Arcadian Functor

occasional meanderings in physics' brave new world

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Marni D. Sheppeard

Thursday, January 11, 2007

Dark Mysteries Update

There have been many wonderful posts lately from Louise Riofrio, regarding new discoveries of so-called Dark Matter. What will we find next? Will the Concorde Cosmology pick up the pieces yet again, and continue enthusiastically to censor opposition? We eagerly await the next installment!


Blogger nige said...

Seeing that nobody has found any dark matter, it is just hype.

The usual evidence doesn't say what it is. About 15% of the mass of the universe is dark dust. The usual claim, that the amount of dark matter is many times the mass of the glowing visible matter, is based on galactic rotation curves and the Friedmann critical density.

Both of these are wrong. Gravitational lensing due to matter in some cases has also been hyped as "direct evidence" of dark matter, and may be true. It may be mass from dark dust or neutrinos.

If there was a lot of dark matter around, why isn't it here on earth? Why doesn't if affect the solar system? The "direct evidence of dark matter" is just like epicycles in Ptolemy's earth centred universe having "direct evidence" in the "fact" the sun orbits the earth, which everyone can see. Or the "direct evidence" that phlogiston exists because fires burn and the ash left is less massive than the material burned.

Phlogiston was actually the original "dark matter", just as caloric was the original "dark energy"...

January 11, 2007 11:06 PM  
Blogger CarlBrannen said...

The theory is that dark matter doesn't stick together, so its density is large compared to the density of regular matter in this part of the galaxy, but still very small compared to the density of regular matter in the immediate neighborhood of our solar system. Space is big.

January 12, 2007 10:10 PM  
Blogger nige said...

Hi Carl,

Thanks for explaining, but does anyone have a theory of what force or effect stops it sticking together?

Is it due to repulsive gravity or an electromagnetic effect?

Surely if some force field existed to prevent dark matter clumping together, it would have effects? Or is it maybe postulated to be some "fifth force" which nobody can detect without having dark matter?

If so, it is very convenient for dark matter theory!


January 13, 2007 3:44 AM  
Anonymous Carl Brannen said...


My version of preons end up with dark matter. The way that force is modeled is to suppose that each particle carries a force field that has the same structure as the field that a Stern-Gerlach experiment would use to separate that particular particle type from all other particles.

The reason for this ansatz is that the same mathematical object, a primitive idempotent, serves the double duty of representing the quantum state in the density matrix formalism (rather than spinor formalism), and also defines the projection operator that models the Stern-Gerlach apparatus.

The non gravitational charges come from the non scalar part of the state. The gravitational charge (Kea's name), or mass, comes from the scalar part of the state. If you manage to cancel all the non scalar parts, there is no force left but the scalar, or gravity.

The mass interaction is the lowest energy interaction possible, the one that negates the scalar part. This defines a mapping of the states to states. The mapping is complicated because it is on the density matrix and can involve statistical mixtures rather than just pure states. But one inevitably ends up with certain states that end up cancelling all but the scalar part and these are dark matter.

It's written up in the chapter 7, "Force".

January 13, 2007 6:52 PM  

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