Fuck Dark Matter; It's a sprinkler, not a whirlpool.

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skolnick1
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Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Mon Aug 25, 2014 9:58 pm UTC

Spoiler:
Image


Why the hell is it just an unspoken assumption that galaxies formed in the same way that our solar system did?
Much of the evidence that leads us to postulate the existence of dark matter is predicated on this assumption, but there's absolutely no reason why two systems that exist at such different scales should automatically be assumed to have similar formation dynamics.
The most common answer I've gotten to this question is "Well how else would it have formed?", to which I have an answer.

A black hole has a maximum angular momentum, determined by its mass, the gravitational constant, and the speed of light. If we treat a black hole as a purely mathematical object and ask what happens when it exceeds its maximum angular momentum, it has been said that it becomes a "black donut", as the toroid allows wider distribution of its mass.

This seems unlikely.

A more plausible answer is that the black hole would shed angular momentum by spitting out massive particles in the plane of its rotation. Spatial energy density at the ergosurface is more than adequate to generate neutrons, perhaps with their antineutron counterparts on the inside of the surface. If we examined the case of two black holes orbiting one another, inducing such an effect, one might observe matter flung off from either side of this system of bodies. The high-energy collisions of these particles could lead to ionization and charge.

Look hard at that image and ask yourself which seems more likely:
a) It started as a massive cloud, and a pre-formed halo of invisible, exotic matter pulled it down into its current shape and binds it together to maintain its spiral structure.
or
b) It started in the middle and spun out from there, flung away at great speed but remaining bound by the mass still at the center.

There have been clues to this throughout recent astronomical history, from Rubin's observation of a gas jet being ejected from Andromeda's nucleus to the dusty cross at the heart of M51, and the counterintuitive advanced age and lower metallicity of halo stars at the edge of galaxies.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Tyndmyr » Mon Aug 25, 2014 10:00 pm UTC

How would you test this theory?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby brenok » Mon Aug 25, 2014 10:12 pm UTC

A sprinkler left running for billions of years would flood the whole space. How do you explain the empty space between galaxies?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby speising » Mon Aug 25, 2014 10:42 pm UTC

are the stars at the center junger than the ones at the rim?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Mon Aug 25, 2014 11:57 pm UTC

brenok wrote:A sprinkler left running for billions of years would flood the whole space. How do you explain the empty space between galaxies?

The sprinkler analogy isn't perfect; it'd be more akin to a water balloon if you want to get technical.

Primordial black holes would have a finite, but large (on the order of galaxies) amount of mass and kinetic energy to them; once they wind down and let loose a lot of that angular momentum, there's no more need for them to throw off mass.

With regards to testing the hypothesis...I suppose the ultimate test would be to simulate it, and see if some combination of starting parameters shits you out a galaxy.

Other than that? Observational astronomy! The model would provide a number of testable hypotheses; for example, older galaxies would tend to have more massive cores. We see additional redshift from further (older) galaxies, but it's currently ascribed to the doppler effect, which is where we get the notion that some kind of "dark energy" is accelerating these things away from us.

However, if an active galactic nucleus were more massive the older it was, we'd see more gravitational redshift the further out (back in time) we looked, which would create an effect much the same as what we see.

It'd be nice if we didn't need anything with the word "dark" in it to explain the shape of things. "Dark" anything smells very hand-wavey to me.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Tue Aug 26, 2014 1:39 am UTC

skolnick1 wrote:"Dark" anything smells very hand-wavey to me.

More hand-wavey than making up entirely new models of black hole physics with no basis in General Relativity?

Your model adequately explains the gravitational lensing we currently believe is from dark matter, too, does it? We're well past the era where the only anomaly connected with dark matter is galactic rotation curves.

Edit: Oh, apparently you have already invented new laws of physics incompatible with GM. Is your current "black holes spewed out galaxies" story related to your "photons as gravity waves" one, or is this new?
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Meteoric » Tue Aug 26, 2014 3:40 am UTC

skolnick1 wrote:The model would provide a number of testable hypotheses; for example, older galaxies would tend to have more massive cores.

Er, perhaps I'm being dense, but why?
No, even in theory, you cannot build a rocket more massive than the visible universe.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Tue Aug 26, 2014 4:22 am UTC

gmalivuk wrote:More hand-wavey than making up entirely new models of black hole physics with no basis in General Relativity?


