The story of gravity begins with the famous experiment of Galileo Galilei in the late 16th century at the tower of Pisa. In his experiment, he showed that gravitational acceleration is the same for all objects. Later in 1687, Sir Isaac Newton showed in his famous book (Philosophiæ Naturalis Principia Mathematica) that Gravity follows inverse square law. In his own words, “I deduced that the forces which keep the planets in their orbits must be reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force requisite to keep the Moon in her Orbit with the force of gravity at the surface of the Earth; and found them answer pretty nearly”.
Later around 1915 Einstein came with his new visualization of gravity. In his theory of General Relativity, he said that the gravity is just a manifestation of space-time fabric. The curvature of space-time produces gravity. But the Theory of General Relativity has some failures like at the center of black holes where space-time diverges or instances where we cannot ignore the quantum effects, very early cosmology, the structure of nature at a very short scale, etc.
Basically, Quantum Gravity is a framework where we understand gravity in the light of Quantum Mechanics. But to understand Quantum Gravity we must understand the language of it and it is quantum space and quantum time. Now the quantum gravity starts with a mistake by Russian physicist Lev Landau. In 1931 paper of Landau and Peierls suggested that the commutation relation of Heisenberg [q,p]=i{\hbar} did not work well when it applied to the electromagnetic field. After publishing the paper in 1933 Neils Bohr with Rosenfeld published a paper where they showed that in the quantum theory of the electromagnetic field, the Heisenberg uncertainty relation holds. But Landau also had his friend, Matvei Petrovich Bronstein who was a brilliant young physicist. Bronstein repeated the analysis of Bohr and Rosenfeld and applied this into the gravitational field indeed electromagnetic field which turned out that Landau was right. So this is the story that how quantum gravity turns out.
Now quantum gravity gives a new notion of space-time fabric, that in our universe there has a minimum length which is plank length, above that scale we treat space-time as smooth and below that scale, there is no meaning to talk about distance. At that scale, quantum fluctuation takes place with a gravitational field so the space-time no longer is viewed as a smooth manifold but rather forms a foam-like structure called quantum foam.
As you can see in the above picture, when you view space-time above plank length spacetime looks continuous but you go finer and finer through it, you see that space-time is not smooth at all rather than it has a foam-like structure.
This theory is not complete yet but we hope that with this fascinating structure one day it may reveal the deepest mysteries of our universe.
Have a look at our Recent Article: EPR: Paradox or Possibility?
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