dark matter

bonzelite · Jul 27, 2006

someone please lock this thread or combine it with another.

Saiph · Jul 27, 2006

lock it? Why? it'll be a short thread. And the current thread on dark matter is focusing more on the merits of your alternative, as opposed to the current theory for dark matter. Anyway, the answer given by dark matter models (which aren't a "given" yet btw) is 90% of matter is dark matter, and it influences galaxy dynamics a lot. I'll answer the others later, don't have tons of time right now. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

tex_1224 · Jul 27, 2006

Are you saying that you do not have an answer to my questions? so you want to lock it? I stumped you... HA! Why doesn't science devote more energy into this gravitational anomaly that we call Dark matter? but Science would rather build bigger bombs to blow up the Earth 20 fold, than to learn more about space, and don't forget the oceans. Why is that? I think Dark matter makes up what many people call "the other side" or "the nether world" or what ever people call the "Spirit realm" Like magnetism, dark matter cannot be seen, we know it's there, but we can't see it. I think dark matter is the static that binds all matter together. It's the energy that keeps our flesh from falling apart. The same static that gives birth to Stars. the static that when the moon slammed into Earth reshaped the two into what they are now. the static that gives someone goose bumps. the static that ignites a lightning bolt. Dark matter is around all of us, all the time. we are swimming in it. But thats just what I think. Anyone else have any ideas???

Saiph · Jul 27, 2006

he suggested locking or merging it due to an active dark matter thread already present, and it's one in which he's making an attempt to disprove newtonian gravity and dark matter. But, back onto this topic: Science is devoting a lot of resources towards dark matter and dark energy. Well, the astronomical field is. Astronomy has very few people in it compared to other branches of science, even "pure" science like particle physics. One of the reasons is the amount of work a single person can do in astronomy is still quite large. Particle physics requires dozens of people to analyze a particular experiment, astronomy often needs only one (or a small handfull of graduate/undergraduate students). The big reason though, is application. The knowledge astronomy gains has little to no direct impact or application to the real world. Some of the methods developed for the field are used elsewhere, but very little of the actual answers. As such it isn't funded nearly as much as say, again, particle physics. While particle physics is also "pure" science, it's research can lead to stronger and more exotic materials or devices due to a better understanding of the underlying atoms and quantum mechanics. As for your notion that dark matter binds us all...it's only in the broadest sense, as gravity is very weak. On our scale, electric forces do far, far more to shape us than gravity does. It's only when you get to a planetary scale that gravity wins. Even then, dark matter is generally believed to be very dispersed, and so you need to get to the size scale of solar systems or star clusters to actually feel it's influence. Dark matter requires only two properties, it doesn't interact with light (i.e. it has no charge, like neutrons or neutrinos) and it has mass. Neutrinos fit the bill quite well, they have no charge, and have mass. The big problem with them as far as dark matter models are co <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

enigma10 · Jul 28, 2006

Since i raised the subject of consolidating dark matter threads into a common place, i doubt he was fully motivated by his discussion in another thread. <div class="Discussion_UserSignature"> "An organism at war with itself is a doomed organism." - Carl Sagan </div>

docm · Jul 28, 2006

One candidate for dark matter is the Axion, and Scientific American has an interesting article here; http://sciam.com/article.cfm?chanID=sa004&articleID=0006BA85-FC58-1492-BAAC83414B7F0000 that says it may have been detected. If confirmed it'll make for some late nights in the worlds physics labs. <div class="Discussion_UserSignature"> </div>

Saiph · Jul 28, 2006

Consolidating has it's drawbacks. First, the discussion usually hares off into two or three different directions anyway. At the moment we have the tangentially related expanding earth discussion, and this one. Second, the length will put off new readers a bit, I know I occassionally balk at catching up to a thread with 100 new posts over the last day and a half. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

enigma10 · Jul 29, 2006

Its true drawback is more work maintaining/moderating an additional column. The other areas you talked about can be remedied. Locked F.a.q. sticky posts takes care of run away threads or buried threads. Get enough of those, and the long winded wont have to repost across 100 different columns in 100's of different threads. More importantly, the newly arrived dont have to re-ask questions already answered hundereds of times. Also, most discussions hare off into several well known paths. Often involving 2 - 3 people riposting back and forth, often on borderline personal attacks. <div class="Discussion_UserSignature"> "An organism at war with itself is a doomed organism." - Carl Sagan </div>

brazilian_and_proud · Sep 5, 2006

what is dark matter ????? and how much of the universe is dark matter?????