Please see the equivalence principle and my previous comments on redshift prediction for a basis in General Relativity. I would recommend reading up on the Kerr effect, Hawking Radiation, the Penrose Process, and the nature of the ergosphere for additional theoretical foundation. To get you started, here's a lovely article on primordial black holes.

gmalivuk wrote:Your model adequately explains the gravitational lensing we currently believe is from dark matter, too, does it? We're well past the era where the only anomaly connected with dark matter is galactic rotation curves.


Forgetting for a moment the fact that anomalies are often misattributed, it might. Younger galaxies would have more mass at their centers than you'd expect based on stellar luminosity.

It's rather ugly of you, especially as a mod, to use an ad hominem argument to try and discredit a new idea, and doubly so when the alternative you've adopted by default sounds like a lazily-written science fiction plot device. Dark Matter has no basis in any theory*, and the search for it has yielded practically nothing but an exceedingly long list of things we're certain that it's NOT. It's the lumpy remainder you get when you try to apply solar system formation models on galactic scales.
*Edit: That is to say: Unpredicted and, to an extent, unpredictable by any theory not heavily contrived to allow its presence.

When new evidence indicates that your current model would need twenty times the observed mass to sustain itself, you revise your fucking model. When it's between "Someone who published before me goofed" and "The universe is comprised of 95% invisible mystery jizz", it seems like the safe money would be on the former.
Last edited by skolnick1 on Tue Aug 26, 2014 4:44 am UTC, edited 1 time in total.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Tue Aug 26, 2014 4:25 am UTC

Meteoric wrote:
skolnick1 wrote:The model would provide a number of testable hypotheses; for example, older galaxies would tend to have more massive cores.

Er, perhaps I'm being dense, but why?

Ah! My mistake--I meant to say "younger"; confusion stemmed from "older" meaning "further out" in my mind, as the light we receive from them is "older". In reality, we are looking at young galaxies where most of the mass has not yet been ejected from the core.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Meteoric » Tue Aug 26, 2014 5:18 am UTC

This is all way above my pay grade. Two questions that may or may not be stupid:

1) If black holes have a maximum angular velocity, does it work to posit that primordial black holes were born exceeding it? What exactly does "maximum" entail, here?
2) If galaxies form from matter thrown off of primordial black holes spinning down, that suggests some things about galaxy formation over the age of the universe. For one, we would definitely not expect some galaxies to be much younger than others - there aren't any new primordial black holes. Does this reconcile with observation?
No, even in theory, you cannot build a rocket more massive than the visible universe.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Copper Bezel » Tue Aug 26, 2014 7:40 am UTC

Another clarifying question - you seem to have taken a pot shot at the idea of the accelerating expansion of the universe. What does your model posit instead - what does the expansion of the universe "really" look like in your model?

Edit: And I'm sure you're quite aware of this, but gma is quite familiar with the concepts you're invoking and not going to be impressed by you name-dropping some topics. I do have to point out that Hawking radiation as proposed (and not, to my knowledge, observed in any way) is a very different process from what you're describing, so I don't see the relevance (since its a prediction, not an observation, it doesn't make sense to propose an alternative explanation for it.)
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Tue Aug 26, 2014 11:18 am UTC

Also, whatever process might lead to black holes spewing out entire galaxies worth of material, it can't rightly be called Hawking radiation, given that Hawking radiation (according to Hawking's own equations) is much lower for larger black holes.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby PM 2Ring » Tue Aug 26, 2014 2:29 pm UTC

skolnick1 wrote:A more plausible answer is that the black hole would shed angular momentum by spitting out massive particles in the plane of its rotation. Spatial energy density at the ergosurface is more than adequate to generate neutrons, perhaps with their antineutron counterparts on the inside of the surface. If we examined the case of two black holes orbiting one another, inducing such an effect, one might observe matter flung off from either side of this system of bodies. The high-energy collisions of these particles could lead to ionization and charge.

So are you proposing that the high angular momentum somehow gives a massive boost to Hawking radiation, or invokes a process similar to Hawking radiation? That seems counter-intuitve, since increasing the energy of a black hole normally reduces its Hawking radiation temperature (as gmalivuk just said).

Either way, why does it spit out fermions, when photons are much more likely to be generated according to standard Hawking radiation theory? And if it does emit fermions, why do the matter fermions mostly end up on the outside of the ergosurface? Surely there would be an (almost) equal probability for antimatter fermions to be emitted?

