravitational collapse occurs that either result in Neutron stars or white dwarfs but still there is the maximum mass limit for white dwarfs and neutron star. If mass exceeds this value then due to gravitational collapse they become Black holes.

**FACT:-**Even earth can deflect the light because of the property of relativeness.

### BLACK HOLE: google gravity

These are believed to be the monsters of space from which even light can’t pass. For them, the value of relativism is >1. This means they are highly relativistic. Photons travel in circular a path in the photon sphere of a black hole. Black holes are considered a sphere because R is properly interpreted.

### Specifics

#### Earth’s Gravity: google gravity

**google gravity-**Every planetary body (including the Earth) is surrounded by its own gravitational field, which can be conceptualized with Newtonian physics as exerting an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point above the surface is proportional to the planetary body’s mass and inversely proportional to the square of the distance from the center of the body.

https://astrophile0.space/wp-content/uploads/2022/12/Gravity_action-reaction.gif

The strength of the gravitational field is numerically equal to the acceleration of objects under its influence. The rate of acceleration of falling objects near the Earth’s surface varies very slightly depending on latitude, surface features such as mountains and ridges, and perhaps unusually high or low sub-surface densities. For purposes of weights and measures, a standard gravity value is defined by the International Bureau of Weights and Measures, under the International System of Units (SI).

### Gravitational radiation

General relativity predicts that energy can be transported out of a system through gravitational radiation. The first indirect evidence for gravitational radiation was through measurements of the Hulse–Taylor binary in 1973. This system consists of a pulsar and neutron star in orbit around one another. Its orbital period has decreased since its initial discovery due to a loss of energy, which is consistent for the amount of energy loss due to gravitational radiation. This research was awarded the Nobel Prize in Physics in 1993.

The first direct evidence for gravitational radiation was measured on 14 September 2015 by the LIGO detectors. The gravitational waves emitted during the collision, of two black holes 1.3 billion light years from Earth were measured. This observation confirms the theoretical predictions of Einstein and others that such waves exist.

It also opens the way for practical observation and understanding of the nature of gravity and events in the Universe including the Big Bang.Neutron star and black hole formation also create detectable amounts of gravitational radiation. This research was awarded the Nobel Prize in physics in 2017.

### Speed of gravity: **google gravity**

In December 2012, a research team in China announced that it had produced measurements of the phase lag of Earth, tides during full and new moons which seem to prove that the speed of gravity is equal to the speed of light. This means that if the Sun suddenly disappeared, the Earth would keep orbiting the vacant point normally for 8 minutes, which is the time light takes to travel that distance. The team’s findings were released in the Chinese Science Bulletin in February 2013.

In October 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma ray satellites and optical telescopes seeing signals from the same direction. This confirmed that the speed of gravitational waves was the same as the speed of light.**google gravity**

* ALSO SEE OUR POST ON WORMHOLES*..

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