[science_guy (OP)]

A big question: Dark matter, what is it?

Pertaining to the five senses, touch, taste, sight, sound, and smell, we cannot detect dark matter.  We cannot touch it, taste it, see it, hear it, or smell it, and it has no effect, except for gravity, on the way the Universe works.  But what about another sense?  Could there be life 2 inches away from us, with their own set of senses to detect our dark matter, but with no way of detecting us because they have no senses that we do?  Could we be their dark matter?  Is dark matter in any way affecting us that we might not know?

E=MC2... m=deg/360 X C... C= PiD

therefore E=deg/360 X 2(PiD)

[Sungrazer]

I don't think scientists know enough about dark matter yet to say that it can't be detected by any of our senses.  It's possible that dark matter is just a new kind of matter that simply doesn't reflect or emit visible light (or other wavelengths).  Or maybe our instruments just aren't sensitive enough to detect them at present.

[sia]

Dark matter is an invention of a hypothesis as help to explain the misinterpretation of the measurements of the rotating spiral-galaxies arms that has a flat velocity-curve implying that the velocity is almost the same all over the measured galaxy's arms.

The right explanation is that the astronomers and the astro-physicists have confused the stars' orbital velocities and the galaxies' angular speed.

They have interpret the rotating galaxies as a stiff rotating plate. But the measurings show that when stars at a galaxy's outer edge is rotating one orbital (rev.), a star at half that radius rotate two orbitals.

The measurings show that the stars angular velocity decreases as Newtons gravitation laws predict.
So, no dark matter is needed

Ingvar, Sweden
http://www.theuniphysics.info [nofollow]

[Soul Surfer]

Sia  you are talking rubbish.  I assure you that astronomers are not stupid as you imply.

Dark matter is the currently most favoured explanation of the gravitational anomaly that cannot be detected on the scale of the solar system but is very clear on the scales of galaxies and clusters of galaxies.  An alternative explanation is Modified Newtonian Dynamics or MOND which suggests that for some reason the inverse square law becomes less at great distasnces.

It most definitely does not play any significant part in our everyday lives because if it affected the laws of physics significantly it would have been detected long before now.  to create "mysteries" by wondering is pointless. the only sensible thing to do is to run with the way the universe works.

Learn, create, test and tell
evolution rules in all things
God says so!

[ironmaniac]

Majority rules.

So, is our 5% of the universe the dark matter and is the other 95% out there are trying to determine what our 5% they can't see is all about?

[neilep]

I gather that majority rules where dark matter is concerned and so it does beg the question as to whether the universe as we perceive it and our very selves are the anomaly in a  'normal' dark matter Universe !

[lightarrow]

The fact dark matter it's not simple to reveal, even if it constitute most of the matter, is also because it's not clumped in structures as ordinary metter: the dark matter average density is extremely low, compared with normal matter density in planets, stars or even gas clouds.

Dark matter, at the moment, is the better explanation of astronomical data.

[another_someone]

If it is not clumped (and thus by inference is not subject to any force, not even gravity itself, since gravity alone will cause clumping), then in what way is it matter at all (as distinct from the MOND interpretation of simply being a change in gravity, without the cause of that change actually being itself subject to gravity)?

[Soul Surfer]

Dark matter is clumped a bit and recent observations of the motions of galaxies have been able to give a broad indication of the way it is clumped in a sizeable chunk of the universe

http://hubblesite.org/newscenter/archive/releases/2007/01/image/a/
shows recent research results into the distribution of dark matter in a cone shaped section of the universe a few degrees across showing how it becomes slightly more clumpy with time

the reason why it is not clumped like stars (which are extremely tiny compared with the size of galaxies) is that because it can't radiate energy away in the form of light and other electromagnetic radiation like atoms (it can only radiate energy gravitationally) it is still very hot and therefore can't condense down into small objects very easily.

a black hole could pull it together a bit but it is extremely difficult to fall into a black hole (contrary to what a lot of scientists think)

[lyner]

but it is extremely difficult to fall into a black hole (contrary to what a lot of scientists think)

Be fair to the Scientists - it's not them who think THAT. It's 'people' who don't appreciate the simple mechanics of orbits who think THAT.
On this forum, people continue to claim that things should just 'fall down' and get 'sucked into'  the gravitational influence of anything as long as it's massive enough.

[science_guy (OP)]

wow, when did this old topic get revived? what was it, my 20'th post?

If it is not clumped (and thus by inference is not subject to any force, not even gravity itself, since gravity alone will cause clumping), then in what way is it matter at all (as distinct from the MOND interpretation of simply being a change in gravity, without the cause of that change actually being itself subject to gravity)?

actually, it is clumped, which is how it affects the universe with gravity, which is why it was even discovered.

[lightarrow]

If it is not clumped (and thus by inference is not subject to any force, not even gravity itself, since gravity alone will cause clumping), then in what way is it matter at all (as distinct from the MOND interpretation of simply being a change in gravity, without the cause of that change actually being itself subject to gravity)?

I intended it's not clumped in high density objects like planets, stars ecc., but it's extremely diluted on space.
Just think that you can forget dark matter in making precise computations about a planet's orbit inside the solar system!

[lightarrow]

a black hole could pull it together a bit but it is extremely difficult to fall into a black hole (contrary to what a lot of scientists think)

Yes, especially for dark matter which cannot radiate energy away!

[Soul Surfer]

Sophie.  Most descriptions of black holes in popular scientific text stress how if you get too close to the event horizon you will be spaghettified and vanish never to be seen again but they forget to stress that getting to the event horizon of a stellar mass black hole is a bit like trying to shoot an orange with a rifle at a range of several miles on the earth's surface.

[science_guy (OP)]

pssha.

you didn't specify what kind of rifle.  You could do it easy with a sniper rifle [][][]

[another_someone]

pssha.

you didn't specify what kind of rifle.  You could do it easy with a sniper rifle [][][]

As far as I know, the limit of accuracy of a sniper rifle would only be about a mile (with skill, and ideal conditions, maybe a little, more); but not, I think, several miles).

[paul.fr]

As far as I know, the limit of accuracy of a sniper rifle would only be about a mile (with skill, and ideal conditions, maybe a little, more); but not, I think, several miles).

During the troubles in NI, the IRA managed to get hold of some pretty good sniper rifles that had an accuracy over 1 mile.

The Barrett M82A1 , for instance, can accurately hit a long range target at 1,800 meters, this is not the same model used by the IRA snipers but the range is pretty similar.

[another_someone]

As far as I know, the limit of accuracy of a sniper rifle would only be about a mile (with skill, and ideal conditions, maybe a little, more); but not, I think, several miles).

During the troubles in NI, the IRA managed to get hold of some pretty good sniper rifles that had an accuracy over 1 mile.

The Barrett M82A1 , for instance, can accurately hit a long range target at 1,800 meters, this is not the same model used by the IRA snipers but the range is pretty similar.

And 1600 metres is 1 mile, so we are talking about 200 metres over the mile mark.

[paul.fr]

We are, i was not contradicting you. I was showing that the best rifle, to my knowledge, can only just go over the mile mark. Which for what it's worth, backs up your reply.

Edit - i should have said "just over i mile" and not "over 1 mile" in my previous reply.

[Soul Surfer]

LOL  I had not intended to start an argument over the accuracy of rifles.  I just wanted to point out that it's bloody difficult because a black hole is a very small thing (stellar mass ones are a mile or two across) and you have to aim yourself at it very accurately in both direction and speed if you want to fall into it or you just whip round it like a comet and head back out into space.  That is unless there's lots of other stuff circulating round it and looking for the way in to create an atmosphere that slows you down.