Astrophysics and Cosmology - Discuss the Universe here

[Agent : Orange]

Agent - in that video I posted of the recent Carroll talk (the hour long NSF one), at 35:00 roughly he's talking about the Bullet Cluster and how this is a white crow for dark matter existing because the mass of the galaxies should have been in the gas, not in the galaxies themselves.  How can he be sure of this?  He mentions they have a method of determining this by the matter of the gas being heated and giving off x-rays.   But is it not possible for the galaxies to have multiple SMBH's or some other massive objects that have more mass than the gasses left over from the collision?  I understand he has to gloss over this stuff, but it's like saying "christ is god because the bible says so."   How do you know if the bible is correct... see what I'm saying?

I bet!  And couldn't it be that some gas clouds are thin, such that they don't have a lot of mass but still reflect light back at us?

The bullet cluster (the actual name is 1E 0657-56) is actually composed of two separate, colliding galaxy clusters. The smaller one acts like a bullet in the collision. Here's a picture of it below:

I'll explain this image and what the colors mean in more depth later on. For now, let me start by saying that when clusters of galaxies hit one another, it's rare that individual galaxies actually collide with one another. Instead, it's more like two people shooting birdshot from shotguns into the air, if the blasts pass through one another, few (if any) pellets score a direct hit on one another. Instead most of that stuff just passes through the collision, and that's what we can see from the clumps of individual galaxies here. This should be similar to the dark matter in the cluster as well. We expect that DM only interacts through gravity with regular matter and does not interact in any other way even with itself. So we expect that the DM will act much like the individual galaxies, and pass right through the collision. But how can we prove this, and how to study matter distributions that you can't directly observe?

The DM distribution can be studied by looking at the statistical distortion of background objects. When individual objects in the background of the image are not exactly aligned with the cluster itself, we can see distortions of their shapes, which is called gravitational shear. In general, we expect a random sampling of many galaxies to be an unbiased distribution of shape, and shear acts to distort these shapes in preferred directions. Many background galaxies have to be observed to say anything about the average gravitational shear. There is a relationship between the shear and mass density, so once you know the average shear you can do the calculation and get the average mass density responsible for lensing the background objects into these sheared shapes. Here is an ideal case that makes use of a uniform background just to make the effect I'm talking about clear:

In the upper right we've got a sheared field of ideal sources. Lower right is the mean shear field that we get from that observation, and then we calculate the mass density responsible for creating that shear in the lower left. This is a map of the total mass distribution, both luminous and dark that's responsible for the shear. In the upper left I show the original undistorted field. This is of course idealized and real observations of shear are usually very messy and averaged. It's more subtle than I make it out to be in this image but the principle is there. A better example is shown below.

Here we've got some shapes on the left and a subtle shear acting to align them in the direction shown on the right. This is a more accurate description. You can see why many objects are needed to measure an average shear if you look at the background objects in a strongly lensed image like the one below:

Forget about the large arcs for a second and just look at the stuff near the periphery of this image. All of the shapes show a systematic distortion and they all point around the lens as if in a circle. This is again very idealized but the principle is there. In reality much smaller and more subtle gravitational shear can be measured from images. Finally here's a spherical mass moving among a background set of objects, just because it looks cool.

The shear in the regular grid of background spots can be clearly seen as the lens moves through the field.

Anyway the point is that once you have measured the shear you can get an estimate and make a map of the total amount of matter that's responsible for the background shear. When you do this with the bullet cluster, you get an image like this one:

This is a mass map of the total mass in the cluster that shears the background galaxies. Note the two separate lobes of matter, one from each cluster. These mass components have passed through one another collisionlessly, like we expect. The surprising thing is when you look at the total number of galaxies in the cluster and the estimate of the total mass there's a discrepancy by a huge factor - there must be almost 10x more mass in these lobes than we can account for from the luminous matter of the galaxies alone. This is the "dark" component of the cluster.

However, galaxy clusters are also made up of hot gas between the component galaxies. In a collision, this gas should strongly interact, unlike the galaxies and dark matter components which are collisionless (remember the birdshot analogy). The gas clouds in the cluster will impact one another and be shocked. This shocked gas will be extremely hot and emit x-rays. But the key point is that when this gas is shocked, it will interact under more forces than just gravity. Turbulence in the flow and electromagnetism will play an important role in the physics of how the intercluster medium behaves and emits thermal radiation. We expect this gas to have a few unique properties: we expect it to be shocked, and we expect it to stick around near the point of impact, since it is interacting with itself. When we look at the bullet cluster in X-rays, we see the following:

Note the huge bow structure on the right. This is a textbook example of a shock front, caused as the warm gas of the small cluster slammed into the large one. This shock front then points in the direction of motion of the "bullet". Also note the difference in position of the mass components and the shocked intercluster medium: individual galaxies and dark matter go sailing right through the collision, while the X-ray emitting gas stays put at the center. This collision has separated the dark and normal matter in this collision, and left the X-ray hot and shocked intercluster medium behind.

This observation is key for the dark matter picture and really puts a nail in the coffin of the modified gravity camp. It's extremely difficult, if not impossible, to explain these dynamics by a modification of gravity alone. In fact, the leading favorite and general go-to, Mordecai Milgrom's MOND theory (MOND = Modification Of Newtonian Dynamics) reduces the amount of necessary dark matter, but still requires a dark component. That's a bad sign, because MOND was introduced to do away with DM by modifying gravity in the first place, so the fact that it requires dark stuff at all is a serious contradiction. There are now about half a dozen of these interacting clusters and they all - ALL - behave in the way we would expect if some portion of matter within them is not observed (ie, dark). This is one of the big reasons why DM is the favored theory, it explains all of the observations (including those from other fields, like cosmology, and other physical regimes like on the scale of individual galaxies, for example) very well. In fact, there are no other alternatives out there right now that do as well with all of the data as the DM picture does, like it or not. There is a ton of evidence to support it, which is why I say any modification of gravity that can explain all of it without needing DM has big shoes to fill.

Just as one last thought, look at how well the bullet cluster can be simulated in a computer assuming a dark matter component that interacts under gravity and an intercluster medium that obeys fluid dynamics.

The blue stuff is the mass distribution from the galaxies and dark matter, and the red stuff is the X-ray emitting gas of the intercluster medium. Look at the configuration in panels 3 and 4, and compare that with the actual cluster that's shown at the beginning of this post. The similarity is no coincidence.

[area51drone]

Thank you for that excellent post.   Now let me play devil's advocate.   Here are my questions, and it probably reflects my complete misunderstanding of what dark matter is.   I think dark matter is a terrible name for it, as it implies that there is physical stuff you can't see.  The more I'm learning about what physicists know about it, the less it seems like it is matter at all, more just like a field of interaction.  Terrible name I tell you!

In the video, Carroll says that the vast majority of mass in the galaxy clusters is the gas.   The gas remains towards the point of collision - if this were the case, wouldn't the dark matter interact with the vast majority of mass and stay with the gas cloud, and NOT move with the clusters?  Are you saying that if there was no EM forces at work, the gas would have moved right along through with the clusters, but because DM is not supposed to interact with EM forces, then this is why it did?  Surely some of the DM would have interacted with some of the gas, and itself as well, as it was colliding, and stuck behind.

To me, by saying that dark matter is staying with the clusters means really that it's only in areas where stuff is "packed" together.  Ie, like in the galaxies themselves, yet the "blue patch" distribution says to me that dark matter is still floating around between the individual galaxies in the clusters, more like a gas.   Is that so?  Is that how DM is supposed to be - floating around galaxies and around clusters, but not anywhere else, not even in large gas clouds?   Not even in floating free space?   You would think if DM exists, it should be distributed throughout the universe, not just in clusters or galaxies.   To say that they are in clusters and galaxies implies there's something wrong with the theory of gravity itself, even though you claim it's difficult to explain modified gravity.

But aside from that, how is it known that there aren't way more SMBH's and perhaps other massive objects that are making the mass and we just don't know it?   That would make a hell of a lot of sense, in that they would be the buckshot through the cloud, just like the matter we can see.   It also might go to explain the rotational speed of galaxies that are spinning at the same rate as well.    You also did not explain Carroll's comment that most of the mass is the gas.  How do we know that there is that much gas out there since we couldn't see the gas separate from the galaxies in their pre-collision state?

Also, I'm not completely convinced with the gravitational lensing theory.   I'd love to know why it is they say they can prove a galaxy is slightly sheared - how do they know it isn't just that shape to begin with?  With your first purple image example, I see no reason to believe that either image couldn't exist AS IS.  Unless they're guessing at what the lens distortion would be, I don't see how that could be accurate to say it's sheared one way or the other, even if you had some idea of the amount of mass in the galaxies.   I realize you *could* say, as in your purple example, "well we have 4 galaxies in this cluster of 6 that have a shear towards the right" but that doesn't prove anything.   That is such a small statistical sample.  There's no reason why they couldn't just be that way.

