Ask-a-Physicist (Electric Currents in Space?)

[MGmirkin]

Well, I think the old post got gobbled up in the last site outage?

I forget what exactly prompted me to write to the Ask-a-Physicist page, but here was my submission (more-or-less):

Okay, since you want to know, I'm 28 (almost 29), out of school (BA, 2001 from the University of Oregon). As a hobbyist I've been reading a lot of news releases lately about space, and have a slightly loaded question:

What role does electricity play in space? Does it play an organizing role, as some sources have suggested?

I will refer you to several items I believe are of interest to the discussion:

Firstly, from your own site:

http://helios.gsfc.nasa.gov/qa_gp_elm.html#maglines
http://helios.gsfc.nasa.gov/qa_gp_elm.html#magrev
http://helios.gsfc.nasa.gov/qa_gp_elm.html#stopmag

It appears that electric currents are the source of magnetic fields. Period.

If those are insufficient resources, I refer you to these others:

http://hyperphysics.phy-astr.gsu.edu/hb ... agfie.html
http://www-istp.gsfc.nasa.gov/Education/wmfield.html
http://www.who.int/peh-emf/about/WhatisEMF/en/
http://en.wikipedia.org/wiki/Electromagnetic_field

They appear to be unanimous in declaring that ONLY electric currents are responsible for magnetic fields, in accordance with Maxwell and Ampere (whether they be currents in wires, or electrons in lock-step around the nuclei of their "parent" atoms in permanent magnets, the positive charges being locked in place and the electrons free to move about; the curie point simply being where that lockstep breaks down and random chaotic motion of the atoms / electrons takes over).

Furthermore, it has been noted that magnetic fields can be used diagnostically in the lab for assessing electric currents, field strengths, etc.

http://en.wikipedia.org/wiki/Electric_c ... omagnetism
"Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.

Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices used for this include Hall effect sensors, current clamps, current transformers, and Rogowski coils."

This all then bears on my question about the universe. We know that the visible universe is 99.999% plasma, which is highly conductive. We also know that the raw electric force is orders of magnitude stronger than the gravitational force, where there are electrical goings on (currents, electric fields, etc.), and fall off more slowly with distance than the gravitational force at the same distances.

Several articles in particular that I'm interested in include:

http://www.astronomy.com/asy/default.aspx?c=a&id=4215
http://www.sciencedaily.com/releases/20 ... 221049.htm
http://www.sciencedaily.com/releases/19 ... 080925.htm
http://www.space.com/scienceastronomy/p ... 50301.html

It seems that astronomers are confused. They see magnetism everywhere, but rarely, if ever, have I seen mention of the electric currents (unambiguously noted above) that MUST be present to power them. Their world view apparently sees "hot gas" rather than plasma, and magnetic fields divorced from electric currents. Am I wrong in wondering whether many astronomers have failed to see what is plainly in front of them?

If magnetic fields are diagnostic for electric currents in the lab, why not in space? The laws of electricity and magnetism are suppsedly universal. Ergo, where we see magnetic fields in space (everywhere), must not we consider the possibility (nay probability bordering on certainty based upon definition) that electric currents are flowing there and doing the heavy lifting of organizing the structures seen thereabouts? (Other things that have been linked to "magnetic fields" include galaxy clusters; the THEMIS results RE: "magnetic flux tubes" carrying a 650,000 Amp current between the sun and Earth; the Double-Helix Nebula, etc. etc.)

I'd be interested in the opinion of Dr. Charles W. Smith, who authored several of the "Ask a Physicist" entries on the electricity / magnetism part of the site. He appears to "get it" about the relationship between the two.

Apologies if this e-mail was overly long... It's an interesting topic, and requires a few references to properly frame the question.

Regards,
~Michael Gmirkin

I just today received a response to my inquiry, and would be interested to know what people thought about it...

Dear Michael,

There is no doubt but that you "get it" and you understand what is being said about electricity and magnetism. All that is left is to find the root of your concern and address it.

First, a couple of things I think we all agree on:

1) Magnetic fields are due to currents. The currents can occur over vast scales, intermediate scales very easy for a human to grasp, or over very minute scales. Currents are just moving charge, and if there is a net motion of charge, there is a current.

