Non-baryonic cold dark matter ("CDM"), the observational evidence

[DeiRenDopa]

I agree on the science by headlines not being science. Remember though, I am not writing those headlines and I never intimated that the science was wrong, only that the headlines seem a bit hyped. Hence the Carl Sagan quote.



I will most certainly read the thread and links more deeply, thats why I saved the entire thread as I stated



Here I interprete you saying that CDM is cold ie no IR emission and non baryonic ie not normal matter. So you have stated what it is not rather than what it is.

What I dont understand perhaps are the implications that observations of WD, NS etc are comparable to observation of dark matter.
In other words, I can understand observations of "normal" stellar objects to be direct but observation of CDM in laymans understanding to be indirect ie observation of the effects.

when you observe an eclipsing binary, you obseve a direct consequence of one object eclipsing another. You can see both objects.

When you observe gravitational lensing you can only see one object, and can only infer things about the unseen object.
Now, as I have stated many times, I am not a scientist, just an interested observer, so I accept gross deficiencies in my understanding and am hoping that participation in these discussions will widen my scientific understanding rather than trying to elevate confrontation and troll behaviour.

Hmmm ...

When you observe some of the beautiful planetary nebulae, what do you see? If you take a spectrum of one, you'll see a strong emission line at ~500.7 nm, and your textbook will tell you it's a 'forbidden' transition of a doubly ionised oxygen atom ... but no one has ever seen this line in any lab spectrum! So why are astronomers (etc) so confident that this nice green line is, in fact, a [OIII] transition (the square brackets mean a forbidden transition)?

Take something much more mundane, acceleration due to gravity.

As far as I know, the strongest acceleration due to gravity directly tested is that here on the surface of the Earth ... of course, there are centrifuges which can create 'g forces' as high as a million gs, but whether they give the same effect as gravity depends on what sort of philosophy of science you follow. If you accept all the results of all the tests that GR (General Relativity) has been subject to to date (and which it has passed, with flying colours), then you'll have no intellectual problems with accepting that atoms behave on the surface of high density star (with an acceleration due to gravity of a million gs) the same as they behave in an ultracentrifuge in an Earthly lab.

But then if you accept GR for the behaviour of atoms (etc) under a million gs, why not accept CDM from gravitational lensing? Sure the logic chain is longer (you have to estimate all the baryonic matter that is not 'visible' and subtract it from the estimate of the total mass causing the lensing), but the philosophical principle is the same, right?

Oh, and "cold" in CDM doesn't refer to any blackbody temperature ... matter of this kind does not 'feel' the electromagnetic force, so does not emit photons period. Instead, "cold" refers to the average speed of the CDM particles, and means 'non-relativistic' (or something similar) ...

 

[DeiRenDopa]

[...]

when you observe an eclipsing binary, you obseve a direct consequence of one object eclipsing another. You can see both objects.

Are you sure?

I thought you observe only the light curve of a single point source ('star'), and from that light curve you infer that there are, in fact, two stars in a mutual orbit whose plane has a certain geometric relationship to your line of sight ...

When you observe gravitational lensing you can only see one object, and can only infer things about the unseen object.

[...]

(bold added)

Indeed ...

... just like an eclipsing binary (or a spectroscopic binary, or ...)!

 

[Herzblut]

If we begin assuming that:

Then I can barely understand how to get to:

Not that I know what this is all about, but..

For a radially symmetric grav. field, simply use the Laplace operator in spherical coordinates in the Poisson (field) equation, ignoring the two angular gradients. By differentiating the equation of state you can then, in the field equation, eliminate the gravitational field in favor of mass density. By integration you get to the result straight away.

 

[Skwinty]

Hi DRD

When observing eclipsing binaries, you can see both objects prior to eclipsing.
During the eclipse the light curves can be used to infer all sorts of things.

As for the forbidden transitions. When the lab here on Earth can perform spectroscopy on the same volumes of gas and conditions that occur in the universe, then your argument about forbidden transitions may not hold water.

Why are you implying that I do not accept CDM. I have stated numerous time that I do not have a problem with the issue or your observations of the effects of dark matter. My issue is with the claim that Dark matter has been observed.
My argument is that the effects have been observed. When science can state that CDM consists of neutrolinos, axions or any other blend of exotic particles and this has been corroborated by at least three different types of measurement, then you can state that CDM has been observed. Until then, only the effects have been observed and science can make many inferrances about this, but its based on the observation of effect.