I certainly can understand lens shearing when it's obvious, but I can really not see any galaxies the bullet clusters that are sheared, say for maybe 3 shear lines - they're hard to see.      Also, are the lens modellers taking into account that an individual galaxy should be lensing itself?  Really, there are lenses upon lenses, not just "one cluster makes one lens" if you see what I'm saying.   Okay, I just went and found a much larger version of this picture, and just looking at it, it looks like there are definitely lenses upon lenses - take a look at the center of the "target" cluster on the left.  There is massive shearing right at the middle which suggests a much larger lens.   Link: http://apod.nasa.gov/apod/ap060824.html

I love it too when Carroll says in the video "to the trained eye, you'd say 'here's a cluster of galaxies'"... bullshit, take away the fancy colors and it looks just like the rest of the image.  Maybe the left cluster is more tightly packed, but the right cluster definitely is not.  Without redshift data, we wouldn't know squat.  And you *know* what I think of redshift.

[area51drone]

I hope you're not in the process of replying to my post yet, because I just edited it a million times.

[zeebo]

Agent Orange & area51drone ... just want to say very cool posts ... I'm just lurking as I have nothing useful to add, but it's fascinating stuff.

[Agent : Orange]

Now let me play devil's advocate.   

Excellent

Here are my questions, and it probably reflects my complete misunderstanding of what dark matter is.   I think dark matter is a terrible name for it, as it implies that there is physical stuff you can't see.  The more I'm learning about what physicists know about it, the less it seems like it is matter at all, more just like a field of interaction.  Terrible name I tell you!

The standard picture has it acting like matter we can't see, but matter that only interacts through gravity, which is unlike the "normal" (baryonic) matter we know of.

In the video, Carroll says that the vast majority of mass in the galaxy clusters is the gas.   The gas is left towards the point of collision - if this were the case, wouldn't the dark matter interact with the vast majority of mass and stay with the gas cloud, and NOT move with the clusters?  Are you saying that if there was no EM forces at work, the gas would have moved right along through with the clusters, but because DM is not supposed to interact with EM forces, then this is why it did?

Most of the baryonic matter is made up of the intercluster medium (ICM). But there has to be usually about 4 or 5 times more dark stuff than total baryonic matter (both galaxies and hot gas). The gas is a fluid, which is different than the galaxies themselves (the birdshot). This gas is shocked and stays behind while the individual galaxies move through one another. The DM is collisionless so it should also pass through the point of collision, which is what we see. The DM is still attracting both the haloes and the gas itself but has a large initial velocity, so most of the DM goes sailing through. There are other clusters we know of now that have much slower collision speeds and that makes everything more messy. The most famous of these is called the musketball cluster because musketballs are slower than bullets
The forces at work here are very complicated especially in the ICM because there you have fluid dynamics, gravity and thermal transport all taking place at the same time.

To me, by saying that dark matter is staying with the clusters means really that it's only in areas where stuff is "packed" together.  Ie, like in the galaxies themselves, yet the "blue patch" distribution says to me that dark matter is still floating around between the individual galaxies in the clusters, more like a gas.   Is that so?  Is that how DM is supposed to be - floating around galaxies and around clusters, but not anywhere else, not even in large gas clouds?   Not even in floating free space?   You would think if DM exists, it should be distributed throughout the universe, not just in clusters or galaxies.   To say that they are in clusters and galaxies implies there's something wrong with the theory of gravity itself, even though you claim it's difficult to explain modified gravity.

DM is distributed throughout the universe along with normal matter. When you look at the universe at the largest scales it seems to have a filamentary or weblike structure. In fact this web has to be made of huge amounts of dark matter for which the baryons act like a tracer. At the intersections of these filaments we have galaxies forming, which should all have a statistical population of satellite galaxies around them, some of which will be dark on their own. So we expect a lot of structure on very large scales.

The left part of the image shows huge simulations that are done from billions of years in the past (large z) to the present (z=0). This shows the web of dark matter and the brightest parts of the image are giant baryonic matter clumps - actually the visible part of galaxies. Note that they form at the intersection of filaments and that they have a large number of satellite galaxies. The image on the right is actual data, comprised of millions of galaxies (!!) arranged by redshift. We're at the center and the visible galaxies in the "N" and "S" wedges are arranged by redshift z. Note the similarity between the simulations (left) and the actual observations on the right. Galaxies in the universe really are clustered in the way DM predicts, at least on the largest scales.

On smaller scales, the scales of clusters and individual galaxies, we expect the DM to be spread out around the galaxies like a cloud of stuff out there. It has to be in very large haloes in both individual galaxies and in clusters for the dynamics to work properly. Of course clusters are clumpier than the haloes of normal galaxies, so there can be complicated structure in there - ie the blue lobes in the bullet cluster image are not perfectly uniform. We have just begun to detect hints of the cosmic web through weak lensing and large "tails" and "bridges" connecting clusters together. So it seems like we are on our way in terms of the observations.

But aside from that, how is it known that there aren't way more SMBH's and perhaps other massive objects that are making the mass and we just don't know it?   That would make a hell of a lot of sense, in that they would be the buckshot through the cloud, just like the matter we can see.   It also might go to explain the rotational speed of galaxies that are spinning at the same rate as well.    You also did not explain Carroll's comment that most of the mass is the gas.  How do we know that there is that much gas out there since we couldn't see the gas separate from the galaxies in their pre-collision state?

Let me address your second point first. We know there is a lot of mass in the ICM from X-ray observations of the clusters that are not involved in collisions and we see warm ICM there. And it's true that there is more mass in the ICM than there is in the galaxies - but the census of both ICM and galaxy mass is still small compared to the DM halo.

Great question, why can't the DM be compact objects like black holes or maybe small stars that are too dim to see? This idea has been suggested and it was a major contender for an explanation of DM in the 90s. This camp was interested in looking for MAssive Compact Halo Objects (MACHOs).  In fact, it's been shown that MACHOs can only make up 20% or so of the halo of the Milky Way. We assume other galaxies are likely similar so that still leaves us with 4 times the amount of DM  than we can account for. The halo of our galaxy is not clumpy enough to be made of MACHOs, they can only account for a small fraction of the halo mass. I predict the next question you ask will be "how do we know only 20% of the halo is made up of compact objects?" which is a bit of a complicated explanation that needs a bit of set up. More than I'm willing to put in tonight, anyway

Also, I'm not completely convinced with the gravitational lensing theory.   I'd love to know why it is they say they can prove a galaxy is slightly sheared - how do they know it isn't just that shape to begin with?  With your first purple image example, I see no reason to believe that either image couldn't exist AS IS.  Unless they're guessing at what the lens distortion would be, I don't see how that could be accurate to say it's sheared one way or the other, even if you had some idea of the amount of mass in the galaxies.

The shear is determined by looking at the preferential direction of galaxy shapes. In other words, the image on the left has more of the long axes of each galaxy pointing in a given direction. This is what we look for on a statistical basis - that's why its so important to have good statistics. We need to look at many (thousands) of galaxies to measure given shear, and then the best we can do is find an average. That's still good enough to derive an average mass density though. To simplify things a bit from my original post, if you fit each galaxy in the "upper right" image with an ellipse and then looked at how the ellipses are oriented with respect to one another then you'd find something like the measured field in the "lower right" panel, or an average shear.

I certainly can understand lens shearing when it's obvious, but I can really not see any galaxies the bullet clusters that are sheared, say for maybe 3 shear lines - they're hard to see.     Also, are the lens modellers taking into account that an individual galaxy should be lensing itself?  Really, there are lenses upon lenses, not just "one cluster makes one lens" if you see what I'm saying.

We're not interested in the light from the lens galaxies, only the light from the background objects. In that case the self lensing doesn't do much of anything unless you're very close up. You need to worry about self-lensing when you're talking about neutron stars or the lensing effects of black holes in our galaxy, for example. But for objects that are far away we only get light rays that undergo small bending from the emitter, and in fact the bending angle of the lens is small in all cases of astrophysical interest (letting us use the weak field limit of General Relativity). Which simplifies things quite a bit.

I was commenting on your original post for most of the night, so let me get to your modifications. I think you only changed the later stuff (or at least that's all I noticed anyway).

