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

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Thu Sep 11, 2014 11:40 am UTC

Except your case is even worse than the creationist's!

He had a few hundred data points where you have zero (I still haven't seen any numbers or math from you). He didn't have competing ideas because he was too lazy to seek them out where you have to purposefully ignore or dismiss them.

Sorry dude, but you're not on the side of this analogy you'd like to think you're on.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Thu Sep 11, 2014 2:06 pm UTC

skolnick1 wrote:Hypno: Geometrically, two isolated distributions of mass are incapable of doing anything but attracting or repelling one another. If either one had an initial velocity besides directly towards or away from the other, they wouldn't collide directly. Sorry, with the game you were talking I assumed you'd understand vector math.

Uh, so now you're just saying that their velocity vectors need to be pointing "directly towards or away from the other"? That's completely different from the ridiculous statement you made earlier (you know, the one I was actually responding to) that they needed to be "initially at rest with respect to each other, which is the only way that the acceleration which brought them together could send one straight through the other". But in any case, your revised argument that their velocity vectors need to point at one another (even thought these vectors can be nonzero in the center-of-mass frame, in which case the clusters wouldn't be 'at rest with respect to each other') in order for them to collide isn't true either, they just need to both have velocity vectors that are both aimed at the same region of space (in whatever coordinate system you use), such that they will both reach that point at the same moment. For example, say we have two objects moving inertially in a 2D plane, and their initial positions and velocities in some inertial frame are as follows:

At t=0 s, object A is at position x=0 meters, y=4 meters. The component of its velocity vector in the x direction is vx=2 m/s, and the component in the y-direction is vy=-2 m/s.

At t=0 s, object B is at position x=24 meters, y=0 meters. The component of its velocity vector in the x direction is vx=-10 m/s, and the component in the y-direction is vy=0 m/s.

Given these initial conditions, what will their positions be at t=2 s? Well, object A will have changed position by 4 m in the x-direction and -4 meters in the y-direction, so it will now be at x=4 meters, y=0 meters. And object B will have changed position by -20 m in the x-direction and 0 m in the y-direction, so it will be at x=4 meters, y=0 meters. Hence, the two objects will meet at this time, either colliding or passing through one another, depending on their composition.
skolnick1 wrote:And no, they're not points. They're clouds, but if you're going with the LCDM model you're telling me that those clouds used to be larger than they are now, and since they've shrunk down anisotropically, they should have some momentum. This momentum is highly unlikely to be distributed in a fashion that would lead to a direct collision course.

What does this have to do with your statement that "they'd have to have identical mass distributions, because the velocity vector of a cloud that's been condensed to a point depends on the geometry of the initial cloud's density"? And the statement that "the momentum is highly unlikely to be distributed in a fashion that would lead to a direct collision course" is rather vague--sure, if you randomly select two galaxies or galaxy clusters in a given large region of space containing many different galaxies/galaxy clusters, it's unlikely that those particular two random selections will be on a collision course, but if you look at all the galaxies or galaxy clusters in a large region containing billions of them, then assuming all their velocities relative to the local CMBR frame are randomly distributed, it's likely you'll find plenty of pairs that are on a collision course. Similarly if you randomly select two air molecules from a roomful of air it's unlikely those particular two are on a collision course, but if you look at all the molecules in the room there will be plenty of pairs that collide.
skolnick1 wrote:Not only that, it's a pointless assumption to make, because you'd then, logically, see them bounce back toward one another, if you're assuming it was the gravity of these galaxies that brought them together to begin with.

There is no need to assume it was "gravity" that brought them together, just the velocities they had some large number of years prior to the collision. You do realize that galaxies, and galaxy clusters, have a random distribution of velocities relative to the local CMBR frame, right?
skolnick1 wrote:As for the masslike distortions we see: Maybe it's known massive particles spat out in a Fermi bubble, maybe we're just seeing through the gravitational or electromagnetic heat shimmer that would extend beyond those. If the matter bubbles stick out a few thousand lightyears, imagine how much light is out there by now that's completely invisible to us, to say nothing of gravitational waves.

Are you forgetting that we are here dealing with giant galaxy clusters, not individual galaxies? If each galaxy's Fermi bubble only extends a few thousand light years, then in an image which included the entire bullet cluster the Fermi bubble wouldn't extend more than a pixel or two past the edge of the cluster, since the cluster is about 3 million light years across (see this page). And yet the gravitational lensing indicating a collection of unseen mass which seemed to extend about as far beyond the edge of the visible cluster as the size of the cluster itself, i.e. millions of light years beyond the position of the galaxies at the edge of the cluster. Here's the image again, with the visible cluster in pink and the mass inferred from gravitational lensing in blue:

Image

Even if you wanted to postulate some new phenomenon similar to Fermi bubbles but on a much larger scale, an inconvenient fact for your argument is that we can actually see Fermi bubbles if we choose the right wavelength of light, we don't just infer them based on gravitational lensing. As explained on this page, the image of the Fermi bubbles is based not on gravitational lensing but on radiation in the x-ray (blue) and gamma (purple) frequencies:

Image

So, why don't we see any sign of the extra mass causing the gravitational lensing when we look at the bullet cluster in x-ray or gamma frequencies? It's almost like it's dark on all frequencies of electromagnetic radiation or something! (I know the bullet cluster has definitely been observed on x-ray frequencies, not sure what others--would you make the prediction that observations on gamma frequencies would show bubbles analogous to Fermi bubbles in the region where dark matter has been inferred from gravitational lensing, or are you unwilling to make a falsifiable prediction about this?)
skolnick1 wrote:The simulations you bring up make me think of young earth creationism. I met an Intelligent Design guy on the train recently--a small, balding programmer recently out of work. We became friends through a mutual love of science, despite our differences. When we went out for pho the other day and I asked how he wound up Christian, he started talking about a book some friends showed him in college, and about how clear evidence demonstrated that we started at genetic perfection and, since man first sinned, corruption and harmful mutation have entered the gene pool. I never read the book, but I know that full genomic data has only been available the last few decades, and the guy's sample size was likely something like a hundred people in Boise, Idaho over fifteen years, at most.

In your example with the creationist, I think it's a safe bet the assumptions behind the rules governing the time-evolution of whatever mathematical model they were using (whether it was a computer simulation or something simpler) were ones that mainstream biologists would disagree with (i.e. it assumed that harmful mutations continually build up rather than being continually selected out by natural selection, or it assumed that harmful mutations do sometimes get weeded out but that the rate at which they accumulate could be extrapolated in a linear way from the small sample observed over 15 years or so). The dynamics of the astrophysical simulations I brought up are based completely on accepted laws for gravitational interactions and hydrodynamics, or so the authors claim. If you think that they are wrong or lying, and that the rules for the time-evolution of their simulation include assumptions which might be seen as controversial to a physicist who was a critic of dark matter (but who assumed that no new laws of fundamental physics were needed to explain the things dark matter explains, as you claim to do), then you should answer "no" to the simple yes-or-no question I asked you to address, since part of the premise of the question was that the creators of these simulations had used "only known laws of physics" (and if it helps to clarify the question, I'll add 'and widely accepted' to that):
Regardless of whether you think dark matter exists in the real world, do you accept the physicists' claims in their papers that they have reproduced these features using only known [and widely accepted] laws of physics and certain mainstream assumptions about the behavior and amount of dark matter? Please give me a clear yes-or-no answer to this question, or I will take this as evidence you're being intentionally evasive.

If you continue to avoid answering this question "yes" or "no", I'll have to conclude that you are not really interested in a back-and-forth dialogue where we each try our best to address each other's points, but that instead you just want to play rhetorical games and make a lawyer-like case for your view which simply ignores questions that you have no good answer for. If that's the case, then to me this qualifies as a form of trolling (even if you are totally sincere in your beliefs), and so I won't continue this discussion if you keep refusing to answer this question in a straightforward way.

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Thu Sep 11, 2014 3:21 pm UTC

If you are not dismissing some of the ideas you hear in class, even in science class, you are not having original thoughts.
Man, of course I don't have math yet. You don't come to a forum once you've got the math done, you publish. You think the laws just popped into Faraday's head fully written?

I don't think you get this; as of 2010, we have free reign to assign just about any smoothly-varying density maps we want to the billion cubic parsecs on either side of the galactic plane. If we can't reproduce the galaxy's rotation curve with that kind of liberty, I will be truly shocked.

