Dark Matter

[Fat Nick Davies]

The notion of dark matter was invented to make cosmology work. Science contains several other examples of substances that were invented to make the theories of the time work. Phlogiston was one, luminiferous ether was another. Both inventions hid the truth and held up progress for too long. I suspect later generations may point and laugh at dark matter as we now laugh at phlogiston.

It all starts with the red shift which is completely ascribed to the doppler effect. (I may have skipped a step or two here, but bear with me...) And then we get into some uncomfortably circular definitions concerning the brightness of distant objects and the speed at whch distant objects are receding from us. But what if the doppler effect is not the whole story. What if something else is affecting the spectrum of distant objects? Might we find perhaps that when the universe was so much younger and smaller and more dense that the speed of light was different. The photons emitted by those ancient and now-distant objects were created when the physical laws which dictated their generation and propagation were subtly different because there was a difrent value for c.

Now I am no astrophysicist, nor am I enough of a mathematician to take this notion a step further. I am certainly no Newton or Galileo so I cannot produce a frightening and elegant demonstration to prove my point. I think one would have to measure the speed of light to the nth level of precision over geologically long periods of time to establish whether it might change over that period. Either that or come up with something of Einsteinian grandeur to show that the speed of light is not constant but a variable and depended on the age of the universe.

With the prize of eternal fame and the title of being the hero that fixed 20th century cosmology, who would like to take this one on?

Read more at: http://fatnickdavies.blogspot.com/

[Thanatos]

The doppler effect is the only current viable explanation for redshift of distant galaxies. Alternative explanations [e.g., tired light, compton scattering] have fatal flaws. The key issue with any alternative explanation is how to account for spectral line shifting. Only the doppler effect and gravitational redshift are currently known to induce this phenomenon - and I believe we can safely rule out gravitational redshift as a global explanation.

[Fortis]

The notion of dark matter was invented to make cosmology work. Science contains several other examples of substances that were invented to make the theories of the time work. Phlogiston was one, luminiferous ether was another. Both inventions hid the truth and held up progress for too long. I suspect later generations may point and laugh at dark matter as we now laugh at phlogiston.

It all starts with the red shift which is completely ascribed to the doppler effect. (I may have skipped a step or two here, but bear with me...) And then we get into some uncomfortably circular definitions concerning the brightness of distant objects and the speed at whch distant objects are receding from us. But what if the doppler effect is not the whole story. What if something else is affecting the spectrum of distant objects? Might we find perhaps that when the universe was so much younger and smaller and more dense that the speed of light was different. The photons emitted by those ancient and now-distant objects were created when the physical laws which dictated their generation and propagation were subtly different because there was a difrent value for c.

Now I am no astrophysicist, nor am I enough of a mathematician to take this notion a step further. I am certainly no Newton or Galileo so I cannot produce a frightening and elegant demonstration to prove my point. I think one would have to measure the speed of light to the nth level of precision over geologically long periods of time to establish whether it might change over that period. Either that or come up with something of Einsteinian grandeur to show that the speed of light is not constant but a variable and depended on the age of the universe.

With the prize of eternal fame and the title of being the hero that fixed 20th century cosmology, who would like to take this one on?

Read more at: http://fatnickdavies.blogspot.com/

I'm afraid that you seem to be confusing two different things. Dark matter was postulated to explain the radial rotation distribution of galaxies. You seem to be talking about dark energy.

As an aside, there have been many studies that have looked at the stability of c (or at least alpha, the fine structure constant, that contains c) over geological time. While there have been hints that it may have changed very very slightly, the concensus is that there has been no significant change.

[Tim Thompson]

The notion of dark matter was invented to make cosmology work. ... I suspect later generations may point and laugh at dark matter as we now laugh at phlogiston.

I am really tired of all this garbage about how silly dark matter is supposed to be. Dark matter is nothing more profound than more of the same stuff we already have except that it's dark. What's so bothersome about that?

It all starts with the red shift which is completely ascribed to the doppler effect.

Actually, it's not ascribed to the Doppler effect. The cosmological redshift (i.e. the redshift induced by the expansion of the universe is not interpreted in general relativity as a Doppler shift. Only the redshift (or blueshift) induced by motion in a local rest frame of the distant galaxy is a Doppler shift.

... I think one would have to measure the speed of light to the nth level of precision over geologically long periods of time to establish whether it might change over that period. Either that or come up with something of Einsteinian grandeur to show that the speed of light is not constant but a variable and depended on the age of the universe.