Okay, I just went and found a much larger version of this picture, and just looking at it, it looks like there are definitely lenses upon lenses - take a look at the center of the "target" cluster on the left.  There is massive shearing right at the middle which suggests a much larger lens.   Link: http://apod.nasa.gov/apod/ap060824.html

You oversimplify things. There's no way you can get any sense of shear at all examining a weakly lensed field by the naked eye. Only in the most extreme cases is the shear perceptible, like in those strong lensing examples that I showed in my post. There it's very obvious what's happening. When the lensing is weak the effect is subtle and requires statistical methods to measure. This is why I kept on stressing "subtle" in my post. I gave examples of strong lensing that hit you over the head with a shear signal. But if it was as easy as you suggest for real data, looking at the image and proclaiming you see this or that, it would have already been done by someone and they would have collected the grant money for that project! In reality there is a large amount of statistics and computing time that are needed to identify shear and whole careers are built on this one skill. The tools you use to go from shear to density is a piece of math called a Fourier transform, and it's probably beyond the scope of the conversation we can have here. Unless we ditch English and start throwing calculus around, and no one wants that. Anyway I want to stress the shear effect for a weak lens (what we're dealing with in the Bullet cluster) is extremely subtle and it requires a lot of statistics, a high number of background galaxy samples and a whole bunch of computing power to hunt down. This is different than in strong lensing, where you get dramatic arcs formed like in the examples I gave.

I love it too when Carroll says in the video "to the trained eye, you'd say 'here's a cluster of galaxies'"... bullshit, take away the fancy colors and it looks just like the rest of the image.  Maybe the left cluster is more tightly packed, but the right cluster definitely is not.  Without redshift data, we wouldn't know squat.  And you *know* what I think of redshift.

Well to be fair the redshift business is your own unique problem. I've given many examples why redshift is a valid and useful cosmological tool, and refuted the anti-redshift arguments you put up. I feel like if I can't convince you of that then all of this is for nothing. It's like you challenge me to build a house, I do it and then you say "well you didn't make your own nails, you bought them at a store so you didn't really build it". If you don't buy my arguments about redshift, the connection to Doppler shift and the expanding universe against that Halton Arp crap I'm wasting both of our time and fingers.

The redshift issue is a stumbling block to us making progress in this conversation. It's impossible to prove a negative, so maybe you should say why you feel uncomfortable with the standard interpretation of the redshift and the evidence you have that convinces you the standard view is incorrect and we can go from there.

[Agent : Orange]

Agent Orange & area51drone ... just want to say very cool posts ... I'm just lurking as I have nothing useful to add, but it's fascinating stuff.

I'm sickened by the walls of text I continue to put up. And with that, let me say I'm glad you're enjoying it though
It's just tough to get across all the ideas I want to a short space.  Nevertheless hope you stick around.
And comment often!

[Camazotz Automat]

Maintenance post.

Still lurking like a graviton in a vintage can of Silly Stringâ,,¢ theory.

[area51drone]

I'm sickened by the walls of text I continue to put up. And with that, let me say I'm glad you're enjoying it though
It's just tough to get across all the ideas I want to a short space.  Nevertheless hope you stick around.
And comment often!

Sickened because it took so much of your time, or because you feel like I'm such an idiot that it takes that much to explain it to me? LOL...   my retort is coming, I promise!

[area51drone]

Excellent
The standard picture has it acting like matter we can't see, but matter that only interacts through gravity, which is unlike the "normal" (baryonic) matter we know of.

Okay, I suppose I can accept that.  But still, it's more of a misnomer.  You can't bump into the stuff, right?  So my statement that it's more of a field of "extra gravity" is basically a better explanation, wouldn't you say?

Most of the baryonic matter is made up of the intercluster medium (ICM). But there has to be usually about 4 or 5 times more dark stuff than total baryonic matter (both galaxies and hot gas). The gas is a fluid, which is different than the galaxies themselves (the birdshot). This gas is shocked and stays behind while the individual galaxies move through one another.

But you're saying the gas is shocked by EM forces, NOT gravity, right?

The DM is collisionless so it should also pass through the point of collision, which is what we see. The DM is still attracting both the haloes and the gas itself but has a large initial velocity, so most of the DM goes sailing through. There are other clusters we know of now that have much slower collision speeds and that makes everything more messy. The most famous of these is called the musketball cluster because musketballs are slower than bullets

Please provide links, I'd like to look at these myself.   The problem I have with what you're saying is why is DM collisionless?  Why shouldn't it collide?  What is it's density?

DM is distributed throughout the universe along with normal matter.

Are there any instances where dark matter is supposedly detected by lensing without having any normal matter around?

Note the similarity between the simulations (left) and the actual observations on the right.

First off, I think this is an unfair image comparison.  The bright spots on the left indicate areas of high density mass, and the image on the right indicates areas of mass that moving in a particular fashion.

Even so, honestly to me they don't look all that similar upon close inspection.   In fact, the simulation at Z=0 looks almost nothing like the right image.  You have many clusters that are not connected to anything in the real data image, and in the simulation you have everything connected.

I think it's bad science to say "this looks like my simulation" for two reasons - one, it's subjective, and two, simulations can be done and redone until they match the data.  What math is the simulation based on?  What happens when Z = -100?  According to Kaku and others, and everyone who believes in the big bang, the universe should be tearing these filaments apart (even from z=18 to z=0) and beyond z=0 right?   We're supposed to see our galaxy in the future, and nothing else.  We're told that gavity acts weakly at a distance.  If dark matter is so dense/strong as to have an effect at inter galactic scales, then why on earth wouldn't it be dense enough to have an effect and collide with the gas in the bullet cluster, or do more interacting inside galaxies themselves?

On smaller scales, the scales of clusters and individual galaxies, we expect the DM to be spread out around the galaxies like a cloud of stuff out there. It has to be in very large haloes in both individual galaxies and in clusters for the dynamics to work properly.

If DM exists, there should be well defined expected behavior of it according to the theoretical laws, correct?  Completely ignoring the real data, what are the properties of DM?  You say that it is a cloud of stuff out there around galaxies.  Does it stretch between galaxies, or is it held within a bubble?   Is it in the ICM gasses?  If not, why not?  Is it in and around the solar systems within the galaxies?  Is it in the inter stellar medium?  How should it interact with planets?   How should it affect the rotation and orbit of sun by the earth, for example?   

Rereading your quote there, you say it's like a halo around the galaxies.  Almost like the gravity of the galaxies is pushing it away from it's bubble it sounds like.  If that's what you're saying,why would it be in this shape?

Let me address your second point first. We know there is a lot of mass in the ICM from X-ray observations of the clusters that are not involved in collisions and we see warm ICM there.

Excuse my ignorance, but how exactly does this tell you exactly how much mass is there? 

And it's true that there is more mass in the ICM than there is in the galaxies - but the census of both ICM and galaxy mass is still small compared to the DM halo.

It's not that the ICM vs galaxy mass is a problem for me necessarily, but I'd like to know why if the ICM has more mass that the DM would follow the galaxies and not the majority of the mass (the ICM, which stayed behind).

Great question, why can't the DM be compact objects like black holes or maybe small stars that are too dim to see? This idea has been suggested and it was a major contender for an explanation of DM in the 90s. This camp was interested in looking for MAssive Compact Halo Objects (MACHOs).  In fact, it's been shown that MACHOs can only make up 20% or so of the halo of the Milky Way.

Link please. I'd love to know how someone can prove such a thing, and yet say that enough DM can be there creating gravitational effects (evidenced by lensing) without having the same problems the MACHOs might create.

The halo of our galaxy is not clumpy enough to be made of MACHOs, they can only account for a small fraction of the halo mass. I predict the next question you ask will be "how do we know only 20% of the halo is made up of compact objects?" which is a bit of a complicated explanation that needs a bit of set up. More than I'm willing to put in tonight, anyway

No, my next question would be how the hell does anyone know the stuff is in a halo in the first place?   LOL  If we have evidence only through lensing and through looking at the rotational speed of galaxy arms, that isn't a hell of a lot of data to be making such claims.   It seems to me that perhaps a lot of claims about DM are based on simulations which I would think you would have to admit are prone to error and conjecture.   My next question would be how is it that enough distributed MACHOs wouldn't be able to make such a halo?  (in addition to why is there a limit on Machos as in my previous question above)

The shear is determined by looking at the preferential direction of galaxy shapes. In other words, the image on the left has more of the long axes of each galaxy pointing in a given direction. This is what we look for on a statistical basis - that's why its so important to have good statistics. We need to look at many (thousands) of galaxies to measure given shear, and then the best we can do is find an average. That's still good enough to derive an average mass density though.

I'm well aware of what you're saying.  And to some extent, I agree with you.   But how many galaxies are in this particular cluster and behind them? And how does this say that many MACHOs couldn't exist even between galaxies?   There must be a dozen theories as to why this could happen without DM, right?  Isn't it possible that perhaps there are MACHOs that are closer to us than the galaxies themseslves creating lensing?  Go back to the big image I linked to.  Look at the lensing of the galaxies right in the middle of the "target" cluster on the left.  They are dramatically lensed in an arc, and suggest an area of mass that is probably 10-20 times larger than the blue area and centered somewhere far "south" and "west" of the blue area. You also have the great example of the very obviously lensed line that has ripples in it. If it weren't individual galaxies creating these ripples, what would it be?  I see nothing other than a couple galaxies right next to that one.   I would love to see this as a 3d map, perhaps with some software that would allow one to simulate the lensing effects as well.

