Shedding a Little Light on Dark Matter?

"Their formula suggests that gravity drops less sharply with distance as in Einstein,..."

Then how are we able to successfully predict forces necessary to direct spacecraft in a planned mission? Am I missing something here?

What you're missing is that this proposed non-Newtonian gravity formula diverges from Newton's only at spatial dimensions larger than our solar system. With distances between bodies smaller than our solar system, Newton's equations works perfectly until velocities approach the speed of light. For directing a spacecraft within our solar system, Newton's law [F=G*m₁*m₂/r²] will work quite accurately. For an example, possibly a more accurate gravity equation would be with k≡5*distance to the Oort cloud (several light years) then F=G*m₁*m₂*(1+r/k)/r² could be the actual attraction between two bodies. Some people have proposed that the Pioneer anomaly shows an early effect of this non-Newtonian gravity effect. But those that propose this have not (to my knowledge) had success fitting the observed Pioneer data to anything that would successfully refute the need for dark matter.

Hi redfred,

Thanks for the reply. I was suspecting a scale issue, and you fell right into my trap.

From your previous posts, I am thinking that you are an electrical engineer (if I'm wrong, I'm sorry). How is it then, that you know so much about the current topic? Is it an intense area of interest for you?

Thank you for the in-depth explanation as well as having flawless grammar and spelling!

Mike

Rather interesting idea, but I fail to see how the cosmological equations can be balanced if gravity follows the (1+r/k)/r² rule. Unless it cuts off again at ranges above supercluster size, so that the normal 1/r² rule is restored there.

Another thing is the apparent clumping of dark matter (appearing as the most dominant mass inside galaxies, but with little apparent effect outside it).

-J

Jorrie,

I'm pleased and honored that my idea intrigues you.

But as you noted my quick modification of Newton's gravity law was only intended to provide a simple explanation of a possible variation of this reliable law that deviates at dimensions larger than our solar system. I was not trying to explain the theory identified by the OP article nor Milgrom's earlier work. My equation solves nothing outside of showing a method to modify this force equation at very large distances.

But I have also found the need for 90% of the mass of the universe being dark matter a little suspect. Our local space of the solar system has nowhere near this ratio between light and dark matter. This seems more like a "fudge factor" explanation than a concrete explanation of our universe. Particularly when some explanations require dark matter to attract only within a galaxy but not outside. But now cosmologists have introduced the even more confusing concept of dark energy that appears to be accelerating things away from each other long after The Big Bang occurred. This leads me to wonder if some of our understandings of the laws of physics required to make these weird conclusions don't hold up at these astronomical distances. Particularly when some of the few probes we've sent approaching this distance sent usable data that deviates from standard Newtonian relations.

I do have faith in the scientific method. We will continue our asymptotic approach to a clear understanding of our universe. Along the way, discussions like this make the ride fun.

Hi Redfred, you wrote: "But I have also found the need for 90% of the mass of the universe being dark matter a little suspect. Our local space of the solar system has nowhere near this ratio between light and dark matter."

But the standard LCDM model does not predict that inside the disk of a galaxy, or in the "disk" of the solar system, there must be 90% dark matter. Dark matter is thought to be clumped in a roughly spherical shape around the galaxy, with only a small part present in the disk. I have calculated that the spherical amount of dark matter around the solar system (to the outer Kuiper belt radius) cannot be more than 10¹⁴ kg. Compare that to the mass of the Solar system of more than 10³⁰ kg and you will see what I mean. Between us and the Sun there can only be some 10⁸ kg of dark matter and hence negligible.

Dark matter may sound like a 'fudge factor', but the fact is that it still fits all the available data!

-J

Hello Jorrie,

Unless I've misunderstood your point (quite possibly), I believe you made my point with your numbers. With more than half of the mass of the solar system being the luminous sun of 10³⁰ kg, the requisite amount of dark matter for 90% dark matter is 9*10³⁰ kg. The observed local quantity of dark matter (10¹⁴ kg) out to the Kuiper belt is sixteen orders of magnitude to small to establish this ratio.

At this point I'd like to propose an additional point in my disbelief of dark matter based on our observed solar system. If 90% of the matter in the Milky Way is dark matter so that gravity and only gravity maintains our trajectory around our galactic center, why aren't the orbits of our planets more elliptically skewed toward the galactic center?

Hi Redfred,

No, I think you misinterpreted my figures (unless I understand you wrongly ). The Sun's 10³⁰ kg amounts to 99%+ of the total mass of the Solar system (not merely more than half). The amount of dark matter in the sphere enclosing the Kuiper Belt (10¹⁴ kg) is negligible in comparison. There is no observable dark matter in our solar system - it is spread too thinly to make any sort of difference.

Also, recall that observations fit dark matter spread spherically around the Milky Way, consequently with very little inside the disk or the bulge, when compared to the normal (bright) stuff there. In any case, the mass of the Milky way center does not skew the orbits of the planets - it just influences the orbital speed of the Sun around the center. The orbits of the planets depend only on the mass of the Sun, each others mass and their relative positions.

