Dr. Stern,

    Upon looking at many web sites regarding geomagnetism, I wish to inquire of you about the following
   

1. Does the earth radiate energy because of its magnetic field? In any manner, similar to or dissimilar from pulsars, does the rotating non-axisymmetric field produce any radiating energy? Assuming it does, what rate of production (power output) exists or has existed in the past?

    2. Does magnetic pole reversal dissipate internal energy from the earth? Does the reversal represent a reduction from a high-energy state (wound up magnetic field lines as in the sun), to a lower-energy state (relaxed in some way)? What amount of energy release accompanies such a change? What form does it take (radiation, temperature increase at depth, something else)?

    I am interested in earth's energy budget through geologic time, and the major components of it--additions and subtractions.

REPLY

Dear Mark

    Any loss of the Earth's rotational energy to electromagnetic radiation (as a rotating asymmetric dipole) is probably completely negligible. If I recall right, the radiated energy of a Hertzian oscillator goes like the 4th power of the frequency, which comes to a very small amount, because the Earth rotates so slowly. Furthermore, the dipole is shielded from infinity by electric currents on the magnetopause. I would think that other effects associated with the rotating magnetic field may be more important (but still negligible).

    The energy balance of magnetic pole reversal is complicated, and we don't really have all its factors yet. It is not that the Earth has a primordial magnetic field which is gradually being dissipated--in which case one could indeed ask whether the dissipation is affected by reversals. Rather, that field is constantly being regenerated by the dynamo mechanism, driven by convection due to various types of heat release. We are yet uncertain what heat sources contribute--the two main suspects are heating by radioactive elements (although most such elements seem to be in the crust, not the core) and by solidification of molten iron onto the surface of the inner core--but the magnitudes of these processes are uncertain.

Greetings and thanks for such an informative and enjoyable website. My adventure in the study of 'electric and magnetic energy' has just begun. In my studies I have come across some of the writings of Nikola Tesla and have become intrigued. Tesla seemed to have been able to "tap" into one or more of the levels of the earth's magnetoshpere through several different methods. At this time, I am interested in one of his methods (see copies of Tesla's patents at http://project-ufo.com/tesla/database_tesla.htm). Also, in his other research he was able to produce and maintain "Ball lightning (spherical plasmoids, foudre spherique,or kugelblitz)."

    My questions are these:

1. What is the radiant energy that Tesla was utilizing?
2. What is ball lightning?

    "A fluorescent tube glows when an electrical voltage is set up across it. The electric field set up inside the tube excites atoms of mercury gas, making them emit ultraviolet light. This invisible light strikes the phosphor coating on the glass tube, making it glow. Because power lines are typically 400,000 volts, and Earth is at an electrical potential voltage of zero volts, pylons create electric fields between the cables they carry and the ground.

Dear Don

    I am afraid I cannot help you much. Tesla's language is not transparent, but after reading his patent, my guess is that he wrote about some photo-electric effect, a novelty in 1901. Consider a satellite in sunlight: the sun's rays eject electrons from its atoms, and cause it to accumulate some positive electric charge. The charge is small, however, because the electrons are ejected with an energy of only a few electron volts. So, once the charging brings the satellite up to (say) 10 volts, no more electrons will leave, they will all be repelled back to the metal skin of the satellite. If somehow one of the floating electron hits the skin and is re-absorbed, another "photoelectron" can take its place, but the total charge stays the same.

    Maybe something similar happened in Tesla's apparatus, and if a capacitor is connected ("condenser") it can accumulate charge and slow down the rise of voltage. The amount of energy is however negligible.

    Similarly, I suspect the amount of power extracted by the fluorescent tubes of Richard Box is small. I remember how in my army service, our barracks had electricity leak into the cinderblock (from private lines soldiers rigged up, using poorly insulated phone wire). Before an officer found out and stopped the practice, you could stick a neon lamp onto the wall (one of those the little circuit-tester lights), hold the other end between two fingers, and it would light up: the voltage was enough for that, but the current was too small to feel. There does exist an electric field near power lines, but air is still a good insulator and allows very little leakage (though the AC field may also excite atoms inside the lamps).

    In short, there's no secret source of energy.

    About ball lightning a lot gets written, but no testable evidence exists. "Plasmoids" of glowing plasma can exist in very rarefied gas, for small fractions of a second. In air of atmospheric pressure, though, they would get almost instantly dissipated, as ions and electrons collide and recombine.

Can electricity be generated from Earth's magnetic field?

    I have heard that this could be done, but would like to hear your understanding about it.

REPLY

Dear Tim

    Yes, it can be done, but the answer probably isn't the one you want. We can get electricity from the magnetic field, but we need invest energy equal to what we get out, or a little more to take care or electric resistance and friction.

    Specifically, you can whirl around a "search coil" in the Earth's magnetic field, and extract an induced current due to its motion in a magnetic field. It's a bit like the way an electric generator creates a current from a coil rotating between its pole pieces. Some spinning satellites and space probes have used search coils to observe the ambient magnetic field, or at least its two components perpendicular to the spin axis.

I have a question about decrease of strength of magnet with respect of time.

    There are three magnets.

(1) First magnet's poles are kept in direction of East and West,
(2) second magnet's poles are kept in direction of North and South poles, and
(3) third magnet's poles are kept opposite to second position.

All three magnets are kept in only Earth's magnetic field. My question: among these three which magnet loses maximum strength after a period of long time?

