Gravity

**Gravity** is one of the four fundamental forces which causes mutual attraction between objects with mass or energy. With the old laws of physics, gravity is understood to be 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. Because it is so weak, it has little influence at the microscopic scale, with atoms and subatomic particles. However, it has significant influence at the macroscopic scale, determining the motion of planets, stars, galaxies, and even light.

With the new laws of physics, the theory of everything allows gravity to be united with the other three fundamental forces.

### History

For thousands of years it was thought that heavier objects fall at a faster rate, and gravity was not generally thought to be a force. After 1604, Galileo and others confirmed that the distance of a falling object is proportional to the square of the time elapsed. They also calculated the magnitude of the Earth's gravity by measuring the oscillations of a pendulum.

In 1684, Newton described gravitation as a universal force, and formulated the inverse-square law. Newton's law was well-received by the scientific community, and remained in use for hundreds of years to predict the existence of planets for example.

Eventually, astronomers noticed an eccentricity in the orbit of the planet Mercury which could not be explained by Newton's theory. Finally, in 1915, 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 spacetime curvature instead of a force. Einstein proposed that spacetime is curved by matter, and that free-falling objects are moving along locally straight paths in curved spacetime which are called geodesics. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon.

Today, Einstein's theory of relativity is used for all gravitational calculations where absolute precision is desired, although Newton's inverse-square law continues to be a useful and fairly accurate approximation, and is studied in schools.

### Impact of general relativity

* In 1919, Arthur Eddington was able to confirm the predicted gravitational lensing of light during that year's solar eclipse. This experiment made Einstein famous almost overnight and caused general relativity to become widely accepted in the scientific community.
* In 1959, American physicists experimented with gamma rays to confirm the prediction of gravitational time dilation.
* In 1971, scientists discovered the first-ever black hole in the galaxy Cygnus. Einstein's equations implied that light could not escape from a sufficiently large and compact object, and this helped in the detection.
* A sufficiently massive object could warp light around it and create gravitational lensing. This phenomenon was observed for the first time in 1979, when the Hubble telescope saw two mirror images of the same quasar whose light had been bent around a galaxy. This effect is also noticed in the galaxies of the first image taken by the James Webb Space Telescope.
* In 2015, the LIGO observatory detected gravitational waves, the existence of which had been predicted by general relativity.
* In 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 gravity* was the same as the speed of light.

### Cosmic Impact

The earliest instance of gravity in the universe, possibly in the form of a gravitational singularity, developed during the Planck epoch up to 10−43 seconds after the Big Bang. The gravitational attraction between this primal gaseous matter in the universe allowed it to coalesce and form stars which eventually condensed into galaxies, so gravity is responsible for many of the large-scale structures in the universe. Gravity has an infinite range within the universe, although its effects become weaker as objects get farther away.

On Earth, gravity gives weight to physical objects, and the moon's gravity causes tides in the oceans. The Earth has its own gravitational field which keeps objects and us from floating away into space. The sun has a gravitational field which keeps planets and objects in its solar system in a fixed orbit. Every galaxy has a gravitational field likely generated by supermassive black holes at their centers, that keep stars in orbit around them.

### G-force

The **gravitational force equivalent** or **g-force** measure the force of typically acceleration that causes a perception of weight. The value of gravitational acceleration on Earth, *g*, is about 9.8 m/s2, so that coincides with a g-force of 1 or *1g*. Gravitational acceleration is the cause of an object's acceleration in relation to free fall.

The g-force experienced by an object is due to the sum of all forces acting on an object's freedom to move. Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. The larger the g-force, the more destructive it can be. This g-force calculator says that if you weigh 60kg, have no seat-belt, and travel at 60km/h, and crash your car, then you will experience over 350g, which is equivalent to a 21 tonne weight on you.

Objects allowed to free-fall under the influence of only gravitation feel no g-force, a condition known as weightlessness or *zero-g*. This is demonstrated by the zero g-force conditions inside an elevator falling freely toward the Earth, or certain conditions inside a spacecraft in Earth orbit.

### Theory

Gravity is mediated by elementary particles called gravitons. This is the hypothetical quantum of gravity and a massless state of a string. Becaused the graviton is the lightest particle known, at 1.07×10−67 kg, higher dimensions are rolled up into tiny, compactified loops.

The Randall-Sundrum (RS) brane theory in Type 0 tries to address why the force of gravity appears to be so much weaker than other fundamental forces such as the electromagnetic force and the strong and weak nuclear force. According to the RS theory, gravity may be weak because it is concentrated in another dimension. Our visible universe with its three dimensions of space and one dimension of time is a visible brane (where particles in the Standard Model reside). Another brane may reside a short distance away in another spatial dimension. It is on this other hidden brane that gravitons may reside. Gravity may actually be as strong as the other forces, but it is diluted as it 'leaks' into our visible brane. Photons that are responsible for our eyesight are stuck to the visible brane, and thus we are not able to see the hidden brane.

In Type I once 5d is discovered, gravity is a known as a *strong force* that holds a plane of probability together that contains branching timelines. An infinitesimally small amount of gravitons leak into lower spacetime dimensions, creating visible evidence that gravity is weak, but is strong in a 5d reality.