There are already papers in print claiming to see evidence that the fine structure constant has varied as a function of redshift, but the results are inconclusive (i.e., Webb, et al., 1999 and the many citations thereto). There is also the variable speed of light cosmology championed mainly by Joao Magueijo (i.e., Albrecht & Magueijo, 1999 and the many citations thereto).

So scientists are almost 10 years ahead of you in investigating the possibility of a cosmologically variable speed of light. The problem is that the people who actually do know what they are talking about have a lot of problems making an idea like that work. So I am not really too impressed when the people who actually do not know what they are talking about insist that it must be so.

Cheers.

[captain swoop]

So I am not really too impressed when the people who actually do not know what they are talking about insist that it must be so.

Sig worthy

[TomT]

I am really tired of all this garbage about how silly dark matter is supposed to be. Dark matter is nothing more profound than more of the same stuff we already have except that it's dark. What's so bothersome about that?

Isn't this a bit of an oversimplification? The "stuff we already have" is matter we can physically detect, i.e. baryonic. Dark matter is claimed to be non-baryonic and to interact with baryonic matter only by gravitational attraction. We can't detect it directly, but must infer that it exists because of various observations such as the need for more gravitational force to explain the rotation curves of spiral galaxies or to hold clusters of galaxies together.
If it is the same as what we already have, it must be ordinary baryonic matter yet to be found/verified such as dust, plasma, warm gas in the intercluster medium as detected by soft xrays, etc. If you mean the latter rather than the non-baryonic type, then I tend to agree, but that isn't what the majority of Mainstreamers think.

[Hornblower]

I would say that the reputed dark matter is a pretty good analogy to the neutrino as originally proposed many decades ago. Something was needed to account for the anomalous motion of some of the fragments generated by the atom smashers in those days. Perhaps an analogous advance in experimental technology will enable us to detect this stuff directly, should it really exist, just as we now are able to detect neutrinos by their interaction with various atoms.

[Tim Thompson]

Isn't this a bit of an oversimplification?

Not really. Neutrinos are in fact non-baryonic dark matter, but we know that they are not massive enough, so even in "astronomically" large numbers, they still don't represent enough mass. So, we do in fact already have non-baryonic dark matter detected and on hand.

The non-baryonic dark matter we are looking for is not neutrinos. But massive dark matter particles are probably unstable. So, Ibarra & Tran, 2008 argue that their detection of excess high energy positrons is consistent with positron emission by decaying dark matter. Meanwhile, Cembranos & Striagri, 2008 argue that the observed X-ray & Gamma-ray halo around the Galactic bulge can be explained in the context of decaying dark matter WIMPs (Weakly Interacting Massive Particle). These are just two examples, but they are enough to show that non-baryonic dark matter is not undetectable, and may already have been indirectly detected (of course much more work needs to go into this).

The idea of Dark Matter is a perfectly ordinary, reasonably intelligent idea. My frustration is that so many of the ill-informed and un-informed are so ready to proclaim it to be an essentially stupid idea, as if they were in a position to know anyway.

[TomT]

..............
The non-baryonic dark matter we are looking for is not neutrinos. But massive dark matter particles are probably unstable. So, Ibarra & Tran, 2008 argue that their detection of excess high energy positrons is consistent with positron emission by decaying dark matter. Meanwhile, Cembranos & Striagri, 2008 argue that the observed X-ray & Gamma-ray halo around the Galactic bulge can be explained in the context of decaying dark matter WIMPs (Weakly Interacting Massive Particle). These are just two examples, but they are enough to show that non-baryonic dark matter is not undetectable, and may already have been indirectly detected (of course much more work needs to go into this).

I know next to nothing about the positrons and WIMPS you mention here, but the description in connection with decaying massive dark matter particles does bring up a question of interest to me. The description of dark matter WIMPS causing phenomema around the Galactic bulge, implies the dark matter being located in or adjacent to the galactic disk as opposed to forming large diameter spherical shells around the disk. Where are the detected high energy positrons located?

[Cougar]

The description of dark matter WIMPS causing phenomema around the Galactic bulge, implies the dark matter being located in or adjacent to the galactic disk as opposed to forming large diameter spherical shells around the disk.

This is the problem with the prevailing terminology of galactic dark matter as "a dark matter halo," which I believe is misleading. According to the observed gravitational dynamics of the components of the galaxy, the "missing" dark matter must be in and throughout as well as surrounding the disk of the galaxy. Also note that Newton proved several centuries ago that given a sphere of uniform density, all matter at a radius greater than the radius of an arbitrary body has NO gravitational effect on that body.

Where are the detected high energy positrons located?

Well, according to the abstract of the article Tim cited, the authors investigated whether there was any indication of a hypothetical decay of dark matter "through an anomalous contribution to the cosmic positron flux." A little more detailed reading might pin that down more.