-J

Jorri-

If I understand this right, the dark matter actually "exists" as a halo about the galaxy, not widely distributed within. If this is the case, then, as we observe the rest of the Universe, we are actually looking through a "lens" of dark matter, which may or may not distort the image we are receiving, depending on how the halo affects the electromagnetic radiation that we are using to build our image of the universe. It seems that if the MOND hypothesis or its derivitives can explaining the gravitational effect of the galaxy without the catch-all bucket of dark matter, would this not indicate that the image we are building is more reliable?

Hi CW, yes, they speak of a dark matter 'halo', but this cannot be a physical "hollow shell" type of halo. In order to fit the data, it must be a spherical 'ball' of dark matter, centered on the galaxy, possibly more dense towards the center of the galaxy.

A 'hollow shell' type of halo does not have any gravitational influence inside the shell, just outside. A sphere has progressively more and more influence the farther you go from from the center (but still inside the sphere), since only the matter inside that radius has gravitational influence there. This explains the galaxy rotation curves more or less.

On lensing: only gravitational lensing is possible with non-baryonic dark matter (the favorite species) - no refraction, because it does not interact with ordinary matter. Gravitational lensing is most evident when light passes a galaxy, not when it enters the galaxy and ends up in a local astronomer's telescope. The small effect that does remain is easy to compensate for, if required. So, no, I do not think our images are distorted by dark matter, except where we view distant light passing very heavy concentrations of matter. Then it is fortunate, because it tells us the mass of that concentration.

MOND has difficulties explaining the "Bullet Cluster" observations; dark matter has no problem with it, so it remains the favorite catch-all.

-J

Jorrie,

I did remember that the sun's mass greatly dominated the mass of the whole solar system. But with so many Plutoid objects recently identified and an unknown number of smaller objects out there along with them, I choose the very safe ultra-conservative statement that more than half of the mass of the solar system was the sun.

Something I'd like for you to clarify for us though that seems to be a contradiction. Dark matter is supposed to be 90% of the mass of a galactic system to not have stars wandering away from a galaxy. Also dark matter is uniformly spherically distributed through our galaxy. Yet in our solar system the amount of hidden dark matter (non-Baryonic matter) is so minute that no noticeable effect on the observed dark matter (Baryonic matter like planets) found in our solar system. (I worked so hard to make that not a run on sentence, too.) So is this apparent contradiction supposedly resolved by the scale in size between stars being much larger than the size of the star's solar systems? Or am I missing another piece of this puzzle? A crude estimation seems like there must be more than six orders of magnitude of a difference in space volumes for undetectable mass to now become 90%. Also our sun is only an "average" size star, there are many more massive luminous objects in our galaxy, so maybe I again grossly underestimated the required near empty space between stars.

Thanks for the enlightenment.

Hi Fred, you wrote : "Dark matter is supposed to be 90% of the mass of a galactic system to not have stars wandering away from a galaxy. Also dark matter is uniformly spherically distributed through our galaxy. Yet in our solar system the amount of hidden dark matter (non-Baryonic matter) is so minute that no noticeable effect on the observed dark matter (Baryonic matter like planets) found in our solar system."

Correct, I think. I have made some rather simple calculations, based on some reasonable assumptions. Please cross-check my assumptions - there may be gross errors...

The radius of the sphere just including the Kuiper belt is ~55 AU -> ~ 1E13 meter, with a volume of ~4E39 m³.

The average density of dark matter in the universe is about 2E-27 kg/m³. Multiply that by 10 to allow for larger local density due to gravitational clumping, giving the average density of dark matter in our Galaxy of ~ 2E-26 kg/m³. (Since these are OOM calcs, the exact value is not important).

Assume that this is the density of dark matter in the solar system, giving the dark matter in the "Kuiper-belt sphere" ~ 4E39 x 2E-26 = 1E14 kg. Compare with the mass of the Solar System of at least 2E30 kg and you see what I mean

I would not trust the interstellar 'empty-space' volumes in such a calculation...

-J

Hi again Fred.

I might have been out on the dark matter density in our Galaxy by some factor of a million, due to an underestimate of what gravitational clumping can do. Here is a new estimate, which still does not make dark matter a factor in our solar system...

I wrote: "The average density of dark matter in the universe is about 2E-27 kg/m³. Multiply that by 10 to allow for larger local density due to gravitational clumping, giving the average density of dark matter in our Galaxy of ~ 2E-26 kg/m³"

If our galaxy weighs in at 1E42 kg (normal matter), then a sphere of 60,000 ly or ~ 1E21 meter, or volume ~ 1E63 m^3 will have a density of 1E-21 kg/m^3. The average normal matter density of the universe is ~ 1E-27 kg/m^3, which means that the clumping of galaxies produces an average local density about a million times larger than the cosmic average (the universe comprises mostly of empty space).

If we assume that dark matter clumps roughly proportional to normal matter, then the total dark matter competing with the Sun on the scale of the Kuiper belt is about 1E20 kg (where I had 1E14 kg above), still 10 orders of magnitude smaller than the Sun's 1E30 kg.