I'm not ignoring or dismissing anything, any more than the scientists who figured out that combustion is an oxidation chain reaction were ignoring phlogiston theory. It was useful for a time, then it was a dead end. But its inconsistencies with the observable world (e.g. magnesium gaining weight when it burned, or 90% of the fucking universe being undetectable at any wavelength) were signposts to a finer structure waiting to be elucidated.

Except now we've got eight different hypothesized structures of phlogisticule (flavor-mixing allows negative mass to explain the behavior of Magnesium and others!) and elaborate models of solar phlogodynamics.

Hypno: Of course I accept the physicists' claims in their simulation results! But you are showing me phlogiston-distribution-based simulations of fifty different types of log burning, which reproduce the behavior of real fire to within three sigma, and I am saying that yes, I understand that, but you are not properly explaining combustion!

As for why we don't see gamma rays from distant bubbles...are you being deliberately thick?
a) they're trying to look at high-energy photon sources behind those bubbles. Hell, you could be getting binning errors from stray photons generated in the cloud, they could be seeing it and filtering it as noise. Ever hear the phrase "Can't see the forest for the trees"?
b) Maybe you missed the part where we only just discovered the ones that are attached to the milky way. Atmospheric effects prevented us from seeing them in the first place, and do you know how much background filtering they had to do to get a solid image of those things?
Something tells me that you are an astronomy enthusiast and not an astronomer.
Something tells me that, in the absence of something to shine it on, you'd conclude that a laser pointer must be off if it's pointed anywhere other than directly into your fuckin' eye.

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Thu Sep 11, 2014 5:31 pm UTC

skolnick1 wrote:If you are not dismissing some of the ideas you hear in class, even in science class, you are not having original thoughts.

Dismissing them confidently based on your own gut feelings or conceptual arguments that seem plausible to you, no, that's a crackpot's mentality. Seeing them as open to question, sure, with the proviso that if you think you have stumbled on some clever argument against them or some creative alternative, you should have the intellectual humility to recognize there's a high probability that the argument or alternative has already occurred to one or more scientists in the field at some point, so that further research would either turn up a more developed version which had already been written up somewhere, or that it turned out to have some fatal flaw that caused all the experts who thought of it to abandon it. Occasionally a layman may come up with a great idea that just hasn't occurred to any scientist anywhere, but one should recognize that this is highly unlikely a priori. This cartoon applies pretty well to any instance in which a layman who's new to a subject thinks they've come up with some brilliant argument to overturn a mainstream theory:

Image

skolnick1 wrote:Man, of course I don't have math yet. You don't come to a forum once you've got the math done, you publish. You think the laws just popped into Faraday's head fully written?

But if you "don't have math yet", the reasonable position to take would not be "I'm sure this idea will work!" but rather "this might be an alternative, but it might be that further investigation by someone well-versed in the math would show there's no way to develop it mathematically into a model that's consistent with all known observations, and is just as successful as dark matter in accounting for the quantitative details of things like galaxy rotation curves, anisotropies in the cosmic microwave background radiation, the distribution of structure on large scales, and the detailed features of the bullet cluster".
skolnick1 wrote:I don't think you get this; as of 2010, we have free reign to assign just about any smoothly-varying density maps we want to the billion cubic parsecs on either side of the galactic plane. If we can't reproduce the galaxy's rotation curve with that kind of liberty, I will be truly shocked.

How do you figure we have "free reign"? If it's supposed to be some known form of baryonic matter that's not inherently invisible on all electromagnetic frequencies, the possible distributions must be constrained by the fact that many distributions would predict too much radiation, more than we have actually observed when we point telescopes sensitive to various frequencies in the appropriate direction. And it's also constrained by the fact that large amounts of unseen baryonic matter would be predicted to have a different effect on the spectrum of the CMBR than large amounts of dark matter, as well as different predictions from Big Bang nucleosynthesis on the ratios of different isotopes like deuterium, as mentioned in the wikipedia baryonic dark matter and in the introduction to this article (for a lot more detail, see the "cosmological evidence" starting on p. 4 of this paper).
skolnick1 wrote:I'm not ignoring or dismissing anything, any more than the scientists who figured out that combustion is an oxidation chain reaction were ignoring phlogiston theory. It was useful for a time, then it was a dead end. But its inconsistencies with the observable world (e.g. magnesium gaining weight when it burned, or 90% of the fucking universe being undetectable at any wavelength) were signposts to a finer structure waiting to be elucidated.

For a model to be inconsistent with the observable world, you have to be able to imagine a hypothetical universe in which the model was correct, and show that it would predict specific observations which differ from what we see in the real world (the hypothetico-deductive model, basically). If someone was able to come up with a model of phlogiston that accounted for all the detailed observations that are used to support the statistical mechanics account of heat, like the blackbody spectrum of heated objects, Brownian motion, and the fact that magnesium gains weight when it's burned, then phlogiston would still be a viable hypothesis. "90% of the fucking universe being undectable at any wavelength" is not a specific observation that you would predict should be different in a hypothetical universe dominated by dark matter and dark energy, it's just a statement of emotional incredulity about the basic premises of the model (and I'm not sure if you realize, but in the context of quantum field theory there's nothing inherently implausible about particles that are undetectable at any wavelength of the electromagnetic spectrum--this is already true of neutrinos, which only interact via gravity and the weak nuclear force, although the mass of neutrinos is too small for them to be a candidate for dark matter). And in this case physicists haven't been able to find an equivalent of the statistical mechanics theory of heat, an alternative theory in which most of the mass of the universe is baryonic, and which is equally good at accounting for the detailed quantitative observations that have been used as evidence for dark matter. Believe me, it's not for lack of trying!
skolnick1 wrote:Hypno: Of course I accept the physicists' claims in their simulation results! But you are showing me phlogiston-distribution-based simulations of fifty different types of log burning, which reproduce the behavior of real fire to within three sigma, and I am saying that yes, I understand that, but you are not properly explaining combustion!

Except, as I said, no such phlogiston model reproducing all real-world aspects of heated objects exists, and if it did then physicists would be perfectly justified in considering it a viable alternative. A predictively accurate physics theory is never rejected because it fails to 'explain' something in a more conceptual way--note that one of the items on the famous crackpot index (written by a physicist who writes a lot of internet articles, and presumably gets a lot of mail from crackpots) is '10 points for arguing that while a current well-established theory predicts phenomena correctly, it doesn't explain "why" they occur, or fails to provide a "mechanism".' (another one is '10 points for each statement along the lines of "I'm not good at math, but my theory is conceptually right, so all I need is for someone to express it in terms of equations".')

It seems like there are two main things leading you to this false swaggering certainty that you've come up with a workable alternative to dark matter:

A) You have this fantasy that it's trivially easy to come up with a mathematical model that is constrained by broadly-accepted laws (like general relativity, and quantum field theory for any new types of particles postulated), and which reproduces all known observations. This leads you both to downgrading the significance of successful dark matter models (since you imagine that with the freedom to invent bogus types of matter, even with the constraints imposed by quantum field theory, it would be easy to come up with a model that reproduces just about any set of observations), and to think it would be easy to find a distribution of baryonic matter that would accurately reproduce real-world observations like galaxy rotation curves (without emitting more radiation than has been observed, and presumably without producing wildly inaccurate predictions about Big Bang nucelosynthesis and the CMBR spectrum, although you may not have been aware of these issues with baryonic theories of missing mass).

B) You seem to be underestimating the intelligence/creativity of physicists, assuming that if they haven't come up with a baryonic model like the one you sketch, it must be because the idea just hasn't occurred to any of them, or because they are all ideologically biased in favor of dark matter being a new type of particle, not because there are inherent difficulties in fleshing out the idea into a detailed mathematical model.
skolnick1 wrote:As for why we don't see gamma rays from distant bubbles...are you being deliberately thick?
a) they're trying to look at high-energy photon sources behind those bubbles.

So would you predict that if they were trying to look for gamma rays in the immediate vicinity of the bullet cluster itself, they would see them in the region where gravitational lensing has been observed?
skolnick1 wrote:b) Maybe you missed the part where we only just discovered the ones that are attached to the milky way. Atmospheric effects prevented us from seeing them in the first place, and do you know how much background filtering they had to do to get a solid image of those things?

