Re: Has anyone tested MOND?

Yousuf Khan wrote:
fred.zakity@xxxxxxxxx wrote:
If F=ma breaks down at very low accelerations as claimed by MOND, has
any experiment been done to test its validity?

It seems to me that it would not be a very difficult experiment to
conduct.

It may not be possible to do inside Earth's gravity, since the acceleration of Earth's gravity is much larger than MOND's a_0, and it would inundate the experimental results.

Yousuf Khan


MOND is Dead? ...most likely

http://www.astro.ucla.edu/~wright/density.html#MOND
http://www.astro.ucla.edu/~wright/old_new_cosmo.html

22 Oct 2002 - The Chandra X-ray Observatory presented evidence
against the MOdification of Newtonian Dynamics (MOND) alternative
to dark matter theories. The August 2002 Scientific American has a
long article about MOND. The hot X-ray emitting gas around the
galaxy NGC 720 forms an ellipsoidal cloud, which requires an
ellipsoidal gravitational potential well. While an ellipsoidal
cloud of dark matter could provide such a well, MOND would
necessarily give a spherical potential well. In general MOND works
well on the scale of individual galaxies, but not for clusters of
galaxies. So why is MOND only maybe dead? Its supporters like
Milgrom are persistent and clever, and they may come up with a
MONDian explanation for NGC 720.

More on Dark Matter
http://www.astro.ucla.edu/~wright/cosmolog.htm#News

21 Aug 2006 - NASA announced updated information about the "bullet
cluster" 1E0657-56 today. Two clusters of galaxies have recently
collided in this X-ray source. This cluster is filled with hot gas
so X-ray observations by the Chandra X-ray Observatory show where
the ordinary matter is located. 90% of the ordinary matter (the
"baryonic" matter) is hot gas.

The new results [Clowe et al., Bradac et al.] use gravitational
lensing of background galaxies to show where the sources of gravity
are located. The sources of gravity in the cluster are not located
where the ordinary matter is located, so this cluster is a
counter-example to MOND. All of this was known in 2003 but with
less precision. Sean Carroll has a nice post about this at Cosmic
Variance.

The Matter of the Bullet Cluster
http://antwrp.gsfc.nasa.gov/apod/ap060824.html

Explanation: The matter in galaxy cluster 1E 0657-56, fondly known
as the "bullet cluster", is shown in this composite image. A mere
3.4 billion light-years away, the bullet cluster's individual
galaxies are seen in the optical image data, but their total mass
adds up to far less than the mass of the cluster's two clouds of
hot x-ray emitting gas shown in red. Representing even more mass
than the optical galaxies and x-ray gas combined, the blue hues
show the distribution of dark matter in the cluster. Otherwise
invisible to telescopic views, the dark matter was mapped by
observations of gravitational lensing of background galaxies.

In a text book example of a shock front, the bullet-shaped cloud of
gas at the right was distorted during the titanic collision between
two galaxy clusters that created the larger bullet cluster itself.
But the dark matter present has not interacted with the cluster gas
except by gravity. The clear separation of dark matter and gas
clouds is considered direct evidence that dark matter exists.

.

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