Reinventing Gravity: A Physicist Goes Beyond Einstein by John W. Moffat Search Amazon for other books by or about John W. Moffat. Rating: Reviewed by: Maurice Williams

We hear a lot today about black holes, singularities, string theory: many, hard-to-visualize concepts proposed by modern cosmology. I came across Reinventing Gravity by John W. Moffat, and found it an easy-to-understand book on cosmology covering all of the above and suggesting a modification to our understanding of gravity that will do away with black holes and singularities. Moffat is not an untrained critic of cosmology. He is a mainstream cosmologist with impeccable credentials.

One item that impressed me is Moffat's description of a singularity, like a black hole. I had already picked up a simplified definition from the media that a singularity occurs in a cosmological situation where all the known laws of physics no longer apply. That definition baffled me. I have problems visualizing situations where all the laws of physics no longer apply. Moffat gives a better explanation. A singularity is a theoretical situation arrived at mathematically where the mathematical numbers become extremely large, too large to calculate, so large, in fact, that if a computer were used to make the calculations, the computer would crash. This definition does not baffle me.

Cosmologists view the cosmos through the window of mathematics because mathematical computations can be precise enough to predict hitherto unknown behavior in the cosmos (and in physical nature), behavior that can subsequently be searched for and authenticated by observation. The mathematics already derived from human understanding of nature has served us well in engineering, medicine, electronics, and space age exploration. There has to be a lot of truth in those mathematical calculations. Moffat mentions a famous case in point: Jean J. LeVerrier's prediction that the orbit of Uranus has to be affected by another undiscovered planet.

In 1846, LeVerrier, while observing the newly discovered planet Uranus, noticed that Uranus was making some unexpected movements as it orbited the sun. He concluded that Uranus was being influenced by the presence of another not-yet-discovered planet. He named the new planet Neptune. Later in that same year, Neptune was discovered very close to where LeVerrier predicted it would be. This was a spectacular confirmation of Newton's theory of gravity

In 1859, LeVerrier made a similar prediction about the wayward motion of Mercury. He named the unobserved planet Vulcan, but nobody could verify its existence by observation. Finally in 1915-16, Albert Einstein solved the mystery, and Einstein's theory of relativity was born. Mercury's wayward motion was caused by the sun's mass warping the space surrounding the sun. Here was a spectacular case where a prediction based on mathematics was not confirmed by observation, but led to a new understanding of the universe.

Due to recent far more detailed observations of distant stars and galaxies from telescopes orbiting Earth, cosmologists see evidence that the current theories cannot explain the rapid rotation of distant galaxies. If gravity were the only force holding these galaxies together, they would have spun apart long ago. There simply isn't enough mass within those galaxies to counteract the centrifugal force of the outermost stars orbiting at observed speeds. Also, recent observations from space indicate that the expansion of the universe is accelerating. This implies that there is an unknown force causing the acceleration.

To reconcile these observations with current understanding, cosmologists have proposed the presence of dark matter that would strengthen gravity in distant galaxies and also dark energy to account for the driving force for the acceleration. Both dark energy and dark matter have never been observed or directly detected. Yet modern cosmology proposes that dark energy and dark matter comprise a whopping 96% of the entire universe. Moffat is not comfortable with this. No dark matter or dark energy has ever been observed, even though there have been very expensive experiments set up to detect them.

Current Newtonian Einstein relativity and Quantum mechanics cosmology proposes four basic forces in nature: gravity, electromagnetism, weak nuclear force, and strong nuclear force. Moffat proposed a Modified Gravity hypothesis that adds a fifth force to the four already recognized. The fifth force can be thought of as a gravitational degree of freedom: part of the overall geometry or warping of space-time. Newton's gravity constant would now no longer be a constant but be a variable force in time and space. This variable force of gravity, together with the new force, strengthens the pull of gravity in far away galaxies and in clusters of galaxies. Moffat feels confident in his hypothesis because mathematical equations expressing his concepts do not need the presence of dark matter or dark energy, and the equations produce no singularities.

Moffat has described a very difficult subject, usually understood only through mathematics, in plain English easily understood by the average reader. You will learn quite a bit about the positive contribution of cosmology helping us understand the universe, and you will realize that human understanding of the universe is still an ongoing (and unfinished) process. If you are interested in science, I recommend Reinventing Gravity as must read.