2) Gravitational force seems to give structure to the universe and bind together what is bound on the largest of scales. There are several reasons why gravity dominates and not electric or magnetic fields. The first is that magnetic forces vary as the inverse of distance cubed, while the others vary as the inverse of distance squared, so magnetic forces are the shortest range of the three.
Another thing to consider is that electric forces can both attract and repel. A positive charge tends to become surrounded by negative charges. From a distance, they neutralize one another and no net charge is seen. In plasmas this is called Debye shielding, and over distances bigger than a surprisingly small distance (Debye length), one does not observe the buildup of charge. This tends to cancel electric forces at these distances.
Nothing neutralizes gravity. So gravity is left to have its way over the vast distances of space.

So, if magnetic fields exist in space where are the currents? There is more subtlety to this question than you may appreciate. The first point is that there are currents - there have to be currents to get magnetic fields. However, consider this: A current confined to a wire produces a magnetic field that fills the space around the wire. So we can measure magnetic fields everywhere, but the currents that produce them may be much more isolated.

Let's think about what creates a current. Two things cause currents to flow: separation of charge and electromotive force via Faraday’s Law. The latter can be used to create separation of charge, as when you charge a battery. Separation of charge in space can be accomplished, but it is difficult. Many of the currents that flow in space are the result of an electromotive force. When you consider that a conducting fluid such as a plasma will convect the magnetic field and carry it with the flow, it isn't hard to imagine that the magnetic field can be rapidly changing at any point in space and can become quite complex. So are the currents that support the fields.

In magnetospheric physics, there are two schools. One school attempts to understand the complex dynamics of the magnetosphere by specifying the currents and the other by way of the magnetic fields. If the currents are localized, we may not have spacecraft in the proper place to measure them. Since the magnetic fields fill space, it is more likely that we can study them, in an attempt to better understand the currents that produce them. Add to that the difficulties in measuring currents in space and you may begin to appreciate why so many people choose to address the magnetic fields and not the currents that produce them. However, the current approach has a strong following in magnetospheric physics.

You seem very well read, so let me recommend a book to you: Eugene Parker's "Conversations on Electric and Magnetic Fields in the Cosmos". It is very good and he tackles exactly the problem you pose. Gene is in many ways the father of modern space physics, and while he is now retired, he speaks and writes wonderfully. The book is excellent, but it is advanced.

I've offered you my prejudicial view of why people talk more about magnetic fields than the currents that produce them. One thing is true - you can't have one without the other. You need to decide which half of the pair will give you the information you need, and then decide how to get at it. It's a complicated subject, but you are headed in the right direction.

I hope that helps. Thanks for your question.

Charles W. Smith
for Cosmicopia

http://helios.gsfc.nasa.gov

He makes a few interesting notes. He does seem to get it. Though I might quibble with his note about plasma "dragging" magnetic fields along with it... Any other points to ponder or corrections to be made?

Regards,
~Michael Gmirkin

[redeye]

When you consider that a conducting fluid such as a plasma will convect the magnetic field and carry it with the flow,

This statement seems to be at odds with his admission that: electric currents/magnetic fields = cause/effect.
And I don't know why he has used "convect". Heat transfer plays no role as far as I'm aware.

It's an honest, and quite detailed answer though. I'm not criticising the guy.

Cheers!

[MGmirkin]

When you consider that a conducting fluid such as a plasma will convect the magnetic field and carry it with the flow,

This statement seems to be at odds with his admission that: electric currents/magnetic fields = cause/effect.
And I don't know why he has used "convect". Heat transfer plays no role as far as I'm aware.

It's an honest, and quite detailed answer though. I'm not criticising the guy.

Cheers!

Yes, that's what I was referring to with my snipe about "dragging" field lines around. Seems predicated on "frozen-in" field lines.

It's also at odds with his prior statements in response to other questions stating that magnetic fields can't be cut, and twiddled around but are resultant from currents (links in the original e-mail).

I'm thinking about sending him an e-mail with Alfven's paper about frozen in field lines... IE, plasma is not a permanent magnet and field lines aren't "frozen-in," currents are required to maintain the magnetic field. If current dies off, so too the magnetic field.

Regards,
~Michael Gmirkin

[MGmirkin]

Sent a slightly-lenthier-than-intended response to the gentleman. Will see if / how he responds.