To simplify things a bit from my original post, if you fit each galaxy in the "upper right" image with an ellipse and then looked at how the ellipses are oriented with respect to one another then you'd find something like the measured field in the "lower right" panel, or an average shear.
... Which simplifies things quite a bit.

When you're talking about something brand new, simplifcation seems like a major problem to me.  I don't think anyone should be simplifying anything here. All things need to be accounted for.   With that said, based on your fit analysis, I call bullshit!  You as everyone else who knows a little math should understand that statistics are great, but they do have a margin of error.  In this case, when you're talking about something billions and billions and even more than billions of miles away, it is very difficult to ignore the possibility that these are just the way these are aligned and shaped, and the magin of error can be quite large.   I don't see how you can accurately predict *minor* lensing effects like what you're saying.

You oversimplify things. There's no way you can get any sense of shear at all examining a weakly lensed field by the naked eye. Only in the most extreme cases is the shear perceptible, like in those strong lensing examples that I showed in my post. There it's very obvious what's happening.

I call bullshit again!  In your example, it is certainly easy for a person to say that they are sheared, but there is no reason why they couldn't have existed that way in the first place.  So you CAN say they are sheared to some degree satistically, even if it is very very minor and calculated by a computer to the nth degree.   But let's even say that THAT is true and you're accurate.  So then, let's you and I talk about how the shape of the galaxies are determined... you are either basing the edge of the galaxies on some level of illumination (light, xray or other wave), correct?  Are you taking in every bit of data so that the galaxies are fuzzy, or are you cropping off certain levels of luminosity?  If so, what levels are cropped off and how is that determined?  It seems like it would be pretty easy to crop until the data fit.  Was the shearing data run with different crop points?  When you have data that is overlapping two galaxies distant from each other, where is that data attributed to or is it thrown out?   I hope you see what I'm getting at.  I am highly suspicious of all scientists, because nearly every damned one of them is looking for data to support their theory.   

Now, let's get back to reality.  The probability that I'm going to flip a coin once and it's going to land on heads is 50%. The next time I flip a coin, it has the same chance of landing on heads again, 50%, not less because you just flipped heads previously.  And going forward, you'll always have a 50% chance of flipping heads even if you just flipped 100 heads in a row.    YOU are saying that because 20 galaxies are arranged in such a manner that they must be sheared.  I am saying that because 20 galaxies are out there, there's just as even of a chance that they are arranged that way as they would not be arranged that way.   Who is correct?  I believe I'm just as correct as you are. But you're (the metahphorical you) are looking at anything to match your theory.   Give me something else.

The tools you use to go from shear to density is a piece of math called a Fourier transform, and it's probably beyond the scope of the conversation we can have here. Unless we ditch English and start throwing calculus around, and no one wants that.

I told you in a private email my math is rusty if not some of it gone altogther!  But shear to density doesn't negate the fact that you have to determine if something is sheared in the first place. I'm not arguing the fact tha you can say "we expect them to look like X but statistically we're seeing shear".  I'm arguing that your assumptions about X *might* be wrong in the first place.  I understand you're saying X is based on the rotation and shape of say 100,000 galaxies, and  you are comparing that small portion of shape behind the cluster to the 100,000.  Certainly as you are able to provide more and more examples the probability of what you're saying goes up.  But is anyone looking at cases where you'd expect DM to behave in a certain way and the statistics is going against you?

Well to be fair the redshift business is your own unique problem. I've given many examples why redshift is a valid and useful cosmological tool, and refuted the anti-redshift arguments you put up. I feel like if I can't convince you of that then all of this is for nothing. It's like you challenge me to build a house, I do it and then you say "well you didn't make your own nails, you bought them at a store so you didn't really build it". If you don't buy my arguments about redshift, the connection to Doppler shift and the expanding universe against that Halton Arp crap I'm wasting both of our time and fingers.

I think it's for people to decide on their own.  You say that they are separate, and with all your knowledge and the fact you do this for a living, certainly more people are going to believe you straight up.  But, and I hate to do this, but quoting Richard C Hoagland - "if they would just look at the data!"   

I go back to your statement:

There are a lot of these coincidences but they're statistical, meaning that for a population of distant objects and a uniform distribution that are closer to you there's a certain number that are expected to be fairly well aligned. It's actually not even that bad, if you look at most of these they're not sufficiently aligned to be gravitationally lensed and for those that are the redshifts of the background objects are always larger than the lenses. It's hard to argue with that fact.

Which states nothing to me really about the specific case of NGC 4319 and Markarian 205. (readers again see http://electric-cosmos.org/arp.htm  It's hard to argue looking at the data that they're not just aligned, but connected in some way that does not make sense in the classical redshift sort of way.   So you and I will have to agree to disagree.   Do I think redshift exists and probably tells us something about the universe?  Yes.  Do I think it's always accurate and applicable in every case?  No.   Especially when you start throwing "it's statistics" in my face.   But for the sake of not pissing you off, let's just say redshift works in all cases.


There's an old saying..."there are lies, damn lies and then there are statistics".   

Also, please remember, some of this is argument just for the sake of trying to get you to prove your point better.  I'm not saying I completely disagree with anything you've said, I just want to understand it more.

[Agent : Orange]

Sickened because it took so much of your time, or because you feel like I'm such an idiot that it takes that much to explain it to me? LOL...   my retort is coming, I promise!

Never to either of those things! Sickened because walls of text are supposed to be the death knell of a thread, and I want this one to go on and attract new readers, which will be tough if people have to go over so much stuff all in one blast.

[Agent : Orange]

Okay, I suppose I can accept that.  But still, it's more of a misnomer.  You can't bump into the stuff, right?  So my statement that it's more of a field of "extra gravity" is basically a better explanation, wouldn't you say?

It should be incredibly rare that you bump into that stuff. But once in a while it should happen and we should see a nuclear recoil because of it. That's what the LUX dark matter detection experiment was trying to observe, but did not. So you may be right that it's better described by a modification of gravity but that brings up big problems because if you throw away our current theory of gravity, general relativity (GR) you have to replace it with something. And GR is our most well tested theory on Earth and outside of it. So the new theory has to do everything GR does and more. Look, I've said many times that I'm fine if it turns out gravity needs to be modified, it's just going to be very difficult to do and GR should only be discarded when it's successor is properly vetted in all observational settings.

I'll try to include more links from now on as well.

But you're saying the gas is shocked by EM forces, NOT gravity, right?

The difference between a collision of galaxies and intercluster medium is that there's turbulence and fluid dynamics at play in the gas, which is heated by the collision, forms shocks, heats up and emits X-rays by EM. It's a fluid component of the cluster.

Please provide links, I'd like to look at these myself.   The problem I have with what you're saying is why is DM collisionless?  Why shouldn't it collide?  What is it's density?

Collisionless means that the DM has a small chance of interaction with anything else (collision = interaction through EM, strong or weak nuclear force). So it interacts under gravity only, and it's rare that it ever does anything other than attract by gravity even when it comes extremely close to another DM particle, which is constrained by physical observations like those made at LUX. In terms of that experiment, the interaction cross section must be very small. This is the whole point of why DM is different than baryonic matter.

The current standard model is that DM must be collisionless (or nearly so) because when we do the calculations we get the right kind of galaxy behavior using DM and not using a self interacting dark matter. Here's a link that states this result right in the abstract:
http://iopscience.iop.org/1538-4357/535/1/L21/pdf/1538-4357_535_1_L21.pdf
Like any model, we could find new evidence that points us in a different direction tomorrow. There are no absolutes in science, so I can't give you an absolute answer other than to say this is the best explanation we have at the current time.

I'll have to get to the rest later, once again I'm heading out the door!

[area51drone]

Note that I was saying it behaves like a field of gravity not that it is gravity itself, and the name "matter" has no real bearing on the observed behavior.   

So let's clearly define this then, because there is a lot of talk.   I will throw some of what you've said and some random ideas, and you say what is true and what isn't without a whole lot of explanation.   

DM is predicted to:

1)  Behave like regular matter with respect to known gravity
2)  Be collisionless in an EM sense except in extremely rare cases
3)  Provide a field of gravity that bends light
4)  Provide a field of gravity that slows down and affects the orbits and movement of regular matter
3)  Be distributed throughout intergallactic medium like a gas
4)  Form in "halos" around galaxies, but not exist in them (?)
5)  Not exist on its own away from regular mass (?)

Correct these statements if necessary.   I know you didn't say #5, but I'm wondering if it's true or not.

[area51drone]

Since I can't go back and edit my original post, let me make these changes, and work from these Agent..

