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Good bye Dark Matter, Hello General Relativity
dr. loser writes "The CERN newsletter reports that a new paper by scientists at the University of Victoria has demonstrated that one of the prime observational justifications for the existence of dark matter can be explained without any dark matter at all, by a proper use of general relativity! What does this imply for cosmology and particle physics, both of which have been worrying about other aspects of dark matter?"
The paper only concerns itself with the observed rotation speeds of galaxies, for which "maybe there's something we don't understad about gravity" has always been just as convincing an explanation as dark matter. However, the recent cosmic microwave background radiation data *also* implies dark matter, and doesn't have such an easy alternative explanation. The data tells us that (at least, at the moment the univers first became transparant) baryons only account for 20% or so of mass.
Socialism: a lie told by totalitarians and believed by fools.
Even if the article was correct, and dark matter was not needed to explain rotation curves in galaxies, dark matter is still needed to explain the acceleration of the universe, its large scale structure and the primordial anisotropies in the cosmic microwave background.
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Wrong. Copernicus still had the planets moving in circles. The big difference (and the reason of the rejection by the church) was that in his model he put the sun instead of the earth in the center.
It was Kepler who found that the planets don't really move in circles, but in ellipses.
The Tao of math: The numbers you can count are not the real numbers.
I'm in Dr. Cooperstock's General Relativity (GR) class this semester. I must agree, he's a great teacher, and definitely a little quirky. Also he's quite old and some of that quirkiness may come from age.
As an aside, what's different about his lectures is that he uses a transparency roll and an overhead projector instead of the blackboard, and writes/derives everything with us in class, unlike many other professors who merely present slide shows or just talk a lot and write very little (very common among astronomy professors). I really dislike slideshows, and prefer Dr. Cooperstock's method because as he does so, we learn about how he thinks, why he makes the decisions he makes in the derivations, and the usual pitfalls in dealing with all the notation used in GR. That for me is far more valuable than just seeing an amalgamation of details presented on slide shows with a short verbal summary from a professor. Any textbook could provide me with that. The other advantage with the transparency roll is that if we ever need to go back to a previous lecture to revisit something that was discussed there, he just has to put up the roll corresponding to that lecture, and we have it right there in front of us. If we missed any lecture notes, we can just borrow the transparency rolls from him and copy the notes from them.
Back to the topic, I believe that what's important is that we must realize that dark matter is still just a hypothesis. There may be overwhelming signs pointing to something that we call dark matter, but this paper reminds us that dark matter is still only just a hypothesis. It is one of the easiest hypotheses to make, because simply adding a spherical distribution of dark matter to a galactic halo produces the observed rotation curve, but is not the simplest, because it postulates the existence of particles that we cannot yet prove to exist, at least not in such large quantities. If simplicity is a valid reason to accept or refute theories, then Dr. Cooperstock's model appears to me to be simpler because it requires fewer postulates to make things work.
However there are other observations such as satellite galaxies and gravitational lensing and galaxy clusters, all of which appear to require a huge amount of dark matter that we cannot observe. While Dr. Cooperstock's model may not explain all of these yet, this is work that has yet to be done, and so his model cannot be ruled out. One must realize that dark matter is really just a fudge factor to make the theory work out the same way as observations. Until there is good evidence from astronomers and from particle physicists, the arena should be open and impartial to other candidate hypotheses. It is good to see that despite most of the world jumping on to the dark matter band wagon, there are people who stand back and persist with their own ideas. We've seen this happen so many times in history.
Besides, it is still possible that despite GR explaining the galactic rotational curves, dark matter may still exist, but then its role and distribution would change. Oh, the fun of physics...