Posted on 11/05/2014 5:04:12 PM PST by LibWhacker
Dark matter might not be nearly as exotic as most theories about the stuff suggest. Instead, it could be macroscopic clumps of material formed from common particles already found within the Standard Model of particle physics. This argument comes courtesy of physicists at Case Western University, as presented in a new paper posted to the arXiv pre-print server.
Dark matter is usually thought of in terms of exotic, so-far undiscovered particles. The leading candidates are known as weakly interacting massive particles, or WIMPs. This is where most of our dark detection efforts are focused, but a small handful of projects are also hunting for “hidden light” particles called WISPs, or weakly interacting slim particles.
Both varieties of particle are characterized by a disinterest in the fundamental forces of nature. WIMPs feel only gravity and the weak force (which drives nuclear decay), while WISPs feel gravity and, just the tiniest bit, electromagnetism (light, thermal energy, etc.). In the absence of these interactions, both sorts of particles behave as sorts of ghosts, existing but not existing.
These particles, while refusing to interact with photons (particles of light, e.g. the carriers of the electromagnetic force), add up to enormous masses. Together, dark matter makes up about 85 percent of all matter in the universe. This mass, acting as a sort of gravitational scaffolding, is what allows for the formation and persistence of galaxies. We live because of dark matter.
The catch is that we’ve never really detected dark matter, at least directly. We know it’s out there because of its gravitational effects, but despite an impressive array of deep-underground detection experiments, we’ve yet to see an actual dark matter particle.
For those in the business of describing reality, this absence is alarming. For one thing, it provides fertile ground for alternative theories to grow. One example is known as MOND, for modified Newtonian dynamics. Basically, it says that there is no dark matter, and the gravitational effects we observe are merely the result of an ecstatic force of gravity. That is, Newton’s equation for gravitational attraction changes dynamically with distance.
At first glance, the Case Western theory is almost as extreme. For one thing, it too suggests that there are no dark matter particles, at least none that exist outside of current knowledge. Instead, there are macroscopic (baseball-sized, say) clumps of “regular” matter formed from unexpected combinations of Standard Model particles. The physicists behind the current paper, led by CWU physicist Glenn Starkman, call this dark matter simply “macros.”
The defining component of macros would be the strange quark, a highly unstable, extremely light variety of particle observed in high-energy collision experiments. (Quarks as a particle class are one of the fundamental constituents of matter.) Starkman and his team suggest that in the very early universe it may have been possible for these strange quarks to get together with more reasonable particles into stable nuclei of matter. They would have to do this with 90 percent efficiency to account for the dark matter we see in space, leaving the non-dark world with enough (but not too many) particle leftovers to form neutrons and protons.
“As pointed out, there is no experimental evidence for any particle candidate for the [dark matter] yet,” Geoffrey Taylor, a physics researcher at the University of Melbourne, noted in an email.
"That some heavy dense objects with properties consistent with [dark matter] constraints, might be speculated is reasonable," he said. "There is no theoretical motivation for such objects. but a cursory look at the paper suggests this simple approach using only necessary constraints from experiment and theory give a range of possibly interesting candidate DM objects."
In order for macros to fit our view of reality, a few things would have to be true. The clumps would have to be more massive than 55 grams, or else they would have been observed in Skylab’s strongly-interacting dark matter detectors. Macros would then have to be less than 1024 million billion billion grams, or else they would be massive enough to bend starlight.
You can't argue with the motivation for looking into this, which is that we know very little about the nature of dark matter.
This bending of starlight hasn’t been observed. Possible masses for macros are further constrained by the indirect astrophysical history provided by sheets of mica buried several kilometers below Earth’s surface.
“If the Macros have a low enough mass, their number density would be high enough to have plausibly left a historical record on earth,” the current paper notes. “If they have a low enough [density] so that they would have penetrated deep (about a few kilometers) into the earth’s crust, a record would have been left in ancient muscovite mica.” No record has been found.
The role of density here is worth unpacking a bit. The density of a given dark matter candidate is given by a ratio of σX/Mx, where σX is a region of space (in which interaction might take place), and Mx is a mass. The standard dark matter models assume a very small space compared to the material’s mass, with the result being very low densities and less interaction (weakly interacting). It’s possible, however, to have strongly interacting dark matter if, instead of making the region of space very small, we make the mass very big.
This is intuitive: Adding a droplet of red dye to a glass of water and dumping a bucket of that same dye to a swimming pool might come up with a similar dilution, or dye density.
The dark matter macro theory isn’t as out there as it might seem. In 1984, the astrophysicist Edward Witten proposed something similar: “dense, invisible quark nuggets.”
