Understanding Dark Matter: A Simple Explanation

[julcab12]

If it looks like a duck, swims like a duck and quacks like a duck, then why not call it a duck.
Enough of this nonsense about 'what it really is'. What is anything, 'really'.

... But taste like chicken for now. They haven't found/cook the exact duck 'flavor' yet. ^^

 

[mesa]

"...I certainly understand resistance to invisible fairy explanations.

I would think this is the major reason why some people have so much resistance to the idea. There is a certain uneasiness to 'pixie dust' explanations in Science and this isn't the first time we have tried to 'solve' problems by inserting invisible matter we can not see or test in order to make a model work (e.g. aether, caloric).

Questioning thinking is how Science advances and so I say bring it (just have something better to bring to the table than 'I don't like this explanation!').

 

[ZapperZ]

I would think this is the major reason why some people have so much resistance to the idea. There is a certain uneasiness to 'pixie dust' explanations in Science and this isn't the first time we have tried to 'solve' problems by inserting invisible matter we can not see or test in order to make a model work (e.g. aether, caloric).

Questioning thinking is how Science advances and so I say bring it (just have something better to bring to the table than 'I don't like this explanation!').

But you also need to look at the OTHER side of it. Neutrino WAS invented exactly that way, to account for the missing momentum in beta decay. It was years before its existence was verified.

People seem to forget, or simply don't understand, the process of discovery. When you see something new, the first thing you try to do is to try and figure it out using the available tools and knowledge that you know works. It is when, after you try and try, that it can't work, and then somebody comes along and proposed something new that not only explain the new discovery, but also all the previous existing understanding, that's when we have expanded our knowledge!

Is there compelling evidence for the existence of dark matter? Sure! But is dark matter verified? No! If it is, then we will have zero reason to spend all the millions of dollars/euros/yen/etc. in the numerous different experiments to detect dark matter. I wish the General Public has a bit more of a sense that we are STILL in the middle of the discovery phase in understanding this. This could change, and in fact, I am sure that things WILL change as we learn more and more about how to explain the observations that we currently have.

But does not detract for the fact that, while we have not make any discovery yet on the existence of dark matter, based on what we have observed, we know what it has and doesn't have. We have a list of characteristics, a phenomenological model, of this dark matter. So if someone asks "what is dark matter", the appropriate response will be to describe what we know about it so far!

Zz.

 

[mesa]

But you also need to look at the OTHER side of it. Neutrino WAS invented exactly that way, to account for the missing momentum in beta decay. It was years before its existence was verified.

People seem to forget, or simply don't understand, the process of discovery. When you see something new, the first thing you try to do is to try and figure it out using the available tools and knowledge that you know works. It is when, after you try and try, that it can't work, and then somebody comes along and proposed something new that not only explain the new discovery, but also all the previous existing understanding, that's when we have expanded our knowledge!

Is there compelling evidence for the existence of dark matter? Sure! But is dark matter verified? No! If it is, then we will have zero reason to spend all the millions of dollars/euros/yen/etc. in the numerous different experiments to detect dark matter. I wish the General Public has a bit more of a sense that we are STILL in the middle of the discovery phase in understanding this. This could change, and in fact, I am sure that things WILL change as we learn more and more about how to explain the observations that we currently have.

But does not detract for the fact that, while we have not make any discovery yet on the existence of dark matter, based on what we have observed, we know what it has and doesn't have. We have a list of characteristics, a phenomenological model, of this dark matter. So if someone asks "what is dark matter", the appropriate response will be to describe what we know about it so far!

Zz.

Absolutely agree, this is the best we currently have and it will likely change with time, my apologies if my post came across the wrong way.

 

[Vanadium 50]

MOND has a problem with the Bullet Cluster - LCDM does a better job with its mass and its distribution. But the collisional velocity is something that MOND does better than LCDM. Also, Abell 520 is sort of an anti-bullet cluster in that the mass coincides with the has and not the galaxies.

What I find annoying is that many of the same people (some of whom are friends) who say that the Bullet Cluster is the clear smoking gun for LCDM and that no alternative is possible also say when asked about Abell 520 that you can't tell anything from a single pair of interacting galaxies because things are all weird and confusing.

