Dark Matter

[Nereid]

You were asked about this before, I think, but didn't answer ... how does the composition of the Sun relate to the three sets of good astronomical observations of the size and distribution of mass in rich clusters (gravitational lensing,

Those lensing papers demonstrate that the "missing mass" tracks to the infrastructure (solar system) components of the galaxies, not the ionized gas between the galaxies. That observation alone bolsters my case significantly IMO. Your missing mass has to be inside the solar system components of the two colliding galaxies, not the gas between the solar systems, otherwise the lensing would have stayed with the interacting gases and would not have tracked with the galaxy infrastructures.

Please present at least one reference to support this assertion.

For the information of other readers: the kind of test Michael is hinting at here has been done ... and found seriously wanting. The best estimates of the distribution of the mass of rich clusters, obtained by analysis of (optical) images using gravitational lens models, is aligned (within the observational uncertainties) with estimates of the distribution of the mass in the same clusters, from analyses of x-ray observations. Or, to turn it around, the gravitational lensing data is (seriously) inconsistent with hypotheses to the effect that the majority of the mass in rich clusters is contained within the constituent galaxies.

the dispersion of radial velocities of cluster galaxies,

I personally think you'll need to include electron flow and kinetic energy from electron flow in these radial velocities, as well as heavy solar system concepts.

When you have written a paper showing that your personal feeling has (quantitative) legs, and had it published in a relevant, peer-reviewed journal, please let us all know.

Until then ...

and the intensity and temperature of x-ray emission)?

X-ray emissions from the solar atmosphere are electrically driven. The temperatures required to release some of these photons is measured in the millions of degrees. You aren't going to get million degree temps on top of a 6K photosphere without electrical flow. The x-ray emissions from Hinode show that even "quiet" areas of the sun are highly electrically active.

When you have written a paper showing that your personal feeling has (quantitative) legs, and had it published in a relevant, peer-reviewed journal, please let us all know.

Until then ...

Also, in which published paper, in a relevant, peer-reviewed journal, have you presented this 'heavy suns' account of the observed mass distribution in rich clusters?

I've proposed iron rich suns in every paper I've written. I've never personally tried to apply the concept to mass distribution in rich clusters.

When you have written a paper showing that your personal feeling has (quantitative) legs, and had it published in a relevant, peer-reviewed journal, please let us all know.

Until then ...

FYI, whether I can or cannot produce such papers is irrelevant to my ability to demonstrate the lack of empirical evidence in your dark matter theory related to these particular observations. There is no requirement on my part to present any alternatives to simply point out the flaws in your interpretation of these observations.

We have been over this, and over it, and over, and over, ...

A) If you have a viable alternative, please get it published (in a relevant, peer-reviewed journal); when you have such a paper, please let us know

B) If you truly can "point out the flaws in [...] interpretation of these observations", then please write a paper on this topic, and get it published (in a relevant, peer-reviewed journal); when you have such a paper, please let us know.

Until then ...

I am simply noting that heavy solar system theories could be used to replace your missing mass from your lensing papers. Any movement of whole galaxies will need to include current flow and the kinetic energy of current flow to have any hope of success IMO. My opinion is that it makes up a consider amount of the "non-baryonic" matter you are looking for.

You have stated your opinions, here, many many times.

When you have something more to offer than your opinions - specifically, when you have published a relevant paper in a relevant, peer-reviewed journal, please let us know.

Until then ...

[Nereid]

Nereid,
Do these aforementioned "Relavent, peer reviewed Journals" publish papers which present views tangent to modern accepted theories WRT BBT, Dark Matter, etc.? Or does the peer review process "weed out" the alternate viewpoint papers?

http://arxiv.org/find/grp_cs,grp_math,g ... /0/all/0/1

Not really. A published, peer reviewed paper is not an automatic guarantee of something being true.

It would seem to me that you might be asking the impossible of Michael and others to reference theory papers that peer review Journals will not publish.

You'll notice that Nereid will have to qualify her publishers list to exclude my materials. It's not only that she requires it to be 'published', it has to b published by the mainstream, which is certainly skewing the conversation toward a mainstream position, as though the peer review process guarantees truth. It is in essence an appeal to authority fallacy.

In your view, to which peer reviewed journals should they turn to find the data needed to qualify as acceptable references?

Good question. Her list of "acceptable" publications will certainly not include any that have published my work.

Maybe you can help me out here Michael ... I'm having difficulty finding any papers in "Physics of Atomic Nuclei" or in the "Journal of Fusion Energy" on dark matter ... or on astrophysics in general.

Would you be able to point to a half dozen (say) relevant 'dark matter' or astrophysics papers in each journal (other than those by you and/or Manual)?

Thanks.

