Dark matter and Shell Theorem by Isaac Newton

[David Levy]

Why is it so difficult to agree or disagree? Yes or no?

You claim:

The simulations are tested against observation and produce the right results.

So, is it correct that the science had used a simulation to estimate all the ideas about the dark matter in the Galaxy?

Yes or no?

 

With regards to the dark matter between the galaxies –

The amount of dark matter in galaxy clusters is based on the orbits of galaxies.

As I have stated, I couldn't find it in the articles which you have pointed. Would you kindly direct me to the specific article? Edited March 21, 2015 by David Levy

[Strange]

You claim:

So, is it correct that the science had used a simulation to estimate all the ideas about the dark matter in the Galaxy?

Yes or no?

 

No. (Again.)

 

 

With regards to the dark matter between the galaxies –

As I have stated, I couldn't find it in the articles which you have pointed. Would you kindly direct me to the specific article?

 

I will try when I have time. But it isn't hard to find (I just suspect you don't want to find it.)

[David Levy]

 

No. (Again.)

Why?

It is clearly stated that a simulation had been used:

"Numerical galaxy formation simulations can provide guidance for the expected local DM density and velocity distribution, and their spatial and halo-to-halo variance."

So why do you try to contradict this statement?

Prove it please.

 

 

I will try when I have time.

Thanks

 

(I just suspect you don't want to find it.)

Why do you claim so?

I have invested significant time to read those articles.

Please don't underestimate me.

[Strange]

 

Why?

It is clearly stated that a simulation had been used:

"Numerical galaxy formation simulations can provide guidance for the expected local DM density and velocity distribution, and their spatial and halo-to-halo variance."

So why do you try to contradict this statement?

 

I am not contradicting that.

 

You said "science had used a simulation to estimate ALL the ideas about the dark matter in the Galaxy"

 

Which is obviously not true.

 

That sentence says "provide guidance" which obviously is true.

 

 

Why do you claim so?

 

You appear to reject so much information as if you have an emotional dislike of dark matter, for some reason.

[swansont]

 

Why?

It is clearly stated that a simulation had been used:

"Numerical galaxy formation simulations can provide guidance for the expected local DM density and velocity distribution, and their spatial and halo-to-halo variance."

So why do you try to contradict this statement?

Prove it please.

 

Perhaps because your original statement was "science had used a simulation to estimate all the ideas about the dark matter in the Galaxy" (emphasis added)

 

Simulations were run. But they do not comprise all of the ideas about dark matter in the galaxy. Thus, your claim is false and it is perfectly reasonable to disagree with it.

 

edit: xpost with strange

[Mordred]

Have you ever tried programming? In order to program a simulation you have to have a mathematical model in the first place. A simulation doesn't make a model, it merely tests a model to see if it works.

It is simply a tool,

Edited March 21, 2015 by Mordred

[David Levy]

 

I am not contradicting that.

 

You said "science had used a simulation to estimate ALL the ideas about the dark matter in the Galaxy"

 

Which is obviously not true.

O.K. sorry for using the "ALL"

However, the "ALL" was integrated in the following statement:

"While we don't know what the dark matter (DM) is, we have a fairly reasonable idea as to how much of it there is in the Galaxy, how it is distributed, and how fast it is moving. This information comes from the rotation curve of the Milky Way, and is crucial to "ALL" the direct searches for dark matter."

Hence, even if isn't "ALL", it is clear that the distribution of the dark matter and how fast it is moving "comes from the rotation curve of the Milky Way".

In order to extract those figures from the rotation, the science had used simulation.

It is stated:

"In order to elucidate the effects that the dissipational baryonic physics has had, we compare to results from ErisDark, the DM-only counterpart to Eris. We _rst briey review the properties of the two simulations, then describe the local DM density and velocity structure."

Hence, let me ask as follow:

Is it correct that the science had used simulations to estimate the local DM density and velocity structure of the dark matter in the Galaxy?

Yes or no?

