Einstein's gravity theory--his general theory of relativity--has served as the basis for a series of astonishing cosmological discoveries. But what if, nonetheless, Einstein got it wrong? Since the 1930s, physicists have noticed an alarming discrepancy between the universe as we see it and the universe that Einstein's theory of relativity predicts. There just doesn't seem to be enough stuff out there for everything to hang together. Galaxies spin so fast that, based on the amount of visible matter in them, they ought to be flung to pieces, the same way a spinning yo-yo can break its string. Cosmologists tried to solve the problem by positing dark matter--a mysterious, invisible substance that surrounds galaxies, holding the visible matter in place--and particle physicists, attempting to identify the nature of the stuff, have undertaken a slew of experiments to detect it. So far, none have. Now, John W. Moffat, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, offers a different solution to the problem. The cap#65533;stone to a storybook career--one that began with a correspondence with Einstein and a conversation with Niels Bohr--Moffat's modified gravity theory, or MOG, can model the movements of the universe without recourse to dark matter, and his work chal#65533;lenging the constancy of the speed of light raises a stark challenge to the usual models of the first half-million years of the universe's existence. This bold new work, presenting the entirety of Moffat's hypothesis to a general readership for the first time, promises to overturn everything we thought we knew about the origins and evolution of the universe.
One of the many items that impressed me is Moffat’s description of a singularity, like a black hole. I had already picked up a definition from the media that a singularity is a situation where all known laws of physics no longer apply. I always wondered about that. Moffat describes a singularity as a theoretical situation arrived at mathematically where the mathematical numbers become extremely large, too large to calculate, so large that if a computer were used to make the calculations, the computer would crash. Cosmologists are in the habit of describing the cosmos through 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. This is how science progresses.
The present understanding of what holds the cosmos together is a combination of Newton’s theory of gravity, Einstein’s relativity, and quantum mechanics. All three theories have been proven reliable, but attempts to unify all three into a single Grand Unified Theory have failed. These theories of cosmology propose four basic forces in nature: gravity, electromagnetism, weak nuclear force, and strong nuclear force. Moffat’s work indicates that there is another force to consider.
There is much new information obtained from telescopes orbiting the Earth. Distant galaxies show evidence that they are rotating too fast for the galaxies to hold together. If current understanding of gravity is 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. To make the current understanding of gravity sufficient to counteract observed centrifugal forces, cosmologists have presumed that there must be unseen dark matter within the galaxies. Recent observations also indicate that the expansion of the universe is accelerating, implying that there is an unknown force causing the acceleration. Cosmologists propose that, in addition to dark matter, there must also exist dark energy, a proposed undetected energy that serves to explain the acceleration. Dark matter and dark energy have never been observed even though there have been very expensive experiments performed to detect both.
Moffat spent many years studying whether gravity really is a force of uniform and constant strength throughout the universe or might it be a variable-strength force, especially outside the solar system. He proposes 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 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 relates that mathematical equations based on the addition of his new force can explain all current and past observations without singularities or the need to propose dark matter or dark energy. In addition, his hypothesis holds that, when a star collapses under its own gravity, it does not form a black hole (a singularity where there is a reversal of time and space at the “event horizon”). A collapsed star forms, instead, a very massive and very small object that he calls a “grey star.”
Moffat has described a very difficult subject, usually understood only through mathematics. He describes his position in plain English easily understood by the average reader. This is a very informative and interesting book written by someone who has the credentials to know what he is talking about. “Reinventing Gravity” may well be the book that will introduce you to the new frontier on cosmology.