doubletruncation · Sep 5, 2006

what is dark matter ????? We'd all like to know! See http://en.wikipedia.org/wiki/Dark_matter for a discussion of what the term means and why people suspect that there is this large amount of matter that, so far as we can tell, only interacts gravitationally with the matter that we're made of. and how much of the universe is dark matter????? The estimate from combining various cosmological tests is that 23% of the total energy density of the universe is dark matter, or roughly 85% of all matter is in this form (the other 15% of matter is in atoms). <div class="Discussion_UserSignature"> </div>

search · Sep 6, 2006

Dark matter: In 1930 a Dutch astronomer, Jan Oort (more known because of his work of comets), was studying stellar movement measuring relative velocities of the local group of stars that surround our solar system and found that at the measured speed this stars would not be able to stay together by gravity. Something else must account for the mass necessary (3x) for that to happen. Another astronomer the Bulgarian (working in Swisserland and later in California) Fritz Zwicky calculated that the individual velocity of the galaxies within the Coma Cluster was too high for them to be kept together. Jan Oort came up with the idea (for the solar system) that there should be a large ammount of debree beyond Pluto (the later found Oort Cloud) but that was not enough. Zwick proposed "dark matter" should exist within the galixies but his study of only one Cluster remained ignored and the idea also. During the 60's a woman astronomer Vera Rubin measured rotation rates of spiral galaxies and encountered same problem: velocity too high for stars to stay together unless the mass was considerably higher than calculated. Needed to say that it was then believed that the vast amount of mass was in the center of the galaxies. Galaxy mass calculation: http://users.pandora.be/nicvroom/program2.htm During the 70's she went further and observing Andromeda (using the dynamic of its motion instead of distribution of the stars as it was then normal) noticed that the galaxy had only 10% of the stars necessary to generate enough gravity to hold itself together (calculated via first process) and the extra 90% hidden mass had to be in the outer regions of the galaxy disk. This really prompted the astronomers to look for other examples and the result was consistent everywhere. This gave birth to the Dark Matter idea. But nobody saw the DM since then eit

alokmohan · Sep 6, 2006

Searh,it is such a nice post.But what about brown dwarfs?Astronomers have started discovering brown dwarfs and they are probably big in number.They are posssible candidates of dark matter ship.

search · Sep 6, 2006

Brown dwarfs are included in the MACHOs. They are the objects in size order between Jupiter and the sun (failed stars). See MACHO section above and the site below: http://xrtpub.harvard.edu/xray_astro/dark_matter3.html

robnissen · Sep 6, 2006

Very interesting post. But what is the basis for putting a limit on "the amount of atoms formed in the Big Bang." Scientists have absolutely no idea of the mass of universe immediately prior to the big bang (if any), so how can there possibly be a limit on the number of atoms made?

kyle_baron · Sep 6, 2006

what is dark matter ????? This is a guess, but I think it's probably just the Multi-Dimensions ( Universes) GRAVITY, within our own space. I say this , because gravity is universal, or spreads itself thru other dimensions, according to String Theory. <div class="Discussion_UserSignature"> </div>

summoner · Sep 6, 2006

Thank you Search, one of the best and most comprehensive posts I've yet to see. <div class="Discussion_UserSignature"> <table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

search · Sep 7, 2006

I had a already the feeling that phrase was going to be controversial I will try using an analogy I hope it will be clear if not let me know: Imagine that you are inside a room and you cannot see the outside. You need to explain what this room is made of and how it was built. In order to do this you must look at the inside walls find out what is made of (elements) and then calculate how much matter you have (density). Now you have to mathematically calculate the process (from present to past). You need to define some laws that do cannot contradict what you have presentely So lets say that the room is 2x2x2 (Volume), you have a driller (scientific instruments) that can reach 1 thick and when you drill you discover that the wall is made of a special sand and cement that grows when exposed to heat (25 % helium and 75% hydrogen elements) and that the structure changes as you drill deeper and that although you cannot see the outside you can listen the outside noise (CBR Cosmic Bakground Radiation) which gives you a hint that you are very close but you will never be able reach the outside because your driller is not long enough. Then you have a weight balance with you and you find that the weight of sand and cement is not enough to account for the total weight and actually its missing 90% of it so there must be another compoud (dark matter) used that its totaly unknown to you (or maybe the noise you hear is giving you the wrong idea of how far you are from the outside...). Your laws tell you that to make the room and for the walls to hold together you need to mix the elements in certain propotion and that it was not an homogenously (primordial fluctuations) mixture. With all this elements in hand you can find what was the initial mixture for that house to be there. Though dough... Structure of macrocosmos: http://www.seas.columbia.edu/~ah297/un-esa/universe/</safety_wrapper