I very much appreciate the reply to my inquiry. I hope that it's not improper to sidestep the Ask-a-Physicist interface & contact you directly, as I had a couple additional questions that your response raised.

I was under the impression that magnetic fields cannot be "dragged" along with plasma (the "frozen-in" field lines condition was argued against, I think strongly, by Hannes Alfvén; he also called "reconnection" a pseudoscience from the get-go), so I might quibble with the notion of of magnetic fields "convecting." As it sounds like one is saying that the magnetic fields are somehow "frozen-in" to the plasma as though it's a permanent magnet... I assume that what's actually going on is that the currents generating the magnetic fields change (direction, strength, etc.), and the magnetic fields simply dynamically reconfigure as a result of the changes to thedynamic currents.

(Double layers and circuits in astrophysics)
http://ntrs.nasa.gov/archive/nasa/casi. ... 013880.pdf

Though it seems this paper and various other iterations or spin-offs have not received the attention they should in the astro community, hence we're still in a mire of "frozen-in" field lines and "reconnection," where modeling / studying currents should be primary.

Also, it would seem that the fact that we see magnetic fields, thus there must be underlying currents belies the notion that there can't be charge separation in space. Wouldn't there have to be some kind of charge separation in order to get the flowing currents that must be present in order to sustain the observable magnetic fields we see?

It just seems to me that if we must admit that electric currents are the source of magnetic fields, we must also determine what causes the electric currents to flow. Would that not implicate that there is in fact a separation of charges, leading to a voltage potential and at some point to the motion of charges.

One observation (magnetic fields) with links to other processes (electric currents, etc.) cannot stand in vacuo, so to speak. Perhaps that's just my opinion. It just seems like there's a chain of logic that must apply in these situations. If magnetic fields -> then electric currents. If electric currents -> then charge separation (or some other process that gets the charges flowing)?

If electric currents must inevitably force us to the conclusion that charges have to be separate for the currents to flow, must this also force us to re-evaluate the idea that charges cannot be separated in space or that "instant neutralization" of charges must always occur? Just an open ended question, that.

Double layers apparently have the ability to screen off regions of differing characteristics from interacting: temperature, ionization potential, charge etc. Is it not possible that this ability could lead to or in some way mantain separation of charges, leading to some of the electrical effects we see? IE, if a double layer breaks down, exposing regions of differing charge.

You state that "it's difficult to get charges separated." This appears to presuppose that the Big Bang model is the only possibility for the genesis of things as they currently stand in astrophysics (I'd disagree, as some of the assumptions and predictions appear to be getting rather shaky these days, but that's another discussion for another day).

If one does not presuppose that the Big Bang is the only possibility, is it not possible that the charges BEGAN separated, and are slowly moving toward neutrality via the electrical processes that MUST be going on in order to generate the magnetic fields we've seen? Alfvén once said "gravitational systems" are the ashes of prior electrical systems. What with Marklund convection as a mechanism for sorting elements by ionization potential along current filaments, is it not possible that the "neutral" matter we see around us is merely the end product of electrical processes sorting and piling up neutralized matter into clumps along the filaments?

(Marklund convection)
http://www.plasma-universe.com/index.ph ... convection

Also, while I agree that magnetic fields extend further into space, more or less "occupying" a larger volume (potentially) than the currents, that still doesn't excuse us from understanding that currents are present and attempting to measure or model them. Just my opinion, of course. ;o)

I'd refer back to the notion that magnetic fields are diagnostic for currents, and that, as you say we should observe whatever is easiest to observe, BUT apply that observation gain knowledge about the CAUSATIVE event and not just the byproduct. IE, SEE the magnetic field, but track it back to the source current and TALK ABOUT what the current is doing, since the magnetic field seems to be dependent on the behavior of the current. Current goes up, magnetic field gets stronger / bigger. Current goes down, magnetic field drops off. Current paths change, magnetic topology changes as well.

Anyway, it's a great subject to investigate. I wish I had more formal training in the subject... But, I guess I've been able to pick up a surprising amount on my own. Still learning, of course!

Right now I seem to be interested in the chain of logic that goes into sussing out additional details and motivating processes. IE, magnetic fields track back to electric currents. The currents track back to separated charges or some other process causing charges to flow in a circuit (else charges would buildup, neutralize as you say, and current flow would stop).