DM is predicted to:

1 )  Behave like regular matter with respect to known gravity
2 )  Be collisionless with regular matter in an EM sense except in extremely rare cases
3 )  Be collisionless and non-interacting with itself
4 )  Provide a field of gravity that bends light
5 )  Provide a field of gravity that slows down and affects the orbits and movement of regular matter
6 )  Be distributed throughout intergallactic medium like a gas
7 )  Form  "halos" around galaxies, but not exist in them (?)
8 )  Not exist on its own away from regular mass (?)

BTW, it would help for you to strictly define halo, or provide a link so we know exactly what you're talking about.   Also BTW, I got my first "Great Course" purchased off ebay in the mail today - "Experiencing Hubble: Understanding the Greatest Images of the Universe" by David M Meyer Northwestern University  ... looking forward to watching it!

[Agent : Orange]

First off, I think this is an unfair image comparison.  The bright spots on the left indicate areas of high density mass, and the image on the right indicates areas of mass that moving in a particular fashion.

Edwin Hubble showed in the 1930s that distance and redshift are related to one another due to the expansion of the universe; his results convinced Einstein (http://en.wikipedia.org/wiki/Hubble%27s_law). At this point your personal biases about redshift are getting in the way of making progress, and you have asked me to go into detail about many subjects that depend on fundamentals like the Hubble law (redshift/distance comparison). Now these basics are getting in the way of furthering our discussion, and then when I try to explain more complicated things you dismiss it by waving your hand and saying "that's bullshit".

I think there's probably too much here for me to answer in any timely way without writing a huge essay on the subject. I've pointed you to many examples of the relevant subjects.   

I think it's bad science to say "this looks like my simulation" for two reasons - one, it's subjective, and two, simulations can be done and redone until they match the data.  What math is the simulation based on? 

When I say "looks like" I mean using an objective well defined mathematical comparison we're able to quantitatively say how well the distributions of structure and the formation of galaxies match what we observe in the universe through our instruments. (http://en.wikipedia.org/wiki/Chi-squared_test, http://en.wikipedia.org/wiki/F-test). There is nothing subjective about such a comparison. And I'd say that both of those images look similar to one another, even if you'd disagree you've just said what we see with our eyes on such a thing is subjective anyway so there you are. Moreover, the entire point of posting these simulations is that they're done using the standard cosmological model and they produce objectively better results than any other model out there now.

What happens when Z = -100? 

Negative redshifts are blueshifts. Cosmologically you are looking out in the universe (back in time) to progressively higher redshift.

According to Kaku and others, and everyone who believes in the big bang, the universe should be tearing these filaments apart (even from z=18 to z=0) and beyond z=0 right?   We're supposed to see our galaxy in the future, and nothing else.  We're told that gavity acts weakly at a distance.  If dark matter is so dense/strong as to have an effect at inter galactic scales, then why on earth wouldn't it be dense enough to have an effect and collide with the gas in the bullet cluster, or do more interacting inside galaxies themselves?

z=0 is the present time, z=18 is further back (farther away) than lower values. These structures are forming dynamically and their density will decrease as the universe expands.

If DM exists, there should be well defined expected behavior of it according to the theoretical laws, correct?  Completely ignoring the real data, what are the properties of DM? 

"Completely ignoring the real data"? What are you even asking for? How do I describe how something behaves if I don't get that from data? Our theories are motivated by the data.

You say that it is a cloud of stuff out there around galaxies.  Does it stretch between galaxies, or is it held within a bubble?   Is it in the ICM gasses?  If not, why not?  Is it in and around the solar systems within the galaxies?  Is it in the inter stellar medium?  How should it interact with planets?   How should it affect the rotation and orbit of sun by the earth, for example?   

DM is collisionless, see the last few posts. It doesn't react with normal matter except through gravity. It's like a cloud around galaxies and galaxy clusters. It also forms filaments that stretch throughout the universe like a web. We've been through this already.

Rereading your quote there, you say it's like a halo around the galaxies.  Almost like the gravity of the galaxies is pushing it away from it's bubble it sounds like.  If that's what you're saying,why would it be in this shape?

Gravity pulls on matter, not pushes on it. The DM is attracted to the luminous part of the galaxy, it's concentrated in the center like a cloud of matter around the galaxy. This large mass of DM is like a cloud surrounding the galaxy and affects the motion of the outer stars in the galaxy, which is why the rotation of stars in the outer parts of the galaxy are different than what you'd expect from the Newtonian picture. Each galaxy has more mass farther out than you'd expect if you looked at the light emitting part of the galaxy. That's how it was found by Rubin in the 1960s at galaxy scales. 

Excuse my ignorance, but how exactly does this tell you exactly how much mass is there? 

The luminosity, velocity, temperature and mass of clusters are all related to one another, so you get these details from looking at the spectra of the gas in different wavebands. This is actually a bit of a complicated calculation, you can read more about it here (http://ned.ipac.caltech.edu/level5/March02/Sarazin/Sarazin5_1_3.html and http://www.astr.ua.edu/keel/galaxies/icm.html). I really don't want to get distracted by this and be pushed off in yet another new direction.

It's not that the ICM vs galaxy mass is a problem for me necessarily, but I'd like to know why if the ICM has more mass that the DM would follow the galaxies and not the majority of the mass (the ICM, which stayed behind).

There's 10x more DM than normal matter in the bullet cluster. The ICM is shocked and affected by more forces than the DM is, so it sticks around the point of collision.

Link please. I'd love to know how someone can prove such a thing, and yet say that enough DM can be there creating gravitational effects (evidenced by lensing) without having the same problems the MACHOs might create.

http://en.wikipedia.org/wiki/Gravitational_microlensing
http://arxiv.org/abs/astro-ph/0203037
http://cds.cern.ch/record/286370/files/9508071.pdf
http://en.wikipedia.org/wiki/Massive_compact_halo_object
There have been a number of suggestions to what MACHOs could be, all of the results are consistent with one another with current observations.

No, my next question would be how the hell does anyone know the stuff is in a halo in the first place?   LOL  If we have evidence only through lensing and through looking at the rotational speed of galaxy arms, that isn't a hell of a lot of data to be making such claims.   

Uh... That IS a hell of a lot of data we've got. I gave a list of 300 lensed quasars that can be modeled as well as all of the examples of strong lensing and lensing clusters out there. Our models can explain the rotation curves, make sense in terms of structure formation, can be extended to clusters and cosmological scales. There are specific properties of the cosmic microwave background that can't be explained away by DM or dark energy. That is a hell of a lot of data to be making such claims. Strong lensing alone gives us the shape of the DM distribution in individual galaxies and we know of something like a thousand strongly lensed systems and these put huge constraints on what the DM can be and how it must be arranged. Here's a beautiful example of strong lensing, just because.

That blue ring would look like an average galaxy if you could see it in the absence of anything in front of it.

It seems to me that perhaps a lot of claims about DM are based on simulations which I would think you would have to admit are prone to error and conjecture.   My next question would be how is it that enough distributed MACHOs wouldn't be able to make such a halo?  (in addition to why is there a limit on Machos as in my previous question above)

No. Simulations are a strong confirmation of our ideas given gravity, magnetohydrodynamics and the proportion of dark to luminous matter and other cosmological parameters. We find agreement - quantitative agreement as I say previously - with observations. MACHOs are limited in terms of the number of objects that could make them up and microlensing observations which place strong limits on how much of the halo can be made up of MACHOs. Moreover, we know that the ratio of dark to baryonic matter must be fixed because of the measurements we've made of the CMB. Or else there must be another explanation which behaves just like what we call DM now by modifying gravity. But as I've said already this has big shoes to fill.

I'm well aware of what you're saying.  And to some extent, I agree with you.   But how many galaxies are in this particular cluster and behind them? And how does this say that many MACHOs couldn't exist even between galaxies?   There must be a dozen theories as to why this could happen without DM, right?  Isn't it possible that perhaps there are MACHOs that are closer to us than the galaxies themseslves creating lensing?  Go back to the big image I linked to.  Look at the lensing of the galaxies right in the middle of the "target" cluster on the left.  They are dramatically lensed in an arc, and suggest an area of mass that is probably 10-20 times larger than the blue area and centered somewhere far "south" and "west" of the blue area. You also have the great example of the very obviously lensed line that has ripples in it. If it weren't individual galaxies creating these ripples, what would it be?  I see nothing other than a couple galaxies right next to that one.   I would love to see this as a 3d map, perhaps with some software that would allow one to simulate the lensing effects as well.

Are you talking about the link to the bullet cluster from the astronomy picture of the day?
This is why it's important to do statistics in the mathematical sense and not in the subjective kind of sense you may be using that term in. I'm talking about using each of the galaxies in the image above, and comparing with an unbiased (Gaussian) distribution that you'd expect in the absence of lensing, like they do here (http://arxiv.org/pdf/1311.3926.pdf). This is by it's very nature statistical as we have a huge number of shapes and position angles we need to look at. That's the sense I mean statistical in, a large number of calculations which must be done. I think you're looking at one or two galaxies that have an unusual shape and making conclusions from that, whereas the weak lensing analysis is done with millions. If it was so easy to refute these results, many people would be doing just that to prop up their own theories and getting funded for it. It's more complicated than you are making it out to be.