Edited March 21, 2015 by David Levy

[imatfaal]

 

 

O.K. sorry for using the "ALL"

However, the "ALL" was integrated in the following statement:

"While we don't know what the dark matter (DM) is, we have a fairly reasonable idea as to how much of it there is in the Galaxy, how it is distributed, and how fast it is moving. This information comes from the rotation curve of the Milky Way, and is crucial to "ALL" the direct searches for dark matter."

Hence, even if isn't "ALL", it is clear that the distribution of the dark matter and how fast it is moving "comes from the rotation curve of the Milky Way".

In order to extract those figures from the rotation, the science had used simulation.

It is stated:

"In order to elucidate the effects that the dissipational baryonic physics has had, we compare to results from ErisDark, the DM-only counterpart to Eris. We _rst briey review the properties of the two simulations, then describe the local DM density and velocity structure."

Hence, let me ask as follow:

Is it correct that the science had used simulations to estimate the local DM density and velocity structure of the dark matter in the Galaxy?

Yes or no?

 

David - you do realise that there is practically no area of science that doesn't use simulation? It does not obviate the need for experimentation and observation - but it does allow you to move from a sometimes very simple core mathematical model to a realisation of that core within the hurly-burly of numerous interactions.

 

You seem to trying to head - in a lawyerly fashion - towards a tub-thumping conclusion that dark matter is the result of simulations and thus, if the models are incomplete, then dark matter is not needed and does not exist.

 

A. We have other evidence for Dark Matter - Gravitational Lensing, the Bullet Cluster etc. These were predicted and subsequently found

 

B. With respect; from reading your posts you do not have the understanding, technical skill, or knowledge to properly engage with, or criticise the models of galactic rotation.

!

Moderator Note

Chalkman - I split your new question off to a new thread - this topic is pretty specific on David's questions about the mechanics behind the predictions of dark matter existence

[David Levy]

David - you do realise that there is practically no area of science that doesn't use simulation? It does not obviate the need for experimentation and observation - but it does allow you to move from a sometimes very simple core mathematical model to a realisation of that core within the hurly-burly of numerous interactions.

You seem to trying to head - in a lawyerly fashion - towards a tub-thumping conclusion that dark matter is the result of simulations and thus, if the models are incomplete, then dark matter is not needed and does not exist.

Please, don't misunderstand me. Simulation is important tool. In electronics for example, it is vital tool. Actually, it's almost impossible mission to accomplish the design flow without using this key tool.

However, any slight disruption (even few micro seconds in the setup process) could lead to fatal error in the whole design. Therefore, if you want to achieve full function ASIC, it is requested to use high quality design tools (at over than 1M$) and use it correctly.

Therefore, I don't claim that it is a mistake to use a simulation. I just claim that simulation is a very sensitive tool. If the simulation isn't 100% verified and if there is a minor disruption in the setup, it could lead to fatal error result.

In any case, I would expect that the science should highlight that they have used simulation to extract the values for DM. I had no idea about it. Therefore, it is expected that the science should give us this information with some sort of confidence level. (I have already discussed about the importance of using some kind of titles that should emphasis the science confidence level in their theories/hypothesis/idea/speculation).

This has a direct effect on our understanding about the DM. Currently, based on this simulation it is expected that the dispersion of the DM must be very unique in order to meet the rotation curve requirement. For example, they have used "dark disc":

"Regarding baryonic modi_cations of the local DM velocity structure, the e_ect that has received the most attention is the possibility of the creation of a so-called \dark disk"

 

Even so, it is stated, that they didn't achieve yet the high level rotation velocities: "Nevertheless, the peak of the speed distribution in Eris occurs at only vpeak = 195kms1, considerably below that of the SHM (vpeak = 220kms1).

However, it isn't yet a fully verified simulation tool and we must take those results at the correct level of confidence.

Please be aware that in electronics, even 95% confidence level in simulation result could lead to fatal error in the functionality of the design.

Edited March 21, 2015 by David Levy

[Mordred]

Fair enough, but keep in mind the Planck collaboration papers has. Higher confidence level, Google Planck 2015 for the papers.

 

No theory no matter how accurate will ever state 100% confidence.