“Many models that could be defined as Macros have been written down before, including Witten's nuggets of quark matter 30 years ago,” Manoj Kaplinghat, a physics and astronomy professor at the UC Irvine not affiliated with the current paper, told me. “Glenn Starkman was part of a seminal effort in this direction back in 1990. The present article attempts to systematize the description of ‘Macros’ in terms of their mass and how strongly they interact with normal matter, so that viable models can be clearly identified.
“How interesting these viable models are depends on individual taste,” Kaplinghat said, “but you can't argue with the motivation for looking into this, which is that we know very little about the nature of dark matter.”
No, it’s not detected. An affect, that we attribute to SOMETHING being there (in terms of mass) is observed.
This assumes our supporting theories are correct (i.e. mathematical models of gravity, space, etc).
I would like to remind you that Maxwell’s equations (which were until recently thought to be just a strongly “proven”) have been shown to be violated easily.
Maxwell’s equations are why the Tesla wireless power transmission was believed of 80 years to be a hoax.
Until MIT reproduced the results. And many others have. So now we have Maxwell’s equations (classical EM radiation) and “non-classical” EM radiation.
Clearly until we have an explanation that suits both, neither one is quite correct.
For my money, I don’t think dark matter exists, and that our field theories are incorrect. One day we will have a theory that explains our observations without resorting to “creating” out of thin air 85% of the “stuff” of the universe.
As you might be aware, black holes are now teetering on the “believable” abyss.
One thing is for sure, if you have a 10 year old physics book you might need a newer copy. That statement has stood for the history of mankind.
Now we have scientists doing the exact same thing defying the very premise of the scientific method. As an example I present both AGW and DarkMatter. To be fair Dark Matter as a postulated theory may end up being correct in some form, but many people treat it not as a theory but as a fact. AGW, to be blunt, is not just an easily disproven theory, but is also a scam.
You did not understand my position.
I am advocating that since the theory does not fit the observations, we should not blindly assume that out theory is correct.....we should consider alternate explanations, other than assuming dark matter exits.
After all, the whole universe is showing us something is not right - either our theory is wrong, or there is “dark matter” we can’t see.
Gravity is one of the least understood forces, so I believe that our theories are wrong, not that we can’t see 85% of the universe.
SO..... dark matter is what is left inside the bell jar after you pump everything else out ?
Wow. Thank you!
In a way. Dark matter could possibly be made out of “ghost particles” that don’t interact other than gravitationally. In that case, the room you’re sitting in could be teeming with quintillions of then flying a few hundred miles per second. Not enough speed to escape galaxies, just cluster around them. Their density would be very low per square light year, of course, similar to dark energy. But overall, since there is a gawd awful amount of empty space compared to what we think as being normal, that adds up to a lot. And since these “ghost particles” travel below the speed of light, as they must for dark energy theories to be valid, they have mass.
Dark matter theories I mean. And cubic light years.
Soap bubbles on the surface of a container of water will congregate.
An experiment performed on the Space Shuttle showed that material suspended in a liquid in a weightless environment will do the same thing... cluster.
Is that caused by dark matter ?
Van der waals force perhaps. It’s hard to simulate an entire universe within the confines of one space shuttle.
It’s hard to simulate an entire Universe when we have no idea what it is made of, or how large it is.
I would like to resort to Occam’s Razor and use the simplest and most logical theory to the question of how galaxies attract their mass.
It is an electro-magnetic field the keeps mass centered around a galaxy core. The galaxies spin, and they have a massive ‘core’ and it is theorized that massive black holes occupy the center, and they are suspected to have immense ‘energy’.
The Earth has an EM field, the Sun has an EM field, why not the galaxy ? Do they, or do they not all follow the same physics principles ?
Isn't that what I did ?
Galaxies do have magnetic fields which affect the interstellar medium and accelerate cosmic rays, but are not powerful enough to alter the course of stars.
How are we 'sure' of that ? We haven't even been outside our own solar system.
The Great Attractor is pulling galaxies toward itself. What causes that ?
The simplest explanation is gravity because clumping is very hard to explain using magnetic fields. For one thing, they’re dipolar. They attract as well as repel in non-uniform directions. That’s not what we see with superclusters. They’d look like iron filings around a bar magnet if that was the case. For another, we can in fact measure the magnetic field of our own galaxy, and it’s nowhere near strong enough to pull around massive compact objects like stars. molecular dust and subatomic particles, yes.
So we are back to ground zero.
We think it’s gravity, but the data doesn’t fit reality .
I thought we don’t what Gravity is. Yet we say it can’t account for galaxies staying together, so we come up with “dark matter”. Why not say that dark matter is an unknown element of Gravity?
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