 

[DeiRenDopa]

Hi DRD

Hi Skwinty

When observing eclipsing binaries, you can see both objects prior to eclipsing.
During the eclipse the light curves can be used to infer all sorts of things.

It's actually important to get this right, in the sense of us agreeing on a description ...

What's observed: a point source ('star') on the sky - one point source (not two). The source's brightness is observed over time, and the data displayed as a 'light curve'.

AFAIK (as far as I know), there are few, if any, EBs that have been directly resolved as separate point sources - do you know of any?

From the variation in the point source's brightness over time, we infer that the point source is actually an EB.

Why is it important that we reach agreement on this description? There are several reasons, but one has to do with what is 'direct' and what is 'indirect' ("laymans understanding to be indirect ie observation of the effects"); another with the role of (physics) theory in 'observation'.

As for the forbidden transitions. When the lab here on Earth can perform spectroscopy on the same volumes of gas and conditions that occur in the universe, then your argument about forbidden transitions may not hold water.

Yes and no ...

An astronomer shows you the spectrum of a star. She says that certain lines in that spectrum are due to H (say). You do your checking and discover all kinds of consistencies (lab spectrum of H under certain temp and density conditions; the astronomer's telescope, spectrograph, etc; analysis routines and procedures; ...). What - in as much detail as possible - leads you to conclude that there is H somewhere along the line of sight to the star?

From another thread I infer that you have some interest in philosophy; it may be helpful to get over some of the more (to me) unhelpful aspects (of philosophy) as they apply to astronomy, and get on to a clear understanding of what cosmological principle(s) you are comfortable with. For example, perhaps some variant of 'physics is the same everywhere in the universe'.

Back to forbidden transitions ... if the conditions for a particular transition are far, far beyond what can be created in an Earthly lab (we can't make a vacuum hard enough, for long enough, for example), whence comes the certainty that a particular line in a spectrum means the existence of a metastable excited state of a certain ion (or atom or molecule) 'out there'? It's an extrapolation, of at least one kind - I'm keen to know what kinds of extrapolation are acceptable to you, and how you parse extrapolations (in astronomy) into 'direct observation' and 'observation of the effects'.

Why are you implying that I do not accept CDM. I have stated numerous time that I do not have a problem with the issue or your observations of the effects of dark matter. My issue is with the claim that Dark matter has been observed.
My argument is that the effects have been observed. When science can state that CDM consists of neutrolinos, axions or any other blend of exotic particles and this has been corroborated by at least three different types of measurement, then you can state that CDM has been observed. Until then, only the effects have been observed and science can make many inferrances about this, but its based on the observation of effect.

Let's explore this in more detail, later ...

For now, can you confirm that techniques like gravitational lensing can be used to infer something about the distribution of mass between the source object and us ('the lens')?

 

[Skwinty]

Hi DRD

Inferring something about dark matter from gravitational lensing is perfectly acceptable. I dont have any problem with that at all.

Sirius is an example of a visual binary, given the correct "seeing", telescope and hartmann mask. Algol is another and there a lots more. I agree, that there are lots of eclipsing binaries that are not visual and "indirect" methods are required to infer anything about them.

ETA: My interest in philosophy extends only to what Einstein believed about philosophy. I am not a philosopher and I believe that the laws of physics are the same throughout the observable universe. As for the unobservable universe, I cannot be certain, although there should be no reason to believe that it would be any different. But never say never!

 

[DeiRenDopa]

Hi DRD

Inferring something about dark matter from gravitational lensing is perfectly acceptable. I dont have any problem with that at all.

Thanks, that's good to know.

Now if the lurkers who feel otherwise would make themselves known please (and say why, unlike Skwinty, you do have a problem)?

Sirius is an example of a visual binary, given the correct "seeing", telescope and hartmann mask. Algol is another and there a lots more. I agree, that there are lots of eclipsing binaries that are not visual and "indirect" methods are required to infer anything about them.

Indeed.

They are 'visual binaries', and all EBs could be resolved as visual binaries (in principle); however, as I said, I know of none.