I see no example of "dramatic" foreground lensing in the APOD image. In weak lensing you don't expect to see anything like arcs or like the horseshoe mirage I put up a few paragraphs ago. Take a look at this guys excellent blog for some more details on lensing.
http://scienceblogs.com/startswithabang/2011/04/20/how-gravitational-lensing-show/

When you're talking about something brand new, simplifcation seems like a major problem to me.  I don't think anyone should be simplifying anything here. All things need to be accounted for.   

You're kidding. There's no way you can possibly start with the most complicated idea and connect that to data. There are both observational and theoretical limitations to developing theories like this. We didn't get general relativity dropped in our laps, we had to understand Newton's laws first and then see where they fail and expand on them. That's how you make progress, not by starting off with overly complicated ideas that try to explain everything all at once in one go.
"Everything should be made as simple as possible, but no simpler" -A. Einstein

With that said, based on your fit analysis, I call bullshit!  You as everyone else who knows a little math should understand that statistics are great, but they do have a margin of error.  In this case, when you're talking about something billions and billions and even more than billions of miles away, it is very difficult to ignore the possibility that these are just the way these are aligned and shaped, and the magin of error can be quite large.   I don't see how you can accurately predict *minor* lensing effects like what you're saying.

You have a million separate background galaxies that can be distorted by a foreground mass distribution, and then you sample the foreground distribution a million times. Sure there's an error margin but there is on any measurement you make in science no matter what it is. So you're fooling yourself if you think any quantity in the physical sciences is without error. And I'm using "statistical" in the mathematical sense, I'm doing a calculation or measurement a huge number of times. Therefore statistical methods apply to that data set. It's that simple. I do expect some error, but I also expect the large scale details to average out, that the signal is stronger than the noise. Again if it were not that way it would be attacked by folks who have a stake in proving this team wrong.

I call bullshit again!  In your example, it is certainly easy for a person to say that they are sheared, but there is no reason why they couldn't have existed that way in the first place. 

If you're trying to say it's natural to see background galaxies arranged in preferred directions around massive objects that just happen to produce a shear field that produces an inferred density that agrees with the position of the massive objects due to chance, I strongly disagree.
It's a systematic effect.
If that means nothing to you I suspect there's nothing I can say to convince you.

So you CAN say they are sheared to some degree satistically, even if it is very very minor and calculated by a computer to the nth degree.   But let's even say that THAT is true and you're accurate.  So then, let's you and I talk about how the shape of the galaxies are determined...

There is error. But there is a mean above the error if you have good data.

you are either basing the edge of the galaxies on some level of illumination (light, xray or other wave), correct?  Are you taking in every bit of data so that the galaxies are fuzzy, or are you cropping off certain levels of luminosity?  If so, what levels are cropped off and how is that determined?  It seems like it would be pretty easy to crop until the data fit.  Was the shearing data run with different crop points?  When you have data that is overlapping two galaxies distant from each other, where is that data attributed to or is it thrown out?   I hope you see what I'm getting at.

No, they are fit with Sersic profiles (http://en.wikipedia.org/wiki/Sersic_profile) that describe galactic luminosities. If it were that easy to manipulate the data the work would be shredded by the community. Read the blog I posted earlier. A huge part of this kind of work is reproducibility and if it were not reproducible it would be funding someone else's research. The fact that it's held up as an important example in the astronomical community means that it has not yet been refuted.

I am highly suspicious of all scientists, because nearly every damned one of them is looking for data to support their theory.   

Well I think you are talking to the wrong dude then.

Now, let's get back to reality.  The probability that I'm going to flip a coin once and it's going to land on heads is 50%. The next time I flip a coin, it has the same chance of landing on heads again, 50%, not less because you just flipped heads previously.  And going forward, you'll always have a 50% chance of flipping heads even if you just flipped 100 heads in a row.    YOU are saying that because 20 galaxies are arranged in such a manner that they must be sheared.  I am saying that because 20 galaxies are out there, there's just as even of a chance that they are arranged that way as they would not be arranged that way.   Who is correct?  I believe I'm just as correct as you are. But you're (the metahphorical you) are looking at anything to match your theory.   Give me something else.

No, here is what I'm saying: if you flip a coin a million times you build up a statistical distribution of heads and tails. You don't expect to find exactly half a million flips heads and half a million tails. You expect a few more of one or the other at the end of the day, even for a fair coin. Now if you find that 75% of the time you flip heads and 25% tails, you would conclude that the coin is biased. If you flipped the same way each time (or better yet use a machine to flip the coin exactly the same way each time) you have a systematic effect in how the coin flips.

I'm saying that if you find a huge number (a statistically significant number) of galaxies that are arranged in a systematic way then THAT is evidence of correlation. It's like seeing 75% of flips come up heads in a row, at that point you say that you're dealing with a statistically biased coin, and that such a thing is unlikely to occur by chance.

Funny that you're the one accusing the "metaphorical me" of forcing a shoe on the foot after saying you distrust people in my professional. You have presented a situation which is extremely artificial and I have an explanation for it in terms of a specific effect with an explanation of why it is that way.

I told you in a private email my math is rusty if not some of it gone altogther!  But shear to density doesn't negate the fact that you have to determine if something is sheared in the first place. I'm not arguing the fact tha you can say "we expect them to look like X but statistically we're seeing shear".  I'm arguing that your assumptions about X *might* be wrong in the first place.  I understand you're saying X is based on the rotation and shape of say 100,000 galaxies, and  you are comparing that small portion of shape behind the cluster to the 100,000.  Certainly as you are able to provide more and more examples the probability of what you're saying goes up.  But is anyone looking at cases where you'd expect DM to behave in a certain way and the statistics is going against you?

I put the "calculus" comment out there as a joke, a risky thing on a forum where intonation can't carry it. So no need to worry about math here. I don't understand what you mean by the last part though. There are people that are interested in knocking down what is already out there and the analysis holds fast. Again if it were that easy to knock down there are people that are hungry to do it. We have not yet found a case where the DM behaves in a way that was unexpected.

Last year there was a cluster that yielded strange results from the weak lensing analysis but a re-inspection has shown that an analysis problem likely caused the discrepancy, and after a second group did an independent analysis found the cluster DM behaving as expected. Would love to write a bit more about this at some point but there's more than enough on the table now.

I think it's for people to decide on their own. 

No. There is an objective right and wrong idea, and the data is the way to prove it.

You say that they are separate, and with all your knowledge and the fact you do this for a living, certainly more people are going to believe you straight up.  But, and I hate to do this, but quoting Richard C Hoagland - "if they would just look at the data!"   

You are the one who asked my profession and now once again brings up my credentials. I did not mention that until you asked me because I like arguing and debating based on the merit of one's arguments and NOT by making arguments on authority, so I'd prefer that we don't focus on this, thanks.

I have shown why the data (which "they", whoever "they" are, should look at) holds up the standard picture. It is not trivial to knock down so when it finally falls it has to be to a truly superior theory which contains all that came before it.

If Hoagie can do better then by all means...

Which states nothing to me really about the specific case of NGC 4319 and Markarian 205. (readers again see http://electric-cosmos.org/arp.htm  It's hard to argue looking at the data that they're not just aligned, but connected in some way that does not make sense in the classical redshift sort of way.   

It's just not a good argument to use a subjective argument. These are two systems that you've pointed out which look "to the eye" to be related but they're not. It's a chance alignment. You are looking at these two systems and throwing out all other such systems. I gave you the CASTLES data set, 300 lensed quasars which do obey the redshift you expect and summarized the relationship Hubble found, which has generated a number of nobel prizes and Hubble convinced Einstein himself that the universe is expanding, all because of the relationship between distance and velocity (redshift). Here's the modern day plot using type Ia supernovae that won Perlmutter, Schmidt and Reiss the nobel prize in physics in 2011. See the axes? The relationship between distance and redshift that indicate an expanding universe.

You are arguing the weight of this evidence should be thrown out based on two systems which are projection effects that look strange to the human eye. So are these your white crows? You see why I remain skeptical.

So you and I will have to agree to disagree.   

Depressing.

Do I think redshift exists and probably tells us something about the universe?  Yes.  Do I think it's always accurate and applicable in every case?  No.   Especially when you start throwing "it's statistics" in my face.   But for the sake of not pissing you off, let's just say redshift works in all cases.

Who threw "it's statistics" in your face? The mathematical tool for dealing with large numbers of quantities is called a "statistical method" because there are a large number of things you are dealing with. No where in this thread have I put any detail under the rug and I have gone out of my way to expand on the methods, techniques and phenomena that are involved in my arguments. When a large number of observations and measurements are required to make a point I've called it as it is, statistics. So I don't know why you'd be upset at the use of that term.

