View Full Version here: : Dark matter hinted at again
08-09-2011, 12:58 AM
Just in from the BBC
Seems like they are getting more confident by the day of finding dark matter .
08-09-2011, 09:50 AM
I'm still on the fence a bit. Dark matter sometimes feels like Phlogiston, something that is there to make the math work. I suspect that we are missing something fundamentally substantial in Physics which is why so many theories have to have things bolted on.
I'm probably completely wrong, the upper end of the math always burns me out so I miss crucial things when studying, but I keep getting the nagging feeling that a core element is missing that would tidy up our understanding considerably.
09-09-2011, 10:41 AM
Thanks Ron for posting.
We cant move forward with opinion alone but I am with Peter to a large degree.
16-09-2011, 10:33 PM
I once asked a leading professional authority on dark matter this question: how certain are you that the dark "material" actually exists?
He said to me that, while there may eventually turn out be other explanations for why a low luminosity dwarf galaxy holds together (that is, does not dissipate) despite it containing just a smattering of widely spaced stars, we have to go where the data leads, and adopt the simplest explanation;
which is that there is additional gravity being provided by actual physical matter in some unknown form.
Low luminosity dwarf galaxies have a very low spatial density of their constituent stars, but the total matter density of these galaxies, inferred from the amount of gravitational force that is necessary to hold them together, makes them sort of "like cannonballs".
It is a while since I read papers on dwarf galaxies, but I seem to recall that the smallest dwarf galaxies, in order to remain stable under the influence of their own gravity, must contain several hundred times as much "dark" matter as "luminous matter"(luminous matter is matter that is evident in the various wavelength bands that we use to observe a galaxy).
Similarly, given that some galaxies can move around within clusters of galaxies at orbital speeds of ~1000 or even ~2000 km/s, it is perfectly logical to believe that these galaxy clusters could not exist for long without extra gravity (or some other force) coming from within such a cluster. In other words, there is gravity in excess of that coming from the observed constituents of the cluster.
Of course it is possible to be cynical about cosmologists who seem to pull large quantities of dark matter "out of a hat" in order to explain how the existing cosmic structures can form in the requisite amount of time....that is, the additional "dark" matter has to be there for gravity to be able to complete its structure-forming work in the 13 billion years available to form the observed structures in our universe. Indeed, this kind of assumption does seem to be "cooking the books" to try to make the existing cosmic structures as we now observe them.
For instance, is the largest-scale cosmic structure of voids, walls, and bubbles, something that is naturally formed by gravity alone? True, cosmologists can "make" these large-scale structures in only 13 billion years using only the gravitational force and large quantities of non-luminous matter in some unknown form, at least in their computer simulations, but "universe in a computer" does not have to correspond with the real universe.
For the moment, however, "these are the truths that we must cling to".......the most logical inference, for now, is that a galaxy cluster or a galaxy will come apart if there is no additional gravity coming from some form of unseen matter. We can, of course, engage in informed speculation about unknown forces and suchlike that might influence stars and galaxies, but for the moment we must believe at the 70% level of certainty that dark matter really exists. While dark matter is not exactly a fact, we must concede that it is probably there!
(cosmologists are great ones for assigning 100% certainty to their theories....but certainty is the domain of theology, not science.)
17-09-2011, 08:47 AM
Excellent coverage of a complex matter:thumbsup:.
Indeed the problem is simply there is too much gravity for the matter we can observe "visually" and it would seem reasonable given our understanding of gravity to date that we need additional matter to explain the observations.
The amounts of dark matter we need suggests it must make up a great deal of the Universe which is what makes me feel uneasy about using it to explain the observations....however as you say we must stay with the truths we know...
17-09-2011, 09:05 AM
Thanks, Mr Xelasnave, for the complements about the clarity and cogency of my prose and reasoning.
Even the best writers have their "off" days, and science writing is even harder because you have to aim for such crystalline clarity that readers with many and various levels of understanding should all be able to understand the science that one is presenting. (needless to say, the facts must also be correct)
the bad galaxy man
17-09-2011, 09:42 AM
You are most welcome but please call me alex.
I do think science reporters in an effort to convey complex ideas to their readership use "examples" that rather than being helpful perhaps add more confusion than they intended, add to that the desire or need to sensationalize their reporting it becomes difficult to get to a reasonable view.
Here is one of many articles one can find where scientists are seeking an alternative to Dark Matter
I dont know anything about MOND but it is interesting some are tinkering with the rules of gravity to explain dark matter away.
17-09-2011, 10:05 AM
Here is another artile re MOND.
I post this more to make the point of reporters using poor examples..the refernce to a bank loan seems silly to me.
17-09-2011, 01:37 PM
Good to have you contributing to this forum .. its always great to 'see' some more posters appearing here. Thank you also, for your clearly described and considered words on this topic.
I would like to add to some comments about the more philosophical points you raise.
Its interesting for me as I deliberate on the points you raise about the relationships between models/theories, not necessarily having to correspond to the real universe. The models and theories we create are typically based on tested evidence (with a smattering of inference) and provide us with a basis for devising further tests and experiments, which then progresses our understanding. Empirical data is also used to constrain them further.
As such, the progression of these models and theories, in effect, become reality for us within science. (I think you have captured the essence of this in your words about certainty and theology, however certainty also has meaning in science).
