GENERAL RELATIVITY THEORY

            General relativity is physicist Albert Einstein's understanding of how gravity affects of fabric of space-time.

Image credit: American Physical Society

            The theory, which Einstein published in 1915, expanded the theory of special relativity that he had published 10 years earlier. Special relativity argued that space and time are inextricably connected, but that theory didn't acknowledge the existence of gravity.

            Einstein spent the decade between the two publications determining that particularly massive object warp the fabric of space-time, a distortion that manifests as gravity,

according to NASA.

How does general relativity work?

            To understand general relativity, first, let's start with gravity, the force of attraction that two objects exert on the another. Sir Isaac Newton quantified gravity in this same text in which the formulated his three laws of motion, the principia.

            The gravitational force dugging between two bodies depends on how massive each one is and how far about the two line according to NASA even as the centre of the earth is pulling you too it keeping you family larged on the ground your centre of mass is pulling back at the earth but the more massive body barely feels the tag from you while with your much smaller mass you find yourself family rooted thanks to that same force yet Newton's law as you that gravity in an in it force of an object that can act over a distance.

            Albert Einstein in the theory of special relativity determine that the law of physics are the same for all non accelerating observers and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travel according to wired.

Image credit: American Association Of Physics Teachers

            Result he found that space and time where interwoven interesting girl continuum known as space time and events that acute at the same time for one observer could occur at different times for another.

Related what would happen if the speed of light was much lower?

            As he  worked out the equations for his general theory of relativity Einstein realised the Maya saved objects caused at disortion in space time imagine settings hello object in a centre of trampoline. The object would press down into the fabric causing it to dimple if you then attempt to roll a marble around the edge of the trampoline the marble wood spiral involved toward the body fullden much the same way that the gravity of a planet full s a truck in space. In the decades since Einstein published his there is scientist have observed countless of phenomena matching the prediction of relativity.

GRAVITATIONAL LENSING

            Light bands around the massive object such as a black hole causing it to act as lens for the things that lie behind it astronomers routinely used this method to study stores and Galaxy brain massive.

            The Einstein cross quasar in the Pegasus constellation, according to the European space agency ESA and his son excellent example of gravitational that quasar is seen as it was about 11 billion years ago the Galaxy that it seats behind is about 10 thanks closer to earth because the two objects alliance so precisely for images of the quasar appear around the Galaxy because the intense gravity of the Galaxy Benz the light coming from the quasar.

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            In case like Einstein's cross the different images of the gravitationally linked object appear simultaneously but that isn't always the case scientist have also managed to observe lensing example where because the light travelling around the lens takes different parts of different lens different images arrive at different times as in the case of one particularly interesting supernova.

Image the Einstein cross is an example of gravitational and Singh image credit NASA and European space agency ESA

CHANGES IN MERCURY'S ORBIT

            The orbit of mercury is shifting very gradually over time due to the curvature of space time around the massive son according to NASA.

            As the closest planet to the sun, Mercury's perihelion (the point along its orbit that it's closest to the sun) is predicted to follow a slightly different the direction overtime. Under Newton's predictions, gravitational force in the solar system should advance Mercury's precession (change in its orbital orientation) is measured to be 5,600 arcsecond per century (1 arcsecond is equal to 1/3600 of a degree). However there is a discrepancy of 43 or seconds per century something Einstein theory of general relativity accounts for using Einstein's theory of curved space time the precision of mercurys perely and should advines slightly more than under the predictions of Newton since planets don't orbit the sun in a static elliptical orbit.

            Sure enough, several research papers published since that meet 20th century have confirmed Einstein's calculations of Mercury's perihelion processions to be accurate.

            In a few billion years, this wobble could even cause the innermost planet to collide with the sun or a planet.

FRAME-DRAGGING OF SPACE-TIME AROUND ROTATING BODIES

            The spin of a heavy object, such as Earth, should twist and distort the space-time around it. In 2004, NASA launched the gravity probe B (GP-B). The axes after satellite's precisely calebrated gyroscopes drifted very slightly over time, according to NASA, a result that matched Einstein's theory.

            "Imagine the Earth as if it very much in honey," Gravity Probe-B principal investigator Francis Everitt, of Stanford University, said in a NASA statement about the machine.

            "As the planet or rotates, the honey around it would swirl, and it's the same with space and time. GP-B confirmed two of the most profound predictions of Einstein's universe, having far-reaching implications across astrophysics research."

GRAVITATIONAL REDSHIFT

Image credit: Forbes

            The electromagnetic rotation of an object is stretched out slightly inside a gravitational field. Think of the sound waves that emanate from a siren on an emergency vehicle; as the vehicle moves towards an observer, sound waves are compressed, but as it moves away, they are stretched out, or redshifted. Known as the Droppler Effect the same phenomena occurs with waves of light at all frequencies.

            In the 1960s, according to the American Physical Society, physicist Robert Pound and Glen Rebka shot gamma-rays first down, then up the side of a tower at Harvard University. Pound and Repka found that the gamma-rays slightly changed frequency due to the distortions caused by gravity.

GRAVITATIONAL WAVES

            Einstein predicted that violent events, such as the collision of two black holes, create a ripples in space-time known as gravitational waves. And in 2016, the Laser Interferometer Gravitational Wave Observatory (LIGO) announced that it had detected such as signal for the first time.        

            That detection came on September, 14, 2015. LIGO, made up of twin facilities in Louisiana and Washington, had recently been upgraded, and were in the process of being calibrated before they went online. The first detection was so large that, according to then-LIGO spokesperson Gabriella Gonzales, it took the team several months of analysis to convince themselves that it was a real signal and not a glitch. 

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             "They were very lucky on the first architecture that it was so obvious," She said during the 228 American Astronomical Society meeting in June 2016.

            Since then, scientists have been quickly catching gravitational waves. All told, LIGO and its European counterpart Virgo have detected a total of 50 gravitational-wave events, according to program officials, according to the Laser Interferometer Gravitational-Wave Observatory.

            Those collisions have included unusual events like a colision with an object that scientists can't definitively identify as black hole or neutron star, merging neutron stars accompanied by a bright explosion, mismatched black holes colliding and more.

OBSERVING NEUTRON STARS

            

(Image credit: National Radio Astronomy Observatory.

            In 2021 research published in the journal Physical Review X, challenged several of Einstein's predictions by observing a double-pulsar system around 2,400 light-years from Earth. Each of the seven predictions of general relativity was confirmed by the study.

            Pulsars are a type of neutron star that appears of pulse due to beams of electromagnetic radiation and that are emitted from their magnetic poles.

            The pulsar test subjects spin very fast - around 44 times a second - and are 30% more massive than the sun but or only 15 miles (around 20 kilometers) in diameter, making them incredible dense. This means that their  gravitational pull is immense, for example, on surface of a neutron store gravity is around 1 billion times stronger than its pull-on Earth. This makes neutron stars a great test subject to challenge predictions in Einstein's theories, such as the ability of gravity to bend light.

            "We follow the propagation of radio photons emitted from a cosmic lighthouse, A pulsar, and track their motion in the strong gravitational field of a companion pulsar," Professor Ingrid Stairs from the University of British Columbia at Vancouver said in a statement.

            "We see for the first time how the light is not only delayed due to a strong curvature of spacetime around the companion, but also that the light is deflected by a small angle of 0.04 degrees that we can detect. Never before has such an experiment been conducted at such a high spacetime curveture" Stairs adds.