[Nereid]

Specifically, wrt the part of your post I am quoting: if you would like a worked, OOM, calculation of the estimated density of DM (or DE) within the Sun, I (and, no doubt, several others who post here) would be more than happy to oblige.

I think I'd like to take you up on that offer. I would appreciate seeing you do that actually.

No worries!

There are a great many ways to approach this; I'll be using an OOM (order of magnitude) one, aiming for robustness of the conclusions rather than precision of the answers.

Let's start with the average, across the whole universe, mass-energy density of its constituents.

Let's assume the universe is flat - its density is essentially the critical density.

What is this critical density? For our purposes, we can assume 10^-29 grams per cubic centimetre. Note that this corresponds to 150 billion solar masses per cubic megaparsec*, or 5.6 keV/c^2 per cubic centimetre*.

If we take the latest WMAP result re the composition of the mass-energy of the universe (74% dark energy, 22% dark matter, 4% atoms), then on average, a cubic centrimetre of our universe comprises 7.4 x 10^-30 g of DE, 2.2 x 10^-30 g of DM, and 0.4 x 10^-30 g of atoms.

While DE is the most mysterious of these components, it does seem to be distributed uniformly, so each cubic centimetre will have the same amount.

How much DE is there in the Sun then? The radius of the Sun is 695,000 km, so crunching the numbers I get ~10 kg. As the observed mass of the Sun is ~2 x 10^30 kg, this is somewhat below our ability to detect.

How much DE is there in our solar system? Taking the solar system as a sphere of radius 50 au, turning the handle, I get an estimated 13 billion tonnes. It seems a lot ... but it's not; for example, the Moon has a mass that is over 1 billion times greater, and if you made a cube of ice, 200 m per side, it would have a mass greater than 13 billion tonnes. What about the effect of such a mass of DE, on the orbits of solar system bodies? Well, the total mass interior to 50 au, of our solar system is >2 x 10^30 kg (that's just the Sun's mass), so an extra 13 billion tonnes or so is easy to miss.

What about DM?

If DM were also distributed uniformly throughout the universe, then we can simply divide the above numbers by ~3.4* ...

However, DM is clearly not distributed uniformly; it is more dense around (spiral) galaxies, and in rich clusters (for example).

If the local (within the solar system) density of DM were 3.4 times the average in the universe, then we could just use the above DE numbers*.

But suppose DM is much, much more concentrated here ... 340 or 3,400 times more concentrated ...

Then the Sun would contain ~1 tonne or 10 tonnes of DM, and the solar system (out to 50 au) 1.3 trillion or 13 trillion tonnes of DM.

Perhaps we can put these estimates into a different context.

The Sun is active; every so often it burps, and emits a CME (Coronal Mass Ejection). How much mass is there in one of these? Typically, 100 million to 1 billion tonnes. It seems a lot ... but it is far, far too small to have an observable effect on the orbit of any planet, or even any asteroid. Indeed, light may have a greater, more measurable effect.

The solar system contains an amount of DE ~10 times the mass of a large CME, and possibly ~10,000 times a 'large CME's worth' of DM. As it's spread out, and as it interacts with the stuff of the solar system only via gravity (as far as we know), it should come as no surprise that neither DE nor DM have yet been detected in our solar system, let alone in the Sun.

Of course, you may check my arithmetic for yourself, and if you find any mistakes, please do let us all know ...

*Can you see why? If not, ask!

[Nereid]

I think I'd like to take you up on that offer. I would appreciate seeing you do that actually.

No worries!

FYI, I really do appreciate your efforts and your time. I do of course have some basic questions about some of your assumptions that I need to ask you about.

There are a great many ways to approach this; I'll be using an OOM (order of magnitude) one, aiming for robustness of the conclusions rather than precision of the answers.

This sounds like a very reasonable approach from my perspective as well.

Let's start with the average, across the whole universe, mass-energy density of its constituents.

Let's assume the universe is flat - its density is essentially the critical density.

What is this critical density? For our purposes, we can assume 10^-29 grams per cubic centimetre. Note that this corresponds to 150 billion solar masses per cubic megaparsec*, or 5.6 keV/c^2 per cubic centimetre*.

Ok.

If we take the latest WMAP result re the composition of the mass-energy of the universe (74% dark energy, 22% dark matter, 4% atoms), then on average, a cubic centrimetre of our universe comprises 7.4 x 10^-30 g of DE, 2.2 x 10^-30 g of DM, and 0.4 x 10^-30 g of atoms.

I need you to briefly explain the percentages here for me for a moment. How were the actual percentages for DE and DM calculated from WMAP data exactly?

While DE is the most mysterious of these components, it does seem to be distributed uniformly, so each cubic centimetre will have the same amount.

