Originally an email written on June 29, 2010:
Almost at the same time when I finished the book "Reinventing Gravity" of J. W. Moffat, I’ve also read a partly detective / partly magical / partly romantic novel of 林詠琛. Probably because she didn’t study physics in HKU (but English Literature/Psychology), she seems to think that we’re living in a 3D world and the 4th dimension of time (she does know that it’s "time") seems an extra dimension such that people can disappear into this 4D world. I guess we (physicists) haven’t explained well enough to people that even if two friends specify "G/F, 1 Queens’ Road, Central", they most likely wouldn’t meet unless they also specify the time coordinate with some accuracy … For all the lovely characters the author has created, I can volunteer my free consultation ==> she just needs to add the 5th dimension or 6th dimension etc… then it would start to be plausible that her characters may hide in these extra dimension … ~a level of plausibility that’s probably on par with the superstring theorists who have to hide or explain away the 6 or 7 dimensions that nobody have seen or the supersymmetric partners that have never been found.
J. W. Moffat is apparently not a fan of all these extra dimensions … nor inflation (in its usual sense) nor dark matter/dark energy … not even to make use of quantum mechanics.
In recent years or the last decade, I feel that cosmology seems slightly more popular than in the past, probably thanks to all the dark matter/dark energy jargons and search opportunities. Quite a few experimental particle physicists have converted themselves into analyzing all the data from all sorts of telescopes of (just like astronomers) or helping to make gigantic telescopes (CCD/pixel in silicon etc. are something that particle physicists are familiar with) in addition to all the dark matter/dark energy searches.
I remember attending a seminar in which MOG "Modified Gravity" (or another MOND) were seriously discussed. It’s very easy to feel unconvinced and feel dubious towards these people who were strange enough to modify general relativity. But probably there were too much dark matter/dark energy which has lost their sexiness (at least to me) and I feel time is ripe to learn of something else. Moffat’s 2008 book "Reinventing Gravity" serves this purpose very well.
One major "psychological" point that Moffat has conveyed to me quite well is that if people can believe in the exotic ideas of dark matter and dark energy, especially after all the failed efforts to find any dark matter, it only makes sense at least to consider a different approach.
Even without reading books by particle physicists like F. Wilczek’s, one can imagine that particle physicists like "dark matter" because it gives us again something to search. Inventing a particle or 2 to explain some phenomena has had a few successes in the past. When the general relativity with the visible mass can’t explain the large gravitational lensing or the escape velocity of the galaxies are seemingly too big, dark matter was invented. Dark energy was comparatively newer … I still remember the energetic Berkeley guy giving the talk about their observations of supernova Ia leading to accelerating universe in a conference in Puerto Rico which was only 10 years ago.
Moffat claims and explains in his book that his MOG with variable "gravitational constant" does away with the dark matter to explain all the data where general relativity with visible matter can’t explain without dark matter. But throughout the book, the reader may feel that Moffat was just trying to fit the data with all different methods, rather than from one single elegant theory. In fact, probably like all people, Moffat has had to tell us all of his researches in all different directions, rather than a coherent path. He has had his VSL (Variable speed of light) theory which can do away with the (violent) inflation … but VSL doesn’t seem to be related to MOG. He’s also tried using general relativity itself with inhomogeneity to explain the apparent accelerating universe — this is probably a bit similar to the "famous" cosmic void interpretation … He has quite a few students/collaborators and I imagine that his students run the computer program for him whereas he taught them all the equations …
A couple more interesting points … His MOG necessarily has a fifth force and at least a new particle/field "phion" which induces -ve pressure … leading to dark energy. Not immediately apparent at the beginning, his MOG also get rids of the singularities in general relativity and consequently the black hole. Of course, Moffat has to dedicate some pages to make us doubt whether black holes exist — something which many people have assumed. Nevertheless, Moffat has to set boundary conditions at t=0 with zero matter/energy and thus curvature. His beginning of the universe is quantum fluctuations. This seems to be about the only place that Moffat has used "quantum mechanics" ! He’s apparently avoided it in all other places. His universe begins so peacefully such that the density/temperature doesn’t reach the Planck scale and therefore quantum gravity is not needed. This is dubious. People like superstring theorists think that incorporating quantum mechanics with general relativity is the no. 1 goal but that’s definitely not Moffat’s approach. He doesn’t look to be an anti-superstring person on page 1; but gradually, it’s quite clear to the readers that he is obviously not happy with the fact that the superstring community has sucked up most of the fundings and happy to see its decline. He even calls the superstring physicists a "lost generation" ! He doesn’t like anthropic principle/multiverse/string landscape and describe them as "antiscience" approaches which he said would give "intelligent design" a chance
It’s overall an interesting book which has made me ruminate over what I thought I’ve known and learn that there can be other serious approaches, rather than just the popular "dark matter" and "dark energy". Nevertheless, one feels (by false impression or not) that Moffat’s approaches are kind of "ad hoc". He’s emphasized a few times that his MOG can fit the data well in 14 order of magnitudes. Howerver that — fitting the data — is probably the main impression that has left a mark in my mind about his MOG.
This book of a rather unorthodox approach is defintely worth reading … if nothing else, to get some different ideas rather than constantly being bombarded by all the dark matter/dark energy "propaganda" …