While we're dropping names, let's not forget Nikolay Bogoliubov and his eponymous transformation.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby LaserGuy » Tue Aug 26, 2014 2:39 pm UTC

skolnick1 wrote:A black hole has a maximum angular momentum, determined by its mass, the gravitational constant, and the speed of light. If we treat a black hole as a purely mathematical object and ask what happens when it exceeds its maximum angular momentum, it has been said that it becomes a "black donut", as the toroid allows wider distribution of its mass.

This seems unlikely.

A more plausible answer is that the black hole would shed angular momentum by spitting out massive particles in the plane of its rotation. Spatial energy density at the ergosurface is more than adequate to generate neutrons, perhaps with their antineutron counterparts on the inside of the surface. If we examined the case of two black holes orbiting one another, inducing such an effect, one might observe matter flung off from either side of this system of bodies. The high-energy collisions of these particles could lead to ionization and charge.

Look hard at that image and ask yourself which seems more likely:
a) It started as a massive cloud, and a pre-formed halo of invisible, exotic matter pulled it down into its current shape and binds it together to maintain its spiral structure.
or
b) It started in the middle and spun out from there, flung away at great speed but remaining bound by the mass still at the center.

There have been clues to this throughout recent astronomical history, from Rubin's observation of a gas jet being ejected from Andromeda's nucleus to the dusty cross at the heart of M51, and the counterintuitive advanced age and lower metallicity of halo stars at the edge of galaxies.


If the matter had sufficient energy to depart some distance from the black hole, but not escape velocity, I think that this orbit would just send it straight back into the black hole. If the particles have enough energy not to have a closed orbit, how do they shed enough energy to fall back into the galaxy? What happens to the eccentricity of their orbits--what mechanism do they use to transform their angular momentum from a highly elliptical one into a nearly circular one?

And even if this were true, how does it avoid the need for dark matter?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby speising » Tue Aug 26, 2014 3:31 pm UTC

basically, if the sprinkler model, the stars would have radial vector. but they actually move generally in an orbit around the galaxy's center. the image is only an instant in time, comparing a sprinkler with a galaxy over time would show very different behaviours.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Tue Aug 26, 2014 5:04 pm UTC

Yeah, it definitely doesn't avoid the need for dark matter, because it doesn't explain galactic rotation curves, which are actually what led people to speculate about dark matter in the first place, and it doesn't explain gravitational lensing that we believe to be the result of dark matter. All it could explain, if true, would be the initial formation of galaxies, which as far as I know was never a mystery in the first place.

Instead of answering the two questions dark matter currently answers, this hypothesis answers a question no one needed to ask.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Hypnosifl » Tue Aug 26, 2014 6:48 pm UTC

skolnick1 wrote:It's rather ugly of you, especially as a mod, to use an ad hominem argument to try and discredit a new idea, and doubly so when the alternative you've adopted by default sounds like a lazily-written science fiction plot device. Dark Matter has no basis in any theory*

Maybe not, but it's entirely consistent with the basic framework of quantum field theory to postulate undiscovered massive particles that interact only via the weak force and gravity (as some known particles like neutrinos do). And once you make such a postulate you can use the existing framework of semiclassical gravity (which combines quantum field theory with general relativity in a way that physicists expect to be reasonably accurate as long as energy densities are far from the Planck scale) to model how such particles would influence the distribution of matter on cosmological scales. Such models have been constructed and examined, and have proven very successful at reproducing the behavior and structure of observable matter in the real universe. See for example this article on the "Illustris simulation", a supercomputer simulation of the evolution of a universe like ours, which is based on only known laws and includes the estimated amounts of dark matter and dark energy:

http://www.nature.com/news/model-univer ... os-1.15178

As is pointed out in the abstract here, the model did reproduce the formation of spiral galaxies, there's an image of some of the results in this article:

Spoiler:
Image


Do you claim that your "new model" is something that would require no new fundamental physics, so it could be derived purely from quantum field theory and general relativity? If you are postulating new fundamental physics, this is quite a different kind of proposal from dark matter theories that stay within the framework of these very successful theories, you would need to give the basic equations of your new fundamental theory and show that they can be used to match the successful predictions that have been made by quantum field theory and general relativity. On the other hand, if you claim that the model you're imagining of spinning black holes spewing out massive amounts of new particles could be derived mathematically from general relativity and quantum field theory with the right choice of initial conditions, there's no particular reason for anyone else to take this seriously unless you've actually done the derivation, as opposed to just expressing a vague hunch that it could be done. Either way, without any detailed math, calling your ideas "hand-wavey" is entirely appropriate.

