Dark Matter

[Chris Peterson]

It is impossible to say that either matter or energy even exist. We simply find them convenient for explaining our observations. The Universe is full of things we've never touched directly, or had in the lab. That doesn't mean that we can't propose that their existence is likely.

You're going to have to explain this a bit. I can "touch" my desk and my chair and my keyboard in a lab. I know they exist in reality. I can turn my head few a few seconds, look back at my desk, and sure enough the desk, chair and keyboard are right were they were a few seconds ago. I can turn on electric circuits, like those in my computer, and see the flow of energy having a direct effect on matter. I can in fact play with atoms and electricity in a lab and control the parameters one at a time in very precise ways.

These are all indirect measures of or observations of what we call "matter" or "energy". You've never really touched anything in your life. It's just an interaction of fields (yet another abstraction).

No, I have personally heard a Doppler shift. I consider it likely in fact, particularly in a moving universe like the one we live in.

Who said anything about a Doppler shift? I'm talking about gravitational red shift, the metric we use for scaling the Universe. It doesn't have anything to do with Doppler shift, and it's never been created in any lab.

No comment on the iron sun wackiness. As far as I'm concerned, that's what falls into the invisible potato category, not dark matter.

[Chris Peterson]

Ah, my bad (I think). Could you explain how you used gravitational redshift to "scale the universe"?

Sorry, my bad too. We scale the Universe with the cosmological red shift (it might have some other names, too). We do make allowance for the gravitational red shift when making stellar spectroscopic measurements. Neither of these red shift mechanisms (which are different from Doppler shift) have ever been duplicated in laboratory settings, but both are very well accepted because they serve so well to explain what we observe. Not unlike non-baryonic matter as an explanation for very apparent gravitational effects, although that is clearly something that hasn't yet accumulated the weight of evidence that the red shift has. But it is far from pure speculation.

[Nereid]

To the point about invisible potatoes: if the missing mass were such, then the Earth would be being bombarded by meteors, with masses comparable to potatoes, element compositions comparable to those of potatoes, and with impact speeds of many dozens of km/sec.

Er, why would that matter? According to you folks, the stuff passes right through normal matter, no? I fail to see how it would make even the least bit of difference how large it was (within limits of course).

That the Earth is, demonstrably, not being so bombarded is a powerful, observational, reason for rejecting your idea.

If it passes right through normal matter, how would you know whether or not we are being bombarded by the stuff? Regardless of what size it might be, wouldn't it be fair to expect that we are being bombarded by it?

I see ... these are MM non-baryonic invisible potatoes, not ~0.1 to 1 kg compact solid objects composed of C, H, O, N, ... which, on Earth, originated in South America.

a.k.a. unicorns.

My bad.

[Nereid]

Michael, can you point to any relevant papers which provide consistent accounts for both spiral galaxy rotation curves and the estimated mass of rich clusters solely in terms of baryonic matter?

... other than those which introduce new theories of gravity*

By 'consistent accounts' I mean, at a minimum, consistent, quantitative estimates of the forms in which the baryons are to be found.

*Given your oft stated views on the primacy of earthly labs, no such new theory could be acceptable, could it, without its existence being proving in lab experiments, right?

[Nereid]

Michael, can you point to any relevant papers which provide consistent accounts for both spiral galaxy rotation curves and the estimated mass of rich clusters solely in terms of baryonic matter?

No. I never suggested you could explain the rotational curves of galaxies that way in the first place.

[snip]

At face value, this statement seems to be an extraordinary turn-around in your views Michael - perhaps you wrote too quickly?

Are you saying that you do, in fact, need non-baryonic matter to explain the rotation curves of spiral galaxies (and the estimated mass of rich clusters)???

If so, what kind of non-baryonic matter do you propose to use, in your explanation?

(Please note that my question refers to the observed rotation curves, and the estimates of rich cluster mass (from observations), and how they can be accounted for using only baryonic matter ... the question is quite open to how - what physics - you use to do the explaining.)

