In 1686, Sir Isaac Newton published his great work, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). In this book, Newton released his theory of gravity, the first mathematical theory of gravity ever. In order to create his theory, first Newton had to invent a new form of mathematics, Calculus.

Newton was never satisfied with his theory. The idea that the Earth pulls on the Moon with no visible or mediating agent is called action at a distance. Newton never thought this idea was credible, but he was unable to find any alternative.

Newton’s theory of gravity is quite good – NASA uses it almost exclusively for all orbital calculations, and it works just fine. However, very small numerical problems with his theory were found over the years. Also, Newton’s theory was heavily criticised on philosophical grounds. Newton’s theory presumed there were special observers, called “inertial observers,” who were the only ones to see the laws of physics in their pure form.

The current understanding of gravity is based on Albert’s general  theory , which is formulated within the framework of classical physics. On the other hand, the nongravitational forces are described within the framework of quantum mechanics, a radically different formalism for describing physical phenomena based on the wave-like nature of matter.The necessity of a quantum mechanical description of gravity follows from the fact that one cannot consistently couple a classical system to a quantum one.

Although a quantum theory of gravity is needed in order to reconcile general relativity with the principles of quantum mechanics, difficulties arise when one attempts to apply the usual prescriptions of quantum field theory to the force of gravity via gravitationbosons. The problem is that the theory one gets in this way is not renoramisable  and therefore cannot be used to make meaningful physical predictions. As a result, theorists have taken up more radical approaches to the problem of quantum gravity, the most popular approaches being string theory and loop quantum gravity.[5] A recent development is the theory of causal fermion systems which gives quantum mechanics, general relativity, and quantum field theory as limiting cases.

Strictly speaking, the aim of quantum gravity is only to describe the quantum behavior of the gravitational field and should not be confused with the objective of unifying all fundamental interactions into a single mathematical framework. While any substantial improvement into the present understanding of gravity would aid further work towards unification, study of quantum gravity is a field in its own right with various branches having different approaches to unification. Although some quantum gravity theories, such as string theory, try to unify gravity with the other fundamentalforces, others, such as loop quantum gravity, make no such attempt; instead, they make an effort to quantize the gravitational field while it is kept separate from the other forces. A theory of quantum gravity that is also a granduniforation  of all known interactions is sometimes referred to as The Theory of Everything .


In 1905, Albert Einstein shocked the world with three papers. Before he published these papers, Einstein was a clerk in the Swiss Patent office – he had graduated from college with a bachelors (4 year) degree, but his professors considered him a rather indifferent student who was not talented enough to warrant a position in graduate school to pursue a Doctorate degree. Einstein’s three papers were:

  • Brownian Motion – after this paper was published, everyone agreed that matter was made up of atoms. The atomic theory is perhaps the most fundamental part of quantum mechanics.
  • The Photo-Electric effect – in this paper, Einstein coined the work “photon,” and put us firmly on the road to quantum mechanics.
  • Special Relativity – in this paper, Einstein explained that the speed of light was an absolute constant. Everyone who measures the speed of light will get the same number, regardless of how fast they are moving and how fast the light source is moving, and nothing can go faster than light. Special relativity tells us that space and time do not exist as separate entities, as Newton thought, but rather as one union, which we call space-time.

Any one of these three papers would have been enough to ensure that Einstein became known as a superb physicist. The three papers published in one summer were enough to set him aside as someone special. However, Einstein was not by any means done creating.

Einstein realized almost immediately that his theory of Special Relativity had a serious flaw: gravity could not co-exist with his new theory of space and time. So, almost immediately Einstein set out to find a new theory of gravity, a theory to replace Newton’s. In 1916, 11 years later after special relativity and 230 years after Newton, Einstein published his theory of gravity, the General Theory of Relativity. In order to create this theory of gravity, Einstein had to change our notions of space and time yet again. Einstein had to postulate that we lived in a curved space-time, just as we live on the curved surface of the Earth. Einstein showed that there were no such things as Newton’s inertial observers. Also, General Relativity is what is called a field theory, so Newton’s spooky action at a distance was also gone.


Just as Newton was never satisfied with his theory of gravity, Einstein was never satisfied with General Relativity. Einstein was disturbed by two problems: he believed that there should be just one theory to account for both gravity and electro- magnetism, and he believed that this “unified field” theory should get rid of quantum mechanics. Although Einstein himself helped create quantum mechanics, he hated quantum mechanics until his death. One interpretation of quantum mechanics is that everything is uncertain, and everything is fundamentally governed by the laws of probability. Einstein particularly despised this notion, frequently asserting “God does not throw dice!”

Quantum Relativity

Gravity as we currently understand it cannot be reconciled with the laws of quantum mechanics. Since 1930, people have tried to invent a theory of quantum gravity. I believe Enrico Fermi was the first to propose a theory of quantum gravity, in 1931. However, Fermi’s theory predicted that all forces were infinite, and therefore the universe could not exist. Most physicists think the universe does in fact exist, so it was thought that the theory of quantum gravity had some serious problems.

Shortly after quantum field theory was invented, people started trying to invent a quantum field  of gravity. Very quickly, it was shown that this is impossible: there can be no theory of gravity which obeys the rules of quantum field theory. The quantum theory of fields simply will not work for a force with the properties of gravity. It was recognized that a completely new type of theory was required. Since this theory does not currently exist, no one is certain exactly what it looks like. However, most people presume we need a new theory of space and time which will be compatible with the laws of quantum mechanics as we know them, and somehow allow a theory of quantum gravity to exist. This new theory of space and time is often called Quantum Relativity.


 A fantastic Experiment




The most fascinating theory of all



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