Finally, if you don't believe in dark matter, how do you explain the bullet cluster? There's a good discussion in this blog entry, starting towards the middle with the paragraph that begins 'So I was in favor of dark matter, but I wasn’t entirely convinced. I wanted a “smoking gun” piece of evidence for dark matter ...' (basically, the bullet cluster is an example where gravitational lensing indicates that some very massive invisible stuff "overshot" the visible matter in two colliding galaxy clusters, since the visible matter could be slowed down by forms of "friction" involving the electromagnetic force)

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby doogly » Wed Aug 27, 2014 7:40 pm UTC

Basically, if you're just pulling things out of your ass, you can't get pissy if someone notices.

But,
skolnick1 wrote:The sprinkler analogy isn't perfect; it'd be more akin to a water balloon if you want to get technical.

this is hilarious, if this is what "getting technical" means to you. Thank you for the lulz.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby lgw » Thu Aug 28, 2014 3:34 am UTC

Droplets flung from a sprinkler have very little angular momentum, right? They only look like they're spinning because of the emission pattern? They're not strictly radial, but they move in a straight line away from a point very close to the axis of the sprinkler? Even with frame dragging, you can't change this much - the newly formed matter will fly directly away from a point quite close to the center of the galaxy.

So it seems like the theory doesn't explain:
  • Non-spiral galaxies;
  • Galactic rotation rates;
  • The CMBR data showing mostly non-baryonic mass; or
  • Gravitational lensing in dark places.
So, basically, it explains nothing that dark matter does. Spiral galaxies do sort of look like sprinklers, though.

doogly wrote:Basically, if you're just pulling things out of your ass, you can't get pissy if someone notices.

But,
skolnick1 wrote:The sprinkler analogy isn't perfect; it'd be more akin to a water balloon if you want to get technical.

this is hilarious, if this is what "getting technical" means to you. Thank you for the lulz.


Hey, he's pulling things out of a black hole here - oh, wait, I get it. :lol:
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby LaserGuy » Thu Aug 28, 2014 1:59 pm UTC

My memory is that current theories suggest that spiral galaxies are the default shape, and irregular/elliptical galaxies are the result of mergers.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Tyndmyr » Thu Aug 28, 2014 3:09 pm UTC

skolnick1 wrote:Other than that? Observational astronomy! The model would provide a number of testable hypotheses; for example, older galaxies would tend to have more massive cores. We see additional redshift from further (older) galaxies, but it's currently ascribed to the doppler effect, which is where we get the notion that some kind of "dark energy" is accelerating these things away from us.


If it's a sprinkler system, squirting matter out(dark or not), why would we expect the point of origin to become more massive? I'd generally assume that something blowing matter out of it is in the process of becoming less massive.

Ah, nm, see the correction, editing to continue conversation:
skolnick1 wrote:
Meteoric wrote:
skolnick1 wrote:The model would provide a number of testable hypotheses; for example, older galaxies would tend to have more massive cores.

Er, perhaps I'm being dense, but why?

Ah! My mistake--I meant to say "younger"; confusion stemmed from "older" meaning "further out" in my mind, as the light we receive from them is "older". In reality, we are looking at young galaxies where most of the mass has not yet been ejected from the core.


Yeah, younger being more massive would be a reasonable prediction. However, discounting redshift seems like it would introduce a host of other problems. Are you implying that redshift is generally not a result of movement away, and simply indicates mass? What of blueshift, then? Is that negative mass, and how would that work? How do you explain the discrepency between this interpretation and experimentation on red/blueshift inlabs?

Obviously, this would mean a fairly static universe on an intergalactic view, instead of the current expansive model. Why would we expect things to be constantly changing within galaxies, but the galaxies themselves to be pretty stationary?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby drachefly » Thu Aug 28, 2014 5:05 pm UTC

The distribution of dark matter is roughly spherical around galaxies. This would produce a flat disk if it produced any gravitationally bound structures at all.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Wed Sep 03, 2014 8:47 pm UTC

speising wrote:are the stars at the center junger than the ones at the rim?