Many visual binaries are discovered when resolution increases, such as with HIPPARCOS, or the Hubble Space Telescope, or when a ground-based telescope is fitted with the latest in adaptive optics.

A spectroscopic binary is a star (point source) whose spectrum has two sets of lines that move relative to each other in a particular way, corresponding to changes in the line of sight velocity of the two stars in the binary*. In principle all spectroscopic binaries could be resolved as visual binaries (do you know why?), but few, if any, are.

Are all EBs also spectroscopic binaries (if only in principle)?

Are all spectroscopic binaries also EBs (if only in principle)?


Stay tuned, there's more! (and this is all very relevant to cold, non-baryonic dark matter and whether it has been 'observed' or not ... trust me).

ETA: My interest in philosophy extends only to what Einstein believed about philosophy. I am not a philosopher and I believe that the laws of physics are the same throughout the observable universe. As for the unobservable universe, I cannot be certain, although there should be no reason to believe that it would be any different. But never say never!

Thanks, that's good to know.

Now if the lurkers who feel otherwise would make themselves known please (and say why, unlike Skwinty, you think physics may be different in the unobserved universe)?

Note that I changed "unobservable" to "unobserved"; care to guess why?

* any inferences here?

 

[robinson]

My issue is with the claim that Dark matter has been observed.
My argument is that the effects have been observed. When science can state that CDM consists of neutrolinos, axions or any other blend of exotic particles and this has been corroborated by at least three different types of measurement, then you can state that CDM has been observed. Until then, only the effects have been observed and science can make many inferrances about this, but its based on the observation of effect.

Good points. I'm reminded of how planets were first "known to exist" because of gravitational anomalies on other planets orbits. Mercury's orbit led to theorizing there was an unknown planet effecting it. Which was wrong.

But then, Pluto was theorized and turned out to be there. In both cases, something was "observed", and an invisible body theorized to exist. But in both cases, before actual observation of a planet, it would be a stretch to say it was observed.

Proper language would be "evidence for invisible matter that does not act like matter that we know of has been observed". Or something like that.

 

[robinson]

Which, to be quite fair, is also the sort of evidence we have for many invisible things. Like magnetism.

 

[DeiRenDopa]

Good points. I'm reminded of how planets were first "known to exist" because of gravitational anomalies on other planets orbits. Mercury's orbit led to theorizing there was an unknown planet effecting it. Which was wrong.

But then, Pluto was theorized and turned out to be there. In both cases, something was "observed", and an invisible body theorized to exist. But in both cases, before actual observation of a planet, it would be a stretch to say it was observed.

I think you're thinking of Neptune; Pluto was not 'there'!

Proper language would be "evidence for invisible matter that does not act like matter that we know of has been observed". Or something like that.

Stay tuned!

In the meantime, would you care to give us your thoughts on planetary nebulae (PNe)? At least the ones with strong [OIII] lines in their spectra.

Why do I ask? Because the star(s) which are inferred to exist at the heart of such PNe are often not directly observed, as in no point source is seen near the geometric centre of such PNe. Where such stars are directly observed, it turns out they are invariable white dwarf (WD) stars. As I think you now know very well robinson, no one has ever created even a few grams of WD star stuff in any earthly lab.

So, for the PNe for which a central WD star is observed, should we say ""evidence for invisible matter that does not act like matter that we know of has been observed""?

And what about the PNe for which no central star is directly observed? To what extent can we say that such stars very likely exist, in such PNe, based on little more than the detection of [OIII] lines from those PNe?

 

[Skwinty]

Hi DRD

Here is an example of two eclipsing binaries that are visual :

V975 Cen and NSV 15737. These are two bright eclipsing binaries solved with the aid of visual observation. I am sure that there must be more.

As to: "Are all EBs also spectroscopic binaries (if only in principle)?

Are all spectroscopic binaries also EBs (if only in principle)?" it would , I suppose depend on where you are observing from and what resolution you are using.

As far as :
"Note that I changed "unobservable" to "unobserved"; care to guess why?" That would relate to our current capabilities. This of course is subject to change as time and technology progresses.


Originally Posted by Belz...
Indirect observation is as good as direct observation. Otherwise science wouldn't exist

There is no argument with this concept, however there is a difference between direct and indirect in astronomy.

