Frozen-in Magnetic Field Lines - Page 7

Nereid · #**181** (**permalink**) 24-June-2008, 06:31 PM

Out of order, but so be it ...

Quote:

Originally Posted by rcglinsk

[...]

Quote:

Originally Posted by Nereid

So, are you cool with the following statement (usual caveats apply)?

The various methods (galaxy rotation curves, virial theorem applied to velocity or redshift dispersions, gravitational lensing, etc) should give consistent estimates of mass, when applied to the same object.

If so, how about this corollary (usual caveats apply)?

When two methods (from {list}) are applied to an object and give inconsistent estimates of mass, then at least one logic chain contains at least one incorrect assumption and/or there is a significant (astrophysics) element that has not been incorporated into the model(s).

Note that there's nothing in here about 'dark matter'.

Hmmm. OK, that first one is really close to what I think. It's just that by should I feel like I'm making a more sophisticated point that just "they should." In my mind there is a reason why they should give the same answer that has nothing to do with whether there is a dark matter halo or not.

Good!

The point is that the methods should provide consistent estimates of mass ... period. The methods themselves say little about the nature of that mass.

Quote:

I'm not trying to make a blanket statement about consistency. I don't think consistency between the rotation/virial methods is evidence for dark matter because whether or not dark matter exists I think you'll get consistent results. I think that is not the case with gravitational lensing. So the consistency there is evidence for dark matter. To me, consistency between different methods might be evidence in some cases, and might be indetermiante in others. The distinciton is in the particular circumstances, the methods themselves. Why should the results be consistent or inconsistent? Given the methods, what do these results mean?

The second point is very agreeable. There's no telling just from the bad outcome what particular part of the process was a mistake, a bad measurment, a bad calculation, a bad theory etc. But there was some mistake.

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How does "all this inference", wrt CDM, differ from "all this inference" wrt almost all parts of astronomy/astrophysics/cosmology (and, no doubt, large parts of planetary science, space science, geology, ...)?

The big difference is that in many parts of astronomy we're infering emperical reality. So, the [OIII] lines allow us to infer the presence of O2+ ions. The O2+ ion may not be created easily in laboratories, but oxygen is real, electrons are real, we've found oxygen with no electrons at all, so when we infer some O2+ up there we're infering something emperical, even if not completely known and understood. My problems start when people start infering objects that exist only in theory. If my theory is right then there's a charged black hole (call it a 'Shock Dragon?") at this location. OK, so that's all fine and well, but it's all much ado about nothing until we find out whether that first theory is true. Dark matter is similarly non-emperical, in the way that even a difficult to corner species of oxygen ion is emperical. I think the emperical inferences are awesome, the forefront of advanced science, and that the non-emperical stuff is a big mistake, that we're taking a shortcut to understanding.

Looks like we have identified your discomfort, but haven't yet nailed down its boundaries (though you have changed your initial position a great deal, from 'must create/see it in my lab' to 'some extrapolations are perfectly OK').

So which of the following extrapolations do you regard as "infering objects that exist only in theory"?

* metallic hydrogen
* electron degenerate matter (as in the bulk of white dwarf stars)
* nuclear degenerate matter (as in the bulk of neutron stars)
* black holes (in any form; mass that seems to be concentrated into a volume smaller than that defined by the Schwarzschild radius)
* vacuum birefringence
* photon-photon scattering

(this list could, obviously, be extended ...)

Note that 'object' is generalised to include physical processes (or mechanisms) as well as forms of matter.

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[...]

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If you would like to present an ATM case for the Hubble relationship, please go ahead (perhaps start a new ATM thread); if you are simply uncertain of the robustness of the various methods used to estimate (cosmological) distances, why not continue with the thread you started in the Q&A section?

The hubble calculations are very interesting. I really wonder though, where does all the certainty come from? If a type Ia supernova is the only measure we have to distant objects, and we know of around 40-60 such events, we're using far, far too small a data sample to effectively fit a hubble constant, even if the relationship turns out to be true.

I don't know where you got the "we know of around 40-60 such events" from, even for high-z Ia SNe it's a woefully small (and outdated) number.

