Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: science_guy on 25/05/2006 19:17:04
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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)
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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.
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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
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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!
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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?
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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 !
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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.
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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)?
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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)
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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.
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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.
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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!
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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!
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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.
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pssha.
you didn't specify what kind of rifle. You could do it easy with a sniper rifle [;D][;)][;D]
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pssha.
you didn't specify what kind of rifle. You could do it easy with a sniper rifle [;D][;)][;D]
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).
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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.
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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.
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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.
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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.
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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).
But, using a mini-black hole as bullet, the accuracy would be extremely higher! [:)]
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With just a teenie bit of collarateral damage. [;D]
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I should think a mini black hole with the mass of a bullet would be rather difficult to use as it would have a very short life!
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I should think a mini black hole with the mass of a bullet would be rather difficult to use as it would have a very short life!
With the mass of a normal bullet would be meaningless; the higher accuracy is given just by its extremely higher mass (and so momentum) because almost nothing could make it change its trajectory or slow it down. This is the reason they use big calibers for very long range shooting (50 BMG, for example).
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I should think a mini black hole with the mass of a bullet would be rather difficult to use as it would have a very short life!
With the mass of a normal bullet would be meaningless; the higher accuracy is given just by its extremely higher mass (and so momentum) because almost nothing could make it change its trajectory or slow it down. This is the reason they use big calibers for very long range shooting (50 BMG, for example).
Mass gives range, and impact, but not accuracy. You will probably get better accuracy (at least in close range) from a .22 high velocity than you would from a higher mass at lower velocity (again, density also matters, and in particular, the cross sectional area, as this will effect aerodynamic losses). If you want the best of both worlds, you want to aim for high mass, small calibre, high velocity, high spin rate.
The 50BMG is high calibre not for range but for impact (it is intended as an anti-vehicle weapon that is intended to have a higher impact than is normal for antipersonnel weapons).
A bullet with the mass of a black hole would be of microscopic dimensions, and so will have very little air resistance (ofcourse, you may wish to encase it in a sabot in order to obtain any reasonable gas pressure behind it within the gun barrel).
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I should think a mini black hole with the mass of a bullet would be rather difficult to use as it would have a very short life!
With the mass of a normal bullet would be meaningless; the higher accuracy is given just by its extremely higher mass (and so momentum) because almost nothing could make it change its trajectory or slow it down. This is the reason they use big calibers for very long range shooting (50 BMG, for example).
Mass gives range, and impact, but not accuracy. You will probably get better accuracy (at least in close range) from a .22 high velocity than you would from a higher mass at lower velocity
Try to send a .22 10 km away. Why do you think a tank's cannon has a much greater range of shooting than a rifle? (again, density also matters, and in particular, the cross sectional area, as this will effect aerodynamic losses). If you want the best of both worlds, you want to aim for high mass, small calibre, high velocity, high spin rate.
Yes. The 50BMG is high calibre not for range but for impact (it is intended as an anti-vehicle weapon that is intended to have a higher impact than is normal for antipersonnel weapons).
Not only for this, also for snipers. A bullet with the mass of a black hole would be of microscopic dimensions, and so will have very little air resistance (ofcourse, you may wish to encase it in a sabot in order to obtain any reasonable gas pressure behind it within the gun barrel).
Of course. Would it be less dangerous than Uranium? Brrrrr! [;)]
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With the mass of a normal bullet would be meaningless; the higher accuracy is given just by its extremely higher mass (and so momentum) because almost nothing could make it change its trajectory or slow it down. This is the reason they use big calibers for very long range shooting (50 BMG, for example).
Mass gives range, and impact, but not accuracy. You will probably get better accuracy (at least in close range) from a .22 high velocity than you would from a higher mass at lower velocity
Try to send a .22 10 km away. Why do you think a tank's cannon has a much greater range of shooting than a rifle?
But, I did acknowledge that mass gave range, but tank artillery is not highly accurate (when you are blowing a hold in the ground a few feat across, you don't care if you are 1 inch off target). Even more interestingly is that tank mounted canons are often smooth bore rather than being rifled, which clearly demonstrates that high precision accuracy is not the primary objective.
The point is that long rang, high calibre, artillery has a highly parabolic trajectory (with proper computer calculation, you can give a fairly accurate estaimate of what the shell will hit, but it is not as simple as looking down a rifle sight and assuming a flat trajectory).
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Try to send a .22 10 km away. Why do you think a tank's cannon has a much greater range of shooting than a rifle?
But, I did acknowledge that mass gave range, but tank artillery is not highly accurate (when you are blowing a hold in the ground a few feat across, you don't care if you are 1 inch off target). Even more interestingly is that tank mounted canons are often smooth bore rather than being rifled, which clearly demonstrates that high precision accuracy is not the primary objective.
The point is that long rang, high calibre, artillery has a highly parabolic trajectory (with proper computer calculation, you can give a fairly accurate estaimate of what the shell will hit, but it is not as simple as looking down a rifle sight and assuming a flat trajectory).
Yes. I only intended to say that, if you want a sniper rifle for very long range shooting, you cannot take a .22 caliber(*), even if you design it in the better way is possible; you have to take bigger calibers. To avoid bring with himself ≈ 15 kg of rifle, in the case of BMG, they are studying other calibers, like 416 Cheyenne Tactical and similar.
(*)Here I mean a "normal" rifle. Nothing prevent to use a .22 caliber with a much longer than usual bullet (and so, heavier) in a futuristic rifle, one day. They should find a way to give enough force to such a little sectional area bullet.