What I think is a fair description of the situation is:

• LCDM is an ugly theory that does better than MOND at very large scales.
• MOND is a profoundly ugly theory - so ugly that its proponents often argue that it is but an approximation of some future theory - but does better than LCDM at galactic scales.

My conclusion from this is that MOND probably is telling us something about how galaxies form, evolve and behave, much like the Drude model tells us something about metals. But it's probably not how the universe is put together.

 

[Stuart]

careful

Did you even see the video that I linked to in Post #3? It answers/addresses at least a couple of the questions you asked here, if not more.

And yes, we CAN "fully define" gravity, even though we continue to test the General Relativity picture of gravity. Don't you think it is rather silly to not know enough about gravity, and yet, we can predict celestial events with such accuracy? How many other things that you think you can define and have such amazing accuracy?

Zz.

We cannot define gravity, what we can do is describe it. We don't yet posses a complete definition of anything. Worse yet, every particular thing we know is inconsistent with at least one other thing we know.

Ptolemy thought he had great data. Newton in fact did have great data. Even so he lacked an etiology. That's where we're at with dark matter. There's great data, but there's no demonstrable etiology. Any number of alternate explanations are feasible. Topology would seem to offer a more rational explanation. We may not like that idea, but at least we can confirm the existence of spatial topology.

 

[Bobbywhy]

We cannot define gravity, what we can do is describe it. We don't yet posses a complete definition of anything. Worse yet, every particular thing we know is inconsistent with at least one other thing we know.

Ptolemy thought he had great data. Newton in fact did have great data. Even so he lacked an etiology. That's where we're at with dark matter. There's great data, but there's no demonstrable etiology. Any number of alternate explanations are feasible. Topology would seem to offer a more rational explanation. We may not like that idea, but at least we can confirm the existence of spacial topology.

Stuart, do you mean “spatial topology”, for example, this:
“Spatial Topology and its Structural Analysis based on the Concept of
Simplicial Complex”
http://arxiv.org/ftp/arxiv/papers/0707/0707.0920.pdf

or, is there some reference you can post here to direct us to “spacial topology”?
Thank you,
Bobbywhy

 

[Mordred]

here is the problem I'm having with your posts, in your other thread when you were asked for what you mean by topology you posted 1 article on MOND, one article on Branes, and one article on I guess you would call it single wave and one on quantum gravity.

https://www.physicsforums.com/showpost.php?p=4751564&postcount=6
-The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter
-Cosmic Acceleration from Topological Considerations: Branes Filled by Scalar Field
Dark Matter.
-Pattern formation in Hamiltonian systems with continuous
spectra; a normal-form single-wave model
-Quantum Gravity from Noncommutative Spacetime

These are separate models, what you have not done is show us your Specific topological model that you are trying to push on us. What is the name of the model that conforms to your feeling is right in regards to gravity, dark matter and dark energy? Please post an article directly related to all 3 within a single model. At least then we will know which model you specifically support

edit Hamilton mean field model pulls up some google hits,usually just statistical mechanics

 

[Stuart]

I'm not pushing any model. It just seemed to me that people are taking a lot on faith. I provided a variety of alternatives because I'm trying to point out that we have great phenomenology, but extremely weak etiology. DM, MOND, QG, etc.. are etiologies. We have great observational data to evidence, describe and predict phenomena, but I'm aware of no evidence that supports any single etiology.

 

[Mordred]

ah thanks, that makes more sense. In reply to that it only seems that way. LCDM is simply one of the more successful models. As such if you buy a cosmology textbook, it will teach LCDM. However their is plenty of research that tries to find faults within every model, LCDM included. That is good science. Scientifically speaking their is no 100% (this is the final word on this model). No model is ever considered 100% proven. Every model has its successes and its weaknesses.

As far as answering questions on the forum though, its forum policy to teach what would be in those textbooks. Helps the student learn according to academic studies. This is simply good policy.

If your interested and can afford it you should buy "Roads to Reality" by Roger Penrose. In that book he mathematically shows problems within ever major model. He doesn't even place the model he has supported for 40 years with 100% faith. In fact within that book he points out that he knows and admits his favorite model has numerous faults.