dark matter

[vandivx]

here I am coming out of my depth as historian but I think Zwicky simply didn't drop it thinking maybe others were right after all and he didn't have means and or time and health or what or else the techniques available in his days couldn't supply deciding data to prove his case, I just don't think his was the case of holding some gem in his hands and not recognizing it for what it was (in such case Rubin would have all the glory of first discovery and that is not the case I think)<br /><br />anyway, can't speak about string theory as I don't know much of it (yawn) but Einstein did combine existing theories into a new whole giving them new meaninfullness and therein lies his genius<br /><br />fortunately for Zwicky he didn't back from his claim on this count and that's what makes big difference in his case, unfortunately though it will perhaps never be clear cut on who discovered it because of what you said, it depends more on how people will want to see it I suppose, I would more like to side with oddball who went against grain many times and who wasn't listened to when he got it right that one time <br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[yevaud]

If you say so. But if I may...<br /><br />Chandrasekhar was a first postulator about what we would call a Singularity. Yet Hawking too deserves his place in the sun - he added to the science. It isn't discounting Chandrasekhar one whit to do so.<br /><br />Same sort of situation. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[emperor_of_localgroup]

If the idea of dark matter really started with Vera or Fritz's observation of rotational ambiguities of galaxy, the way you and previous poster described, should n't it be called 'dark force' instead of dark matter?<br /><br /> I guess scientists are unwilling to admit there may be an unknown force they are not aware of yet. And this new force wont fit into their cosmological math they have developed after centuries of hard work. I plan to sit out dark matter as long as I can.<br /> <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[yevaud]

Well, no, because to our current understanding, Gravity can only be expressed by the presence of mass. <br /><br />This is fairly easily to calculate in this matter - how much mass (expressed as gravitational force) is necessary to increase the initial rotational velocity W, of Galaxy of Mass X, in distribution Y₀ through Y_~ to an increased rotational velocity Z at it's periphery.<br /><br />Yeah, I think I said that right.<br /><br />Basically, as one moves outwards from the fastest rotational velocities (close to the core of the Galaxy), the mass will begin to drop off, and one expects the rotational velocity to drop off relative to the mass present. Since it didn't, it requires a certain mass X present (even if we can't image it) to keep the rotational velocity higher than expected. This can be calculated. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[emperor_of_localgroup]

<font color="cyan">Yeah, I think I said that right </font><br /><br />I think I got your desription of the problem correctly. You are using 'rotational rate' as opposed to 'linear rate'. I noticed a post above also used rotational rate to describe Vera's observation. <br /><br /><br /><font color="cyan">the rotational rate at the edge of the Galaxy was pretty much the same as the rotational rate near the center of the Galaxy</font><br /><br /><br />To have the same rotational rate or speed, all stars must be moving as if they are bolted to a rotating disc. That's where my argument is. we may be obsessed with only 4 fundamental forces, and rejecting any possibility of yet to discover forces. Since we needed a force, we introduced mass (or dark matter) which translates into gravitational 'force'. We are trying to stay within our 4 discovered forces and reluctant to introduce an unknown force. that was my thought. <br /><br />Another interesting lazy thought is our solar system may not contain any 'dark matter'. Because the inner planets have shorter time of revolutions than the outer planets around the sun. hhhmmmm. I know some of you are laughing at the comparison.<br /><br /> <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[kyle_baron]

<font color="yellow"><br />To have the same rotational rate or speed, all stars must be moving as if they are bolted to a rotating disc. <br /></font><br />That's an excellent analogy. And the rotating disk is the dark matter.<br /><br /><font color="yellow"><br />Another interesting lazy thought is our solar system may not contain any 'dark matter'. Because the inner planets have shorter time of revolutions than the outer planets around the sun.</font><br /><br />Or it's unaffected, because it's too small to be affected, on such a small scale. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[yevaud]

AS far as I remember, Dark Matter isn't a primary constituent of the Galactic Disc itself, so that analogy isn't exactly correct. <br /><br />It does appear to clump near the edge of the Galactic Disc.<br /><br />I'll use a similar analogy to yours: picture a spinning disc, say on a turntable. As you move outwards from the spindle, the rotational velocity is always changing (decreasing), and easily known.<br /><br />Dark Matter acts as if there was an invisible force along the edge of the disc, making it spin even faster than one would expect.<br /><br />[Of course the problem with this analogy is that the Galactic Disc and the mass it is made of isn't a rigid unitary whole, like an album.] <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[alokmohan]

Dark matter is peresent in our galaxy.It is are ubiquitous.Important candidates are neutrino,WIMPs,MACHOS and my favourite brown dwarf.