I suppose it's a fair point that if there was a cloud the size of the bullet cluster which emitted about the same amount of gamma and x-ray radiation per cubic volume, it might well be too weak to detect at the distance of the bullet cluster even if we were searching the bullet cluster's vicinity with our most powerful x-ray and gamma telescopes. But has it occurred to you that the weakness of the radiation suggests something about the bubbles' density? The exact cause of the gamma radiation isn't certain, but I believe the models that have been proposed all suggest a density much lower than the density of observable matter (including stars) in the galaxy itself, see for example this paper which offers a model in which the estimated density is given at the end of page 1 as about 0.005 hydrogen atoms per cubic centimeter, while this page says the density of baryonic matter within the milky way is about 4*10^6 nucleons per cubic meter, or 4 nucleons per cubic centimeter (a nucleon would be a proton or neutron, and an ordinary hydrogen atom consists of a single proton and no neutrons, with the extra mass of the electron being tiny compared to that of the proton). Again, if there was some model which allowed them to have a density great enough to account for the "missing mass" indicated by galaxy rotation curves, and still emit such weak radiation, then unless you assume physicists are all idiots, it's a safe bet it would have occurred to some of them that this could be an alternate source for the missing mass.

Finally, I note that you dropped the subject of there being something unlikely about the velocity vectors lining up, or whatever argument you were trying to make about clouds "compressed to a point"--does that mean you have abandoned these arguments, or do you still think there are some basic physical flaws in the standard view of the bullet cluster that would remain even if you grant, for the sake of argument, the existence of large amounts of dark matter?
Last edited by Hypnosifl on Thu Sep 11, 2014 7:42 pm UTC, edited 3 times in total.

User avatar
LaserGuy
Posts: 4581
Joined: Thu Jan 15, 2009 5:33 pm UTC

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

Postby LaserGuy » Thu Sep 11, 2014 6:16 pm UTC

skolnick1 wrote:Yeah. Those.
Once you've accounted for THOSE, you're allowed to start inventing new forms of matter, okay? 'til such a day as you can provide me an upper bound on the mass-energy in God's Testicles over there, dark matter is going to seem like a shoddy, contrived excuse for a theory.


They look like jets to me. Most likely they are result of matter accreting into the SMBH in the galactic center. Here's one paper that models them pretty well. It's interesting, but it's not clear how it's relevant. They're big, but that doesn't mean they're massive. In fact, we've already estimated the mass of them, looking at the few papers on this I've seen, and it's nowhere near the order of magnitude that you're looking for--much less than the mass of the galaxy, let alone the mass of the dark matter halo. Also, the jets are not that old. Their age is only around 10^8 years, which means that they weren't around even at the time of the dinosaurs. I'm not sure how you could argue that they have anything to do with galaxy formation, regardless of their origin.

I might point out that this energy is clearly distributed in such a way that it would increase the gravitational pull felt by mass in the galactic plane, thanks to its spectacular symmetry. You could probably, with relative ease, assign a density map to that bubble which would account for our rotation curve. (Again, if anyone actually bothers to do this, dibs on Corresponding Author.)


No, they aren't massive enough, and they aren't old enough. I'm also not sure exactly how you think having mass in this particular configuration would actually cause the galactic rotation curves to behave in the manner that they do. Even if these were really massive, I think the net effect of this extra mass would be more or less to increase the mass of the galactic center.

I might also point out that they're attached to our own fucking galaxy, but we didn't notice them until four years ago because they're not pointed in our direction, which makes them "dark" like a proton beam fired perpendicular to your line of sight.


We didn't notice them because the Earth's atmosphere blocks gamma rays pretty effectively, and they're basically invisible in other wavelengths. The Fermi Gamma Ray telescope was only launched in 2008, so we pretty much saw them as soon as we started looking.

But good luck trying to get a look at the sky behind one of those things without getting some very funny distortions, and have fun trying to guess the mass of a distant galaxy by counting stars.


They're transparent at most other wavelengths. So no, they won't cause distortions.

Also, your merging black hole video didn't produce outflows of this nature either, and it's not clear to me how a "sprinkler", would.

Tyndmyr
Posts: 11443
Joined: Wed Jul 25, 2012 8:38 pm UTC

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

Postby Tyndmyr » Thu Sep 11, 2014 7:06 pm UTC

skolnick1 wrote:The spiral origin model also answers the Lithium problem, and predicts Hydrogen and Helium emission and absorption lines near galactic centers. This is in concordance with what we observe. It is also the most plausible mechanism I can imagine generating the kind of emissions we see in the fermi bubbles.
Tyndmyr wrote:I do have some problems with dark matter theories in general, but...they're not resolved by this proposition. You need more matter on the edges. Or a modification of some major portion of physics. Or maybe both. There's some unknowns still there, but the sprinkler theory doesn't clear them up, so it's kind of unhelpful in finding a replacement answer for dark matter.


You should look into Gravitomagnetics if you still want to modify the physics. The kind of angular momentum you'd find in an decaying-orbital-origin system could probably get you beyond the limit where gravitostatics is sufficient for description.


I don't particularly WANT to modify physics. If anything, I have a slight preference for physics I already understand...but anything that offers a fairly elegant explanation for observations is highly interesting.

Do you have a particular source that you recommend for a decaying orbital origin/gravitomagnetic explanation? I'm trying to get a handle on what exactly you're proposing still.

skolnick1 wrote:Hypno: Geometrically, two isolated distributions of mass are incapable of doing anything but attracting or repelling one another. If either one had an initial velocity besides directly towards or away from the other, they wouldn't collide directly. Sorry, with the game you were talking I assumed you'd understand vector math.
...
And to Gmalivuk I say:
Phlogiston! I'm not contradicting "what scientists say it is", because dark matter is a non-answer! It's a place-holding fudge factor mathematically retrofit to the data to show us what the galaxy would look like if we had all the facts and our math checked out. Lambda CDM is the product of minds which think they are impervious to confirmation bias, arrogant enough to forget that when your predictions and the universe disagree, it's usually the prediction that needs a double-check. It is a security blanket against the terror that rang deep in the hearts of the first people to look to the most distant points of light and realize that, for all our spaceships and digital watches, we know pathetically little about the workings of the larger universe.


See, all of this isn't persuasive. These are personal attacks aimed at credibility, etc. Merely insulting those associated with another theory does not support yours.

They may be wrong. But them being wrong doesn't make you right.

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Thu Sep 11, 2014 9:57 pm UTC

Hypnosifl wrote:For a model to be inconsistent with the observable world, you have to be able to imagine a hypothetical universe in which the model was correct, and show that it would predict specific observations which differ from what we see in the real world.


Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally? Are you postulating some "weak repulsion", or angular momentum vectors that keep DM lumps at their current size? Hold up any DM candidate, even hypothetical ones, to the same standards you're holding these ideas to. They crumble in your hands.

Hypnosifl wrote:B) You seem to be underestimating the intelligence/creativity of physicists, assuming that if they haven't come up with a baryonic model like the one you sketch, it must be because the idea just hasn't occurred to any of them, or because they are all ideologically biased in favor of dark matter being a new type of particle, not because there are inherent difficulties in fleshing out the idea into a detailed mathematical model.

Better than I can say it.
Astronomy took until 2010 to catch up with Zwicky, and provide another shoulder adjacent to his from which we could build a truly stable structure. A spectacular amount of new data has become available to us in recent years, but no one wants to suggest that we need to tear down the scaffolding and start fresh from ~1970.
Hypnosifl wrote:Finally, I note that you dropped the subject of there being something unlikely about the velocity vectors lining up, or whatever argument you were trying to make about clouds "compressed to a point"--does that mean you have abandoned these arguments, or do you still think there are some basic physical flaws in the standard view of the bullet cluster that would remain even if you grant, for the sake of argument, the existence of large amounts of dark matter?

So you're saying that the attractive force between them ISN'T responsible for their spatial proximity. That you prefer a model where we're looking at one bullet which has just shot through another bullet, and that they are both about to continue on their merry way, because their collision had nothing to do with the attractive force that pulls them together. Proposing that their vectors just happened to intersect is like arguing that it's statistically possible for the last three hundred rolls to have come up "7", when the reality is that I've caught you playing with loaded dice.