[Nereid]

So, the correct answer to my question ("can you point to any relevant papers which provide consistent accounts for both spiral galaxy rotation curves and the estimated mass of rich clusters solely in terms of baryonic matter?") is ...

a) No; there are, AFAIK, no such papers?

b) I don't know; I hope there are some, based on plasma physics?

c) Yes, {insert list of references here}?

d) something else?

[Nereid]

Michael, can you point to any relevant papers which provide consistent accounts for both spiral galaxy rotation curves and the estimated mass of rich clusters solely in terms of baryonic matter?

No. I never suggested you could explain the rotational curves of galaxies that way in the first place.

... other than those which introduce new theories of gravity*

I would think it would be more productive to try to spread the mass out horizontally and introduce current flows, nothing more. No metaphysics, no dark stuff, nothing that can't demonstrated to actually exists in reality.

By 'consistent accounts' I mean, at a minimum, consistent, quantitative estimates of the forms in which the baryons are to be found.

I'm going to have to peruse some of Alfven's modeling of galaxy formation. I've been so fixated on solar theories, I've not really payed much attention to how he describes their formation in the absence of dark things. I would start with his work to be sure.

*Given your oft stated views on the primacy of earthly labs, no such new theory could be acceptable, could it, without its existence being proving in lab experiments, right?

Everything I would attempt to introduce would be a function of plasma physics. To the degree we can test plasma physics, we should be able to test plasma cosmology theory.

So we can reasonably expect that, until you do produce such papers, you will admit that there are no 'baryonic mass only' scientific explanations for the millions of high-quality astronomical observations, of spiral galaxies and rich clusters (and ...)?

[Nereid]

So, the correct answer to my question ("can you point to any relevant papers which provide consistent accounts for both spiral galaxy rotation curves and the estimated mass of rich clusters solely in terms of baryonic matter?") is ...

a) No; there are, AFAIK, no such papers?

b) I don't know; I hope there are some, based on plasma physics?

c) Yes, {insert list of references here}?

d) something else?

Let's start with c):

http://xxx.lanl.gov/abs/astro-ph/0507619

Been there, done that (my bold)

Comment on ``General Relativity Resolves Galactic Rotation Without Exotic Dark Matter'' by F.I. Cooperstock & S. Tieu:

The general relativistic model of Cooperstock & Tieu, which attempts to fit rotation curves of spiral galaxies without invoking dark matter, is tested empirically using observations of the Milky Way. In particular, predictions for the mass density in the solar neighbourhood and the vertical density distribution at the position of the Sun are compared with observations. It is shown that the model of Cooperstock & Tieu, which was so constructed that it gives an excellent fit of the observed rotation curve, singularly fails to reproduce the observed local mass density and the vertical density profile of the Milky Way.

Comment on the Relativistic Galactic Model by Cooperstock and Tieu

It has recently been suggested that observed galaxy rotation curves can be accounted for by general relativity without recourse to dark-matter halos. A number of objections have been raised, which have been addressed by the authors. Here, the calculation of tangential velocity is questioned.

(there's more).

In short, 'nice try, but maths are wrong, and even if right, predictions are inconsistent with good observational results'.

Next?

I'd really prefer one about rich clusters ... they contain much more mass than spiral galaxies, most of the baryonic mass is in the form of a high temperature, low density plasma, and there are three independent sets of observations pointing to a big mismatch between the observed (baryonic) mass and estimated (total) cluster mass.

[rodly]

It seems to me that maybe dark matter had a hand in creating the hurricane as well.

Enough already, let us just call it unknown matter without any theories.

There are lots of forces at play here on earth that we don't understand fully, yet to assume that we can explain something we'll never get close to definitively may be expecting too much from the human brain at the present time.

It is also possible in the light(no pun intended) of new discoveries in space that it might be time to revamp the gravitational theories. While both Newton's and Einstein's have served us well over the years a little tweaking may provide the answer and none of us will be in the dark. I doubt that one individual will be capable of doing it on their own, for there are just too many significant elements to consider.

