The Pioneer Anomaly Options

[remcook]

http://www.planetary.org/news/2005/pioneer_anomaly_faq.html

The planetary society may be checking it out...

The Planetary Society has committed to raise the funds to preserve the priceless Pioneer data from destruction.


After years of analysis, but without a final conclusion, NASA, astonishingly, gave up trying to solve the "Pioneer Anomaly" and provided no funds to analyze the data. The Pioneer data exists on a few hundred ancient 7- and 9-track magnetic tapes, which can only be read on "antique" outdated computers. The agency is going to scrap, literally demolish, the only computers able to access and process that data in the next few months!

[Jeff7]

Concerning dark matter, I remembered some article that had a theory for why dark matter need not exist at all - that we only need to use relativity properly, and apply it to gravity. Something along those lines.
Link - it has a summary of this theory, and a link to the full abstract. It seems to say that, when looking at something small, like a single star, Newtonian physics may be an adequate approximation, but this doesn't work when you're looking at the way an entire galaxy behaves.

[Mongo]

Concerning dark matter, I remembered some article that had a theory for why dark matter need not exist at all - that we only need to use relativity properly, and apply it to gravity. Something along those lines.
Link - it has a summary of this theory, and a link to the full abstract. It seems to say that, when looking at something small, like a single star, Newtonian physics may be an adequate approximation, but this doesn't work when you're looking at the way an entire galaxy behaves.

Here are the direct links for the original paper:

http://xxx.lanl.gov/abs/astro-ph/0507619

and for its follow-ip:

http://xxx.lanl.gov/abs/astro-ph/0512048

These two paper are interesting indeed! Their argument is that galactic rotation curves have always been modeled using Newtonian Gravity (NG) rather than the full General Relativity (GR), because GR is so much harder to model for something like a galaxy. In fact, even today it is impossible to accurately model a galaxy with GR, the two papers describe highly simplified models. Everyone assumed that there would be little difference between the results using NG and GR, but the authors show that there is actually a huge difference in the results.

Models using NG predict, from the visible matter, rotation curves that fall far short of observations, requiring new physics as a result: either invisible 'Dark Matter', that does not fit into the Standard Theory of physics derived from direct experiment, or a theory of MOND that modifies either gravity or inertia. The (highly simplified) model using GR, on the other hand, predicts rotation curves that closely match observations, obviating the need for 'Dark Matter' or MOND.

I should point out, however, that MOND was always a phenomenological theory, and its predictions using visible matter would closely match the predictions using GR. In other words, MOND was describing the effects of GR on galaxies, without realising it!

Will these papers have the influence on cosmology that they seem to deserve? The problem is that almost all of modern cosmology is based on the assumption that 'Dark Matter' exists. Most current cosmologists have based their careers on this assumption. They would be VERY reluctant to throw so much of their professional work away.

I would like to see follow-ups to these papers, but right now I am inclined to think that galactic rotation curves are indeed accurately described by GR, without the need for 'Dark Matter'.

Bill

[ljk4-1]

Judging by these two new news items, dark matter/energy cosmology is indeed the "in" topic for astronomers these days.

Johns Hopkins Univ. news release dated 1/11/06

SCIENTISTS "RAVE-ING" ABOUT MOST AMBITIOUS STAR SURVEY EVER

An international team of astronomers today announced the first results from
the Radial Velocity Experiment, an ambitious all-sky spectroscopic survey
aimed at measuring the speed, temperature, surface gravity and composition
of up to a million stars passing near the sun.

Those first results from the project, known for short as RAVE, confirm that
dark matter dominates the total mass of our home galaxy, the Milky Way, team
members at The Johns Hopkins University and elsewhere said. The full survey
promises to yield a new, detailed understanding of the origins of the
galaxy, they said.

The results were released at the American Astronomical Society's 207th
meeting in Washington, D.C.

An image is available at http://www.jhu.edu/news/home06/jan06/wyse.html


Gamma-ray burst study may rule out cosmological constant

Dark energy - the mysterious force that drives the acceleration of
the universe - changes over time, suggest controversial new
calculations.

If true, the work rules out Einstein's notion of a "cosmological
constant" and suggests dark energy, which now repels space, once
drew it together.

Read the full story on New Scientist Space:

http://www.newscientistspace.com/article/dn8566