Collision dynamics aside, the deceleration of both the subcluster and the main cluster would elicit a burst of gravitational and electromagnetic waves, opposite their acceleration vectors (i.e. away from one another), precisely into the regions you've so complacently accepted as dark matter because someone shaded it in blue. Yes, this is a prediction which follows from well-accepted laws, regardless of your stance on dark matter.

I decided to abandon that argument since I was tired of trying to explain probabilistic logic and bremsstrahlung to a "layman", as you say. Now, I am tempted to abandon this discussion altogether, since you are wasting both of our time by defining the word "nucleon" for a physicist.

LaserGuy wrote:No, they aren't massive enough, and they aren't old enough. I'm also not sure exactly how you think having mass in this particular configuration would actually cause the galactic rotation curves to behave in the manner that they do. Even if these were really massive, I think the net effect of this extra mass would be more or less to increase the mass of the galactic center.


Aha! You're agreeing with me! I've been saying: in the plane of the galaxy's rotation, the net effect would be an increase in the massive pull towards the center, depending on your radius and the density distribution of the bubbles. This would allow objects at the edges to remain bound at a greater tangential speed than we'd currently estimate as possible. This is why the galaxy's rotation curve can be roughly flat.

LaserGuy wrote:They're big, but that doesn't mean they're massive. In fact, we've already estimated the mass of them, looking at the few papers on this I've seen, and it's nowhere near the order of magnitude that you're looking for--much less than the mass of the galaxy, let alone the mass of the dark matter halo. Also, the jets are not that old. Their age is only around 10^8 years, which means that they weren't around even at the time of the dinosaurs. I'm not sure how you could argue that they have anything to do with galaxy formation, regardless of their origin.

Well if you want to hop on board and be a part of "we"...
Your estimates of age are wrong; you're missing something key.
You're off on mass as well; they store tremendous energy
As is below, it's so above, L2, M0, N3.
(It's bound to be the final clue you ever get from me!)

If there's any way in which solar system formation resembles galactic formation, it's in that it is a messy process of masses subsuming and merging with other masses in violent collisions. Why should the sun have started out as a single cloud? Why should the galactic center have? It's a Katamari Galaxy, but set to multiplayer.

Heaven forbid I ever take myself as seriously as you folks, but I thank you all for your input; your questions have helped chip away at the edifice where it is weak, and revealed structures that surprised and delighted me.
Laugh for now, call me a loon and enjoy your certainty. If I return to this forum, I will do so wielding equations to scour the darkness from our skies, and it will be the last time for a very long while you feel such security in your knowledge.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Thu Sep 11, 2014 10:16 pm UTC

skolnick1 wrote:Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally?
The fact that there's no mechanism by which dark matter particles could shed angular momentum.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

JudeMorrigan
Posts: 1263
Joined: Tue Jan 26, 2010 1:26 pm UTC

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

Postby JudeMorrigan » Thu Sep 11, 2014 10:18 pm UTC

I, for one, will look forward to you returning with those equations.

Of course, until you do so, providing something more than wild-ass speculation and objections about dark matter seeming icky to your gut, I'll continue to think you look a lot more like a hack with an overinflated sense of his own competence based on his reading of popsci.

User avatar
eSOANEM
:D
Posts: 3652
Joined: Sun Apr 12, 2009 9:39 pm UTC
Location: Grantabrycge

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

Postby eSOANEM » Thu Sep 11, 2014 11:12 pm UTC

skolnick1 wrote:
LaserGuy wrote:No, they aren't massive enough, and they aren't old enough. I'm also not sure exactly how you think having mass in this particular configuration would actually cause the galactic rotation curves to behave in the manner that they do. Even if these were really massive, I think the net effect of this extra mass would be more or less to increase the mass of the galactic center.


Aha! You're agreeing with me! I've been saying: in the plane of the galaxy's rotation, the net effect would be an increase in the massive pull towards the center, depending on your radius and the density distribution of the bubbles. This would allow objects at the edges to remain bound at a greater tangential speed than we'd currently estimate as possible. This is why the galaxy's rotation curve can be roughly flat.


Adding extra mass doesn't change the shape of the galactic rotation curves you'd expect, just the scale of that curve. The issue isn't the scale, it's the shape. Simply adding more mass will just squish the entire graph horizontally and stretch it vertically. Tell me if I'm wrong, but I'm fairly sure such a transformation won't make the A line on this graph sit on top of the B line.

Image
my pronouns are they

Magnanimous wrote:(fuck the macrons)

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Fri Sep 12, 2014 1:04 am UTC

skolnick1 wrote:
Hypnosifl wrote:For a model to be inconsistent with the observable world, you have to be able to imagine a hypothetical universe in which the model was correct, and show that it would predict specific observations which differ from what we see in the real world.

Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally? Are you postulating some "weak repulsion", or angular momentum vectors that keep DM lumps at their current size? Hold up any DM candidate, even hypothetical ones, to the same standards you're holding these ideas to. They crumble in your hands.

Again you just seem to assume that physicists are dumb and simply haven't thought of an obvious argument that would cause the whole theory to "crumble". Have you really given any thought to why particles that interact almost entirely via gravity, and can otherwise mostly just pass right through ordinary matter (and through each other), should collapse? Say we already have a preexisting ordinary-matter body like a star, and a diffuse cloud of dark matter surrounding it. Why wouldn't the dark matter particles just orbit the center of mass, maintaining the same average distance? And even if a particular particle happened to have no tangential velocity, so it just fell inwards towards the center of mass, since it passes through the star like a ghost there would be no friction to slow it down, the particle would just whiz through the center and pass outward through the other side, decelerating in a perfect mirror of its prior acceleration towards the center, until it reached zero velocity and began falling inward again, repeating the cycle and returning to the same maximum distance each time (this is in fact a type of "orbit", one where one of the ellipse's axes happens to have a size of zero). This symmetrical falling and rising shouldn't be surprising, since gravitation fundamentally obeys time-symmetric equations, meaning that if you have a movie of a system governed by gravitational dynamics and you play it backwards, the reversed movie should still appear to obey exactly the same laws. For physicists, the only reason some macro phenomena are far more likely to happen forwards than backwards (the reason they appear to be "irreversible") is because of a statistical mechanics analysis which shows that the later state has a higher entropy than the earlier state, so that a reversed movie of a given process might be statistically very unlikely even if it respects the fundamental laws of physics.

If we want to examine gravitational collapse from a statistical mechanics point of view, we find that there's a tradeoff between the fact that a more spread-out collection of matter has more possible position states, whereas a more concentrated collection has more possible momentum states (because more of the system's potential energy has been converted to kinetic energy and thus the particles have higher average velocity/momentum). And in statistical mechanics, entropy is a function of the total number of states available, with higher entropy = more possible states. It turns out, though, that this tradeoff alone is not enough to explain why gravitational collapse can happen in some systems--the decrease in the number of possible position states when a cloud collapses is actually greater than the increase in the number of momentum states, as derived on this page, so if these were the only factors at play the entropy would be lower in the collapsed state than the diffuse state, and gravitational collapses would never occur. However, it turns out that if the collapsing matter can radiate energy away as it collapses, in that case the end state of "more concentrated, hotter matter distribution + outgoing radiation" can have a higher entropy than the initial state of "more spread out matter which hasn't yet radiated", and so this is the key to understanding why gravitational collapse respects the 2nd law of thermodynamics. As explained by physicist Lubos Motl here:
If you didn't allow the molecules to emit photons when they collide, they wouldn't ever shrink spontaneously by obeying the laws of gravity. The probability that a molecule slows down (or gets closer) under the gravitational influence of the other molecules would be equal to the probability that it speeds up (or gets further) - in average. If you introduce some objects and terms in the Hamiltonian that allow inelastic collisions, these inelastic collisions will selectively slow down the molecules that happened to be closer to each other, which is the mechanism that will be reducing the average distance between the molecules (the actual rate will depend on the gravitational attraction, too).

I wrote photons because, obviously, the probability of the emission of a photon is much higher for real-world gases because most of their interactions are electromagnetic interactions. Because a photon carries as much entropy as a graviton would, but you produce many more photons by random collisions, the entropy increase is stored in the photons. The entropy carried by gravitons is smaller by dozens of orders of magnitude.