-J

Jorrie, between yourself and Redfred, kindly address a simple question, if there is an answer. A neutron inside an atomic nucleus, or a neutron in a deuteron, is apparently very stable. When we have a free neutron, it's decay time is in the order of 10.3 minutes. What is the physics of a neutron star that allows apparently free neutrons to exist "infinitely"? Is it possible that "dark matter" is simply huge clouds of stable neutrons? In Nova and Supernova events, there would be sufficient enerygy (>1.29 MEV per proton) to convert protons into neutrons, and thus eject clouds of "dark matter" neutrons? There are huge clouds of hydrogen (thus huge masses of protons). Thank you.

Cardio,

Good question but not a simple answer. The obvious quick explanation is that the rest of the nucleus provide the stability for the neutrons inside. The University of Illinois came up with the simplest explanation I could find. But this requires acceptance of the Pauli exclusion principle that no two particles can have the same quantum numbers. ("Acceptance" is an awkward word choice on my part. For this principle is so basic a fundamental of quantum mechanics that the consistent observation of it always being true precludes a proof.)

Hi Cardio07

I think the neutrons inside neutron stars are not free - they are at least intensely gravitationally bound and more or less at a minimum energy level, making it almost impossible to decay. However, what is happening deep inside a neutron star may never be known - perhaps some form of exotic material lives in there...

Free stable neutrons in otherwise 'empty space' probably do not exist, so I doubt if they can be dark matter candidates. And if they could, would they be dark? Definitely not non-baryonic. More I do not know...

-J

I am really curious as to how this new theory differs from Milgrom's work. Milgrom's work has seemed very promising to me- much more palatable than the concept of "Dark Energy"- which sounds too much like the aether of old- a nice bucket to dump all the unknowns into...

As you say, Jorrie, the futher from center of mass you go, the more influence is felt within a given sphere, then it begs the question:Is there some point at the exact center where there is no influence at all?How about a perfect sphere of say, netron star material?Or even a black hole.If gravity is equal from all directions,there should be a null point. An object at this point would also have to be perfectly spherical.

Hi EZStreet, yes, there is no gravitational pull at the exact center of a homogeneous/isotropic density sphere. It is not quite true for a black hole, because our physics breaks down at the central singularity.

Interestingly, a static, perfectly spherical test object at the center of a solid/liquid/gaseous object will stay put, but will be squeezed from all sides, i.e. slightly compressed...

-J

Am I correct to presume that the size of the sphere on the inside does not matter? Then there could be many(infinite?) concentric spheres nested within one another all the way from the outer edge to the center, each having a correlating null point.Shift any one of them, and you upset the whole system.The spheres would alternate off-center positions all the way to the center, creating a wave of sorts

See where this is going? It even looks weird to me.

Must be a flaw in my logic somewhere.

( Yawn!) I'm going to bed.

Hi EZStreet, I do not quite follow your argument about the many concentric spheres. You are right that the null point does not care about the size of the sphere - no gravitational force is no gravitational force...

In a finite, homogeneous sphere, you cannot "shift any concentric sphere" in any way - they are by definition concentric and centered on the single center of gravity of the finite sphere. All points are part of a single sphere and no other point than the center can have zero gravitational force.

I do not understand what "wave of sorts" you are talking about.

-J

OK.Presume a gap between concentric spheres.All gaps are equal and all spheres are centered and concentric.If you upset the outermost inner sphere,it will attract towards the outermost outer sphere and the one inside of it will shift in the opposite direction, and the process will repeat all the way to the center.The spheres are no longer concentric, but a null point exists within each sphere individually.These null points will look serpentine like a wave,will they not?

Sorry for all the redundancy in my descriptions, it just seemed like the simplest way to explain it.

Hi EZStreet, ah, I see you mean concentric hollow spheres. I was referring to solid spheres.

Recall that from the Shell Theorum, a uniform, hollow sphere (or shell) exerts no gravitational forces on any matter inside it (assuming the shell sits in empty space and is not accelerated). So, unless your movement of a single shell bounces it off the other shells, I think there will be no effect if you offset any of the spheres by a little - they should just all sit in this condition.

-J

Thanks EZStreet. Interesting article. I have never been a fan of dark matter, however I'm not going to swallow this new theory hook, line, and sinker either. It is a step in the right direction, I think. Now scientists can start testing and looking for evidence to support it. It will be interesting to see which, if either of these theories exists in 10 years. Both fit the observational data, but I think they are both "fudge factors".

-S

Interesting theory. I wonder if the electromagnetic fields of the stars in individual galaxies and galactic clusters are taken into account in the new formula? They didn't seem to be in the old "Dark Matter" formulas.

Regards Dragon

Is there any known factor that can distort space time (besides energy and mass)?Perhaps space time distortion is non linear on very large scales ?

An analogy:As a ballon inflates, the pressure required to increase it's diameter decreases.With sufficient and stable pressure, the ballon increases in size rapidly at first, then tapers off, though still accelerating at an increasing rate

As a rubber sheet is stretched, it requires less to achieve the same distortion.Perhaps space time loses it's "tenacity" as it is stretched on large scales.This would create a deeper "hole" on galactic scales.