Almost at random, I picked this paper for your consideration:
SNLS Spectroscopy: Testing for Evolution in Type Ia Supernovae

Quote:

Originally Posted by abstract

Aims: We present a quantitative study of a new data set of high redshift Type Ia supernovae spectra, observed at the Gemini telescopes during the first 34 months of the Supernova Legacy Survey. During this time 123 supernovae candidates were observed, of which 87 have been identified as SNe Ia at a median redshift of z=0.720. Spectra from the entire second year of the survey and part of the third year (59 total SNe candidates with 46 confirmed SNe Ia) are published here for the first time. The spectroscopic measurements made on this data set are used determine if these distant SNe comprise a population similar to those observed locally. Methods: Rest-frame equivalent width and ejection velocity measurements are made on four spectroscopic features. Corresponding measurements are presented for a set of 167 spectra from 24 low-z SNe Ia from the literature. Results: We show that there exists a sample at high redshift with properties similar to nearby SNe. No significant difference was found between the distributions of measurements at low and high redsift for three of the features. The fourth feature displays a possible difference that should be investigated further. Correlations between Type Ia SNe properties and host galaxy morphology were also found to be similar at low and high z, and within each host galaxy class we see no evidence for redshift-evolution in SN properties. A new correlation between SNe Ia peak magnitude and the equivalent width of SiII absorption is presented. We demonstrate that this correlation reduces the scatter in SNe Ia luminosity distances in a manner consistent with the lightcurve shape-luminosity corrections that are used for Type Ia SNe cosmology. Conclusions: We show that this new sample of SNLS SNe Ia has spectroscopic properties similar to nearby objects. (Abridged)

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[...]

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Strangely, the results are nearly always consistent, and the same: no matter what detected photons we use to create the rotation curve, we get the same rotation curve (and so the same estimated total mass as a function of radius) ... and the total mass inferred directly from the photons (HI, bright stars, PNe, CO, dust, ...) is always less (and, as a function of radius, the difference gets greater the further out you go) than that derived from the rotation curve (yes, singular; since the curve derived from each set of observations is the same, we can combine them into a single curve).

Yeah, I betya what's going on is that the magnetic field on the charges determines the rotation curve of the galaxy. The reason you can measure the rotation curve the same with all those methods is they're good methods and you're accurately measuring the rotation curve, the rotation curve is real and there's only one of them. You get the same estimated total mass because you're using the equation that says centripetal force is due to gravity. If you used the equation that supposed the magnetic field played a role you wouldn't be able to use the rotation curves to get an estimate for mass, as the magnetic field completely determines the radius at which the charge rotates, just like I wasn't able to get an estimate for mass with my calculation. The shape of the rotation curve is quite predictable. You have regimes of influence, where gravity has an influence at very small radii, and then the magnetic field controls at the larger ones. The HI in the outer-galaxy dust cloud goes through periodic ionization and recombination events. it gets ionized, the magnetic field drags the nucleon into it's appropriate orbit, a recombination event occurs and then the HI drifts out a bit. I bet that if you could look really, really closely at the orbits of the HI's, then you'd see they were like little sin waves.

I'm thinking that the conclusion that there's mass is the result of the nature of the inquiry, not the result of there actually being dark matter.

[...]

If you'd like to work on this and write it up, go ahead! Then we can ask questions about the ATM idea ...

However, don't forget that the H atoms which emit the observed 21 cm line do so only after, on average, some 10 million years, during which time they do not collide with anything; the O²⁺ ions should be affected twice as much by the underlying magnetic field (or is it only ~1/8th as much? what do you think?); and there must be an extraordinary conspiracy among stars (they need to have just the right combination of mass and charge - including synchronised exchanges, in binaries - that they will be affected by the magnetic field in exactly the same way the H atoms, O²⁺ ions, etc will!). More later on this (I expect).

(to be continued)

Nereid · #**182** (**permalink**) 24-June-2008, 07:00 PM

(continued)

Quote:

Originally Posted by rcglinsk

[...]