The gist of where I'm coming from, is that scientific reality is what is contained in these models. Any reality perceived outside of them which isn't objective, independently verifiable, self-consistant or 'disprovable', would seem to be purely philosophical postulates, and would not be a viable basis for assessing the applicability of models developed by the scientific process.
If this is so, then there is no other 'reality' for comparative purposes.
17-09-2011, 02:05 PM
I think that dark matter is all those blue and white invisible teapots orbiting their chosen star/planet as Dawkins pointed out.
We do not know what particle is exchanged to cause gravity as with the other basic forces.
Since gravity is so weak I postulate that it is some force caused by quantum entanglement. Further it does not exist in our space time but exists outside in higher dimensions in the realm of strings perhaps. It leaks into our Universe to keep everything in its place. This is why we form orderly queues.
17-09-2011, 02:38 PM
A short comment by the respected Leonard Suskin ...
17-09-2011, 03:18 PM
If we're onto quantum mechanics, here's an interesting question (and perhaps a good topic for another thread):
Is there really a fundamental difference between a quantum mechanical system and a classical physics system ?
17-09-2011, 03:48 PM
I looked at Wiki as a place to start to establish working definitions..not as simple as one may first think... the thread you suggested Craig would be useful.
Your appreciation of the issues etc no doubt would give members better understanding. As I have said many times you have a happy knack of explaining things that help my understanding and no doubt others must feel the same as me... mmm not necessarily with only one sample:D...anyways without conducting a survey on what others think I am confident others may think similar to me:).
17-09-2011, 04:14 PM
This is interesting but old news. I expect most have heard about this however if not take a look.
17-09-2011, 04:26 PM
Ok .. I'll start another thread when I get the chance .. I look forward to your views on the topic ...
PS: Love Susskind dissertations … he is a pretty cool dude .. although I'll admit I'm surprised by his simplistic view on DM .. I mean I think its discovery might have a lot more implications on other things than the discovery of neutrinos did. :question:
17-09-2011, 04:28 PM
I agree with you, Craig, that for us, as human minds, empirically tested and self-consistent physical models, (which in my view must also incorporate the postulates of causality and the conservation of mass/energy in order to make sense), are the closest thing that we can get to an accurate description of the world.
But beware of theorists and their computer models......for years, theorists were trying to "make" massive stars in their computers, and the stars just wouldn't form in these simulations, due to the many barriers that exist to gravitational contraction, e.g. magnetic fields, photon pressure, angular momentum, etc.
Yet obviously, nature has no trouble making massive stars!!
Yes, the computer models didn't work......so astronomers who study massive star formation are waiting for observations of sufficient angular resolution in order to be able to see how the task is accomplished in the real world.
Similarly, it must be possible that those cosmological simulations that can replicate the observed pattern of the "large-scale structures" in the universe (such as voids, walls, shells, etc.) are missing something.
Ostriker, for instance, suggested a large number of small "mini bangs" to clear matter out of the voids, and to make galaxies form only on the walls of the voids (as they have done!).
In relation to the dark matter idea, which I regard as proven, at least at the level of certainty that constitutes proof in science, I can sometimes understand why people are looking for other factors that might cause the ongoing structure formation in the universe......in a recent informal study of some supercluster structures, I found many galaxies that sit by themselves in splendid isolation, with perhaps only one or two small companions;
so the question that suggests itself is: how can anything form at all, given the ultra-low mass density of some of these regions of space? (dial "DM" for dark matter ?)
17-09-2011, 05:03 PM
I have no problems in recognising that sloppy science exists, as does incomplete knowledge and misleading modelling. This in no way invalidates the process however.
So, in the case you cite, failure to produce a successful star, extended knowledge of how not to make a star, and sparked an enquiry which encourages the development of more objective, verifiable observations.
Knowledge and understanding has also been gained from a "negative" result, without having to revert to philosophy based 'answers'.
Incompletion is part of the next iteration ..
Sure .. a testable result derived from a postulated question .. no problems !
I'm not as convinced as you about this, but that's neither here nor there .. :)
Try on that the structures might spontaneously emerge, as a result of the interacting behaviours of all the individual components .. which are themselves simply following all the laws of and forces in physics … mass density doesn't have to be the only factor 'causing' self-organisation of structure arising from complex systems.
17-09-2011, 05:04 PM
Craig I found Suskins reply rather surprising..and refreshing.
However I think some of the lectures he has been giving are targeted at folk other than grad students and that experience may have produced such a reply.
I think it is wonderful the lectures he has given out of Stanford and freely available.
I think he likes the idea of string theory :D.. I formed the impression that he has contributed to the concept.
17-09-2011, 05:11 PM
.. I thought he more or less, invented it !!?!!
17-09-2011, 05:22 PM
Yes according to him in Brain Green's movie:D
Thats where I first noticed him ...bad first impression as he had crackpot characteristics...saying he worked on this (string theory) alone in his attic and turned to drink when it was not accepted... but that was probably the fault of script writers.
17-09-2011, 05:27 PM
:lol: :lol: :lol::rofl: :lol:
A bit of deliberate mischief there Alex ? (Just kidding).
Fault ??? I'd say that story made him normal !
.. and knowing Susskind .. it was probably a perfectly honest recount of the experience !
17-09-2011, 05:41 PM
No, no, no, no er yes:D
Well at that time Craig folk were refering me to "how to spot a crack pot" so I could examine my behaviour in presenting my views on everything...
He is OK I like the man and loved all his lectures.
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