Binary stars can either be distinguished optically (visual binaries) or by indirect techniques, such as spectroscopy.

Another example would be that you are only indirectly aware of me through this forum and cannot claim to have directly observed me.

At the end of the day, I think that its the interpretation of words that cause the problem rather than the interpretation of scientific fact.

 

[DeiRenDopa]

Hi DRD

Here is an example of two eclipsing binaries that are visual :

V975 Cen and NSV 15737. These are two bright eclipsing binaries solved with the aid of visual observation. I am sure that there must be more.

Nice find!


However, you might like to read the relevant papers a little more carefully ... for example, I can't find anything on V975 Cen being a visual binary ("visual eclipse" doesn't mean what you think it might), and the NSV 15737 system is not a simple binary ...

I don't doubt that there might be some EBs that are also visual binaries, but they are a tiny, tiny minority of all EBs.

As to: "Are all EBs also spectroscopic binaries (if only in principle)?

Are all spectroscopic binaries also EBs (if only in principle)?" it would , I suppose depend on where you are observing from and what resolution you are using.

Indeed.

And unless and until you can go anywhere and observe with any resolution ...

From here in the solar system, what is the answer to each question?

As far as :
"Note that I changed "unobservable" to "unobserved"; care to guess why?" That would relate to our current capabilities. This of course is subject to change as time and technology progresses.

Close ...

... where this mini-thread is headed (well, one place) is that "observe" is so intricately and intimately entwined with physics that "unobservable" takes you out of science (unless, perhaps, you are a philosopher), and this part of the JREF forum would not be the right place to discuss non-science ...

Originally Posted by Belz... [qimg]http://www.internationalskeptics.com/forums/helloworld2/buttons/viewpost.gif[/qimg]
Indirect observation is as good as direct observation. Otherwise science wouldn't exist

There is no argument with this concept, however there is a difference between direct and indirect in astronomy.

Binary stars can either be distinguished optically (visual binaries) or by indirect techniques, such as spectroscopy.

You can't see in IR, or microwaves, or radio, or ... You also can't see in the x-ray waveband (etc).

That makes all astronomy - other than visual astronomy - "indirect" ... or does it?

And even for visual detection, with something like HIPPARCOS I'd be curious to know if you think you could make a case that new "HIP" binaries were discovered "directly" ... (HINT: you might like to read up on that mission, carefully, before you answer ...)

Another example would be that you are only indirectly aware of me through this forum and cannot claim to have directly observed me.

At the end of the day, I think that its the interpretation of words that cause the problem rather than the interpretation of scientific fact.

Yep ...

... but that's only part of the problem ... if you have a chance, you might like to read some of the posts by "robinson" (among others) in this part of the JREF forum. If you do, I expect that you will conclude there's a great deal more to it than "the interpretation of scientific fact".

 

[Skwinty]

You can't see in IR, or microwaves, or radio, or ... You also can't see in the x-ray waveband (etc).

That makes all astronomy - other than visual astronomy - "indirect" ... or does it?

Using a dlsr camera with ir filter removed allows you to see the ir.
With the correct equipment, microwaves, radio x-ray or gamma rays can be directly detected though.

So once again its the damn words causing the problem.

 

[Skwinty]

I can't find anything on V975 Cen being a visual binary ("visual eclipse" doesn't mean what you think it might)

Please elucidate. The paper states the eclipse was visually observed which implies a visual binary.

I don't doubt that there might be some EBs that are also visual binaries, but they are a tiny, tiny minority of all EBs.

Agreed, but this relates to "discovered" EB's. We cant say we have discovered them all as yet, so the possibility exists that there are more.

And unless and until you can go anywhere and observe with any resolution

This limitation is purely financial though.

 

[DeiRenDopa]

Using a dlsr camera with ir filter removed allows you to see the ir.

"the damn words" again?

AFAIK, the human eye is not sensitive to IR ... at least, not in terms of being able to form images on the retina that the rods and cones react to by doing their nerve firing thing ...

With the correct equipment, microwaves, radio x-ray or gamma rays can be directly detected though.

So once again its the damn words causing the problem.

Are you sure?