And as explained in here, this is relevant to why dark matter would "clump" only very weakly (as seen in detailed physical simulations like the ones I have linked to)--dark matter particles would only experience irreversible interactions with other particles very rarely, from either weak interactions or shedding gravitons:
But it's true that dark matter doesn't seem to have collapsed into very dense structures -- that is, things like stars and planets. Dark matter does cluster, collapsing gravitationally into clumps, but those clumps are much larger and more diffuse than the clumps of ordinary matter we're so familiar with. Why not?

The answer seems to be that dark matter has few ways to dissipate energy. Imagine that you have a diffuse cloud of stuff that starts to collapse under its own weight. If there's no way for it to dissipate its energy, it can't form a stable, dense structure. All the particles will fall in towards the center, but then they'll have so much kinetic energy that they'll pop right back out again. In order to collapse to a dense structure, things need the ability to "cool."

Ordinary atomic matter has various ways of dissipating energy and cooling, such as emitting radiation, which allow it to collapse and not rebound. As far as we can tell, dark matter is weakly interacting: it doesn't emit or absorb radiation, and collisions between dark matter particles are rare. Since it's hard for it to cool, it doesn't form these structures.

skolnick1 wrote:
Hypnosifl wrote:B) You seem to be underestimating the intelligence/creativity of physicists, assuming that if they haven't come up with a baryonic model like the one you sketch, it must be because the idea just hasn't occurred to any of them, or because they are all ideologically biased in favor of dark matter being a new type of particle, not because there are inherent difficulties in fleshing out the idea into a detailed mathematical model.

Better than I can say it.
Astronomy took until 2010 to catch up with Zwicky, and provide another shoulder adjacent to his from which we could build a truly stable structure.

Zwicky made a number of interesting predictions, all of which I imagine were supported by mathematical models of some sort. Some of these predictions were accepted quickly, and even those that weren't, like neutron stars, were still seen as a viable hypotheses. In contrast, you can't point to a single maverick physicist who even claims to have mathematical model that accounts for the same quantitative observations that dark matter is intended to account for, but using baryonic matter. And what prediction of Zwicky's do you imagined was confirmed in 2010? He didn't predict Fermi bubbles, and although he did predict dark matter more generally, there is no model that suggests they could possibly have nearly enough mass to account for the gravitational observations that led Zwicky to conclude large amounts of missing matter, and yet still somehow radiate so weakly and only in the gamma/x-ray range. You're just taking it on faith that there could be some form of matter that could be concentrated so densely and yet remain so dark on nearly all frequencies, because you like the idea, even though you have no ideas about any specific known forms of matter that would behave this way, and you have to once again assume that all physicists are idiots to have collectively missed the fact that some known form of matter could do the trick.
skolnick1 wrote:So you're saying that the attractive force between them ISN'T responsible for their spatial proximity. That you prefer a model where we're looking at one bullet which has just shot through another bullet, and that they are both about to continue on their merry way, because their collision had nothing to do with the attractive force that pulls them together. Proposing that their vectors just happened to intersect is like arguing that it's statistically possible for the last three hundred rolls to have come up "7", when the reality is that I've caught you playing with loaded dice.

I didn't say that gravity plays no role, just that the large random velocities that galaxies and galaxy clusters may have relative to the CMBR frame also plays an important role, so you were wrong to argue as if the "default" assumption is that all galaxies start out at rest relative to one another and only move towards each other due to mutual gravitational attraction, which would imply the only collisions would be head-on ones. Maybe you should read up on the notion of peculiar velocity in cosmology--the first graph in this paper indicates that in a large sample of thousands of galaxies, more were found to have a speed of 4000-5000 km/s relative to the CMBR than any other same-sized velocity interval. And for galaxy clusters, this paper indicates a typical peculiar velocity of around 300 km/s. So even if gravitational acceleration was the main source of the relative velocity between the two clusters in the bullet cluster (the paper involving computer models of the collision suggested a likely relative velocity of around 3000 km/s), their peculiar velocities could still have given them a significant velocity component in the tangential direction, in which case the collision needn't have been head-on.

But even if there were no gravitational attraction between galaxies and they just moved inertially with the same peculiar velocity forever, your argument that collisions should be fabulously unlikely still shows an ignorance of statistics. As I already explained to you in an argument you ignored, it's true that if you randomly choose two specific objects from a large group moving in random directions, it's very unlikely those particular two collide, but if the total number of these objects is huge, then the probability that a given one will collide with some other member of the group may be large, given that there are so many to choose from.

If you disagree, then please answer this question: if we choose an air molecule at random in a roomful of air, do you think the probability it will collide with any other air molecule in the next second must be astronomically small, even when there are around 10^21 air molecules in a typical-sized room at room temperature? To make it more closely analogous, we can imagine lowering the pressure in the room so that the average separation between molecules is about 50 times the diameter of individual molecules, which is about the ratio between average galaxy separation and average galaxy size according to p. 1 of this paper (and since space is three-dimensional, the ratio between the volume occupied by galaxies/molecules and the volume of empty space in any given region would be about 1:50^3, or 1:125000). And keep in mind that attractive forces between air molecules are negligible since non-ionic molecules have zero net charge, so any collisions would have to be a matter of two molecules randomly happening to have velocity vectors that caused them to arrive in the same molecule-sized region of space at the same time.
skolnick1 wrote:Collision dynamics aside, the deceleration of both the subcluster and the main cluster would elicit a burst of gravitational and electromagnetic waves, opposite their acceleration vectors (i.e. away from one another), precisely into the regions you've so complacently accepted as dark matter because someone shaded it in blue. Yes, this is a prediction which follows from well-accepted laws, regardless of your stance on dark matter.

I think it's dark matter not because "someone shaded it in blue" but because it emits no detectable radiation (and also seems to have no effect of blocking any of the radiation from bright objects behind it in our line of sight, as things like molecular clouds do), yet gravitational lensing indicates a mass density in those regions that's greater than the mass density in the regions with the observable matter, as seen in a mass density contour from this page:

Image

Again, I'm pretty certain that no physicists have proposed that any known form of baryonic matter could have that sort of density yet neither emit nor block radiation on any observable frequencies, just like I was pretty certain that no physicists have proposed that any form of baryonic matter in the Fermi bubbles could have a mass density greater than the galaxy yet emit/block no measurable radiation on frequencies other than x-ray and gamma (and not a great deal on those). In the case of Fermi bubbles you seemed to have no specific candidate for a type of matter that would do the job, it was pure wishful thinking--and now in the case of the Bullet cluster, are you really arguing that the mass density of "gravitational and electromagnetic waves" from a collision between clusters (in which only a tiny fraction of the stars will actually have collided with other stars, since galaxies and galaxy clusters are mostly empty space) could plausibly have a greater mass density than the galaxy clusters themselves? Since total energy is conserved, this would seem to imply that at least half of the mass-energy of the clusters before they collided was converted into energy carried by electromagnetic and gravitational radiation. Do you know of any calculations that suggest this is remotely possible (pretty sure that such a large fraction of mass can only be converted to radiation energy in extreme cases like matter/antimatter annihilation or collisions at extremely high fractions of the speed of light), or is this just more wishful thinking?
skolnick1 wrote:I decided to abandon that argument since I was tired of trying to explain probabilistic logic and bremsstrahlung to a "layman", as you say.

If you think I am missing something basic about probabilistic logic, please do me the courtesy of answering my question about the frequency of intramolecular collisions in a roomful of low-pressure air where the average separation between molecules is 50 times the average diameter of air molecules. As for bremsstrahlung, I don't recall you even mentioning braking radiation in your posts addressed to me until the most recent one that I am responding to here.
skolnick1 wrote:Now, I am tempted to abandon this discussion altogether, since you are wasting both of our time by defining the word "nucleon" for a physicist.

Are you saying that you're a physicist? You didn't mention this before, I just assumed you weren't since you were posting math-free physics speculations on a webcomic forum. Do you have a Ph.D., or what? Anyway, keep in mind that I am trying to write so that anyone reading can follow along, even if I had known you were perfectly aware of the meaning of nucleons (I didn't think one way or another about whether you knew the meaning, so there's no need to take my explanation as an insult) I still would have explained just so no one would get confused about why I was comparing a number density in Hydrogen atoms per cubic volume to a number density in nucleons per cubic volume.
Last edited by Hypnosifl on Fri Sep 12, 2014 4:58 pm UTC, edited 12 times in total.