Hmm. That seems like a leap of faith from my perspective, since normal matter, while evenly spaced over a wide enough area, is not "uniformly distributed" at the solar system level. Why would DE be distributed uniformly at the solar system level?

Does DE always have the same effect on every area of "space"? In other words if it causes "space" to expand, would it not cause the space between the sun and the earth to expand as well?

How much DE is there in the Sun then? The radius of the Sun is 695,000 km, so crunching the numbers I get ~10 kg. As the observed mass of the Sun is ~2 x 10^30 kg, this is somewhat below our ability to detect.

As it relates to DE, I'm less concerned amount of DE in the sun itself, I'm more interested in it's effect on orbits, including periodic comets, and planets and moons and such. Is the 'space" between subatomic particles expanding, the space between suns and planets, the space between planets and moons, etc?

How much DE is there in our solar system? Taking the solar system as a sphere of radius 50 au, turning the handle, I get an estimated 13 billion tonnes.

Does this flow from some particular direction? How does it interact with matter and DM? Does it's interaction with matter cause it to get "deflected" in any way from it's interactions with matter or DM?

It seems a lot ... but it's not; for example, the Moon has a mass that is over 1 billion times greater, and if you made a cube of ice, 200 m per side, it would have a mass greater than 13 billion tonnes. What about the effect of such a mass of DE, on the orbits of solar system bodies?

Great question from my perspective too.

Well, the total mass interior to 50 au, of our solar system is >2 x 10^30 kg (that's just the Sun's mass), so an extra 13 billion tonnes or so is easy to miss.

[snip]

[snip]

I'll answer your questions in two parts: those relating to dark energy (DE), and those to dark matter.

The former (DE) I will address in a new thread, as this thread is about DM.

But, just to address one question very quickly: "What about the effect of such a mass of DE, on the orbits of solar system bodies?" and your comment "Great question from my perspective too."

The next part of my post that you quote does, in fact, answer this; however, I'll take it a little more slowly.

1) to a first (and probably a second too) approximation, in Newtonian gravity, the orbit of a (small) point mass around a (large) central mass does not depend upon the distribution of that central mass, as long as it is symmetrical wrt the orbit. IOW, if you took the Sun apart, and smeared it out over a volume 10 times as great as it is today, the orbits of the Earth, Jupiter, etc would not change. Or, saying much the same thing from the reverse perspective, the orbits tell you only the total mass 'interior' to the orbiting masses. The orbit of Saturn is obviously influenced by Jupiter ... but Jupiter is not smeared out into a thin disk, or ring (torus); if it were, then (to a first approximation) the orbit of Saturn would be the same whether Jupiter were dumped into the Sun or smeared out into a sphere of uniform density inside Saturn's orbit. So, in the case of DE, assuming uniform distribution (its mass-energy density is everywhere the same), the orbit of a test mass just above the Sun's surface would be different than one at 50 au by the equivalent of the Sun having an extra 13 billion tonnes of mass (once you factored out all the other solar system bodies). I.e. completely undetectable, today.

2) The gravitational effect of a 13 billion tonne point mass, on the orbit of any solar system body, is way below detectability ... except 'near' bodies of comparable mass, say within 3 OOM. Take an example: the observed motion of the Earth (from Mars, say) is obviously affected by the Moon, and if the Moon were completely invisible, you could quite accurately predict where it is (and what its mass is) from your Mars-based observations alone. However, the effect on the observed motion of the Earth due to the ISS is undetectable. Indeed, there have been several Earthly 'close calls' recently, with comets and asteroids; AFAIK, none of these has had any detectable effect on the observed motion of the Earth, or even the Moon. Yet they were all estimated to have masses considerably greater than 13 billion tonnes. If a 13 billion tonne point mass is essentially undetectable, in terms of solar system body orbits, then the same mass smeared out uniformly over a sphere of radius 50 au will be even more undetectable.

(questions on DM addressed in the next post)

[Nereid]

[snip]

Well, the total mass interior to 50 au, of our solar system is >2 x 10^30 kg (that's just the Sun's mass), so an extra 13 billion tonnes or so is easy to miss.

What about DM?

If DM were also distributed uniformly throughout the universe, then we can simply divide the above numbers by ~3.4* ...

However, DM is clearly not distributed uniformly; it is more dense around (spiral) galaxies, and in rich clusters (for example).

How about the mass within solar systems? Wouldn't DM tend to concentrate in and around normal mass?

If the local (within the solar system) density of DM were 3.4 times the average in the universe, then we could just use the above DE numbers*.

But suppose DM is much, much more concentrated here ... 340 or 3,400 times more concentrated ...

Hmmm. I'm a little concerned here frankly. Mass does not necessarily stay uniformly distributed at the solar system level in particular. I don't think your method works if you used this same exact approach to calculate the density of normal matter in our solar system, compared to the whole size of the universe. Whatever concentration patterns you come up with to get normal matter to collect to our solar system density should be the same exactly figure you use for DM, no?

