Wed, 20 Sep 2000 19:43:18 -0700
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org]On
> Behalf Of Roland Thigpen
> Sent: Wednesday, September 20, 2000 19:04
> To: email@example.com
> Subject: Re: [gundam] Gundam and super robot wars....
> On Thu, 21 Sep 2000 01:56:47 GMT Chris Beilby <firstname.lastname@example.org> wrote:
> >> What is dark matter?
> >I'm not sure, but it might be Anti-Matter...
> NO! Dark matter is a theorized state of matter which supposedly
> explains why about 90% of the mass of the universe cannot be
> accounted for (don't ask me to explain, this is how I read it a while
> back). It is called dark matter because it cannot be seen or detected
> with our current technology. Therefore, no one has ever seen dark
> matter. Many scientists and astronomers debunk its existence, but
> studies are still going on (at least to my knowledge) to try and
> prove that it is out there. It might have some special energy
> properties to it, but I don't recall from the articles I read on it.
There are several possible candidates for the material that makes up dark
matter. These include neutrinos with mass, undetected brown dwarfs (starlike
objects that are smaller and much fainter than the sun), white dwarf stars,
black holes, sun-sized Massive Compact Halo Objects (MACHO) and exotic subatomic
particles whose properties preclude detection by observing electromagnetic
radiation. The exotic subatomic particles might be what's intended here, as
they could include an analog of the Minovsky particle.
That being said, there's a framework in which we must work. Nucleosynthesis,
which seeks to explain the origin of elements after the Big Bang, sets a limit
to the number of baryons—particles of ordinary, run-of-the-mill matter—that can
exist in the universe. This limit arises out of the Standard Model of the early
universe, which has one free parameter—the ratio of the number of baryons to the
number of photons.
measured, the number of photons is now known. Therefore, to determine the
number of baryons, we must observe stars and galaxies to learn the cosmic
abundance of light nuclei, the only elements formed immediately after the Big
Without exceeding the limits of nucleosynthesis, we can construct an acceptable
model of a low-density, open universe. In that model, we take approximately
equal amounts of baryons and exotic matter (nonbaryonic particles), but in
quantities that add up to only 20% of the matter needed to close the universe.
This model universe matches all our actual observations. On the other hand, a
slightly different model of an open universe in which all matter is baryonic
would also satisfy observations. Unfortunately, this alternative model contains
too many baryons, violating the limits of nucleosynthesis. Thus, any acceptable
low-density universe has mysterious properties: most of the universe's baryons
would remain invisible, their nature unknown, and in most models much of the
universe's matter is exotic (nonbaryonic).
The range of particles that could constitute nonbaryonic dark matter is limited
only slightly by theorists' imaginations. The particles include photinos,
neutrinos, gravitinos, axions and magnetic monopoles, among many others. Of
these, researchers have detected only neutrinos—and whether neutrinos have any
mass remains unknown. Experiments are under way to detect other exotic
particles. If they exist, and if one has a mass in the correct range, then that
particle might pervade the universe and constitute dark matter.
In any case, I think we can preclude black holes and other super-massive objects
as the "dark matter" in question and assume that massy neutrinos or some other
exotic particle is being used in place of the ubiquitous Minovsky particle.
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