Don't worry about pissing me off or not. I've gone out of my way to argue my point and I think I've done it well. If you choose to "agree to disagree" that's your prerogative.

There's an old saying..."there are lies, damn lies and then there are statistics".   

Again, the kind of statistics I'm talking about are not prone to manipulation like those used in a Diebold voting machine.

Also, please remember, some of this is argument just for the sake of trying to get you to prove your point better.  I'm not saying I completely disagree with anything you've said, I just want to understand it more.

That's interesting, you have a unique way of showing that. You've called my arguments "bullshit" twice in the last post, and then told me you had a distrust of scientists because we try to manipulate the data that we're fitting. So you can see why I'm now scratching my head after putting up yet another wall of text.

I think it's probably going to be better (and more readable) for everyone if we pick one direction to move in for the next while and try to keep things a bit more terse. Or at least I will, just as a heads up. It just gets to be too unreadable otherwise.

[Agent : Orange]

Since I can't go back and edit my original post, let me make these changes, and work from these Agent..

BTW, it would help for you to strictly define halo, or provide a link so we know exactly what you're talking about.   Also BTW, I got my first "Great Course" purchased off ebay in the mail today - "Experiencing Hubble: Understanding the Greatest Images of the Universe" by David M Meyer Northwestern University  ... looking forward to watching it!

http://en.wikipedia.org/wiki/Dark_matter_halo

Enjoy!

[area51drone]

I don't have time to respond to much right now, but just suffice to say my bullshit comments were in regards to the simplification comments, not to your arguments.   One you say things need to be simplified and I don't think they should be, and two, you said I over simplify things.  Bullshit! I don't think anything should be simplified.

As for statistics,  I agree, it's a tool that can be extremely useful.  But it still provides analysis that tends to throw out extremes, and also doesn't fit the real data perfectly - you must agree with me on that point?    Even Carroll in the most recent video I showed you talks about how he throws out(!!!) extremes.  Maybe the extremes are what will help get people to the right thinking.    (At this point I want to mention the Higgs discovery diagram Carroll says is worth 9 billion dollars and how it bothers me, but I won't go there right now).   Back to the coin example, a machine throws 100 coins in the air and they all land on heads.   You're saying "that's a problem, it's a bias."  I'm saying "that's reality."  Statistically, I agree with you that it implies a bias, but it doesn't mean that it is biased.   Scientists can apply statistics and math towards a problem to make assumptions and fit them to their theories.  Maybe the theories are correct.  It certainly gives the theory more weight, but it still doesn't mean it's for certain correct in all cases. 

The problem I see with physicists is that no one is going the Einstein route and is willing to buck they system and say something is different - everyone is towing the line, and pretty much getting no where.   Time and time again I hear from physicists on shows and talks I'm watching  - ones you probably respect - that there haven't been any real great advancements in at least 30 years.   Scientists "understand" a lot, but it still doesn't make sense, even to them. 

With regards to redshift, I gave that to you and you're still mad that we're even trying to talk about it.  Let's let it drop and keep talking.  But, if all we did is agree, then there would be no discussion at all - it would just be you giving lectures and me asking questions about the lectures, and you lecturing some more.    You can throw figures, diagrams, statistics and everything else my way and say "you're wrong, the data says this" but you know, it's  possible that science is wrong too.  It's possible the data has been misinterpreted, or collected improperly and even the best scientists aren't aware of the problem because there is some other unknown.   Having that attitude is what keeps discoveries from happening.    Maybe that's not your attitude, but that's how you come across.

Do I distrust scientists?  Absolutely.  People have to eat.  There are politics in universities and crowds of scientists.   There is group think.  Scientists are people.  If you're saying that no scientist has ever lied to get their data to look better, I want some of what you're smoking!   The body of scientists out there studying this stuff professionally is what, a couple thousand?   And how many of them are studying dark matter in a serious way - maybe a few hundred?   How many different tests are performed to back data up? In the case of the LHC and the Higgs, 2?   That's not a lot.   Yes, there are a number of people looking at the data from these two experiments, and you run the experiments a gazillion times.   But they're still just two detectors, right?   You can't dismiss that that people are fallible, and if people (even groups of people) make experiments, they *can be* (not necessarily are) fallible too.    (and I'm not saying the LHC is broken, I'm just using it as an example that there aren't a bunch of other LHC's out there)

Also to say that "this has been peer reviewed."   People are inherently lazy.  I'll have to look it up but I recall a situation where papers were produced at random and presented to people in the scientific community (I don't think it was physics, but it was some scientific community) and the randomly generated paper was accepted for whatever purpose it was they were trying to achieve (accepted at a talk/go into peer review or something).   You gave the example of how one group got some anomalous results from a weak lensing cluster analysis and another group found the first group to be in error independently.  You said it was "likely" a problem their analysis created the problem.   Why isn't it that their analysis was just plain wrong instead of likely?   Likely throws in some possibility that maybe they were on to something?

I want to understand everything.  I know it's not possible.  I pick and choose what I believe and don't believe.   I'm not getting paid to be a scientist, or even to think about these things.  I'm free to go in whatever direction I want.   If someone says to me "A is correct.  A -> B, so B is correct" I want to know why the hell A is correct in the first place.   Just like today, I was watching that Hubble lecture series (which is great by the way) and he talked about HR Diagrams, and how they know this and that about stars and star fields based on where they fall into the diagrams.   And I was like "woah" slow down - what's the history of the HRD?   How can he say some of this stuff?   There are a lot of assumptions in science based on previous knowledge.   That's fine, I understand that has to happen to get certain things done.  But you know, now and then there's a star that doesn't fit very well into the standard HRD, isn't there?   Some out all by themselves at the extremes?   (readers see http://upload.wikimedia.org/wikipedia/commons/6/6b/HRDiagram.png )   You might say "so what, plot it."  Maybe even "Well, that's been shown in the simulation."   Until the next weird anomalous star comes along that doesn't fit the expectations.

As for bringing up your job, #1 you didn't have to answer me, and #2 it's fair to throw it in your face.   Some taxpayer somewhere is paying your salary.  I didn't ask where you work, but maybe it's me!   

[Agent : Orange]

If someone says to me "A is correct.  A -> B, so B is correct" I want to know why the hell A is correct in the first place.

From my position it seems that you reject A but demand a detailed explanation for B and then wave your hands when you don't like it because it depends on A.

Look, I understand the politics and all of that stuff. Of course scientists are humans and prone to error. I agree completely. All along I've mentioned the weak links and the ideas that could be wrong, and that there are concepts that may be replaced. But I stand by that we have the basics nailed down. There are a lot of other studies to replicate results in this field, because there is a lot at stake. You also downplay the creativity of many new ideas as there are many that have been tested, and if any outperformed what we have it would become the new standard.

There is no institutionalized party line in the large scale global community. The goal of science is to weed out fallacies even within it's own process.

You can throw figures, diagrams, statistics and everything else my way and say "you're wrong, I'm right, I'm the professional, the data says this" but you know, it's  possible that science is wrong too. 

I specifically address above this is not where I want the discussion to go, and you took it there anyway.

Wow, man.

[area51drone]

God damnit, you are on here too much.  I go back to edit my post and you've already responded.  Notice I took out the "I'm the professional" part     and added "It's possible the data has been misinterpreted, or collected improperly and even the best scientists aren't aware of the problem because there is some other unknown."   Also about the coin flipping thing and peer reviews.  And then I threw the professional thing back in at the end, which I flip flopped on though because I didn't think you'd get that 2nd part was a joke and tried to remove but it was too late!  I promise not to mention it again.

I'm told B.  Then I'm told it's because of A.  I want to understand A.  I don't think that's unreasonable.

And again, I'm not saying I don't like science and I don't agree with the hundreds of years of physicists work.   Dark Matter feels wrong to me.   But maybe it's just the name.   I'm not dismissing everything that has been done.  I'm sure 99% of everything is on the up and up.   Maybe I just wanted you to agree with me that there have been errors, and there will continue to be errors.   And maybe I ignored the fact you already were agreeing with me on that point.   I disagree with you though on your idea that "this theory will outperform that theory" and thus become the standard.   From what I've seen it takes a long long long time for people to accept something that isn't the norm, and that's because of the politics.

You gave me a lot to read and learn.   Maybe I'll just shut up now and let you talk. 

[area51drone]

Anyway, taking this back to a normal conversation instead of arguing the semantics:

http://www.csmonitor.com/layout/set/r14/Science/2013/1121/Scientists-witness-massive-gamma-ray-burst-don-t-understand-it

[area51drone]

Man, I really am clueless.  I just now learned about the James Webb Telescope ( http://en.wikipedia.org/wiki/James_Webb_Space_Telescope ) that's due to come online in 2018.   