[TomT]

This is the problem with the prevailing terminology of galactic dark matter as "a dark matter halo," which I believe is misleading. According to the observed gravitational dynamics of the components of the galaxy, the "missing" dark matter must be in and throughout as well as surrounding the disk of the galaxy. Also note that Newton proved several centuries ago that given a sphere of uniform density, all matter at a radius greater than the radius of an arbitrary body has NO gravitational effect on that body.

Hi Cougar,
I essentially agree with your statement. I don't remember if you took part in any of the discussion in this thread -

http://www.bautforum.com/questions-a...lculation.html

A solution for the mass distribution entirely within the galactic core and disk which duplicates the rotation curves using Newtonian dynamics was described and numerical results given. The result was 30% or more reduction in galactic mass than the spherical shell solution of Binney and Tremaine. There is still more mass than given by the M/L ratio generally assumed. I was wondering if the WIMPS brought up by Tim T would account for a sgnificant portion of the missing mass, and be located within and throughout the disk.

[grav]

A solution for the mass distribution entirely within the galactic core and disk which duplicates the rotation curves using Newtonian dynamics was described and numerical results given. The result was 30% or more reduction in galactic mass than the spherical shell solution of Binney and Tremaine. There is still more mass than given by the M/L ratio generally assumed.

The geometry of the observable galaxy itself and its density distribution plays a very big role for the rotation speeds, as you know. It might explain much about the gravity for what lies within the galaxy, although perhaps not fully, and not so much for what lies further out. The article in this post that trinitree88 presented, however, might explain much of the rest. It appears that very long filaments contain half the mass of the galaxy not seen before. That would explain much of the mass deficiency in itself. The geometry of such filaments might also cause a steady rotation speed for galaxies regardless of distance, as the gravity would vary more over 1/r instead of 1/r^2 in that case, without the need for (another form of) dark matter.

[grav]

Dang. I'm getting an error for that link now, and I can't remember who published it.

[TomT]

The geometry of the observable galaxy itself and its density distribution plays a very big role for the rotation speeds, as you know. It might explain much about the gravity for what lies within the galaxy, although perhaps not fully, and not so much for what lies further out. The article in this post that trinitree88 presented, however, might explain much of the rest. It appears that very long filaments contain half the mass of the galaxy not seen before. That would explain much of the mass deficiency in itself. The geometry of such filaments might also cause a steady rotation speed for galaxies regardless of distance, as the gravity would vary more over 1/r instead of 1/r^2 in that case, without the need for (another form of) dark matter.

Hi grav,
I was delayed getting back to this. I have read the article you referenced, and couldn't get to it on your link. Did you take the filaments to extend into and throughout the galaxy itself? I couldn't remember the details of their findings. I think they claimed to find half of the missing baryonic matter. Does this mean they found half of the missing total matter? Was this subject discussed elsewhere on BAUT?
TomT

[matt.o]

Hi grav,
I was delayed getting back to this. I have read the article you referenced, and couldn't get to it on your link. Did you take the filaments to extend into and throughout the galaxy itself? I couldn't remember the details of their findings. I think they claimed to find half of the missing baryonic matter. Does this mean they found half of the missing total matter? Was this subject discussed elsewhere on BAUT?
TomT

If I may answer this on grav's behalf: The warm-hot intergalactic medium is what I think you are describing, and this is thought to account for much of the missing baryonic matter, not the total matter. In the Universe's energy-density budget, the total mass of matter makes up about 27%, while the dark energy makes up around 73%. Of the 27% of total matter, around 23% is thought to be the non-baryonic dark matter, while around 4% is baryonic and only around half of this baryonic matter has been accounted for as stars, gas etc. Anyway, I think an article similar to the one you describe can be found here.

[grav]

Did you take the filaments to extend into and throughout the galaxy itself?

I'm still awaiting more details on that, but if the filaments run through galaxies like wire structures, then that would definitely help explain the constant rotation curves, since the gravity of a very long wire would run with 1/r instead of 1/r^2, producing a constant orbital speed regardless of distance, up to a very large distance for a wire that is finite in length anyway.

[grav]

If I may answer this on grav's behalf: The warm-hot intergalactic medium is what I think you are describing, and this is thought to account for much of the missing baryonic matter, not the total matter. In the Universe's energy-density budget, the total mass of matter makes up about 27%, while the dark energy makes up around 73%. Of the 27% of total matter, around 23% is thought to be the non-baryonic dark matter, while around 4% is baryonic and only around half of this baryonic matter has been accounted for as stars, gas etc. Anyway, I think an article similar to the one you describe can be found here.