Quote:

Originally Posted by Nereid

Not sure I follow this ...

"9.07e23 Coulombs [...] That is the equivalent of 5.66e42 elementary charges." (from your earlier post)

"4pi times the conventional radius squared" (from the one I'm quoting)

That's ~6x1018 "elementary charges" per m2, isn't it?

Could you clarify please?

Yeah, I was very non-descript with the math. What I did was took that 5.66e42 elementary charges number, and I divided by the number of square meters you get from using the number for radius that google gives you for "radius of the sun." When you do that division the number is 9.something times ten to the twenty-third (9e23/m^2), which I then very crudely divided by avagadro's number, and said 9/6 is about 1.5, and the 10^23 nuber is the same, and vioala, 1.5 mols per square meter.

Quote:

Doesn't that depend on the current in the proton shell? At any rate, isn't the physics behind a dual layer that the magnetic forces are a whole lot larger than the electric ones?

I do not understand what you wrote here; could you clarify please?

Sure. I was saying that while a large population of ions could not exist at the surface of the sun ordinarily, that high concentrations of ions or electrons are found in double layers, you know, macroscopic plasma structure.

http://www.answers.com/topic/double-...cat=technology
(they just cut and paste the wikipedia page)

Quote:

OK, so when you've worked out the intermediate steps, I'll be interested to know what you think the difference in the force on a typical ion is, F"gravity" vs F"electric" (or F"magnetic", if you prefer).

I think that at the surface the important forces would be the electric and magnetic ones. The magnetic forces are what allow field alligned currents to flow. The concentration of ions is too high to not fly apart by coulomb repulsion, but because they're contained by magnetic forces they continue to flow and stay close together. The gravitational forces are probably negligible.

Quote:

In the meantime, suppose F"electric" (or F"magnetic") is 10 times F"gravity", and suppose our ion on the surface can travel 1000 km before colliding with anything. Suppose further that F"electric" (or F"magnetic") is radially out (from the Sun). What speed will the ion reach after it's travelled a distance of 1000 km?

Wow, I don't even know where to start. The ion on the surface will travel on some spiral path that is formed from the resultant of the gravitational, magnetic and electric forces. The gravity force is negligible and points toward the sun. The electric force is big and points directly away. The magnetic force is even bigger and forces the proton to move in a spiral on the surface because it constantly changes direction as the proton changes direction. All I remember about figuring out the overall linear distance traveled by something moving on a 1000km spiral is that it was really hard, moreover, if it stays on the surface of the sun then the electric potential didn't change much, so it's hard to say it really moved with an electric force very far. That's too smart a question for me, I don't know the answer or how to derive it.

Quote:

cglinsk, I may have created confusion by not being sufficiently clear ...

In my toy example of the charge on the Sun necessary to produce a force approx equal to that required to keep it in a circular (Keplerian) orbit around SgrA* due to the ISM magnetic field, I neglected to specify some key assumptions ...

* assume that the ISM magnetic field couples directly to the Sun (i.e. there is no heliosphere)

* assume that the Sun is (approximately) spherical

* assume that the Sun's shape and radius are stable.

There's a variant of this toy example: how does a Sun with a net charge and a heliosphere much like the one we observe it to have today couple with an ISM magnetic field (whatever its orientation, and strength anywhere between 0.1 to 10 nT)? Hidden in this question is how can the ISM magnetic field + Sun's net charge result in a force approx equal to that required to keep the Sun in its (approx) Keplerian orbit around SgrA*?

Gosh, I just feel like I don't have a clue here. I'm sorry. I don't know. I don't even really understand the question. You've exposed my level of knowledge, and it's just not this high...

I think my toy example was too unclear, so let me start again.

IF we have a 1 nT magnetic field, and a 1 sol mass, in a vacuum, what does the charge on the 1 sol mass need to be for it to 'feel' a force equal to that required for it to have a circular (Keplerian) orbit of period 200 million years around a point 8kpc distant?

You worked out an answer to that question ... then the toy lost its wheels.