Indeed they are! Halo stars are much older, and have much lower metallicities on average, than disk stars, which is confusing if you assume we started out as a big cloud of hydrogen; you'd expect older stars to have had more time to fuse hydrogen into heavier elements.

drachefly wrote:The distribution of dark matter is roughly spherical around galaxies. This would produce a flat disk if it produced any gravitationally bound structures at all.


You've hit the nail on the head! The flat disk it produces is the disk of visible matter in our milky way; the dark matter isn't necessary.

Tyndmyr wrote: Are you implying that redshift is generally not a result of movement away, and simply indicates mass?


No, I'm applying the equivalence principle, in which a gravitational potential well is identical to an accelerating reference frame:
Spoiler:
Image

You can still have doppler blueshift, and indeed we see it in spiral arms that are receding from us, but you can also have gravitational redshift. That way, the additional redshift of structures much further from us in the universe (i.e. further back in time) don't present the geometric nastiness of a universe where everything is accelerating away from a central point that appears to be our galaxy.

gmalivuk wrote:Yeah, it definitely doesn't avoid the need for dark matter, because it doesn't explain galactic rotation curves

lgw wrote:Droplets flung from a sprinkler have very little angular momentum, right? They only look like they're spinning because of the emission pattern? They're not strictly radial, but they move in a straight line away from a point very close to the axis of the sprinkler?

So it seems like the theory doesn't explain:
  • Non-spiral galaxies;
  • Galactic rotation rates;
  • The CMBR data showing mostly non-baryonic mass; or
  • Gravitational lensing in dark places.


I don't know how to explain to you the way in which it explains galactic rotation rates besides to say that matter is flung out tangentially rather than radially, and the radial component of its momentum is depleted by gravitational pull from the mass remaining at the center. You can't approximate even the black holes as point particles.
Fortunately for you two and Laserguy, the nice folks at NASA once did a simulation of something which I'd consider close enough for government work.
http://www.space.com/25863-neutron-star ... video.html
Hopefully you can see now how, starting from much denser initial objects, you might end up with a nice milky spiral. If not, hopefully you at least enjoyed the cool video.

To address your question of non-spiral galaxies...have you noticed that they're few and far between, and tend to contain stars much older than those found in spirals? They're also much less common in the early universe; this is consistent with Laserguy's postulation that they might be the result of mergers, and also with the idea that older galaxies tend to spread out into more diffuse clouds once they've lost their massive, active cores. Ellipticals tend to be unusually quiet with regards to star-formation, which is consistent with the diffusion model but not so much the "merger" idea.

Meteoric wrote:If black holes have a maximum angular velocity, does it work to posit that primordial black holes were born exceeding it?


It depends! There's a lot of room for interpretation--the maximum angular momentum is determined by M, G and C, so if you'll permit a universe where those are changing, you might have a model where primordial black holes exceed their maximum angular momentum because the gravitational force binding them is growing weaker. This might violate the equivalence principle, though, as a decrease in gravitational energy would lead to a corresponding decrease in momentum. If you want to flux with the values of C, you might be able to skirt that, but I'm far enough out on a limb here as is, for now.

If you prefer static constants (as I do), then the maximum angular momentum is exceeded when two bodies meet. While each was stable before, the system of the two exceeds Lmax, as in the Neutron Star Collision video, above. This was my original hypothesis, but I haven't been watching long enough to tell you you're wrong if you can find some evidence that supports a falling G or something.

To address Copper Bezel and Gma's comments regarding calling the particles "Hawking Radiation"--you're absolutely right. It wouldn't be proper to call it that. The phenomenon wouldn't have a known name, as it's a new amalgamation of a number of already-existing concepts. I bring up Hawking radiation and the Penrose Process merely to illustrate that currently-accepted mathematics allow for the creation of massive and charged particles in regions of space with extreme energy density gradients, such as those one might find near the ergosurfaces of orbiting PBHs. We know that galactic nuclei are tremendously active, spitting out gamma rays of tremendous energy (with a peak at 511 keV...interestingly enough), so it doesn't seem unreasonable to me to assume that baryons could be forged there, too.

AFAIK, we haven't probed the region, but this would tell us to expect a 938 MeV line as well, so if you're an astro grad student looking for a thesis, get to it and dibs on Corresponding Author status if you find it.