[swansont]

 

Please be aware that in electronics, even 95% confidence level in simulation result could lead to fatal error in the functionality of the design.

 

Then again, this isn't electronics. And the amount of error depends on the nonlinear nature of the problem. A simple resistive DC circuit will not have errors propagating in the same way as a more complex circuit. IOW, there are many circuits where a 5% tolerance in the resistance will have zero effect on the functionality of the design. So this is a pretty meaningless objection until you can demonstrate how large of an uncertainty you will have in a result.

 

Keep in mid we successfully do millions of things daily based on "simulations". GPS works pretty well, for example.

[David Levy]

 

Fair enough, but keep in mind the Planck collaboration papers has. Higher confidence level, Google Planck 2015 for the papers.

 

No theory no matter how accurate will ever state 100% confidence.

Thanks

[Mordred]

No problem mate, your definetely dedicated. Not a bad thing, I went through similar learning stages, it's good to question. Just keep in mind the amount of research and minds that go into a theorem. If a theory survives a mere decade, with all the counter arguments, it might just be plausible.

Lol back when I first started studying cosmology in the late 80's dark energy and dark matter was highly contested. WMAP clinched a lot of the debate. I've been studying since, gives me an advantage.

 

So I can understand someone just stepping into the subject. without knowing the history of debates

(Sorry if I sound gruff at times, it gets frustrating trying to teach what I learned at times,easy to forget ppl are just started in a complex field of study)

Edited March 22, 2015 by Mordred

[David Levy]

 

No problem mate, your definetely dedicated. Not a bad thing, I went through similar learning stages, it's good to question. Just keep in mind the amount of research and minds that go into a theorem. If a theory survives a mere decade, with all the counter arguments, it might just be plausible.

Lol back when I first started studying cosmology in the late 80's dark energy and dark matter was highly contested. WMAP clinched a lot of the debate. I've been studying since, gives me an advantage.

 

So I can understand someone just stepping into the subject. without knowing the history of debates

(Sorry if I sound gruff at times, it gets frustrating trying to teach what I learned at times)

Thanks again

I really admire your knowledge and your dedication.

If one day those simple correspondences will lead to a breakthrough – we are partner.

However, I didn't give up yet.

More to come

[Mordred]

(Then again my interest has been in the thermodynamic aspects of particle physics and cosmology.) The two are highly interconnected. This includes the Einstein field equations.

 

Thanks again

I really admire your knowledge and your dedication.

If one day those simple correspondences will lead to a breakthrough we are partner.

However, I didn't give up yet.

More to come

No problem, please study virial theorem and the NFW profile in detail

The key terms on simplifying complex interactions is via ideal gas law approximations.

 

energy/ mass density is a valuable tool

 

 

As a side note it is possible to describe a rock as an ideal gas. Follows the same approximation rules.

here is a good article, thermodynamics is a major study, however vital in Cosmology applications.

http://www.google.ca/url?sa=t&source=web&cd=4&ved=0CCEQFjAD&url=http%3A%2F%2Fwww.physics.uoguelph.ca%2Fpoisson%2Fresearch%2Fspi.pdf&rct=j&q=ideal%20gas%20law%20of%20solids%20pdf&ei=sVQOVdbVOsyyggSHpYOIBw&usg=AFQjCNFnizb_WfYgcrz21lUiy85HUaJnDA&sig2=eyc4ZRHF-lFKY4zKgC3BTg

Unfortunately finding non copy righted literature, limits my coverage.

 

As I have bought numerous textbooks, The second link follows "Modern Cosmology" by Dodelson

 

http://arxiv.org/pdf/hep-th/0503203.pdf "Particle Physics and Inflationary Cosmology" by Andrei Linde

http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

 

Yes good textbooks are often 500+ pages, complex subject matter, I've lost count on number of pages, too long to remember ago.

Edited March 22, 2015 by Mordred

[David Levy]

Sorry

Edited March 22, 2015 by David Levy

[swansont]

Yes, I fully agree.

Science isn't electronics.