The real Sun is surrounded by a heliosphere, which has a radius of ~70au - how can an ISM magnetic field (of any strength) couple with the Sun (no matter what its net charge is)? For your ATM idea (that stars can move in Keplerian orbits, giving spiral galaxy rotation curves, due to the interaction of ISM magnetic fields and net charges on those stars) to work, you need to address this question ... and not simply assume that the heliosphere is a vacuum.

Now if a sol mass object did have a net charge of ~5e23 Coulombs, and a radius of ~7e8 m, and if the charge were on its surface, and if that charge were in the form of electrons, or +1 (or -1) ions, then there'd be ~6e18 of them in every square metre. If we assume the Debye length on the surface of this object is >> 1nm, these charges will 'feel' the full electrostatic force, won't they? If so, what's to stop them being accelerated to near light speed in some trivial fraction of a second?

tusenfem · #**183** (**permalink**) 25-June-2008, 07:07 AM

Quote:

Originally Posted by Nereid

IF we have a 1 nT magnetic field, and a 1 sol mass, in a vacuum, what does the charge on the 1 sol mass need to be for it to 'feel' a force equal to that required for it to have a circular (Keplerian) orbit of period 200 million years around a point 8kpc distant?

You don't need a charge because the sun is so highly conducting that it would be frozen onto the intergalactic field.

Nereid · #**184** (**permalink**) 25-June-2008, 04:23 PM

(continued and concluded)

Quote:

Originally Posted by rcglinsk

[...]

Quote:

Originally Posted by Nereid

I think we've ruled out "magnetic lensing" and "electric (dipole) lensing" now, haven't we? If not, let's see you present a good case that these even exist in the relevant astrophysical regimes (galaxies, clusters of galaxies), and we'll take it from there.

If you can't make a case that any such exist, then isn't postulating them as hypothetical causes on a par with postulating magic pixie dust as a cause?

Yeah, magnetic or electric lensing as an alternative cause is right out. The little effects of QED are most likely not the culprit. I gotta say, you won this argument hands down. For me to go on saying they play a role would be no different from postulating magic pixie dust.

Quote:

Please show - using appropriate equations and input values - just how big an impact "a very weak electric field could make", in realistic astrophysical regimes. For avoidance of doubt, let's say >~ 1 kpc, and typical spiral or elliptical galaxy ISMs.

That is a bit more than a back-o-the-envelope calculation and I think I broke my crayon sharpener...

What about the current that flows between Earth and the sun that powers the auroras? Is that an example of how a weak electric field has an impact?

Whatever it is that "flows between Earth and the sun that powers the auroras", it certainly has no >~1 kpc scale!

For an astrophysically interesting example of a >~1 kpc phenomenon in which currents (quite strong ones!) may play a role, this very recent astroph preprint is good read: Formation of X-Ray Cavities by the Magnetically Dominated Jet-Lobe System in a Galaxy Cluster.

The challenge for a proponent of an ATM idea seems pretty big ...

Quote:

Why not extend the two questions I asked you at the end of my last post, to the environment of a rich cluster (of galaxies)? If you need input parameters (such as the estimated strength of the magnetic fields in the IGM, the error bars on such, and how these estimates were made), why not ask?

I'm sure you'd agree that "I can't think of any reason why the magnetic force doesn't fit the bill", in the absence of even an OOM (order of magnitude) estimate, is a rather underwhelming reason ...

Ok, I see. I thought you meant that whatever force I might suppose is responsible would be able to act on both the galaxies and the interstellar medium, in the most basic physical sense. That actually seems like it might be a fun problem to solve, but I'd need to dust off my excell instruction manual, diff eq. textbook and get ahold of data. Really though, probably excel is not the way to go. I'd want to write a program myself, especially given that whatever data I get is going to be in the form of a C++ data file right?

The combined enthusiasm, knowledge, expertise, etc, etc, of BAUT members is at your disposal ... you have only to start a new thread in the Q&A section (and there is no shortage of examples of just how helpful BAUT members can be, just look at some of the threads grav started, for example).

Quote:

[...]

Are you referring to the content of (at least part of) a new Q&A thread you started?

If this is an ATM idea that you wish to present (and defend), please say so ...