Here's a list of space telescopes, past, present and future.   http://en.wikipedia.org/wiki/List_of_space_telescopes

Agent, do you know much about the DAMPE telescope?

[zeebo]

Man, I really am clueless.  I just now learned about the James Webb Telescope ( http://en.wikipedia.org/wiki/James_Webb_Space_Telescope ) that's due to come online in 2018.   Here's a list of space telescopes, past, present and future.   http://en.wikipedia.org/wiki/List_of_space_telescopes

Agent, do you know much about the DAMPE telescope?

I heard the James Webb might be able to image an extrasolar planet?

[area51drone]

I heard the James Webb might be able to image an extrasolar planet?

I'm sure, as some current instrumentation have already been able to directly image a small number of them.  (See http://en.wikipedia.org/wiki/List_of_extrasolar_planets_directly_imaged )    I want to know if it will be able to tell if Andromeda is moving laterally enough to avoid a collision with the Milky Way.

[zeebo]

I'm sure, as some current instrumentation have already been able to directly image a small number of them.  (See http://en.wikipedia.org/wiki/List_of_extrasolar_planets_directly_imaged )    I want to know if it will be able to tell if Andromeda is moving laterally enough to avoid a collision with the Milky Way.

Wow I didn't know we had images already - Why is this not on the nightly news, it's rather amazing.  As for Andromeda, yeah I hope the collision doesn't happen, would be a shame for our two beautiful spirals to be turned into a giant fuzzball galaxy. 

[area51drone]

A cute little story I have to interject here - my wife was recently helping my four year old son prepare for xmas by picking out toys to donate to other families, to make room for all the gifts he's hoping to get and to teach him a lesson about giving.   So they're going through his hot wheels, picking out the ones he's willing to let go and the ones he isn't.  My wife asks "How about this one?" and he'll say "keep" or "give", usually pretty quickly.  His hot wheels collection also includes all of the small die cast airplanes and helicopters he has, and a die cast space shuttle.   She got to the space shuttle and asked "How about this one?"  and he paused for quite a while, with his little mind whirring - you could see it in his eyes.  Finally, my wife grew tired of waiting so she said "you need this to get to space" and instantly he responded "keep it!"

[Agent : Orange]

A cute little story I have to interject here - my wife was recently helping my four year old son prepare for xmas by picking out toys to donate to other families, to make room for all the gifts he's hoping to get and to teach him a lesson about giving.   So they're going through his hot wheels, picking out the ones he's willing to let go and the ones he isn't.  My wife asks "How about this one?" and he'll say "keep" or "give", usually pretty quickly.  His hot wheels collection also includes all of the small die cast airplanes and helicopters he has, and a die cast space shuttle.   She got to the space shuttle and asked "How about this one?"  and he paused for quite a while, with his little mind whirring - you could see it in his eyes.  Finally, my wife grew tired of waiting so she said "you need this to get to space" and instantly he responded "keep it!"

That's awesome

Wish I had time to comment more but I'm going to be strapped for time for the next few days so I will likely be pretty scarce. Also glad that the huge gamma ray burst was posted. And hopefully WR104 doesn't come anywhere near that strength!

[Agent : Orange]

And again, I'm not saying I don't like science and I don't agree with the hundreds of years of physicists work.   Dark Matter feels wrong to me.   But maybe it's just the name.   I'm not dismissing everything that has been done.  I'm sure 99% of everything is on the up and up.   Maybe I just wanted you to agree with me that there have been errors, and there will continue to be errors.   And maybe I ignored the fact you already were agreeing with me on that point.   I disagree with you though on your idea that "this theory will outperform that theory" and thus become the standard.   From what I've seen it takes a long long long time for people to accept something that isn't the norm, and that's because of the politics.

There are and have been and will continue to be. I have a lot to say about an error that happened and was caught last year with respect to weak lensing that had people tearing out their hair. And look at the neutrino faster than the speed of light claim from a few (?) years ago. Hell look at phlogiston as an explanation for heat transfer, that was around for a long time. And aether. It happens. But if the machine works right eventually the process of research will correct itself when the previous generation retires or dies and the noobs take the reins ready to make a name for themselves.

As for new ideas taking a long time, look at the accelerating universe and dark energy. Discovered in 1998, nobel prize in 2011. Revolutions in science happen. It's not often but they do happen.

You gave me a lot to read and learn.   Maybe I'll just shut up now and let you talk. 

Nah, never stop arguing your case.

[Agent : Orange]

Man, I really am clueless.  I just now learned about the James Webb Telescope ( http://en.wikipedia.org/wiki/James_Webb_Space_Telescope ) that's due to come online in 2018.   

Here's a list of space telescopes, past, present and future.   http://en.wikipedia.org/wiki/List_of_space_telescopes

Agent, do you know much about the DAMPE telescope?

James Webb will be awesome, the resolution is going to be an amazing upgrade to what we currently have up there. Some beautiful images will come from that. I don't know much about DAMPE at all (http://dpnc.unige.ch/dampe/index.html) except that it is a Chinese mission that will likely outperform the AMS02 Experiment which is now onboard the ISS and looking for evidence of dark matter decays from the galactic center where the density of the DM halo should be the greatest.

Also before I call it a week, check these out:

1.) Adaptive optics - an observatory generates an "artifical constellation" on the sky by firing a laser into the ionosphere (the lasing cavity on some of these systems is the size of a schoolbus) and these laser spots are studied to find out how turbulence in the upper atmosphere will affect the formation of images. The telescope mirror is on hydraulic actuators which can flex and adjust it in real time to compensate for the atmospheric blurring, giving ground based telescopes as clear a view as orbital. See the links here: http://www.space.com/14294-gemini-telescope-adaptive-optics-stars.html, http://www.mtwilson.edu/ao/, http://www.astro.caltech.edu/palomar/AO/ and http://www.gizmag.com/magao-adaptive-optics-highest-resolution-astronomical-images/28801/). If you hunt around for more images you can find some really amazing comparisons with and without adaptive optics.

2.) Liquid mirror telescope: When you spin a bucket filled with water or swirl a drink in a glass the surface of the liquid makes a parabola, which is exactly the shape you want a mirror to be to bring an image into focus. So the suggestion is that you could make an effective mirror much larger out of the surface of a fluid than you ever could out of conventional materials. This idea is taken to the extreme by suggesting using a rotating pool of mercury on the moon to make a giant primary "mirror". See http://en.wikipedia.org/wiki/Liquid_mirror_telescope, http://science1.nasa.gov/science-news/science-at-nasa/2008/09oct_liquidmirror/ and http://www.space.com/2030-lunar-liquid-mirror-telescope-studied-nasa.html.

Sick!!

[Agent : Orange]

I'm sure, as some current instrumentation have already been able to directly image a small number of them.  (See http://en.wikipedia.org/wiki/List_of_extrasolar_planets_directly_imaged )    I want to know if it will be able to tell if Andromeda is moving laterally enough to avoid a collision with the Milky Way.

Wow I didn't know we had images already - Why is this not on the nightly news, it's rather amazing.  As for Andromeda, yeah I hope the collision doesn't happen, would be a shame for our two beautiful spirals to be turned into a giant fuzzball galaxy. 

http://www.wired.com/wiredscience/2011/09/exoplanet-portraits/
www.nasa.gov/content/goddard/astronomers-image-lowest-mass-exoplanet-around-a-sun-like-star/

Also lots of "artists impressions" here but they all help set up the mood
http://www.eso.org/public/images/archive/category/exoplanets/

[zeebo]

http://www.wired.com/wiredscience/2011/09/exoplanet-portraits/
www.nasa.gov/content/goddard/astronomers-image-lowest-mass-exoplanet-around-a-sun-like-star/

Also lots of "artists impressions" here but they all help set up the mood
http://www.eso.org/public/images/archive/category/exoplanets/

It's so fascinating to me.  It's only been in what, the last 15 years that they've been able to detect exoplanets?  And now (at least before Kepler's gyroscopes failed) like over two thousand candidates have been found?  It's like all those covers of sci-fi books I've read are maybe actually out there!

[area51drone]

I just finished up the Great Courses' Experiencing Hubble lecture series, and I have to say it was pretty awesome.  I wasn't expecting much, but if this course was an indicator of the others, I'm really looking forward to the ones I have on the way - Sean Carroll's Dark Matter series, Particle Physics for the non Physicist and the behemoth Understanding the Universe in 96 lectures by The Universe's Alexei Filippenko...   But this Hubble one was awesome, and for $13 shipped on ebay, it was a steal of a deal.  I would have gladly paid the $40 they ask on Great Courses for it.  There was plenty I already knew, but I still learned quite a bit over the 6 hours of lecture, and I will actually watch it again to go back over some of the material.   He even covers a bit about dark matter, dark energy and zeebo, you'd love the last lecture - he talks a lot about exoplanet detection.