Have a paper by some legitimate astrophysicists contradicting standard dark matter models, in case you still feel like current theory has fewer holes in it than this one: http://www.space.com/15499-dark-matter- ... tures.html


With regards to the Illustris simulation; it would allow for the formation and interaction of black holes, wouldn't it? It's not immediately apparent from the images how those spiral structures emerge in the simulation--perhaps it's by this method.

Hypnosifl wrote:it's entirely consistent with the basic framework of quantum field theory to postulate undiscovered massive particles that interact only via the weak force and gravity (as some known particles like neutrinos do).


The whole point of this exercise is that, occam's razor-wise, it's inelegant to postulate these particles unless you've exhausted all means of explaining our observations through known mechanisa. I cannot explain your magic bullet at present, but I would question my own imaginative capacity before I started attributing its motion to particles which defy all known mechanics.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby doogly » Wed Sep 03, 2014 8:55 pm UTC

They don't defy all known mechanics. They just interact with the weak and gravitational sectors rather than the electromagnetic. Like all sorts of things we know about.

Occam's Razor isn't about "elegance." Nobody cares which flavor pill you care to swallow. It's about the number of free parameters you need to fit the data. What are the physical parameters in your model?

That is not how gravitational redshift works. The equivalence principle is only a local principle. There is no way the cosmological redshift could be explained as anything other than acceleration.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Wed Sep 03, 2014 9:07 pm UTC

skolnick1 wrote:
gmalivuk wrote:Yeah, it definitely doesn't avoid the need for dark matter, because it doesn't explain galactic rotation curves
I don't know how to explain to you the way in which it explains galactic rotation rates besides to say that matter is flung out tangentially rather than radially, and the radial component of its momentum is depleted by gravitational pull from the mass remaining at the center. You can't approximate even the black holes as point particles.
I'm not approximating black holes as anything. I don't care about black holes, since they don't behave like you need them to for your idea to work, and they aren't relevant to my point.

Which was that the anomalous rotation curves that led to the postulation of dark matter in the first place aren't explained by doing some hand-waving about how a galaxy's central black hole works. As in, even if we ignore how they got tangential velocity in the first place, you still need to explain why the way galaxies rotate now that they've formed is not consistent with Newton or GR if you assume that all the matter is the normal kind.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby doogly » Wed Sep 03, 2014 9:09 pm UTC

It is a rare theory that fails in both the applications and the base principles. But fuck dark matter tho; shit's weird.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Hypnosifl » Wed Sep 03, 2014 9:55 pm UTC

skolnick1 wrote:The whole point of this exercise is that, occam's razor-wise, it's inelegant to postulate these particles unless you've exhausted all means of explaining our observations through known mechanisa.

Are you claiming that a rotating black hole spitting out huge amounts of matter/energy, far beyond what's predicted by Hawking radiation, is a "known mechanism"? Do you claim it's a prediction that could be derived mathematically from existing theories, either pure general relativity or "semiclassical gravity" which is the current most trusted approach for dealing with quantum field theory in curved spacetime (at energy densities far away from the Planck scale where a full theory of quantum gravity would be needed)? If not, postulating some new particles within the well-understood framework of quantum field theory (which has repeatedly accommodated the discovery of new types of particles in the past) seems a lot more "simple" in the occam's razor sense than speculating about totally new fundamental laws (which you don't have any proposed equations for) in order to explain the shape of galaxies.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Copper Bezel » Thu Sep 04, 2014 2:03 am UTC

skolnick1 wrote:Indeed they are! Halo stars are much older, and have much lower metallicities on average, than disk stars, which is confusing if you assume we started out as a big cloud of hydrogen; you'd expect older stars to have had more time to fuse hydrogen into heavier elements.

Uncanny! It's almost as if there was another, completely different quality separating these stars into the categories you're talking about that you've completely left out of your description, but which is more easily determined from observational data than literally anything else you've said about them.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby LaserGuy » Thu Sep 04, 2014 3:10 am UTC

skolnick1 wrote:You've hit the nail on the head! The flat disk it produces is the disk of visible matter in our milky way; the dark matter isn't necessary.


You still haven't explained why it isn't necessary? Why don't aren't galactic rotation curve consistent with the mass of the galaxy being only the visible stuff? Why does gravitational lensing on galaxies indicate that they are way more massive than just the visible stuff? That's the stuff you need dark matter to explain.