Oh yeah, that just keeps getting wierder. So the only data that is on the scale of cosmic redshift is the type Ia supernovae? Out of the billions of known galaxies we have an approximate measure to like 50 of them. And the measures don't agree on a single hubble constant. That's, I don't even know what it is. It's not proof though.

This came up in a subsequent post; I trust that you now realise just how limited your understanding of the (cosmological) distance ladder is (or rather, was), and have a better appreciation for how scary (to quote parejkoj, though Chris Hillman has said similar things)) the degree of consistency is ...

Oh, and let's make sure we close on just what we can ask of astronomy, astrophysics, cosmology, etc in terms of consistency, given our inability to travel much more a trivial distance from Earth, shall we?

Nereid · #**185** (**permalink**) 25-June-2008, 04:52 PM

(continued and concluded)

Quote:

Originally Posted by rcglinsk

[...]

Quote:

Originally Posted by Nereid

Amazing isn't it?

These effects, which are consistent with QM and GR (unless the authors made a subtle error, not all that unlikely as it's a very hairy part of physics), are unlikely to be seen in any lab bench experiment in our lifetimes ... but may be tested in the next decade or three by astronomers.

I hope you realize you've enlightened me in so many ways about so many aspects of astronomy I did not understand. There are many, many things about the universe that will only be observable on the astronomical scale, and I didn't know that before all this, and I thank you.

Quote:

Quote:
Originally Posted by from earlier in this post
Ha ha! And your going to get another [candid, unqualified admission of an error] in a second here.

AFAIK, you are now in the company of only one other BAUT member!

You know, you took all this time to have this discussion with me, it seems the least I could to to point out when you've made an especially effective argument that convinced me that I was wrong. You are here thanking me for owning up to it when really it is I who should thank you for dispelling an ignorant notion from my mind. I'll just say that you've been very classy this whole time and it's impressive.

Thank you.

If I may ask a question then?

I have some pretty good evidence that at least some ardent EU/PU/PC/EC/ES* adherents seem to have a rather different opinion (than "very classy"); would you care to speculate on why?

Quote:

* the distinction between the mass inferred to be the direct cause of the photons we detect ("stars", say), the mass inferred to be associated with those stars (but which we do not detect photons from, "brown dwarfs" in the same cluster for example), and non-baryonic dark matter. IOW, an inconsistent use of "v" and "d" (as in "Fv" and "Fd").

That is true. And to be honest with you, I've argued myself into a corner here. I don't think I can hold that current observations give accurate measures of "visible" mass for the reasons you've described. So much of what I wanted to call "visible" was infered in one way or another.

Perhaps better for the Q/A forum, but this might be easy to settle here. Is there any estimate of the mass of a galaxy that does not solve the following equation for capital M?:

[...]

Indeed, IMHO much more suited for the Q&A section ...

Quote:

Now, isn't this absurd: Nereid, since I think you may understand my point as well or better than I do, can I continue to argue the mass of a galaxy's, hmm, call them "baryonic" (that OK? like not-dark matter?) components has ever been accurately measured? If there's no method other than figuring the centripetal force is due to gravity then I don't think I can argue the magnetic field point and say that visible mass gravity is a known at the same time.

And you thought I didn't care about internal consistency

[...]

I think I mentioned something about a century or more of work was done to get good, robust bounds on estimates of mass, given photons; in fact, if you take a broad view of this, you could argue that we're discussing just about all of astronomy (beyond the solar system), from at least the time of Galileo! I trust that you now have at least a glimmer of why you'd have to embark on a research programme of the kind parejkoj kindly laid out for you in order to get to even the starting line (breadth and consistency comparable to where astrophysics is today), and why it may be more sensible to first pick just one little piece to build an ATM idea around ...

And that, I think, brings me to the end. If you do have an ATM idea you'd like to present, it may be best to do it in a new thread, as this one will close in just a few days' time. For the many, very good, questions you have raised, I look forward to reading the new Q&A section threads, and (perhaps) to trying to answer some of the questions therein ...