Here's what I'm getting at. If a solar system of normal matter attracts DM, and DM if 5 times more plentiful than normal matter, then there is a logical possibility that the "DM" in this solar system is 5 times greater than the normal mass in this solar system. Your "method" should at least allow for that possibility, and I don't think it does.

Then the Sun would contain ~1 tonne or 10 tonnes of DM, and the solar system (out to 50 au) 1.3 trillion or 13 trillion tonnes of DM.

Perhaps we can put these estimates into a different context.

The Sun is active; every so often it burps, and emits a CME (Coronal Mass Ejection). How much mass is there in one of these? Typically, 100 million to 1 billion tonnes. It seems a lot ... but it is far, far too small to have an observable effect on the orbit of any planet, or even any asteroid. Indeed, light may have a greater, more measurable effect.

The solar system contains an amount of DE ~10 times the mass of a large CME, and possibly ~10,000 times a 'large CME's worth' of DM. As it's spread out, and as it interacts with the stuff of the solar system only via gravity (as far as we know), it should come as no surprise that neither DE nor DM have yet been detected in our solar system, let alone in the Sun.

Of course, you may check my arithmetic for yourself, and if you find any mistakes, please do let us all know ...

*Can you see why? If not, ask!

I don't really see any other flaws in your logic besides the afore mentioned issues. If indeed the concentrated amount of DM were as small as your method predicts, then the effect would probably be small. If however DM is "concentrated" to the same percentages as normal matter at our solar system level, your math doesn't apply. I think you method is essentially mathematically sound, but the assumptions your method is build upon (particularly that concentration issue) are highly suspect IMO.

[snip]

Let's make some simplifying assumptions. When we're done, we can go back and see how making the assumptions less simple might change our conclusions*.

Let's consider just 'DM' and 'atoms'. Let's assume that they both interact gravitationally, according to GR (actually, according to just Newtonian gravity will do), but that DM is not affected by the electromagnetic force (EM)^. Atoms are obviously strongly affected by EM.

Let's take a large number of DM particles (which may be of any mass), distributed uniformly over a sphere in otherwise empty space. After a while, they will be no longer distributed uniformly, but in a spherically symmetric way, with a density profile that peaks at the centre of the sphere. The detailed profile depends upon a number of factors, such as how 'hot' the DM was to start with, and how long is 'a while'.

If we run the experiment with atoms, instead of DM, we get a very different result. First, the behaviour is a great deal more complicated - atoms can ionise when they collide; the gravitational potential energy of the system can be 'lost' as photons carry away energy; and so on. The most dramatic result (depending on the part of parameter space we're exploring) is the formation of 'stars' - the process of gravitation collapse (due to the combination of gravity plus loss of energy due to radiation) is halted when gas pressure (etc) produces a stable configuration. Another interesting result is the formation of disks - gravitationally collapsing clouds of atoms produce disks, due (fundamentally) to the ability of atoms to transfer energy and angular momentum in (inelastic) collisions.

Because they have essentially no gas and because stars in them very rarely collide, globular clusters may serve, at one level, to show what DM distributions look like - spherically symmetric, with a central peak.

The Orion nebula serves as a good illustration of what distributions of atoms look like. Note that if the Orion nebula contained no 'metals' (astronomers refer to all elements other than H and He as 'metals'), it would have a very different distribution. At another level, Beta Pictoris illustrates what distributions of atoms look like. Note that no DM distribution could naturally look like either the Orion nebula or Beta Pictoris.

What about if you have a mixture of atoms and (cold) DM? This gets very complicated! However, the good news is that quite a number of just such mixtures have been simulated, in great detail. One the biggest and most extensive simulations is the Millenium simulation.

Back to the solar system.

Here's a method for estimating the mass of DM distributed in a spherically symmetric fashion, centred on the Sun:

-> observe the motions of (massive) solar system bodies - especially planets, their moons, asteroids (and their moons), and KBOs (Kuiper Belt Objects)

-> estimate the mass of the planets, using observations of the motions of their moons (for Venus and Mercury, use the observed motions of the relevant space probes; for asteroids and KBOs without moons, extrapolate from mass estimates of those with moons)

-> analyse the observational data, apply Newton, estimate the mass distributed in a spherically symmetrical fashion, interior to the orbit of each planet, asteroid, and KBO; make sure to take out the effect of the planets (etc), using the masses estimated in the step above

-> search for a trend in the 'mass interior to orbit' estimates, where that mass increases with orbital radius

-> use any such statistically significant trend to estimate the distribution of DM within the solar system.