Anyway, hope this e-mail wasn't too intrusive... I certainly enjoy the dialogue!

Regards,
~Michael Gmirkin

On a related note, is anyone familiar with this book by Eugene Parker?

(Conversations on Electric and Magnetic Fields in the Cosmos)
http://www.amazon.com/gp/product/0691128413/
http://press.princeton.edu/titles/8454.html

It's supposed to be relatively advanced topical info on electricity and magnetic fields in the cosmos. But I'm interested in this bit from the description:

The dynamics he describes represents the Maxwell stresses of the magnetic field working against the pressure and inertia of the bulk motion of ionized gases, characterized in terms of the magnetic field and gas velocity. Parker shows how this dynamic interaction cannot be fully expressed in terms of the electric current and electric field.

I'm wondering whether his assessment is accurate, or if it is faulty. IE, is it predicated on the notions of "reconnection" and the "frozen-in" field lines in plasma (which Alfvén said are both faulty)? Or does he make any more substantive claims as to why electric fields and electric currents are insufficient for figuring out how / why magnetic fields occur in space?

Regards,
~Michael Gmirkin

[MGmirkin]

Received a rather prompt response. Quite friendly:

Dear Michael,

You raise good questions.

I think the thing to do here is (1) I'm copying Beth with this
note and she can decide to include it or not, and (2) I need a
little time to formulate a good answer. So I'll be getting
back to you in a few days.

However, I am wondering why someone as well read as you and as
interested in the subject is not in school studying it further?
You seem to have a real interest.

Chuck Smith

and briefly responded in kind:

Well, I've considered it actually... Going back to school for a bit of electrical engineering, possibly plasma physics, possibly astronomy (possibly a few other things unrelated: computer sciences, programming, deeper database guru-ism, etc.).

Take your time! No rush.

We'll see what he gets back with in a few days. In any event, an enlightening conversation... Quite enjoying it!

I rather like talking to a peer rather than a gatekeeper. IE, someone willing to discuss based upon merits of an argument rather than banning you from a forum for holding an unpopular idea or asking uncomfortable questions.

I like to push the boundaries of our understanding and see whether it breaks or holds... Heh, I guess maybe I'm a scientific Beta-tester. I like seeing if I can legitimately break things to ferret out bugs in the system.

Regards,
~Michael Gmirkin

[redeye]

The problem can be summed up by the fact that you will probably end up studying magnetohydrodynamics, and not electrohydrodynamics...if you know what I mean.

Cheers!

[Grey Cloud]

Hi Michael,
Interesting thread and dialogue.
He wants to get you back into formal education to be re-programmed. Don't do it, before you know it you'll be wearing a white coat and muttering about gravity.
Who is 'Beth' that he is bringing in? A bit early to be callling for back-up?
One to watch.

[SciRPG]

Very interesting post, but I don't think it will get anywhere Michael until we can get solid proof that Electricity and Gravity are related.

I recall Donald's book explaining some experiments Birkeland did with the Terrella. If perhaps someone took that same setup and added a second "body" next to the simulated earth and measured the force of attraction between them, perhaps trying different bodies of different compositions...? Compare masses of different densities?
All we have is Peratt's computer simulations, which is great for us believers, but these guys need something closer to home and something tangible.

So, um... where do we find a Terrella? (starts picking up the phone book... Hmm... Walmart....)

[MGmirkin]

Who is 'Beth' that he is bringing in? A bit early to be calling for back-up?

Ohh, nothing so cloak-and-dagger... That's just the contact person for the Ask-A-Physicist program who had forwarded Dr. Smith's original response. I assume the intention was to keep the related questions together, should they wish to post the Q&A session?

Good times. Though the questions and answers may be too long for the typical AAP snippet they post. (Questions are usually just one or two lines, I think).

Regards,
~Michael Gmirkin

[Divinity]

Well, Michael, I'd say congratulations are in order for some fine writing and a very complimentary acknowledgement from one 'on-high'! Well done. (I'm with Grey Cloud; beware men in white coats and do not allow any mainstream evil influence on that beautiful brain, ).

