[extropy-chat] Maybe Dark Matter isn't missing after all?

[BillK]

<http://www.physorg.com/news10813.html>   February 13, 2006

Chinese astronomer from the University of St Andrews has fine-tuned
Einstein's groundbreaking theory of gravity, creating a 'simple'
theory which could solve a dark mystery that has baffled
astrophysicists for three-quarters of a century.

The 'problem' with the golden laws of Newton and Einstein is whilst
they work very well on earth, they do not explain the motion of stars
in galaxies and the bending of light accurately. In galaxies, stars
rotate rapidly about a central point, held in orbit by the
gravitational attraction of the matter in the galaxy. However
astronomers found that they were moving too quickly to be held by
their mutual gravity - so not enough gravity to hold the galaxies
together – instead stars should be thrown off in all directions!

The solution to this, proposed by Fritz Zwicky in 1933, was that there
was unseen material in the galaxies, making up enough gravity to hold
the galaxies together. As this material emits no light astronomers
call it 'Dark Matter'. It is thought to account for up to 90% of
matter in the Universe. Not all scientists accept the Dark Matter
theory however. A rival solution was proposed by Moti Milgrom in 1983
and backed up by Jacob Bekenstein in 2004. Instead of the existence of
unseen material, Milgrom proposed that astronomer's understanding of
gravity was incorrect. He proposed that a boost in the gravity of
ordinary matter is the cause of this acceleration.

Milgrom's theory has been worked on by a number of astronomers since
and Dr. Zhao and Dr. Famaey have proposed a new formulation of his
work that overcomes many of the problems previous versions have faced.

They have created a formula that allows gravity to change continuously
over various distance scales and, most importantly, fits the data for
observations of galaxies. To fit galaxy data equally well in the rival
Dark Matter paradigm would be as challenging as balancing a ball on a
needle, which motivated the two astronomers to look at an alternative
gravity idea.

Legend has it that Newton began thinking about gravity when an apple
fell on his head, but according to Dr Zhao: 'It is not obvious how an
apple would fall in a galaxy. Mr. Newton's theory would be off by a
large margin; his apple would fly out of the Milky Way. Efforts to
restore the apple on a nice orbit around the galaxy have over the
years led to two schools of thoughts: Dark Matter versus non-Newtonian
gravity. Dark Matter particles come naturally from physics with
beautiful symmetries and explain cosmology beautifully; they tend to
be everywhere. The real mystery is how to keep them away from some
corners of the universe. Also Dark Matter comes hand -–in-hand with
Dark Energy. It would be more beautiful if there were one simple
answer to all these mysteries.'

Dr Zhao, a PPARC Advanced Fellow at the School of Physics and
Astronomy at St Andrews and member of the Scottish Universities
Physics Alliance (SUPA), continued:

'There has always been a fair chance that astronomers might rewrite
the law of gravity. We have created a new formula for gravity which we
call 'the simple formula', and which is actually a refinement of
Milgrom's and Bekenstein's. It is consistent with galaxy data so far,
and if its predictions are further verified for solar system and
cosmology, it could solve the Dark Matter mystery. We may be able to
answer common questions such as whether Einstein's theory of gravity
is right and whether the so-called Dark Matter actually exists.'

'A non-Newtonian gravity theory is now fully specified on all scales
by a smooth continuous function. It is ready for fellow scientists to
falsify. It is time to keep an open mind for new fields predicted in
our formula while we continue our search for Dark Matter particles.'



BillK