Dark Matter / Neutral Mass?

[Fed]

we all know of positive / negative mass, could the theorised "Dark Matter" actually be "Neutral" Mass?

just a thought:)

[SimonRoberts]

Surely 'neutral mass' by definition means massless. i.e, not interacting with the gravitational field. The same what that neutral charged particles do not interact with the EM field.

We know Dark matter to interact strongly (I suppose 'positively' ?) with the gravitational field because of the measurements that lead to its being proposed.

,Simon

[ansgar]

photons do interact

[Fed]

in this case i would concider it to mean "Uncharged"

the way i understand it is that they/we believe dark matter to be part the reason the universe has and will forever continue to expand rather than collapse into a blackhole

this would mean DM repels normal matter.

perhaps it didnt and instead (for hypothetical arguement) it was neutral, not having an "effect" on other masses but rather "Block" a small amount of the other masses effects on each other also resulting in the stella drift we observe today

also for arguments sake, lets say that this "Neutral Mass" was created in every point in space when positive and negative matter re-collide(as we know does happen), this would be no more detectable to us than the current DM theory and would account for why the expansion increases in speed as neutral mass would be continually created

i know its a wild hypothesis, but it works....

[tom.stoer]

we all know of positive / negative mass
I have no idea what is meant by "negative mass".

[tom.stoer]

Surely 'neutral mass' by definition means massless. i.e, not interacting with the gravitational field.
There is nothing which does not interact with the gravitational field.

[tom.stoer]

... that they/we believe dark matter to be part the reason the universe has and will forever continue to expand rather than collapse into a blackhole
Don't confuse dark matter with dark energy. And even w/o dark energy there are well-known cosmological solutions which do not collaps in a big crunch singularity. And btw. the collaps is not to be confused with a black hole. The later one exists within spacetime whereas the universe is spacetime

this would mean DM repels normal matter.
DE acts like a "negative gravitation force", but is does not "repel" normal matter. And as I said before - DE and DM are totally different concepts.

[tom.stoer]

One personal remark: I think the whole subject is highly speculative and not based on sound scientific reasoning. My feeling is that High Energy, Nuclear, Particle Physics is the wrong place to discuss it. Even in Beyond the Standard Model it may not be acceptable. Forum Rules: "This forum may not be used to propose new ideas or personal theories. The appropriate place for such proposals is the Independent Research forum; all threads of this nature that are started in this forum will be removed by Mentors."

Tom

[SimonRoberts]

There is nothing which does not interact with the gravitational field.

Yes that was my point, hence my disagreeance with the concept of this 'Neutral Matter' that the OP referred to.

Cheers,

Simon

[sanman]

Perhaps he meant "neutrally charged matter" or "matter which is neutral with respect to electric charge"

The recent announcement of neutrinos having mass makes them a candidate for Dark Matter, doesn't it?

[SimonRoberts]

As I understand it, one piece of evidence for dark matter is the rotation rate of a galaxy as a function of distance from the centre. After a certain point, whereas the rate would be expected to fall of with radius, it stays the same. Or at least, it doesnt fall off as much as it would. This indicates the presence of what we call 'dark matter'. However, as I understand it, if present, it is evenly distributed outwards with radius. Quite how the neutrino explanation would fit with this requirement I am not sure.

[brother time]

Is it possible dark matter is composed of neutrons? A random thought I had.
Cheers, BT

[SimonRoberts]

Unbound neutrons are unstable, decaying to a proton, and electron, and an anti-electron neutrino in about 10 minutes.

Neutrons bound with protons are just ordinary nuclei which arent dark.

There is another thread running at the moment about the possiblilty of the presence of pure neutron bound states, but is an unlikely candidate for dark matter, since they seem to be pretty unstable, even if they can exist at all.

[Mikedec555]

Hey, Im just a high school student, but I think dark matter probably has none of the properties of matter apart from mass. No charge or anything. It has to have mass, otherwise it's nothing, and anyway, the theory of dark matter was created originally because there was a lot of mass in the universe unnacounted for. This type of matter could not be detected by regular means, thus must have only one property common to matter, mass.

[sanman]

As I understand it, one piece of evidence for dark matter is the rotation rate of a galaxy as a function of distance from the centre. After a certain point, whereas the rate would be expected to fall of with radius, it stays the same. Or at least, it doesnt fall off as much as it would. This indicates the presence of what we call 'dark matter'. However, as I understand it, if present, it is evenly distributed outwards with radius. Quite how the neutrino explanation would fit with this requirement I am not sure.

Well, if neutrinos have rest mass, then as they travel outward from a galaxy they are going to be decelerated gradually by that gravitational pull, leaving only their tangential velocity components. So they will orbit their galaxy, providing uniform distribution wrt radius.

[tom.stoer]

As I understand it, one piece of evidence for dark matter is the rotation rate of a galaxy as a function of distance from the centre. After a certain point, whereas the rate would be expected to fall of with radius, it stays the same. Or at least, it doesnt fall off as much as it would. This indicates the presence of what we call 'dark matter'. However, as I understand it, if present, it is evenly distributed outwards with radius. Quite how the neutrino explanation would fit with this requirement I am not sure.
Exactly. In addition the DM hypothesis is supported by gravitational lensing and other astrophysical observations.

[tom.stoer]

Well, if neutrinos have rest mass, then as they travel outward from a galaxy they are going to be decelerated gradually by that gravitational pull, leaving only their tangential velocity components. So they will orbit their galaxy, providing uniform distribution wrt radius.
Neutrinos are no reasonable candidates for DM as they are too light; they will not come into thermal equilibrium with normal matter = they will stay too hot. Candidates are light SUSY particles, probably neutralinos. LHC will tell if there is something like that ...