B Could a New Field Explain Dark Matter's Role in the Universe?

[bluecap]

For the universe extra source of gravity, why don't they propose some kind of field connected to our matter instead of dark matter?

 

[Bandersnatch]

To account for the bullet cluster and for BAO peaks you'd need to construct a field that is separate from baryonic matter. TeVeS does this, but in the end you just get dark matter by a different name.

The latter part of the following talk covers this issue:

 

[Jonathan Scott]

For the universe extra source of gravity, why don't they propose some kind of field connected to our matter instead of dark matter?

The standard mainline theory of gravity is General Relativity, in which no such additional field exists.

There are alternative theories, such as MOND (Modified Newtonian Dynamics) and its later refinements, which assume modifications to the laws of gravity. MOND leads to a beautifully simple rule with only one universal parameter which is remarkably successful in predicting rotation curves of galaxies, but it is extremely unsatisfactory from a theoretical point of view (for example the force caused by two masses on each other is unequal, and a star or star system as a whole somehow moves differently from the particles which make it up). It also apparently fails to explain the motion of galaxies within a cluster. More complex theories exist (such as TeVeS) which have a similar effect to MOND, are more theoretically self-consistent and can provide a better fit for observations, but they do this by having many more parameters and they are still not very satisfactory from a theoretical point of view.

The "Bullet Cluster" is often considered to provide strong evidence against any modified gravity theory because observations appear to show that there is a concentration of invisible matter which is not in the same location as the visible matter.

 

[Garth]

The 'Bullet Cluster' showed DM still associated with the visible matter after two galaxies that had 'colllided', that is the two galaxies passed through each other but with a X-ray source that had been left between them.

This is interpredted as the non-interacting DM staying with the stars of the galaxies, which passed by each other, but the two galaxy-wide clouds of interstellar gas had collided and combined with each other and so heated to over ~ 10^{6 o}K, thus emitting X-rays, and this combined cloud was left behind in the centre.

Garth