AFAIK, there is no statistically significant trend; ergo, there is no observably detectable DM in the solar system, at least beyond the orbit of Mercury.

While the bounds are not as tight, you can use the observed motions of sun-grazing comets to constrain the mass of DM between (say) 1 million km above the photosphere and Mercury's orbit ... same result, no detectable DM.

*This is a pretty common approach in modern astronomy.
^Adding the strong force - DM is 'blind' to it, 'atoms' are not - makes the situation even more clear; I don't know what difference having DM respond to only the weak force would have ('atoms' also respond to the weak force).

[Nereid]

If we take the latest WMAP result re the composition of the mass-energy of the universe (74% dark energy, 22% dark matter, 4% atoms), then on average, a cubic centrimetre of our universe comprises 7.4 x 10^-30 g of DE, 2.2 x 10^-30 g of DM, and 0.4 x 10^-30 g of atoms.

I need you to briefly explain the percentages here for me for a moment. How were the actual percentages for DE and DM calculated from WMAP data exactly?

How to estimate the composition of the mass-energy of the universe - specifically that of dark energy (DE) and dark matter (DM) - from the WMAP results (and generally)?

Here's a thread on just this question: How to estimate %dark energy and %dark matter in universe?.

[Nereid]

A general comment first, Michael: at a sufficiently high level, the approach I have used, in the post of mine you are quoting, follows the modern (astronomical) scientific method: if a theory can reproduce all the observed phenomena within (the theory's) domain, to within the uncertainties of the good, relevant observations and experiments, well, that's pretty much all you can ask of any such theory.

As we have already established, in your own, personal, view of the nature of astronomy, this may be different.

However, this Cafe is not an appropriate place for you to try to reconcile your own personal views of the nature of astronomy, as a science, with what astronomers actually do, when they do scientific research.

Now for some specifics ...

Let's make some simplifying assumptions. When we're done, we can go back and see how making the assumptions less simple might change our conclusions*.

Let's consider just 'DM' and 'atoms'. Let's assume that they both interact gravitationally, according to GR (actually, according to just Newtonian gravity will do), but that DM is not affected by the electromagnetic force (EM)^. Atoms are obviously strongly affected by EM.

FYI, I'll save my comments for DE in the other thread.

When you make proclamation statements such as these about DM, and assign properties to it (in this case you claim it is unaffected by EM fields), I am at a loss to understand how to test such a concept. I am already having to rely on "faith" here, and simply take your word for it, otherwise you are incapable of demonstrating such a trait in any controlled condition. It is simply "assumed" from the start that this is true, and I have no way to validate or falsify that statement.

This is as good an example as any ...

The modern approach starts with postulates (or assumptions), as I have said in other, earlier, posts. The postulates themselves have no particular meaning, or importance. From the postulates, you can derive - logically, consistently, objectively - conclusions about phenomenology (what you should expect to see, with telescopes, etc). If you see those things, then your theory (and its postulates) have been (provisionally) validated; if not, then not.

A general, non-specific, requirement for 'controlled conditions' is a red herring - should your theory lead to potentially 'in the lab, controlled' testable phenomena, then good ... you can get a grant, buy the equipment (etc), set up the experiment, perform it, write up the observations/results, publish them, and you're done.

If not, you can't ... and that's what astronomy is, to a great extent, about ... you can't make a Sun in your lab, so anything to do with 'Suns' under controlled, lab, conditions is unrealistic (today).

I am still unclear how you arrived at the percentage of DM compared to the percentage of normal matter in the universe based on the WMAP data. Could you explain that part?

There's a separate thread on that.

Let's take a large number of DM particles (which may be of any mass), distributed uniformly over a sphere in otherwise empty space. After a while, they will be no longer distributed uniformly, but in a spherically symmetric way, with a density profile that peaks at the centre of the sphere. The detailed profile depends upon a number of factors, such as how 'hot' the DM was to start with, and how long is 'a while'.

You just assigned several more "properties" to DM that cannot be tested in a controlled manner as far as I know. I now have to 'assume" a density profile of DM as well as several "properties'' that are unique to DM.

We would still expect DM to be attracted to normal matter would we not? We would expect it to affect normal matter (gravitationally) would we not? Wouldn't they tend to attract one another like all forms of mass?

Indeed ... and I covered that later in the same post that you're quoting from!

If we run the experiment with atoms, instead of DM, we get a very different result. First, the behaviour is a great deal more complicated - atoms can ionise when they collide; the gravitational potential energy of the system can be 'lost' as photons carry away energy; and so on. The most dramatic result (depending on the part of parameter space we're exploring) is the formation of 'stars' - the process of gravitation collapse (due to the combination of gravity plus loss of energy due to radiation) is halted when gas pressure (etc) produces a stable configuration. Another interesting result is the formation of disks - gravitationally collapsing clouds of atoms produce disks, due (fundamentally) to the ability of atoms to transfer energy and angular momentum in (inelastic) collisions.