That is very interesting, matt.o, thanks. I thought someone had said it was half of the galaxy's mass that was found, but I was wondering how that was meant if the filaments run between galaxies like popcorn on a string, as one article read, so what you said makes very much sense. The coolest part about it is it's looking like that might then help explain dark matter and dark energy all in one shot.

[grav]

Wait a minute. It's been a while since I've worked with this, so I'm wondering. The missing matter you described, matt.o, sounds similar to the discrepancy for the critical mass density of the universe, determining whether the universe is open or closed. How is that related to dark energy describing an acceleration of the expansion of the universe?

[TomT]

If I may answer this on grav's behalf: The warm-hot intergalactic medium is what I think you are describing, and this is thought to account for much of the missing baryonic matter, not the total matter. In the Universe's energy-density budget, the total mass of matter makes up about 27%, while the dark energy makes up around 73%. Of the 27% of total matter, around 23% is thought to be the non-baryonic dark matter, while around 4% is baryonic and only around half of this baryonic matter has been accounted for as stars, gas etc. Anyway, I think an article similar to the one you describe can be found here.

Hi matt o.
I am not very familiar with all the theory behind the Universe's energy-density budget. But let's break this down to the mass calculation for an entity we can get our arms around like a galaxy cluster.

The total mass of the galaxy can be calculated using observational data and say the Virial theorem. Then the individual mass components can also be estimated from observational data.

For a specific example, I have been investigating the Coma Cluster. The published data for this cluster has estimated the mass of 3 main components:
(1) large bodies such as stars, etc.
(2) the mass of the hot gas within the cluster from high energy xray data
(3) more recently, the mass of the warm gas within the cluster from soft xray data.

I have surveyed the data available and believe it shows that the sum of the 3 constituents above accounts for all the mass, as given by the Virial theorem (no additional dark matter needed).

TomT

[WayneFrancis]

The notion of dark matter was invented to make cosmology work. Science contains several other examples of substances that were invented to make the theories of the time work. Phlogiston was one, luminiferous ether was another. Both inventions hid the truth and held up progress for too long. I suspect later generations may point and laugh at dark matter as we now laugh at phlogiston.

It all starts with the red shift which is completely ascribed to the doppler effect. (I may have skipped a step or two here, but bear with me...) And then we get into some uncomfortably circular definitions concerning the brightness of distant objects and the speed at whch distant objects are receding from us. But what if the doppler effect is not the whole story. What if something else is affecting the spectrum of distant objects? Might we find perhaps that when the universe was so much younger and smaller and more dense that the speed of light was different. The photons emitted by those ancient and now-distant objects were created when the physical laws which dictated their generation and propagation were subtly different because there was a difrent value for c.

Now I am no astrophysicist, nor am I enough of a mathematician to take this notion a step further. I am certainly no Newton or Galileo so I cannot produce a frightening and elegant demonstration to prove my point. I think one would have to measure the speed of light to the nth level of precision over geologically long periods of time to establish whether it might change over that period. Either that or come up with something of Einsteinian grandeur to show that the speed of light is not constant but a variable and depended on the age of the universe.

With the prize of eternal fame and the title of being the hero that fixed 20th century cosmology, who would like to take this one on?

Read more at: http://fatnickdavies.blogspot.com/

Ummm don't know if anyone has corrected you on this yet but "Dark Matter" has very little to do with the expansion of the universe. "Dark Matter" has everything to do with trying to explain how galaxies rotate the way that they do and remain gravitationally bound.

"Dark Energy" a TOTALLY different concept has to do with a seemly negative pressure that at the large scale is causing the universe to not only expand but currently expand at an ever and ever faster rate.

I've just got done with a email to a expansion denier friend of mine about the same topic. Sure we don't know with "Dark Energy" is. It is just a label at the moment. What we do know is that, via multiple independent lines of evidence, the universe appears to be expanding and expanding at an ever increasing rate. Until someone comes up with a consistent alternate explanation of the data then expansion will remain the best explanation. What causes that expansion? We don't know so it was given, probably a bad name for the lay person, "Dark Energy". "Dark" because we haven't not figured out what it is yet, "Energy" because it is performing work to create new space at the rate of ~70k/Megaparsec.

Sure in 100 years we might look back and say "That dark energy idea wasn't right" but that is what science is about. Putting forth the currently best hypothesis for the current data and when a either a better hypothesis comes forward or new data changes the "currently best hypothesis" then we change.

By your own admission you are no astrophysicist, nor are you enough of a mathematician to follow this issue any further. Why not trust in the people that are to make the right judgment. I'm sure you are no physicists to explain QM so why should we listen to you if you claim that energy gaps don't exist? The current model is useful, makes testable predictions and said predictions are being verified. If the universe walks like a duck and quacks like a duck then I'm going to believe that it is a duck until someone shows me another animal it more closely resembles.