observer7 · Sep 7, 2006

An excellent summary. But I think in order to be complete we have to consider the other possibility --there is no such thing as dark matter-- instead, there are other exlainations for the erroneous rotation rates of galaxies. Most notable among the alternate theories is that the gravitational constant is not. For large scale structures, the force of gravity is manifest in a way that is not consistent with what we observe on Earth/Solar System wide scales. This idea appeals to me, because I picture gravity in avery Eistein like fashion (the elastic sheet being bent) and I can visualize little pockets of gravity (stars) that sit in a larger depression (galaxy) in such a way that the sum of the stars gravity is much less then the total of the galaxy. This also works on smaller scales (ie why two bowling balls don't attract each other in a very visible way). Now I know tha the math seems to work for very small and very large masses. It (gravitational constant) also has been measured to very presice values and it works. I just think that this alternate theory has some merits like - doesn't require a new class of "stuff" in the universe - only requires a slight modification in the gravitational constant at different scales - can be used to develop a cosmological model that is consistent with CMB observations and required energy density of the known universe - might explain the observed acceleration of universal expansion (given a proper curve to the scale factor, it is possible that gravity is strongest at galactic/galactic neighborhood scales and falls off on both sides, larger and smaller) - can encompass both Newtonian and Einsteinian gravity within the larger theory I think it might also have implications for quatum gravity and black holes. -- <div class="Discussion_UserSignature"> "Time exists so that everything doesn't happen at once" Albert Einstein </div>

kyle_baron · Sep 7, 2006

The leading alternative candidate to Dark Matter is MOND: http://en.wikipedia.org/wiki/MOND Where gravity acts differently on larger scales, or at greater distances. <div class="Discussion_UserSignature"> </div>

search · Sep 7, 2006

If you noticed the original question was: "what is dark matter ????? and how much of the universe is dark matter?????" I limited the answer to that but I still wrote on both posts two little notes about the fact that may be something wrong in the applicable laws. I did not want to depart from the question because that tend to turn the thread around and it may loose interest (or gain even more). The fact is that if the threads became more organized by subjects so will the thoughts and posts. However I suggest that you try to start a new thread about that subject. It is also very valid and fascinating and as you say a complement to the dark matter theorists. Nevertheless here is an interesting discovery from 2002: http://www.physics.uci.edu/~dbuote/Shedding_light_on_dark_matter+.shtml

jaxtraw · Sep 7, 2006

"Brown dwarfs are included in the MACHOs. They are the objects in size order between Jupiter and the sun (failed stars)." In order to avoid negative stereotyping, brown dwarfs will henceforth be known as "enormously successful planets".

kmarinas86 · Sep 7, 2006

What is weird is that a brown dwarf is larger than Jupiter, a gas giant. between star&planet What about "stanet" or "plar" instead of brown drawf. between ice&planet pluto would be an "icet". between asteriod&terrestrial/planet Mercury would be an "terrestriod". Ceres would be an "astet" (kind of like "asset").

chembuff1982 · Sep 7, 2006

I don't really know much about dark matter. I however do believe like mentioned above, we can not compare gravitational force from other galaxies to ours. There could be unknown variances that we can not see or calculate correctly. There may also be other objects farther away that possibly could be repelling the objects and keeping them in their orbit. If objects attract, by sure means they may repel, even massive objects. Also gravity theoretically is infintesimal, dependent on surrounding sizes of objects, and proportional to the distance and other factors present. Therefore, I cannot conclude if dark matter does exist, or if there is some sort of fluke from another player that we do not know about. <div class="Discussion_UserSignature"> You may be a genius, but google knows more than you! </div>

search · Sep 7, 2006

Most of what you are talking about has to do with the Equivalence Principle: http://en.wikipedia.org/wiki/Equivalence_principle In plain words this is a very important principle to science and scientists and very few are willing to depart from it. It would be like abandoning the car, mobile and computer all at once and start your life again (analogy). Its basic statment is that the laws of physics are the same wherever you are. There are some variations which I gave in some sites (strong and week principle) above but the main idea is that we can calculate what is happening in other galaxies because the laws are the same (with the above considerations). As for objects repelling other objects (antigravity) that is pure science fiction and there is no basis for it no matter how attractive that idea may be. http://en.wikipedia.org/wiki/Anti-gravity Having said this I do agree with you: there is a lot out there we do not know But we should remain real without forgetting man (visionary) like Leonardo da Vinci or Jules Vernes...

search · Sep 7, 2006

According with the thesaurus "dwarf" can be used offensively so the stereotype is already included in the denomination. As far as I am concern can be a failed star or supergiant planet it makes no difference in common talk but scientifically so far they are called Brown Dwarfs.

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