Is gravity weaker than other three forces? A solution to the hierarchy problem in physics

Gravity is the weakest forces of all the four forces of our universe, because, according to the author, it is concentrated in another spatial dimension of the universe, and these extra dimensions could be infinitely large. The summary of this book is as follows: We live in a three-dimensional pocket of higher dimensional space, also called branes. It is like a bead on a wire that can only move along one dimension, a brane may restrict our motion to three dimensions although other dimensions exist around it. The theory of supersymmetry also explains the hierarchy problem by postulating that every fundamental particle has a heavier partner, but the theory currently predicts particle interactions that don't occur in nature. The author predicts that if extra dimensions exist, particles could be separated to prevent unwanted interactions, and that gravity could be concentrated somewhere in an extra dimension. The force's strength becomes exponentially weaker further from the gravity brane. The model consists of a pair of universes, four-dimensional branes (three space and one time), thinly separated by a five-dimensional space called the bulk. The mathematical solutions for this setup suggested that the space between the branes is warped, and objects could grow larger or smaller (less massive or more massive) as they moved back and forth between two branes, a direct result of higher gravitational force. The fifth dimension could be so warped that the number of dimensions you see would depend on where you are in the bulk. In addition, gravity is as strong as the other forces, because it is much stronger on one brane than the other. Therefore our universe is located on a brane where only weak gravitational force is felt. This idea of the author is not new since string theorists, Arkani-Hamed, Divali and Dimopoulos (group A.D.D.) suggested that if one or two of the curled-up extra dimensions of string theory had sizes as big as a tenth of millimeter, then gravity would be similarly diluted and weakened thus explaining the hierarchy problem.

There is increasing perception among some leading physicists like Ed Witten that space and time could be illusions, or it is perhaps made of simpler yet undiscovered physical parameters. We are still long way to clearly understand the concept of space and time, but the author's theory may be a step in the direction of advancement. However, one of the major problems of this theory is that it is all talk (theoretical) but no substance (no experimental evidence). We have to wait a little longer after the LHC data is completely analyzed and understood.

The book is very well written and easy to understand; the author has explained the relevant physical concepts in a simple and lucid manner; highly recommended.

Reference: Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions by Lisa Randall