[makc]

Nobody seems to know where it comes from, or what it's made of...

Why do we have to know that? "It" (whatever it is) is defined as "something that has an effect of extra mass in some of our equations". I wouldn't want to re-type my whole post here, so please feel free to answer it on its thread.

[makc]

Enough already, let us just call it unknown matter without any theories.

I support it. Nereid? Two open threads converging to the same subject, come on.

[Nereid]

Enough already, let us just call it unknown matter without any theories.

Well, that isn't exactly the case however. I have heard all sorts of theories about the alleged properties of "dark matter". I've never held a single gram of it however, nor have I seen any neutrino-like experiment to demonstrate it actually exists. Nobody seems to know where it comes from, or what it's made of, but it's evidently capable of passing through normal matter, etc. There are theories about what it, some of which I'm evidently not at liberty to even discuss here at all.

There are lots of forces at play here on earth that we don't understand fully, yet to assume that we can explain something we'll never get close to definitively may be expecting too much from the human brain at the present time.

Don't sell the human brain short, nor our new technologies short. We're learning an incredible amount of new information about our universe all the time, and Birkeland had many of the basics of plasma cosmology theory worked out over 100 years ago. He certainly realized there was an electric aspect to astronomy.

It is also possible in the light(no pun intended) of new discoveries in space that it might be time to revamp the gravitational theories.

I think that new "discovery" is likely to be "current flow". FYI, Birkeland "discovered it' over 100 years ago. IMO astronomers today simply haven't realized it's full implications as it relates to astronomical movements of matter.

While both Newton's and Einstein's have served us well over the years a little tweaking may provide the answer and none of us will be in the dark. I doubt that one individual will be capable of doing it on their own, for there are just too many significant elements to consider.[/url]

I think Newton and Einstein's theories have served us very well in their own domains and in their own ways. On the other hand I'm not convinced that labeling anything as "dark matter" or "dark energy" gets us any closer to understanding the real physical cause of these phenomenon.

In summary then:

The term "dark matter" (DM) is in widespread use among astronomers, with a pretty precise meaning, and millions of high quality observations pointing to its existence.

No other, scientific, explanation of these millions of observations has (yet) been published in the relevant, peer-reviewed literature*.

Michael doesn't like DM, for various reasons. However, he hasn't (yet) been able to present a scientifically viable alternative explanation for the relevant observations (that does away with the need for DM).

So unless and until he (or another member posting to the Cafe) can present such a case (based on papers published in relevant peer-reviewed astronomy journals), I think this thread has run its course ...

*There is an alternative - some form of modified gravity (such as MOND, or TeVeS). Naturally, this is even more unacceptable to Michael ...

[Nereid]

You might like to check out the Astronomy and "controlled scientific experiments" thread Michael; my last post there summarises what I see as the disconnect between modern astronomy, as a science, and your own views.

In summary then:

The term "dark matter" (DM) is in widespread use among astronomers, with a pretty precise meaning,

It has a little too precise a meaning actually. You've made all sorts of assumptions about it that you cannot actually demonstrate. You've made up an invisible, non barionic that is able to travel though walls sort of matter than nobody has ever actually seen here on earth.

We've been over this, and over it, and over, and over ...

I don't see any value is repeating, yet again, what the standard term means (and commenting on what it doesn't mean).

and millions of high quality observations pointing to its existence.

No. You have millions of high quality observations that point us to the existence of *missing mass*. Whether that missing mass is contained in heavy suns or a new form of mass cannot be determined from 5 billion light years away. Occum's Razor, and common sense should preclude us from simply *assuming* the need for new forms of mass that might exist at that distance.

Ditto ... also a pretty good example of the difference between the way modern astronomy, as a science, works ... and your own approach.

In this case, no 'heavy suns' hypothesis has been proposed (that I know of), but plenty of 'baryonic mass' ones have ... and none has been shown (yet) to match the relevant observations ...

Maybe tomorrow there will be such a paper published, and maybe next year the relevant follow-up work will have been done, and non-baryonic (cold) DM will be sent to the dustbin of astronomy history.