In science they have unlimited time and unlimited resources. No one is going to lose his job if there is an error in the simulation.

 

Um, what? That's an incredibly naive statement. But then, it fits in with the other interpretations of science we've seen here.

[Klaynos]

I think the working world of scientists is very different to what you think.

 

Jobs are very insecure, resources more so. In academia they both require you to win grants which is competitive, if you win one and don't get anywhere before it ribs out (normally 1 to 3 years) you're unlikely to get the next.

 

Science funding on most counties is being cut and more emphasis is being put on short term practical users rather than the fundamentals.

 

Your understanding of simulation in physics also seems flawed, it is a mathematical model where certain new assumptions ate implemented, the results of the simulation are then compared to reality, that's how DM was discovered, the simulations without it don't look like the universe. Simulation is part of the story so far and will continue to be there.

[David Levy]

Sorry for my message

Let me ask again

 

How it could be that with all the advanced technology there is no real signal from the dark matter which matches the simulation in the galaxy?

Outside the galaxy, the density of the dark matter should be significantly lower.

Why the science has full evidence for dark matter outside the galaxy but not in the galaxy.

Edited March 22, 2015 by David Levy

[Strange]

How it could be that with all the advanced technology there is no real signal from the dark matter which matches the simulation in the galaxy?

 

There is: galactic rotation curves and gravitational lensing.

Why haven't we directly detected particles? Because, by definition, they don't interact much (or at all).

[Janus]

Outside the galaxy, the density of the dark matter is significantly lower than in the galaxy itself. However, the science has full evidence for dark matter outside the galaxy but not in the galaxy. How could it be?

How could they detect dark matter in very low density which is located far away from us, while it is impossible mission to detect high density of dark matter in our galaxy?

 

 

Density is a relative thing. While the density of DM does increase as you move towards the center of the galaxy, it is still very low when compared to the localized density of something like our solar system which is denser than the local neighborhood of our galaxy. If we take the Solar system to include everything within a sphere contained within the orbit of pluto, the average density works out to be something in the order of 2.3 e-12 g/cc. If we take the total mass contained in the sphere out to 12 light years from the Sun we include 26 stars. if all those stars were in equal in mass to our own Sun, (which they are not since most of them are red dwarfs which are significantly less massive than our sun), the average density works out to ~8e-24 g/cc or about 1/1,000,000,000,000 the average density of the Solar system.

 

The density of DM in our region of the galaxy is ~0.56e-24 g/cc. This makes the total mass of DM contained in the spherical volume bounded by Pluto's orbit ~5e17g or 5e14 kg, which is equivalent to the mass on one small asteroid, and this mass is evenly spread out over this entire volume. This also puts the total mass of DM contained within the volume of the Earth as ~608 g.

 

Considering the fact that DM is even less likely to interact with baryonic matter than neutrinos are ( of which billions pass through your body every second without with only a very rare interaction.), it is not all that surprising that the DM in our local area is hard to detect.

 

But this does not mean that it's presence cannot be noted on a large scale. If you take that same 0.56e-24 g/cc and consider it over the volume of the sphere contained within the orbit the Sun around the galaxy, you get ~ 22 billion solar masses. This is a significant fraction of the total mass of the visible matter of the galaxy. It is no wonder that this would have a measurable effect on the orbital speeds of the stars of the galaxy.

 

In addition, the visible matter of the galaxy in mainly concentrated in the bulge and disk. The disk is only a few thousand light years thick. The DM extends into the spherical volume above and below the disk. As a result, the increase in gravitational effect as you move outward caused by DM increases faster than the increase in gravitational effect caused by the visible mass in the the disk.

 

So the upshot is that our solar system is a localized high density region of visible matter compared to the galaxy as a whole, and while in comparison, the local density of DM is very very low, and extremely difficult to detect at this scale, when taken over galactic scales, the total mass of the Dark matter adds up to be quite significant when compared to the mass of the galaxy as a whole.

[David Levy]

Thanks

[Strange]

More evidence for the location and behaviour of dark matter: http://www.bbc.co.uk/news/science-environment-32066013