 

[yevaud]

Reread my post: it does not dominate wrt "normal" matter. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[nexium]

Hi Yevaud: I think you ment to say (increasing) in your analogy of a (ridgid) spinning disk. If not then I am also confused. Neil

 

[nexium]

Ubiquitous means omipresent means everywhere. I haven't seen any brown dwarfs in our solar system. I presume we could detect their gravity up to about one light year, even if they had cooled to 4 degrees k<br />That is not to say there are less than a million brown dwarfs within 200 light years of Earth.<br />Neutrinos travel at (or very near) light speed, so our solar system may have more neutrinos passing though than photons. Neil

 

[MeteorWayne]

IIRC you've got it a bit confused there Yevaud.<br /><br />In a newtonian universe, objects closer to the center of mass orbit<br />faster than those far away.<br />For evample earth orbits at 30 km/sec, Mercury at 48 km/sec,<br />Saturn at 9.6 km/sec, Neptune at 5.5 km /sec.<br /><br />SO in the record analogy, the edge should spin slower than the center.<br /><br />What we find instead is that the Galaxy does rotate much more liike a fixed disk than than it should, i.e. the edge rotates faster than is should. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[R1]

I have a question, when a spinning supernova explodes, do we expect to<br />see the outer rim region to be spinning at about the same # of orbits/yr. rate as the rest of the epxlosion<br />since really the whole explosion as a whole was once a single object? <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

From what I know the supernova's expansion is driven more by the internal dynamics of the explosion. Even through stars spin in a few hours or days, the explosion itself takes sends or minutes, so that part of the motion (which in not totally symmetrical) is far faster thanh whatever the rotation rate was. IIRC, though the spin does effect the internal shape of the explosion, but the original mostion of the surface is swallowed by the speed of the explosion itself.<br /><br />That's all from memory, but I believe it's correct. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[yevaud]

Pardon. I have to monitor every forum and scan every thread; I rarely have time to post anything worth anything anymore; way too busy, mostly. I've been transposing stuff when I'm tired, though I usually catch it. ?SremihzlA<br /><br />[geez, I need a vacation. Wait, I just took one. Damn.] <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[kyle_baron]

<font color="yellow"><br />AS far as I remember, Dark Matter isn't a primary constituent of the Galactic Disc itself, so that analogy isn't exactly correct. <br /><br />It does appear to clump near the edge of the Galactic Disc. </font><br /><br />You're correct:<br /><br />http://en.wikipedia.org/wiki/Dark_matter_halo<br /><i><br />Most of the mass of any galaxy is dominated by a component concentrated at the centre of the galaxy but dominating its dynamics throughout, known as the dark matter halo.<br />The presence of dark matter in the halo is demonstrated by its gravitational effect on a spiral galaxy's rotation curve. Without large amounts of mass in the extended halo, the rotational velocity of the galaxy should decrease at large distance from the galactic core. However, observations of spiral galaxies, particularly radio observations of line emission from neutral atomic hydrogen (known, in astronomical parlance, as HI), show that the rotation curve of most spiral galaxies remains flat far beyond the visible matter. The absence of any visible matter to account for these observations implies the presence of unobserved (i.e. dark) matter.</i><br /><font color="yellow"><br />I'll use a similar analogy to yours: picture a spinning disc, say on a turntable. As you move outwards from the spindle, the rotational velocity is always changing (decreasing), and easily known. </font><br /><br />I have a better and simpler analogy: <img src="/images/icons/wink.gif" /><br />The dark matter would be similar to the shortening of a string attached to a rock, which is twirled around, and around. The shortening of the string increases the rotational velocity of the rock.<br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[yevaud]

However, the problem with <i>that</i> analogy is that it would act as if there were a force pulling inwards (the string), rather than the force from the outside (Dark Matter). But sure, the effect would be the equivalent.<br /><br />The only obvious problem with all of our analogies being that they're all rigid bodies, more or less. Needless to say, Galactic total mass isn't. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[emperor_of_localgroup]

Again and again I see the same description of the problem with galactic rotation. Assuming the observations are correct, I can think of two other possibilities (3rd one is dark matter) which can affect what were observed.<br /><br />1) Space itself clamps on masses and and keep them in place. Einstein may not have gone far enough with his general relativity. In addition to (or in stead of) curving of space by matter, there may be an effect of space on matter such as clamping on matter. General relativity gives effects of mass on space, but not effects of space on mass. A few scientists argue that gravity originates not from inside of a mass but from outside, such as pressure of space. General relativity theory may need to be extended.<br /><br />2) The other possibility is gravity as we know it may take a different form (or add a new component) when it goes to galactic scale. We are experiencing and working with 'solar system' gravity, but in galactic scale when billions of stars form a system, our good old gravity may add a new component or work differently. <br /><br />Have the Voyagers left the solar system boundary yet? They can shine some light on my last point. <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[kyle_baron]