[MGmirkin]

I've sent a couple more brief snippets to round out the question set:

A colleague and I were discussing something online, and he made a comment I thought might also be germane to the argument s discussed earlier:

With respect to the

"... argument about Debye shielding of the electric field in space plasma and separation of charge. It assumes electrical neutrality of space plasma. But the best we can say of space plasma is that it is generally quasi-neutral, except in double layers. In the solar wind the Debye length is 10 meters. So all you need is more than one extra charged particle in every sphere of radius 10 meters and you have the makings of a weak electric field in the plasma. In intergalactic space the radius grows to 10^5 meters."

The question may then come down to statistics. Are there in fact one or even a few extra charged particles in one sphere of interest with respect to a related sphere of interest? If so, can the charges be said to NOT be completely neutral (hence only quasi-neutral)? Again, if not completely neutral, can the net effect be an effective charge separation?

I'm not familiar with the statistics and the heavy maths of it all. But it seems to me that the evidence for magnetic fields -> electric current is also an anecdotal / indirect bit of evidence that there *is* in fact separated charge out there somewhere causing some portions of what we're seeing. The question perhaps then becomes, "if so, what have we fundamentally missed such that we have also made an erroneous assumption of charge neutrality? Double layers, some erroneous foundational assumption(s) or something else?"

Food for thought, if nothing else. Sorry to keep bugging you. ;o] Ya' probably have bigger fish to fry!

Sorry to be a bother, but there was one other discussion I thought to be germane to the question. It was with relation to the statement that the force of magnetic fields drops off with the inverse cube of the distance, compared to the square of the distance with gravity. My understanding was the the force of electricity / magnetism was actually stronger that he force of gravity under certain circumstances. Though I wasn't familiar with the entirety of the argument over why. So I asked around briefly. The answer was interesting.

Approximate quotes:
"[In] a spherical isolated body such as a 'lone' star, THOSE B-fields *do* drop off fairly rapidly with distance (inverse cube), but the B-fields produced by a strung out current *do not* drop off so quickly ([inverse] first power drop-off!)."

I was referred to this site in support of that interpretation:
http://www.netdenizen.com/emagnet/index.htm

(Dipole spherical geometry)
http://www.netdenizen.com/emagnet/offaxis/mmoffaxis.htm

(Long straight filament geometry)
http://www.netdenizen.com/emagnet/solen ... htFilament

-and-

"Any decent introductory college level physics text that discusses electromagnetism will have a discussion of this. First they discuss the magnetic field (B-field) produced by a differential (very short) length of current. Then they will do an integration over distance of that differential element. The result is that

B = (uI)/(2pi r).

So we say "The magnetic field strength varies inversely as the first power of the distance from the wire." ('inversely' meaning the 'r' is in the denominator).

See for example page 24 of
http://www.phy.uct.ac.za/courses/phy101 ... gField.pdf"

I don't have the mathematical training to understand some the formulae involved (though I think I sort of get it as I look at it), but the folks I was talking to seemed adamant that they showed the above notion to be true. Is the difference in geometry (linear vs spherical) as important as they've said it is? One would think that a force is a force is a force. But perhaps not if the geometry can affect the outcome that significantly?

In the case of the filaments of plasma strung out through the universe, a spherical geometry seems to be inaccurate to the morphology of the distribution of charged particles seen there. IE, they're long strung out "ropes" of plasma (currents most likely?). In that case the "long thin wire" approach seems the better approach. In that case the magnetic field drops off linearly with distance rather than with the square of the distance, as with gravity. If I've understood the argument correctly.

If it's true that a long straight filament of current has a force that drops off considerably less quickly than that of the equivalent gravity from the same materials in the same position, could it not be that the magnetic fields in that case play the dominant role and the driving electric currents are primary?

Again, thanks for the time and attention. It's nice to be able to communicate with someone who gets it and can maybe give some concrete answers. It's fun trying to unravel some of these little mysteries of the universe. Though it's almost seeming like this question should turn into a paper or dissertation (which is kind of tempting, actually), the way things are going. Hehe. ;o]

Again, sorry for taking up your time... I'll let ya' get back to work (or play, as the case may be).

I just hope I've not overwhelmed him with questions... I tried to keep 'em concise and apologized for taking up more than my fair share of his time.

Regards,
~Michael Gmirkin