Don't you "detect" x-rays (say) via an intricate piece of equipment, a marvel of highly refined materials and electronics? And if your detector is aboard a spacecraft, as it must be for astronomical observations, when you finally get to see something on a computer monitor, hasn't the signal gone through a most marvelous chain of wonderous equipment, gadgets, etc? Hardly "direct detection", is it?

And what about IACTs (Imaging Air/Atmosphere Cherenkov Telescopes, like H.E.S.S.)? Whatever it is that they "observe", surely you can't say they "directly detect" TeV gammas, can you?

 

[robinson]

Semantics. The last refuge when losing the argument

.

 

[Hellbound]

Semantics. The last refuge when losing the argument

.

You should well know.

Much like claiming that "directly detecting" only means "detecting by EM radiation".

 

[Skwinty]

AFAIK, the human eye is not sensitive to IR ... at least, not in terms of being able to form images on the retina that the rods and cones react to by doing their nerve firing thing .

Agreed, but when you look at the picture produced you can see the ir input.

Don't you "detect" x-rays (say) via an intricate piece of equipment, a marvel of highly refined materials and electronics? And if your detector is aboard a spacecraft, as it must be for astronomical observations, when you finally get to see something on a computer monitor, hasn't the signal gone through a most marvelous chain of wonderous equipment, gadgets, etc? Hardly "direct detection", is it?

Using that argument implies then, that nothing is directly observed, as the eye, brain and mind is also a chain of intricate and wonderous equipment.
If you consider the signal, from source to primary detector then that could be called direct, ie there is no intermediary interference or effect between source and detector.

And what about IACTs (Imaging Air/Atmosphere Cherenkov Telescopes, like H.E.S.S.)? Whatever it is that they "observe", surely you can't say they "directly detect" TeV gammas, can you?

Perhaps the HESS is a bad example as the gamma rays do not penetrate the atmosphere and reach the earth 's surface as they interact with the atmosphere and produce cerenkov radiation. The link between the gamma ray and cerenkov radiation is inferred, so the direct observation is the cerenkov radiation and the gamma ray observation is indirect. And its a good solid inferrence.No problem there.

 

[DeiRenDopa]

Agreed, but when you look at the picture produced you can see the ir input.

(bold added)

But your acceptance of it as being an IR picture (or whatever) relies upon your acceptance of the science behind the detection mechanisms/devices and whatever goes on between detection and picture ... and that's my point (well, one of them).

Using that argument implies then, that nothing is directly observed, as the eye, brain and mind is also a chain of intricate and wonderous equipment.
If you consider the signal, from source to primary detector then that could be called direct, ie there is no intermediary interference or effect between source and detector.

Indeed.

That's one of the conclusions I am hoping you will draw ... that however you define "direct", the boundary is essentially arbitrary (you say "direct" and I say "indirect", or something like this).

Alternatively, "direct" can be limited to what you can see with your eyes (i.e. the visual waveband only), whether augmented by dumb telescopes or not (i.e. mirrors and lenses).

Perhaps the HESS is a bad example as the gamma rays do not penetrate the atmosphere and reach the earth 's surface as they interact with the atmosphere and produce cerenkov radiation. The link between the gamma ray and cerenkov radiation is inferred, so the direct observation is the cerenkov radiation and the gamma ray observation is indirect. And its a good solid inferrence.No problem there.

So ...

... we can have "direct detection" (the boundaries of which are somewhat arbitrary), "good solid inference/indirect detection", and {something else}.

And while you seem cool with IACTs, there are several high-post-count folk who most surely would not be ... if only because no one has ever created Cherenkov radiation with TeV gammas in the lab, much less fired them at the atmosphere from above ...

So, would like to try to draw up a set of criteria for how you feel the terms "direct detection" (or "direct observation") and "good solid inference/indirect detection/observation" and {any other categories} should be used?

In particular, how - objectively - does one decide when a detection/observation is indirect but "a good solid inferrence"?

 

[DeiRenDopa]

You should well know.

Much like claiming that "directly detecting" only means "detecting by EM radiation".

I suspect - in robinson's case - that it's much, much worse than this ...

For example, do IACTs "detect by EM radiation"? What about the non-detection of EM radiation (as in, for example, an absorption line)?

Myself, I suspect one deep issue is a very confused, inchoate understanding of the nature of science (and, perhaps, a deep wish that it were other than what it is) ...