[peter eldergill]

I get the feeling the OP isn't coming back. This seems like an advertisement just to get you to go to his website

Pete

[matt.o]

Wait a minute. It's been a while since I've worked with this, so I'm wondering. The missing matter you described, matt.o, sounds similar to the discrepancy for the critical mass density of the universe, determining whether the universe is open or closed. How is that related to dark energy describing an acceleration of the expansion of the universe?

No, the ~4% baryonic component of the total matter density is well constrained by measurements of the relative power in the peaks of the cosmic microwave background, and thus is already known about, although half of this ~4% (~2% total matter) has to date escaped observation, although it was hypothesised to exist in the form of a warm-hot intergalactic gas, which is what is being observed in the article I linked. Thus, dark matter and dark energy remain.

[matt.o]

Hi matt o.
I am not very familiar with all the theory behind the Universe's energy-density budget. But let's break this down to the mass calculation for an entity we can get our arms around like a galaxy cluster.

The total mass of the galaxy can be calculated using observational data and say the Virial theorem. Then the individual mass components can also be estimated from observational data.

For a specific example, I have been investigating the Coma Cluster. The published data for this cluster has estimated the mass of 3 main components:
(1) large bodies such as stars, etc.
(2) the mass of the hot gas within the cluster from high energy xray data
(3) more recently, the mass of the warm gas within the cluster from soft xray data.

I have surveyed the data available and believe it shows that the sum of the 3 constituents above accounts for all the mass, as given by the Virial theorem (no additional dark matter needed).

TomT

At the risk of derailing this thread, could you perhaps provide more information (e.g. calculations, links to papers etc.). I am highly skeptical of this claim, since it is fairly well known that dark matter makes up around 85-90% of the mass in a cluster, while the hot intracluster medium makes up around 10-15% of the mass and the galaxies make up around 2%.

I am also skeptical of virial mass measurements (and indeed any mass measurements which rely on the cluster being in a relaxed state) of the Coma cluster, given its unrelaxed nature.

[mugaliens]

Only the doppler effect and gravitational redshift are currently known to induce this phenomenon - and I believe we can safely rule out gravitational redshift as a global explanation.

Why is that ("safely" ruling out gravitational redshift)? If expansion is indeed both positive and accelerating, how can we be certain that the matter density (kg/m[sup[3[/sup]) of ancient space wasn't sufficiently more dense so as to create more redshift than we think? This would inflate the current redshift vs distance measurements, and mean that we are errantly attributing more redshift to expansion than is appropriate.

I'm not saying I believe this to be the case. I am saying that making sweeping statements as if "everyone knows" is a logical fallacy. It's an "appeal to the people," and is termed, argumentum ad populum.

Avoiding this is simple - provide the reason why you believe we can safely rule out gravitational redshift as a global explanation.

[grav]

No, the ~4% baryonic component of the total matter density is well constrained by measurements of the relative power in the peaks of the cosmic microwave background, and thus is already known about, although half of this ~4% (~2% total matter) has to date escaped observation, although it was hypothesised to exist in the form of a warm-hot intergalactic gas, which is what is being observed in the article I linked. Thus, dark matter and dark energy remain.

Okay, thanks. I am still curious, though. How is it determined that dark energy makes up 73% of the universe and what is that saying about the characteristics or mechanism of dark energy?

[TomT]

At the risk of derailing this thread, could you perhaps provide more information (e.g. calculations, links to papers etc.). I am highly skeptical of this claim, since it is fairly well known that dark matter makes up around 85-90% of the mass in a cluster, while the hot intracluster medium makes up around 10-15% of the mass and the galaxies make up around 2%.

I will submit the info on the Q/A Forum next week, when I get home from the holiday weekend.

I am also skeptical of virial mass measurements (and indeed any mass measurements which rely on the cluster being in a relaxed state) of the Coma cluster, given its unrelaxed nature.

You seemed to think the Virial equation was OK for Coma in this forum. See posts near end.

http://www.bautforum.com/archive/index.php/t-69874.html

[matt.o]

You seemed to think the Virial equation was OK for Coma in this forum. See posts near end.

http://www.bautforum.com/archive/index.php/t-69874.html

You'll note I did say I was skeptical earlier on in that thread. My point is you need to be careful in applying these types of analyses to unrelaxed systems. I'm not going to argue the merits of the mass derived from the virial theorum based on this, it's just a caveat you need to be aware of.

Edit to add: Have a nice holiday!