The quest to unravel the enigma of gravity, the invisible force that governs the motion of celestial bodies and shapes the very fabric of our universe, can be traced back to renowned physicist and mathematician, Sir Isaac Newton. In the late 17th century, Newton's insights into gravity laid the foundation for classical mechanics and provided a broad architecture to comprehend the movement of objects on Earth and around the universe. However, as our understanding of the universe deepened, irregularities arose, challenging Newton's ideas and prompting the inception of a new groundbreaking principle: Albert Einstein's theory of general relativity. In this article, we will explore how the theory of general relativity transformed our understanding of gravity, reshaped the very fabric of modern physics, and anticipated future cosmological events currently beyond our understanding.
It is speculated that Newton acquired the idea of gravity after seeing an apple fall to the ground. Previously, everyone presumed the idea of objects falling to the ground, but Newton questioned this principle and wanted to know why the apple fell towards the Earth while larger objects like the Moon didn’t. Citing his law of inertia, he soon developed a mathematical relationship between any two objects and discovered that the force of attraction is equal to G*M1*M2/R^2, where M1 and M2 are the two objects , R is the distance between the objects’ centers of masses, and G is the universal gravitational constant. Newtonian mechanics became the gold standard in physics for centuries and accurately explained the motion of everything from an apple to celestial bodies across the cosmos. Newton’s theories were very successful when they accurately predicted the existence of Neptune based on the path of Uranus around the Sun. However, when Urbain Le Verrier tried to use these same laws to explain Mercury’s path around the Sun in the late 19th century, his calculations failed yet he couldn't find another piece of contradictory evidence. Many other scientists tried to combine Newton’s laws with the laws of electrodynamics but ultimately failed due to inconsistency. This is where Einstein arrived and changed the state of physics forever.
Einstein first created a theory of relativity in 1905 dictating that the laws of physics are the same for all observers in uniform relative motion (non-accelerating) and that lightspeed is always the same in a vacuum. He later named this his theory of “special relativity” because it did not apply to all situations. He searched for another, more universal theory of relativity that could explain the movements of all objects even in non-uniform motion (accelerating). Using his theory of special relativity, he realized that space and time were closely interlinked as special relativity was really just a showcase of the geometry of “spacetime”. Einstein realized that spacetime curved as a result of masses. He wrote that the curvature of spacetime was proportional to the mass density of a celestial object. Heavy objects, such as the Sun would bend spacetime so that other celestial objects would “fall” towards the Sun. Thus the curvature of spacetime was another explanation for gravity. Einstein’s theory did not entirely disprove Newton’s theory but expanded it for all situations. Einstein’s theory of general relativity accurately explained Mercury’s anomalous precession and became the last classical (non-quantum) field theory. Einstein’s findings were mathematized into the Einstein field equations and continue to be a crucial part of any physicist’s work in cosmology and relativity.
However, there are still many discrepancies with Einstein’s theory of general relativity. As scientists explored the new frontiers of science through quantum physics, they developed the Standard Model; a quantum field theory that is consistent with both quantum mechanics and special relativity, but not general relativity and thus cannot explain gravity, one of the four fundamental forces. The W and Z bosons dictate the weak nuclear force, gluons dictate the strong nuclear force, and photons dictate the electromagnetic force, but a particle dictating the gravitational force is yet to be discovered. The postulated “graviton” is thought to be a massless, electrically uncharged particle like the photon that carries the gravitational force. The graviton would tie together the theory of general relativity and the Standard Model, bringing us closer to a complete “Theory of Everything”.
The future of physics is still bright, though, as a unique solution to Einstein’s field equations mathematically theorizes the existence of wormholes, a hole in the fabric of spacetime that allows an object to pass through to another area of the universe, unlocking the idea of teleportation. The two mouths of such a wormhole would be a black hole. According to the solution, though, not all black holes automatically generate wormholes. In fact, wormholes are predicted to be microscopically small and to close the instant after they open, making travel unrealistic according to our understanding. However, black holes have another defining characteristic, their immense mass. As per the theory of general relativity, spacetime will curve around massive objects such as black holes and thus could create a time dilation effect for any observer near the black hole. Time will thus slow down, creating relativistic effects for the observer and making them experience events slower relative to everyone else. This concept along with the wormhole idea was conjectured by Einstein in his theories but was popularized by the movie Interstellar released in 2014. Einstein’s theory of general relativity offers a captivating glimpse into spacetime manipulation and will shape the way for the next generation of physicists to unravel the mysteries of the universe and expand the horizons of our understanding.
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