Ok, suppose I assume with you that there is an EM difference between normal matter and DM. Even still, the gravitational fields of matter are going to affect the movements of dark matter and visa versa, correct? Even if only in an indirect way, DM is going to be influence by the effect of the EM fields isn't it?

Because they have essentially no gas and because stars in them very rarely collide, globular clusters may serve, at one level, to show what DM distributions look like - spherically symmetric, with a central peak.

That doesn't really make sense from my perspective. If stars do all sorts of cluster dances when they get close to one another, based on GR influence alone, why wouldn't dark matter do similar things as well? In other words even without any EM field present, there isn't really any reason to believe that dark matter won't "clump" into objects of various sizes, or is there some "property" of DM I'm still missing?

In one sense, it's incredibly simple: a bunch (hundred, billion, ...) of objects which interact only via (Newtonian) gravity will evolve into a (relatively) stable (equilibrium) configuration ... 'relaxed' is the technical term. The stars in a globular cluster behave like DM particles - they (effectively) never collide, and their motions are determined entirely by gravity .... and they are relaxed. To a first order of approximation, systems of DM objects will 'look like' globular clusters - nearly spherical distributions, with a distinctive radial profile (and central peak).

At the next level of approximation, various details start to be important ... leading to a number of different profiles (but the Navarro-Frenk-White profile (NFW) is the most widely used).

The Orion nebula serves as a good illustration of what distributions of atoms look like. Note that if the Orion nebula contained no 'metals' (astronomers refer to all elements other than H and He as 'metals'), it would have a very different distribution. At another level, Beta Pictoris illustrates what distributions of atoms look like. Note that no DM distribution could naturally look like either the Orion nebula or Beta Pictoris.

I'm a bit confused now. In theory, DM "could" do anything, but in one moment you were claiming that normal matter and DM can't be compared because of the effect of EM fields on matter, and in the next minute you seem to be suggesting that DM can be compared to material items which I would expect are strongly influenced by local EM fields, particularly the Beta Pictoris option you cited. It seems like you wish to have your cake and eat it too.

If all DM particles (no matter how small, or large; no matter how light, or massive) can do is interact gravitationally, and if there's nothing but DM particles, then no Orion nebulae or Beta Pic discs could ever form.

What about if you have a mixture of atoms and (cold) DM? This gets very complicated! However, the good news is that quite a number of just such mixtures have been simulated, in great detail. One the biggest and most extensive simulations is the Millenium simulation.

As a computer programmer by trade, I appreciate the power of computers to model things. I also know that a computer program can be useless if it is built upon false assumptions. I'd be a lot more impressed by a controlled scientific tests that demonstrated DM existed and had some effect on normal matter that I could replicate here on earth.

Indeed.

One, of many, wonderful things about these kinds of simulations is the stimulus it provides for observational tests.

One serendipitous discovery of SDSS is the richness of stellar streams in the Milky Way's halo ... the PIs got funding to do an extension of SDSS, specifically to look more closely into the nature of the stellar populations in the MW halo.

And what has this got to do with DM? Cosmological-scale simulations, using realistic inputs (DM, 'atoms', etc), produced some interesting patterns at the galaxy and galaxy halo scale. To the extent that our MW galaxy is representative, we should expect to find those patterns in the halo ... let's go look!

Back to the solar system.

Here's a method for estimating the mass of DM distributed in a spherically symmetric fashion, centred on the Sun:

-> observe the motions of (massive) solar system bodies - especially planets, their moons, asteroids (and their moons), and KBOs (Kuiper Belt Objects)

-> estimate the mass of the planets, using observations of the motions of their moons (for Venus and Mercury, use the observed motions of the relevant space probes; for asteroids and KBOs without moons, extrapolate from mass estimates of those with moons)

-> analyse the observational data, apply Newton, estimate the mass distributed in a spherically symmetrical fashion, interior to the orbit of each planet, asteroid, and KBO; make sure to take out the effect of the planets (etc), using the masses estimated in the step above

-> search for a trend in the 'mass interior to orbit' estimates, where that mass increases with orbital radius

-> use any such statistically significant trend to estimate the distribution of DM within the solar system.

AFAIK, there is no statistically significant trend; ergo, there is no observably detectable DM in the solar system, at least beyond the orbit of Mercury.

While the bounds are not as tight, you can use the observed motions of sun-grazing comets to constrain the mass of DM between (say) 1 million km above the photosphere and Mercury's orbit ... same result, no detectable DM.