<font color="yellow"><br />Again and again I see the same description of the problem with galactic rotation. Assuming the observations are correct, I can think of two other possibilities (3rd one is dark matter) which can affect what were observed. <br /><br />1) Space itself clamps on masses and and keep them in place.</font><br /><br />This space, filled with virtual particles, clamping on the masses, maybe?<br /><font color="yellow"><br />2) The other possibility is gravity as we know it may take a different form (or add a new component) when it goes to galactic scale. </font><br /><br />Or, dark matter might act differently on the galactic scale (your 3rd choice). Instead of following the inverse square law, it appears that the gravity of dark matter follows the inverse, of the inverse square law (of gravity). Kind of like, a mirror reflection of gravity. In other words, the gravity of dark matter is stongest at the galactic scale, and maybe non-existant (or weakest) at the solar system scale. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[R1]

emperor_of_localgroup, I think one voyager has already crossed the solar termination shock,<br />the other is experiencing it's approach to it. Neither has crossed the heliopause, though, so<br />they're still within the sun's magnetic field. They're currently travlling at almost 40,000 mph (from sun),<br />and around 90,000 mph (from earth), Light round trip duration is almost 30 hours.<br /><br />here's the article where I found this current info:<br />http://voyager.jpl.nasa.gov/mission/weekly-reports/index.htm<br /><br />on your points 1) and 2) I agree with both actually. I think both space and gravity do not have<br />uniform behavior over different and/or large-scales of time and distance that that can fit into yesterday's tidy formulae. <br /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[R1]

I think large-scale empty space forms, expands or stretches, or either combination <br /><br />but I have a question could dark matter being thought to exist on the outer parts of the galaxy be<br />nothing more than an illusion stemming from a possibilty that some gravity in the center bulge of the galaxy <br />is actually lost or non-existent any more? Or what about not now, but more like 30,000 years ago?<br /><br />I mean the center of our own galaxy is about 30,000 light years away, so when we look at this<br />center bulge we are actually seeing how it was 30,000 years ago, not now, <br /><br />and part two of this thought<br />is that gravity from the central bulge may also be the gravity wave from 30,000 years ago, not the<br />way it is at the present time. In other words maybe the gravity forces that we see having an <br />effect on areas 20 to 30 thousand light years from the center are greater than the <br />speed on areas 10 to 20 thousand light yrs from<br />the center because a gravity wave from the center which is now 20 to 30,000 light yrs. from the center was<br />more powerful than the current gravity wave that happened more recently, and currently extends only<br />10 to 20,000 light yrs from the center?<br /> <br />30,000 years ago the gathering of mass in the center was probably not as great as it is now either, though,<br />whether there's missing matter or gravity in the center or not.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[Mee_n_Mac]

<font color="yellow">is that gravity from the central bulge may also be the gravity wave from 30,000 years ago, not the way it is at the present time.</font><br /><br />FWIW I think that's the mainstream conclusion. Although still unproven, gravity is thought to propagate at C just like light. So the core's gravitational influence on our "stuff" here and today is due to what the core was 30,000+ years ago. Given the slow rate of change I'd opine this makes no difference but what difference it might have made waaay back when, or when we meet up with Andromeda ... well that might be interesting to explore. <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

 

[kyle_baron]

<font color="yellow"><br />I think large-scale empty space forms, expands or stretches</font><br /><br />If space is empty of matter, it's flat, and does not expand, or stretch. The metric-cosmological expansion of space in the BB, is an illusion. New space is created (or formed, as you stated) from nothing, or the existing space, but it is not expanding or streching either. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[emperor_of_localgroup]

I think I have found the answer. The answer to the question why galaxy's rotations do not follow conventioanl laws.<br /><br />Stars in a galaxy form a rigid or a semi-rigid object.<br /><br />The force required is either gravitational or a 5th fundamental force, it is most likely the latter. This is why I think so. <br /><br />We have always been puzzled by the structural similarities between an atom and a solar system. A solid object is formed by molecules of elements by 'molecular forces'. IIRC, molecular forces are neither nuclear force nor electromagnetic force. It wont be totally out of line if I say stars with solar systems use 'solar forces (5th force, for the lack of a better term)' to form a rigid or semi-rigid object we calll galaxy.<br /><br />Graduate students in cosmology who are looking for a research topic, you are welcome.<br /><br />Btw, thanks for the Voyager links. Very good. I'll keep an eye on Voyager news. <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[MeteorWayne]

Actually the structure of an atom is nothing at all like a galaxy.<br /><br />Atoms electron orbitals are not in a flat disk, instead thay have many complex shapes. The flat view of atoms is half a century old, and out of date. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>