User avatar
LaserGuy
Posts: 4581
Joined: Thu Jan 15, 2009 5:33 pm UTC

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

Postby LaserGuy » Fri Sep 12, 2014 3:11 am UTC

skolnick1 wrote:
LaserGuy wrote:No, they aren't massive enough, and they aren't old enough. I'm also not sure exactly how you think having mass in this particular configuration would actually cause the galactic rotation curves to behave in the manner that they do. Even if these were really massive, I think the net effect of this extra mass would be more or less to increase the mass of the galactic center.


Aha! You're agreeing with me! I've been saying: in the plane of the galaxy's rotation, the net effect would be an increase in the massive pull towards the center, depending on your radius and the density distribution of the bubbles. This would allow objects at the edges to remain bound at a greater tangential speed than we'd currently estimate as possible. This is why the galaxy's rotation curve can be roughly flat.


No, it wouldn't change the shape of the curve in this manner at all. I don't know why you think it would. Hypnosifl sketched out the problem nicely. The equations of motion are not so complicated here. You could probably calculate for yourself what would happen were you change the density profile in the manner you describe. In fact, I highly suggest it, as it would bring some much-needed credibility to your argument.

Although I find it a bit confusing that you're talking about Fermi Bubbles now as it is a central thing to your model, didn't mention them at all when you first started this discussion or until the subsequent two weeks. If you wanted to talk about Fermi Bubbles, what was all this business with black hole mergers and sprinklers? Why didn't you just say from the beginning what you were trying to say? What about this business about tangential velocities? Reread your first post again and explain to me how on Earth what you're talking about has any relation to what you're saying now.

LaserGuy wrote:They're big, but that doesn't mean they're massive. In fact, we've already estimated the mass of them, looking at the few papers on this I've seen, and it's nowhere near the order of magnitude that you're looking for--much less than the mass of the galaxy, let alone the mass of the dark matter halo. Also, the jets are not that old. Their age is only around 10^8 years, which means that they weren't around even at the time of the dinosaurs. I'm not sure how you could argue that they have anything to do with galaxy formation, regardless of their origin.


Well if you want to hop on board and be a part of "we"...
Your estimates of age are wrong; you're missing something key.
You're off on mass as well; they store tremendous energy
As is below, it's so above, L2, M0, N3.
(It's bound to be the final clue you ever get from me!)


Post the paper here when you've been published and I'll be happy to read it.

User avatar
BlackSails
Posts: 5315
Joined: Thu Dec 20, 2007 5:48 am UTC

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

Postby BlackSails » Fri Sep 12, 2014 5:21 am UTC

gmalivuk wrote:
skolnick1 wrote:Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally?
The fact that there's no mechanism by which dark matter particles could shed angular momentum.


Even if they could, they would have some temperature and condensation could take a long time.

User avatar
mosgi
Posts: 46
Joined: Thu Jul 17, 2014 8:19 pm UTC
Location: Somewhere in your past light cone

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

Postby mosgi » Wed Sep 17, 2014 9:08 pm UTC

I went away from the fora for a while and seem to have missed all the fun in this thread! However, I do have one question for the GR people around here, based on something skolnick1 said on the second page:

skolnick1 wrote:When you accelerate an electron, you get Bremsstrahlung, or "braking radiation", opposite its acceleration vector.
IF the bullet cluster experiences significant acceleration towards its companion (which would be true regardless of whether this is a straight pass-through or an orbit), it would let off an unholy amount of such radiation, given any charged substructure to it.


Is this actually the case? I know in SR an accelerating charge should emit Bremsstrahlung, but orbits are inertial paths in GR. So my question is really: does Bremsstrahlung depend on proper acceleration or coordinate acceleration? Or is it one of those annoying cases where it's a bit of both?
(they pronouns please)

Nicias
Posts: 167
Joined: Tue Aug 13, 2013 4:22 pm UTC

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

Postby Nicias » Wed Sep 17, 2014 9:19 pm UTC

mosgi wrote:I went away from the fora for a while and seem to have missed all the fun in this thread! However, I do have one question for the GR people around here, based on something skolnick1 said on the second page:

skolnick1 wrote:When you accelerate an electron, you get Bremsstrahlung, or "braking radiation", opposite its acceleration vector.
IF the bullet cluster experiences significant acceleration towards its companion (which would be true regardless of whether this is a straight pass-through or an orbit), it would let off an unholy amount of such radiation, given any charged substructure to it.


Is this actually the case? I know in SR an accelerating charge should emit Bremsstrahlung, but orbits are inertial paths in GR. So my question is really: does Bremsstrahlung depend on proper acceleration or coordinate acceleration? Or is it one of those annoying cases where it's a bit of both?

Proper.

User avatar
mosgi
Posts: 46
Joined: Thu Jul 17, 2014 8:19 pm UTC
Location: Somewhere in your past light cone

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

Postby mosgi » Wed Sep 17, 2014 9:31 pm UTC

Nicias wrote:
mosgi wrote:I went away from the fora for a while and seem to have missed all the fun in this thread! However, I do have one question for the GR people around here, based on something skolnick1 said on the second page:

skolnick1 wrote:When you accelerate an electron, you get Bremsstrahlung, or "braking radiation", opposite its acceleration vector.
IF the bullet cluster experiences significant acceleration towards its companion (which would be true regardless of whether this is a straight pass-through or an orbit), it would let off an unholy amount of such radiation, given any charged substructure to it.


Is this actually the case? I know in SR an accelerating charge should emit Bremsstrahlung, but orbits are inertial paths in GR. So my question is really: does Bremsstrahlung depend on proper acceleration or coordinate acceleration? Or is it one of those annoying cases where it's a bit of both?

Proper.

So, to make sure I'm understanding correctly, an charged body in a purely-gravitational orbit shouldn't emit EM radiation then? That does make sense, otherwise I guess it would spiral in pretty darn quickly, as opposed to the fairly slow process of losing energy to gravitational waves.
(they pronouns please)

SU3SU2U1
Posts: 396
Joined: Sun Nov 25, 2007 4:15 am UTC

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

Postby SU3SU2U1 » Sat Sep 20, 2014 2:40 am UTC

mosgi wrote:So, to make sure I'm understanding correctly, an charged body in a purely-gravitational orbit shouldn't emit EM radiation then?


This is not correct, in so far as its well posed. Radiation is frame dependent, but an observer at infinity will see radiation and the object will spiral in.

An easier case to think about- imagine a charged brick sitting on a table in a gravitational field (i.e. on earth). An observer sitting on the table with the brick cannot see radiation, or else we could easily violate local energy conservation. A free-falling observer, falling past the table, however, will see an accelerating charge object, so obviously radiation.

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Sat Sep 20, 2014 3:28 am UTC

SU3SU2U1 wrote:
mosgi wrote:So, to make sure I'm understanding correctly, an charged body in a purely-gravitational orbit shouldn't emit EM radiation then?


This is not correct, in so far as its well posed. Radiation is frame dependent, but an observer at infinity will see radiation and the object will spiral in.

An easier case to think about- imagine a charged brick sitting on a table in a gravitational field (i.e. on earth). An observer sitting on the table with the brick cannot see radiation, or else we could easily violate local energy conservation. A free-falling observer, falling past the table, however, will see an accelerating charge object, so obviously radiation.

Interesting, I hadn't known radiation was frame-dependent in this way--I see the issue is discussed in this paper on arxiv.org.

User avatar
doogly
Dr. The Juggernaut of Touching Himself
Posts: 5526
Joined: Mon Oct 23, 2006 2:31 am UTC
Location: Lexington, MA
Contact:

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

Postby doogly » Sat Sep 20, 2014 3:57 pm UTC

Another basic example for radiation being frame dependent is the Unruh effect. Curved space is full of surprises!
LE4dGOLEM: What's a Doug?
Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.

Keep waggling your butt brows Brothers.
Or; Is that your eye butthairs?

User avatar
Yakk
Poster with most posts but no title.
Posts: 11115
Joined: Sat Jan 27, 2007 7:27 pm UTC
Location: E pur si muove

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

Postby Yakk » Mon Sep 22, 2014 7:15 pm UTC

gmalivuk wrote:
skolnick1 wrote:Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally?
The fact that there's no mechanism by which dark matter particles could shed angular momentum.