I'm not convinced that is a valid argument. If we can't see DM, then it could be liberally dispersed throughout the solar system with enough mass on the outside of the solar system to "offset" much of it's effects inside the solar system. In other words, you are excluding the option that DM exists inside *and* outside out solar system of planets. Furthermore you do seem to be excluding the possibility that the sun itself and every planet is composed of a certain amount of dark matter, meaning you could actually be *overestimating* the amount of normal mass in the sun and planets, or you could be underestimating that mass depending on the distribution of DM in and around the solar system.

[snip]

Not really.

Remember that I've only sketched, in the briefest possible way, just one test.

And most of your (good) questions are beyond the scope of the specific hypothesis I set out to test.

Let's take "lots of DM outside the solar system": unless it were distributed in a particularly non-uniform way, or unless there were a very great deal of it, the test I described won't show it. However, there are plenty of other tests ...

Or "lots of DM inside each and every planet, moon, asteroid, the Sun ...": the test I described in my post is mute about this; to put strong constraints on the amount of DM within the solid, liquid, or (some weaker constraint) gaseous boundary of any (large) solar system body, you need to do different tests.

Would you like me to sketch some such tests?

[Nereid]

A general comment first, Michael: at a sufficiently high level, the approach I have used, in the post of mine you are quoting, follows the modern (astronomical) scientific method:

I am aware of that.

if a theory can reproduce all the observed phenomena within (the theory's) domain, to within the uncertainties of the good, relevant observations and experiments, well, that's pretty much all you can ask of any such theory.

Well, as you know, I can certainly ask for more of your theory (all theories actually). That doesn't mean that you can provide it, or that it cannot be provided to me in other scientific theories, even scientific theories related to the same observations.

I'm simply noting that as it relates to DM, I am at a complete loss to begin to test any of the properties you have ascribed to your it. Contrast that with the known energy state of a neutrino. I simply have to "assume" that DM actually exists, and that it has a number of "properties" which I cannot test in any controlled way the way I can test the properties of something like a neutrino. Were I to posit an iron sun explanation for this missing mass, you would expect me to demonstrate it somehow. Whatever the claim, the onus of responsibility always falls the the individual(s) making the claim.

Which part of "if a theory can reproduce all the observed phenomena within (the theory's) domain, to within the uncertainties of the good, relevant observations and experiments, well, that's pretty much all you can ask of any such theory" did you not understand, Michael?

As we have already established, in your own, personal, view of the nature of astronomy, this may be different.

However, this Cafe is not an appropriate place for you to try to reconcile your own personal views of the nature of astronomy, as a science, with what astronomers actually do, when they do scientific research.

I'll try to save most of that particular part of the discussion for the scientific method thread (which I will take up again at some point by the way).

Indeed, that's what the thread is for.

You seem to imply however that criticism and skepticism of mainstream thinking is not welcome here. Why would you shy away from a skeptical review of your industry? What do you have to hide or be afraid of from me? I'm just one lowly skeptic among a chorus of believers.

We have been over this several times Michael.

We have established that your, personal, approach to matters astronomical and cosmological is at odds with that of the modern astronomers and cosmologists, in respect of their 'doing' of scientific research.

You are most welcome to be critical and sceptical about that work, within the framework of the scientific methods they use.

Your personal opinions on those scientific methods have had an extensive airing here.

However, you should find another forum in which to pursue continuation of your criticism and scepticism of those scientific methods.

This is as good an example as any ...

The modern approach starts with postulates (or assumptions), as I have said in other, earlier, posts. The postulates themselves have no particular meaning, or importance. From the postulates, you can derive - logically, consistently, objectively - conclusions about phenomenology (what you should expect to see, with telescopes, etc). If you see those things, then your theory (and its postulates) have been (provisionally) validated; if not, then not.

When you claim that postulates have no particular meaning or importance, I can't help but wince. Were it not for the postulates you include that are related to the "properties' of DM, we could not "fill the gaps" between our expectations and our observations. In other words, the entire purpose of these postulates is to provide us with a way to make up the difference between expectation and observation. It seems to me that these are highly important, not unimportant. If these attributes were unimportant, you wouldn't need to assign these various attributes to DM in the first place. The more of them that you require that you cannot demonstrate, the more it takes on the appearance of ad hoc gap filler.

Indeed ... and as we have already discussed, here in this thread and in others, your personal views are different from those of modern astronomers, in respect of the nature and role of theories.

We have also, to some limited extent, covered what adopting your personal preferences re the application of science to astronomy would mean. It's time to move on.

A general, non-specific, requirement for 'controlled conditions' is a red herring

Not in every other area of science it's not. Physicists sat down to try to create controlled tests that would reveal the nature and mass, and the effects of neutrinos on mass. They didn't just leave the theory of neutrinos hanging and unverified. They looked for ways to validate and/or falsify the concept in controlled tests. This is SOP for nearly all areas of "science". We test things, whenever and wherever possible. Why shouldn't we try to test your ideas too?