However, until then, it's the best theory we have ...

No other, scientific, explanation of these millions of observations has (yet) been published in the relevant, peer-reviewed literature*.

So what? That does not mean that you personal theories have any legs to stand on. The fact that something is published does not make it true, otherwise my theories are "true" Nereid. Publishing a paper about an idea is not the be-all-end-all of "truthiness".

Of course.

However, that's the way the science of astronomy works today, and as we are a scientific forum, that's the standard we will use.

Let's be clear about one point here. Even if there are no "better" explanations out there, that is not evidence that your pet theory has merit. You cannot point to a published paper and *assume* it is accurate by virtue of being published. You cannot assume that another explanation must exist for your own theory to be falsified. I can disprove your theory without providing *any* alternative whatsoever.

You could ... in which case you'd have something like 'the Pioneer anomaly' - good observations about which no hypothesis presented, to date, adequately addresses.

The case of (non-baryonic) dark matter, however, is nothing like such an anomaly ... in fact, the consistency across much of astronomy, and from quite different physical mechanisms, is astonishing: rich clusters (at least three different, independent kinds of observations), spiral galaxies, and cosmology (large-scale structure, evolution, the CMB, ...).

Michael doesn't like DM, for various reasons.

The most important reason I don't like DM is because I don't have any faith in the belief that it actually exists. If one is a skeptic of an idea, one cannot just wave their hand and stop being a skeptic. I need some empirical evidence that DM actually exists. If you can provide that, then I'll be happy to let you speculate about how much DM might exist in deep space. If you can't produce a single gram of DM, nor any experiment to show it has an effect on matter, I very much doubt it actually exists., and it have no reason to believe it has any effect on nature. That's is the "reason" for my skepticism in a nutshell.

And, AFAIK, no one is asking you to give up your scepticism - what you choose to believe, or not believe, is no concern of anyone posting in the Cafe (I think).

However, if you continue to insist that 'non-baryonic DM' is bad astronomy (as a science), you need to start engaging in a scientific discussion*.

However, he hasn't (yet) been able to present a scientifically viable alternative explanation for the relevant observations (that does away with the need for DM).

I'm not required to do that! You keep insisting that you are right by default. Science doesn't work like that Nereid.

This is another disconnect between modern astronomy, as a science, and your views.

It is precisely one way that science does, in fact, work.

Oh, and I'm not 'right by default'; all I strive to do is accurately represent the current state of astronomical (scientific) research - if you find my summaries inaccurate, by all means correct them!

Your theory must stand on it's own merits irrespective of any alternative. Since you can't produce any dark matter, it has no "dark" legs to stand on, with or without an alternative to choose from.

I hope, by now, you realise that this is not the way modern science (astronomy) works.

Also, see above (re 'anomalies').

So unless and until he (or another member posting to the Cafe) can present such a case (based on papers published in relevant peer-reviewed astronomy journals), I think this thread has run its course ...

Why are you so intent on closing dissenting threads Nereid? Why can't your theories about astronomy and your opinions about DM include room for a few vocal skeptics like me?

As I have stated - once or twice - this is a scientific forum.

If you wish to express your opinions on the nature of modern astronomy, as a science, we may be able to accommodate you, to a limited extent (as we have already done).

If you wish to present ideas that have not yet been shown to be scientific (my 'three criteria', in short), then once you have stated those ideas and cannot produce support for them (in the form of papers published in relevant, peer-reviewed journals) - which you have done, many times - that will be the end of such presentations.

*FWIW, a great many scientists find much of modern physics deeply unsettling, and are, in the MM mold, deeply sceptical. Quantum mechanics is one arena where this is particularly so ... yet QED (a quantum theory) is the most precisely tested theory in the history of science (and tested in earthly labs to boot)!

[makc]

...an invisible type of non barionic matter that is able to travel though walls and that nobody has ever actually seen here on earth...

Isn't that because it is... cough... invisible?