I don't know how to explain to you the way in which it explains galactic rotation rates besides to say that matter is flung out tangentially rather than radially, and the radial component of its momentum is depleted by gravitational pull from the mass remaining at the center. You can't approximate even the black holes as point particles.


Er, where does the radial part of the momentum go? Momentum is conserved. So is angular momentum.

Fortunately for you two and Laserguy, the nice folks at NASA once did a simulation of something which I'd consider close enough for government work.
http://www.space.com/25863-neutron-star ... video.html
Hopefully you can see now how, starting from much denser initial objects, you might end up with a nice milky spiral. If not, hopefully you at least enjoyed the cool video.


I'm not sure what this has to do with your point. This isn't even addressing the same type of problem. It also doesn't explain why you don't need dark matter in your model to explain the observable properties of galaxies.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby drachefly » Thu Sep 04, 2014 3:08 pm UTC

skolnick1 wrote:
drachefly wrote:The distribution of dark matter is roughly spherical around galaxies. This would produce a flat disk if it produced any gravitationally bound structures at all.


You've hit the nail on the head! The flat disk it produces is the disk of visible matter in our milky way; the dark matter isn't necessary.


Agree on the first sentence. The second sentence is nonsense that illustrates how little you understand the argument for dark matter.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Quizatzhaderac » Thu Sep 04, 2014 3:39 pm UTC

If an object travels a straight line (according to Cartesian coordinates) starting with purely tangential velocity, then it's tangential velocity will decrease and it's radial velocity increase as it's distance from the center increases.

The galactic rotation curves show tangential speed increasing with radius.
LaserGuy wrote:Er, where does the radial part of the momentum go? Momentum is conserved. So is angular momentum.
Radial momentum isn't conserved, because the same radial velocity at θ=0 and θ=180 represent opposite linear velocities. The linear momentum goes into the rest of the galaxy, which is balanced out by a symmetric event on the other side of the galaxy.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Thu Sep 04, 2014 4:50 pm UTC

Nobody said anything about "radial momentum", though...?
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Quizatzhaderac » Thu Sep 04, 2014 5:37 pm UTC

Sorry, I tried to respond without sounding a wise-ass, but I honesty can't find the phrasing.

1) Did you see "radial part of the momentum" in Laserguy's post (which I quoted) or "radial component of its momentum" in Skolnick1's post (to which Laserguy was responding)?
2) If you did, could you please skip to explaining how "Radial momentum" is completely unrelated?
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby gmalivuk » Thu Sep 04, 2014 5:49 pm UTC

Yes, the radial part of the momentum, as opposed to the tangential part.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Quizatzhaderac » Thu Sep 04, 2014 6:40 pm UTC

The radial part of the momentum has a direction and magnitude proportional to change in position over time and mass; it meets the definition of momentum all by itself.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Tyndmyr » Thu Sep 04, 2014 6:51 pm UTC

skolnick1 wrote:
Tyndmyr wrote: Are you implying that redshift is generally not a result of movement away, and simply indicates mass?


No, I'm applying the equivalence principle, in which a gravitational potential well is identical to an accelerating reference frame:
Spoiler:
Image

You can still have doppler blueshift, and indeed we see it in spiral arms that are receding from us, but you can also have gravitational redshift. That way, the additional redshift of structures much further from us in the universe (i.e. further back in time) don't present the geometric nastiness of a universe where everything is accelerating away from a central point that appears to be our galaxy.


Ah. As I understand it, the popular theory is not so much that our galaxy is at the center, and everything is emanating from that point, so much as it is EVERYTHING is expanding, and you would expect to observe a similar effect from any other point.

Explanations that don't invoke special explanations for our location being unusual seem generally more likely to be correct, of course, which is what I think you're driving at...but that's already not an issue in current models.

Now, on to explaning how galaxies stay together. If there is a sprinkler like effect for some reason, how can matter be moving fast enough to escape the gravitational pull of the core to the degree observed, and yet...not continue escaping? Would we not expect, instead of well defined galaxies, to see simply matter spreading away basically indefinitely from ever-shrinking galaxies? Surely the gravitational attraction of the core must decrease as matter continues to spew forth, and as the spewed matter gets further distant. One would not expect to see very constant galaxies at all...and certainly, the nature of the mechanism that does the actual spewing must attract questions. Why does it emit only at certain points? Why must it spin? In fact, how do the immense forces needed to spit out such quantities of matter get generated at all?