To elaborate:

Think of a cloud of gas. Now, a cloud of gas is actually a bunch of particles, flying around.

In order to collapse inward, the gas particles have to collide. Imagine if you took one particle, and made it immune to collision. The one particle will continue in an endless orbit along pretty much exactly its current path.

Now do it for every particle. If it falls into the potential well, it gains kinetic energy, which it cannot lose by collision, so it still has it and it falls back out again.

Real gas particles collide with each other. They heat up, and emit light, bleeding energy. They trade angular momentum: some end up with more angular momentum and energy and fly out of the system entirely, escaping, or two particles with opposite momentum collide and fall inward.
One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision - BR

Last edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Mon Sep 22, 2014 7:25 pm UTC

Yakk wrote:
gmalivuk wrote:
skolnick1 wrote:Alright, fine. What keeps dark matter from collapsing, if it only interacts gravitationally?
The fact that there's no mechanism by which dark matter particles could shed angular momentum.

To elaborate:

Think of a cloud of gas. Now, a cloud of gas is actually a bunch of particles, flying around.

In order to collapse inward, the gas particles have to collide. Imagine if you took one particle, and made it immune to collision. The one particle will continue in an endless orbit along pretty much exactly its current path.

Now do it for every particle. If it falls into the potential well, it gains kinetic energy, which it cannot lose by collision, so it still has it and it falls back out again.

Real gas particles collide with each other. They heat up, and emit light, bleeding energy. They trade angular momentum: some end up with more angular momentum and energy and fly out of the system entirely, escaping, or two particles with opposite momentum collide and fall inward.

And as I mentioned earlier in this post, a statistical mechanics analysis suggests that even if they can collide, the net effect would tend to be to knock them into higher orbits or escape trajectories if not for the fact that collisions can also cause them to lose energy to radiation of some kind--mostly electromagnetic radiation in the case of charged particles, as the amount of energy lost to gravitational radiation in a collision is far smaller unless the particles involved are incapable of creating photons, as is theorized to be true of dark matter particles.
Last edited by Hypnosifl on Mon Sep 22, 2014 8:26 pm UTC, edited 1 time in total.

lgw
Posts: 437
Joined: Mon Apr 12, 2010 10:52 pm UTC

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

Postby lgw » Mon Sep 22, 2014 8:23 pm UTC

Hypnosifl wrote:And as I mentioned, earlier in this post, a statistical mechanics analysis suggests that even if they can collide, the net effect would tend to be to knock them into higher orbits or escape trajectories if not for the fact that collisions can also cause them to lose energy to radiation of some kind--mostly electromagnetic radiation in the case of charged particles, as the amount of energy lost to gravitational radiation in a collision is far smaller unless the particles involved are incapable of creating photons, as is theorized to be true of dark matter particles.


Does the galactic rotation rate imply a spherical halo of dark matter? I ask because it's technically possible that dark matter does have some dark friction-equivalent, and does shed angular momentum (assuming the radiation thus emitted also doesn't interact with us). IIRC the observed galaxy rotation rates imply spherical halos, not disks, and so do a pretty good job of ruling that out (but I don't trust my memory here).
"In no set of physics laws do you get two cats." - doogly

Hypnosifl
Posts: 257
Joined: Wed Mar 02, 2011 10:05 am UTC

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

Postby Hypnosifl » Mon Sep 22, 2014 8:42 pm UTC

lgw wrote:Does the galactic rotation rate imply a spherical halo of dark matter? I ask because it's technically possible that dark matter does have some dark friction-equivalent, and does shed angular momentum (assuming the radiation thus emitted also doesn't interact with us). IIRC the observed galaxy rotation rates imply spherical halos, not disks, and so do a pretty good job of ruling that out (but I don't trust my memory here).

According to this article, measurements suggest something like an ellipsoid, but counterintuitively, the diagram seems to show that the flatter axis of the ellipsoid is not the same as the flattest axis of the observable matter in the Milky Way. And this pdf is on the trends in dark matter halo shapes in simulations of dark matter, on the "Summary of main systematics trends" page it says "The more massive a halo the more triaxial it is" (which I think means it is more likely to be well-approximated by a triaxial ellipsoid function) and "Halos of a given mass are more triaxial at earlier times" and "Halos are increasingly rounder at larger radii".

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Sun Feb 15, 2015 2:14 am UTC

Reviving this thread because Gmal threw a tantrum. Move it to Fictional Science if you have to.
Hypnosifl wrote: on the "Summary of main systematics trends" page it says "The more massive a halo the more triaxial it is" (which I think means it is more likely to be well-approximated by a triaxial ellipsoid function) and "Halos of a given mass are more triaxial at earlier times" and "Halos are increasingly rounder at larger radii".

The article defines triaxial to mean "having different lengths along all three axes", and describes it as a "cosmic beach-ball that's been squashed from the side".

So here's my thing. Here's why I won't quit.
I'm not suggesting that there's no additional mass there. I'm suggesting that, rather than a "squished beach ball" which requires all kinds of strange non-interacting particles, the missing mass is bound in one or more of the following lovely shapes, by orbital dynamics similar to those that govern the behavior of electrons around a nucleus.
Spoiler:
Image


Look at (4,3,0) on that chart. Bears just a little resemblance to these things, if you'll notice.
Now, try to get a sense of scale on this, will you? If the galaxy were an atom like that, then we'd be standing on a rock orbiting a quark and I think that, from there, it might be hard to tell whether the atom you're in is a (4,3,0) or a (4,0,0) based on a few femtoseconds of data on gravitational effects in the equatorial plane.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Sun Feb 15, 2015 2:30 am UTC

skolnick1 wrote:it might be hard to tell whether the atom you're in is a (4,3,0) or a (4,0,0) based on a few femtoseconds of data on gravitational effects in the equatorial plane.
It might be if you don't know even basic Newtonian mechanics, sure...
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
sevenperforce
Posts: 658
Joined: Wed Feb 04, 2015 8:01 am UTC

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

Postby sevenperforce » Sun Feb 15, 2015 2:40 am UTC

skolnick1 wrote:...the missing mass is bound in one or more of the following lovely shapes, by orbital dynamics similar to those that govern the behavior of electrons around a nucleus.

Orbital dynamics governing the path of massive objects does not come close to approximating the electron orbitals of an atom.

Same word? Yes. Same mechanics? Not in the slightest.

User avatar
Xanthir
My HERO!!!
Posts: 5400
Joined: Tue Feb 20, 2007 12:49 am UTC
Location: The Googleplex
Contact:

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

Postby Xanthir » Sun Feb 15, 2015 7:28 am UTC

(4,3,0) doesn't even come close to looking like the galaxy, either. There's large lobes at top/bottom, yeah, but the galaxy is otherwise a flat disk, while (4,3,0) is two funky donuts stacked on top of each other, with basically *nothing* there in the equatorial disk area.

ETA: And orbital dynamics doesn't look even a little bit like the quantum mechanics defining the electron shell. Electrons don't orbit, you're stuck in some weird hybrid of the Bohr model and tiny bits of misunderstood QM.
(defun fibs (n &optional (a 1) (b 1)) (take n (unfold '+ a b)))

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Sun Feb 15, 2015 7:52 am UTC

Xanthir wrote:(4,3,0) doesn't even come close to looking like the galaxy, either.

What's especially funny is that it also doesn't come close to looking like the Fermi bubbles he's so obsessed with. Why not at least go with (3,2,2) or (4,3,3) if you want to suggest some kind of vague similarity in appearance?
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

FancyHat
Posts: 341
Joined: Thu Oct 25, 2012 7:28 pm UTC

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

Postby FancyHat » Sun Feb 15, 2015 8:02 am UTC

skolnick1 wrote:Look at (4,3,0) on that chart. Bears just a little resemblance to these things, if you'll notice.

Your tendency, whether it's with Europa or galaxies, to place emphasis on very superficial similarities of appearance reminds me of Electric Universe cranks who rely on astronomical things looking a little bit like manifestations and effects of various electrical and related phenomena.

I can see how those two lobes on either side of that galaxy can be visually reminiscent of depictions of electron orbitals, but that doesn't mean it makes sense to then run off with the idea that they're therefore the same kind of thing.