* Electric Universe/Plasma Universe/Plasma Cosmology/Electric Comet/Electric Sun

Nereid · #**186** (**permalink**) 30-June-2008, 04:49 PM

Quote:

Originally Posted by tusenfem

You don't need a charge because the sun is so highly conducting that it would be frozen onto the intergalactic field.

Thanks tusenfem.

I get easily confused about plasmas behaving cosmologically (or universally), and wasn't sure whether the magnetic field lines would be frozen-in, or whether Birkeland double layers of fractal dimension 2.2 would form, or whether (Punnet?) Z-pinches would begin to explode but would be stopped by magnetic reconnection in the Weibel instabilities that would start to grow out of the plasma jets responsible for the EDM on comet surfaces. Perhaps it's as well, then, that I didn't have salad for lunch today (though I did buy a nice chunk of Gloucester double in the cheese shop) ...

korjik · #**187** (**permalink**) 30-June-2008, 06:18 PM

Quote:

Originally Posted by Nereid

Thanks tusenfem.

I get easily confused about plasmas behaving cosmologically (or universally), and wasn't sure whether the magnetic field lines would be frozen-in, or whether Birkeland double layers of fractal dimension 2.2 would form, or whether (Punnet?) Z-pinches would begin to explode but would be stopped by magnetic reconnection in the Weibel instabilities that would start to grow out of the plasma jets responsible for the EDM on comet surfaces. Perhaps it's as well, then, that I didn't have salad for lunch today (though I did buy a nice chunk of Gloucester double in the cheese shop) ...

Ow. Just OW!

You nearly shorted out my brain before I got to the punch line.

tusenfem · #**188** (**permalink**) 01-July-2008, 07:58 AM

Quote:

Originally Posted by Nereid

Thanks tusenfem.

I get easily confused about plasmas behaving cosmologically (or universally), and wasn't sure whether the magnetic field lines would be frozen-in, or whether Birkeland double layers of fractal dimension 2.2 would form, or whether (Punnet?) Z-pinches would begin to explode but would be stopped by magnetic reconnection in the Weibel instabilities that would start to grow out of the plasma jets responsible for the EDM on comet surfaces. Perhaps it's as well, then, that I didn't have salad for lunch today (though I did buy a nice chunk of Gloucester double in the cheese shop) ...

hehehehehehe!!!!!!!!!!!!!!!!!!
I love you Neiried! You just made my day.

tusenfem · #**189** (**permalink**) 01-July-2008, 08:02 AM

On a more serious side. Another more likely procedure, if one wants to go EU is that there are "Birkeland currents" flowing along the magnetic field lines, connected to the star. The star is "loading" the field line, i.e. it is slowing it down, which the magnetic field does not like, and thus starts up a current system, which will flow in on one side and out on the other side, and through the start flows as a Pederson current (i.e. perpendicular to the magnetic field) and thus creates a jxB-force, which will accelerate the star. One can compare this with the currents flowing in the Io flux tube at Jupiter.

Whether this model is feasible is a whole other question.

DrRocket · #**190** (**permalink**) 01-July-2008, 06:58 PM

Quote:

Originally Posted by tusenfem

You don't need a charge because the sun is so highly conducting that it would be frozen onto the intergalactic field.

Have you had any further thoughts on the approximations used to justify dB/dt=0 ?

Nereid · #**191** (**permalink**) 01-July-2008, 09:43 PM

Quote:

Originally Posted by DrRocket

Have you had any further thoughts on the approximations used to justify dB/dt=0 ?

Sound like a great question for the Q&A section, don't you think?

(i.e. I'm not sure why this is an ATM idea ... but maybe I missed it, and you can tell me?)

tusenfem · #**192** (**permalink**) 02-July-2008, 06:53 AM

Quote:

Originally Posted by DrRocket

Have you had any further thoughts on the approximations used to justify dB/dt=0 ?

Hi DrRocket! Haven't you taken off yet! Man am I funny this morning.

As I have seen that you have taken up the task of debating Michael Mozino on space.com, I think that only therefore you deserve an answer from me. I will post is soon (hopefully today) probably in "general science".

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