First, they're not 'my' ideas; as I have said, several times, I am merely trying to present summaries of the results of the work of modern astronomers. Please refer to the work of modern astronomers more accurately.

Second, if you know of a way to do controlled tests, in an Earthly lab, of a system of 100 billion solar mass objects, please do tell us. There are a few other branches of science that share some of the characteristics of astronomy in this regard - geology, for example (controlled labs tests of plate tectonics over (tens/hundreds of) million-year histories anyone?).

Third, to the extent that astronomical theories point to possible lab tests, such testing is often done (there are many, many examples).

Fourth, and perhaps most important, the relationship between theory, physics, astronomy, and cosmology is much richer and multi-faceted than your rather one-dimensional characterisation.

- should your theory lead to potentially 'in the lab, controlled' testable phenomena, then good ... you can get a grant, buy the equipment (etc), set up the experiment, perform it, write up the observations/results, publish them, and you're done.

Well, in theory, if we can find neutrinos, we can find DM too, right? How do we know if it's there or not if we don't look?

We've been over this too ... would you be interested in a recent paper which summarises the large number of 'dark matter searches' in earthly labs?

If you can think of some region of DM parameter space which is accessible to searching, in earthly labs, and which has not yet been examined, I think a dozen university physics departments would be very interested!

If not, you can't ... and that's what astronomy is, to a great extent, about ... you can't make a Sun in your lab, so anything to do with 'Suns' under controlled, lab, conditions is unrealistic (today).

Actually IMO, Kristian Birkeland created a pretty good lab simulation of a sun in his lab over 100 years ago.

He did? How did he do that?

[snip]

In one sense, it's incredibly simple: a bunch (hundred, billion, ...) of objects which interact only via (Newtonian) gravity will evolve into a (relatively) stable (equilibrium) configuration ... 'relaxed' is the technical term. The stars in a globular cluster behave like DM particles - they (effectively) never collide, and their motions are determined entirely by gravity .... and they are relaxed. To a first order of approximation, systems of DM objects will 'look like' globular clusters - nearly spherical distributions, with a distinctive radial profile (and central peak).

I think you missed my point. If matter is going to attract other matter around itself purely through gravitational attraction, then in theory at least normal matter and dark matter could and would interact and be "mixed together" in some ratio, presumably the same sorts of ratios we might expect from the abundance percentage numbers. With all this DM around, one would expect someone could produce a gram of this stuff for us to inspect and play with in controlled tests.

If it interacted with other forms of matter only via the gravitational force, how could you obtain a gram or so of it? In what container would you keep it?

We have no reason to believe that DM and normal matter would remain "separated" in any way. It should mix with normal matter if only through the forces of gravitational attraction.

At the next level of approximation, various details start to be important ... leading to a number of different profiles (but the Navarro-Frenk-White profile (NFW) is the most widely used).

So in terms of grams or kilograms, how much dark matter might I hope to find within our own solar system? How about the amount I might expect to find on earth?

[snip]

Good questions! I thought you'd never ask.

(to be continued)

[Nereid]

How much DM might I hope to find in the solar system?

or on/in the Earth?

If we take this from the astronomical point of view, rather than a particle physics one, we have three different approaches we could consider:

1) bounds on local (solar system, Earth) DM, from cosmological considerations

2) ditto, from galaxy cluster estimates

3) constraints from estimates of DM in our own Milky Way galaxy.

The first approach isn't at all helpful: while the average density of DM, throughout the universe, is easy enough to state, and while we know the density of DM will vary, depending on local environment, cosmological modelling is far too large-scale to tell us much more than a likely range of DM density, depending on the history of our galaxy. The 'overdensity range' I used earlier in this thread (say, between 10 billion and 10 trillion tonnes in the solar system*) may be consistent, it may be too low or narrow (more likely).

The second approach won't work at all: we are not part of a rich cluster.

That leaves the third approach.

It seems that ~0.3 GeV per cubic centimetre is a fairly typical value for the average DM density in our part of the Milky Way, from observation-based models of the (broad) DM distribution. What is that, expressed in g/cm^3, or tonnes within 50 au of the Sun?

I'll introduce a paper or two on this 'Milky Way based approach' later.

For now, here is a paper on observational limits on the mass of DM throughout the solar system, and on its distribution. "[A]t the Earth's location," the authors write, the maximal (DM) density "is of the order 10^5 GeV/cm^3."

*Assume uniform distribution throughout the solar system (gamma = 0), then the amount in the Earth is simply calculated: what's the ratio of the volume of the Earth to that of the solar system? Assume an NFW profile (gamma = 1), how much greater is it?