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby doogly » Thu Sep 04, 2014 6:56 pm UTC

Quizatzhaderac wrote:If an object travels a straight line (according to Cartesian coordinates) starting with purely tangential velocity, then it's tangential velocity will decrease and it's radial velocity increase as it's distance from the center increases.

The galactic rotation curves show tangential speed increasing with radius.
LaserGuy wrote:


These are complete nonsequiturs.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby Quizatzhaderac » Thu Sep 04, 2014 7:14 pm UTC

Skolnick1's suggestion involves mater being ejecting from the center without further tangential acceleration, therefore the first statement applies as it's an implication of the original post.

The second statement is relevant because it directly contradicts an implication Skolnick1's suggestion. Rotation curves have already been mentioned, but without the specifics that pose a problem to Skolnick1's suggestion.
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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby skolnick1 » Thu Sep 04, 2014 7:17 pm UTC

Quizatzhaderac wrote:Sorry, I tried to respond without sounding a wise-ass, but I honesty can't find the phrasing.

1) Did you see "radial part of the momentum" in Laserguy's post (which I quoted) or "radial component of its momentum" in Skolnick1's post (to which Laserguy was responding)?
2) If you did, could you please skip to explaining how "Radial momentum" is completely unrelated?


Gmalivuk reads just enough of each post to conclude that any non-standard-model theories don't make sense and issue a scathing rebuttal. Can't blame him, he's a busy guy.

doogly wrote:That is not how gravitational redshift works. The equivalence principle is only a local principle. There is no way the cosmological redshift could be explained as anything other than acceleration.


What on earth do you mean "only a local principle"? The deeper the potential well a photon comes out of, the more redshift it will experience, period.

drachefly wrote:Agree on the first sentence. The second sentence is nonsense that illustrates how little you understand the argument for dark matter.


gmalivuk wrote:the anomalous rotation curves that led to the postulation of dark matter in the first place aren't explained by doing some hand-waving about how a galaxy's central black hole works.



I see now that I wasn't clear enough in my initial phrasing, so let's please put the sophomorically combative tone aside and I'll try and explain how I got here, as well as my understanding of the motivation for dark matter in the first place. Please correct me if this is not how you understand it.

Current theory starts from the assumption that galaxies began as massive clouds of gas and dust, which coalesced down into a central massive object surrounded by smaller, orbiting bodies, much like our solar system.
These orbiting bodies apparently don't behave the same as the planets in our solar system: if they were captured by our central SMBH and sustained in orbit by their tangential velocity, the objects near the edge should have more time to "fall" inward, and thus trace out elliptical orbits in accordance with Kepler's laws.

This does not match our observations; the orbital speed of objects does not decrease as the inverse of the square root of their distance from galactic center; instead, it remains relatively constant. This can be accounted for by introducing a tremendous amount of nonluminous mass in a halo permeating the disk of the galaxy, which we call dark matter.

I'm postulating that the observation could instead be accounted for by assuming a non-capture model of galactic formation, where the similar orbital velocity of these bodies is due to the momentum imparted on them at the time of their departure from a common source.

Hypnosifl wrote:Are you claiming that a rotating black hole spitting out huge amounts of matter/energy, far beyond what's predicted by Hawking radiation, is a "known mechanism"?


If you spin a glass sphere fast enough, it will fly apart, and the bits into which it disintegrates will be moving with roughly the same "orbital" speed. I am simply assuming that, despite their mysteries, black holes follow the same rules as other things in our universe. (Yes, I understand, glass is geometrically frustrated and not gravitationally bound. It's a fucking analogy.)
Moreover, black holes most definitely spit out huge amounts of matter and energy. This is a fact, and if you contest that "spaghettification" of infalling matter is responsible for the activity of galactic nuclei, I would ask you to consider what might happen when one black hole tries to spaghettify another.

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Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Postby doogly » Thu Sep 04, 2014 7:20 pm UTC

A different model of galactic evolution isn't going to get you a violation of Kepler's laws. That is what we observe.

The indistinguishability of gravity and constant a is local. If you come out of the well, you have to do an integral. I apologize if this sounds like work. Yes, you get a shift, but no, you cannot get the supernova data from gravity wells.
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