It's a huge mistake to think, 'this thing obviously looks like that thing,' (which it may well do, superficially), 'therefore, this thing is likely to be like that thing,' regardless of what's already known (by plenty of other people even if not by you) about whatever this and that thing are.

Please don't put yourself on the wrong side of Dunning-Kruger, for that way lies the path to crackpottery.
I am male, I am 'him'.

User avatar
Fractal_Tangent
Today is my Birthday!
Posts: 923
Joined: Thu Feb 19, 2009 9:34 pm UTC
Location: Here, I suppose. I could be elsewhere...

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

Postby Fractal_Tangent » Sun Feb 15, 2015 11:02 am UTC

So I found a thing about Fermi Bubbles. It states that these Fermi Bubbles appear to be short lived in comparison with our galaxy. If they're short lived then they're not really the best candidate for dark matter. Also because outflows similar to this have been seen on other galaxies but not all galaxies but the rotation curves that we see are pretty much universal (with regards to shape) this also shows that your theory about Fermi Bubbles is tenuous at best.

I would also like to point out (though I feel it's been done) that orbital mechanics inside of an atom where quantum phenomena is king is far, far different from large scale phenomena. Quantization of orbits is so interesting because they only happen on a small scale. I don't know if I can drive that home any harder. You don't get quantization of gravitational orbits - sorry about it.
eSOANEM wrote:
right now, that means it's Nazi punching time.


she/her/hers
=]

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Mon Feb 16, 2015 9:04 pm UTC

Fractal_Tangent wrote:So I found a thing about Fermi Bubbles. It states that these Fermi Bubbles appear to be short lived in comparison with our galaxy.


I found another thing that says they're not.
Goddard's astronomers are back-calculating, assuming that the edges of the structures correspond to the time they began flowing out. That makes me skeptical for a number of reasons, least of all being that the estimates of outflow speed from an active quasar in that article you cited were within a factor of 2 of local galactic escape velocity

Xanthir wrote: There's large lobes at top/bottom, yeah, but the galaxy is otherwise a flat disk, while (4,3,0) is two funky donuts stacked on top of each other, with basically *nothing* there in the equatorial disk area.


Guys. I get that they're not the same thing, I understand quantization; I bring these up only to point out that a spherical orbit through a rotating disk isn't sustainable, while a P orbit is. Think about it: quantum or macro, the more angular momentum a composite nucleus has, the lower your chance of finding any one particle at its center at a given point in time. Those models are of electron density, so when the nucleus has angular momentum, its constituents are most likely to be found in the plane with the least electron density, i.e. the eqauatorial disk area, whereas the electrons fill the rest of the space in the smoothest manner possible.
I'm saying that, on a large scale, you might not need weird non-interacting particles if you can explain the non-interaction geometrically.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Mon Feb 16, 2015 9:57 pm UTC

skolnick1 wrote:I get that they're not the same thing, I understand quantization; I bring these up only to point out that a spherical orbit through a rotating disk isn't sustainable, while a P orbit is. Think about it: quantum or macro, the more angular momentum a composite nucleus has, the lower your chance of finding any one particle at its center at a given point in time. Those models are of electron density, so when the nucleus has angular momentum, its constituents are most likely to be found in the plane with the least electron density, i.e. the eqauatorial disk area, whereas the electrons fill the rest of the space in the smoothest manner possible.
Your saying this proves quite handily that you don't understand quantization.

And again, the rotation curves you'd expect in visible matter in the disk quite simply are not the same for a spherical dark matter halo as they are for Fermi bubbles, regardless of the amount of hand-waving comparisons to electron orbitals you come up with.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Mon Feb 16, 2015 11:30 pm UTC

Gmal, please read the rest of the thread before polluting it again?
Hypnosifl wrote:
lgw wrote:Does the galactic rotation rate imply a spherical halo of dark matter?

According to this article, measurements suggest something like an ellipsoid, but counterintuitively, the diagram seems to show that the flatter axis of the ellipsoid is not the same as the flattest axis of the observable matter in the Milky Way. And this pdf is on the trends in dark matter halo shapes in simulations of dark matter, on the "Summary of main systematics trends" page it says "The more massive a halo the more triaxial it is" (which I think means it is more likely to be well-approximated by a triaxial ellipsoid function) and "Halos of a given mass are more triaxial at earlier times" and "Halos are increasingly rounder at larger radii".


Again, triaxial means "having different lengths along all three axes".

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Mon Feb 16, 2015 11:35 pm UTC

skolnick1 wrote:Gmal, please read the rest of the thread before polluting it again?
Hypnosifl wrote:
lgw wrote:Does the galactic rotation rate imply a spherical halo of dark matter?

According to this article, measurements suggest something like an ellipsoid, but counterintuitively, the diagram seems to show that the flatter axis of the ellipsoid is not the same as the flattest axis of the observable matter in the Milky Way. And this pdf is on the trends in dark matter halo shapes in simulations of dark matter, on the "Summary of main systematics trends" page it says "The more massive a halo the more triaxial it is" (which I think means it is more likely to be well-approximated by a triaxial ellipsoid function) and "Halos of a given mass are more triaxial at earlier times" and "Halos are increasingly rounder at larger radii".


Again, triaxial means "having different lengths along all three axes".
And "ellipsoid" means "ellipsoid", which a pair of Fermi bubbles most definitely isn't.

Did you look at the images in the pdf link you quoted? They look nothing like that Fermi bubble graphic you keep posting.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Tue Feb 17, 2015 12:19 am UTC

gmalivuk wrote:Did you look at the images in the pdf link you quoted? They look nothing like that Fermi bubble graphic you keep posting.

You do realize that's an artist's representation, yeah?
Look at the actual heatmaps and the amount of filtering they had to do to get them. As you said, this isn't quantized; it's not that that's the only path the particles can take, just one of the most sustainable, with the least chance of catching on another body as it passes through the plane and having its orbit disturbed.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Tue Feb 17, 2015 12:31 am UTC

skolnick1 wrote:
gmalivuk wrote:Did you look at the images in the pdf link you quoted? They look nothing like that Fermi bubble graphic you keep posting.

You do realize that's an artist's representation, yeah?
You can't have it both ways. Either that is what they look like, in which case they don't give the same velocity curves which we observe (and which are predicted by ellipsoidal dark matter halos), or that isn't what they look like, in which case your tenuous comparison to electron orbitals makes even less sense than it already did.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

skolnick1
Posts: 113
Joined: Sun Mar 16, 2008 9:29 pm UTC

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

Postby skolnick1 » Tue Feb 17, 2015 3:16 am UTC

gmalivuk wrote:You can't have it both ways. Either that is what they look like, in which case they don't give the same velocity curves which we observe (and which are predicted by ellipsoidal dark matter halos), or that isn't what they look like, in which case your tenuous comparison to electron orbitals makes even less sense than it already did.

I would say less that it doesn't make sense and more that you either aren't reading or aren't comprehending these posts.
skolnick1 wrote:I bring these up only to point out that a spherical orbit through a rotating disk isn't sustainable, while a P orbit is.

User avatar
doogly
Dr. The Juggernaut of Touching Himself
Posts: 5526
Joined: Mon Oct 23, 2006 2:31 am UTC
Location: Lexington, MA
Contact:

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

Postby doogly » Tue Feb 17, 2015 3:24 am UTC

I am so sorry that Bohr ever used the word "orbit" for those things. You're not dead though, you can just stop now. Please, please stop.
LE4dGOLEM: What's a Doug?
Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.

Keep waggling your butt brows Brothers.
Or; Is that your eye butthairs?

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26725
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

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

Postby gmalivuk » Tue Feb 17, 2015 3:32 am UTC

Yeah, a P orbit isn't a gravitational orbit at all. Period. I don't know what "a spherical orbit" is supposed to mean, either.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
Izawwlgood
WINNING
Posts: 18686
Joined: Mon Nov 19, 2007 3:55 pm UTC
Location: There may be lovelier lovelies...

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

Postby Izawwlgood » Tue Feb 17, 2015 4:01 am UTC

Obviously an s-orbital. Because p- and s-orbiting electrons always be colliding, yo. I know this because I play KSP.
... with gigantic melancholies and gigantic mirth, to tread the jeweled thrones of the Earth under his sandalled feet.


Return to “Science”

Who is online

Users browsing this forum: No registered users and 9 guests