REPLY

    I am no expert, but as far as I know, under usual circumstances magnets stay magnetized, with no change. After all, lodestones--natural magnets--may be many thousands of years old yet remain strongly magnetic. The spreading basalts of the ocean floor have kept their magnetization (a weak one, true) for millions of years. So I don't expect ordinary steel magnets to grow weaker, although in some substances weakening might perhaps occur.

    Heating a magnet above a certain temperature ("Curie Point") will cause it to lose magnetization. Exposure to rapidly alternating magnetic field can erase magnetism, and I think (not completely sure) that intense vibration can also do so. Under ordinary circumstances, however, none of your three magnets is expected to change.

Is it possible to impart magnetic character to a piece of glass from a radio wave? The thought is similar to rubbing a piece of glass with wool to place a charge on it. Could a radio wave make a thin, hanging piece of glass magnetic?

REPLY

Dear Chris

    I am sorry to disappoint you, but sources of electric and magnetic fields are quite different.

    Glass can indeed be electrified by rubbing. I remember as teaching assistant (while in graduate school) I would tell a student that I can erase the picture on the screen of an oscilloscope (which actually had a transparent plastic cover) by rubbing it with a cloth. "No, you cannot!" the student would protest, "you are rubbing on the outside while the picture on the screen is traced by a beam of electrons inside!" But I would pull out a clean handkerchief and wipe off the picture. Of course, it was the electric charge on the plastic cover that did it, by repelling the electrons and diverting them to the sides of the tube. After a while, as the charge leaked away, the picture would creep back

    Magnetism on the other hand needs electric CURRENTS, steady flows of electric charges, or at the very least ordered atomic magnets (especially electrons, which are miniature magnets by virtue of their "spin"). I know no way of providing either in glass.

My name is Catrina. I am currently in a geology class and we have recently studied Earth's magnetic field. I have been trying to find out why, if you break a magnet in half, one fragment will reverse polarity. A second part to this question is why do nails become magnetized when placed on a magnet and does this weaken the magnet's magnetism? :)

Also, could Earth's magnetic liquid core slowly magnetize the solid inner core over a long period of time until a point when the outer core, because of it's liquidity, becomes unattached and reverses polarity?

    Second: Could the fact that, as much new crust is being formed, it has magnetic makeup that forms in agreement with the current polarity, contribute an additional source of magnetism? As more crust is created with concurrent polarity to the liquid outer core, the crust as a whole is slowly being magnetized toward that direction because new crust will not form in a polarity opposing Earth's current polarity; and although some rock is eroded, warped and moved; the majority is stable and relatively still. Could it be possible that this continues until the majority of Earth's crust is polarized in agreement with the liquid core to a point when the liquid core flips polarity?

REPLY

Dear Catrina

    Like most correspondents, you did not say which of my web pages you have read (clearly, you got my address from one of them). If you have not done so yet, please read all parts of "The Great Magnet, the Earth," where many of your concerns are addressed.

    Very briefly now:

    (1) Breaking a bar magnet in two does NOT produce reverse polarity: If (say) the original magnet had the N pole on the left and the S pole on the right, each of its pieces, after the break, will also have N on the left and S on the right.

    (2) Nails do not weaken a magnet, but they channel magnetic field lines, concentrating them in the iron and spreading them apart (which makes the field weaker) in the space not occupied by iron.

    (3) The Earth's core is much too hot to be permanently magnetized. I am not sure how hot--more than 3000 deg C I think--but permanent magnetism disappears around 500 deg. or lower, depending on the material.

    Hi, your web site is really awesome, but it doesn't answer the one question that sent me looking for info on the web in the first place. From everything I have ever heard, the only magnetic field that can induce a current is a fluctuating one. Per my understanding a static magnetic field does NOT cause electrons to flow, only a varying one. The magnetic field of the earth doesn't fluctuate around, so how is that the charged particles started circling around the lines of force. And why would they spiral in towards the N/S magnetic poles? I thought that the current is supposed to run strictly at right angles to the magnetic field??

Thanks for your help.

REPLY

Dear Diane

    As the poet wrote, "a little knowledge is a dangerous thing." There is so much involved in magnetism, in current and trapped particles, that a short message here won't do it justice! My advice is look up my web sites on the magnetosphere and the Earth's field, and take your time.

    Still, some quick answers:

I am a seventh grade student in Denver, Colorado. I am currently working on a science fair project. My project is about what materials make good magnetic insulators. I would greatly appreciate any information you could send me on this topic.

REPLY

    There exist magnetic shields, but they are not made of "magnetic insulators." On the contrary, they are excellent "conductors" of magnetic field, and their role is to divert the magnetic field--instead of continuing straight to whatever is being shielded, the field lines are grabbed by the shield and flow through it, around the shielded object.

    I do not know the situation nowadays, but it used to be that TV video tubes and cathode ray tubes in oscilloscopes had magnetic shields wrapped around their necks. Both these use a beam of electrons to "paint" a picture on a glowing screen, and the shield was meant to stop any existing magnetic fields from interfering with the beam. High magnetic permeability (denoted by the Greek letter mu) helps here, so one alloy used is called "mumetal."

    I am trying to discover a way of inserting magnets into pottery. I understand however that when heat is applied to magnets they lose their properties. I would like to use magnetic filings rather than a lump of metal. Is there any possible way of magnetising the filings perhaps after they have been kilned in the clay?

REPLY

    The question your are asking goes well beyond my area of expertise, but perhaps I can guide you to a better resource.

    Yes, permanent magnets indeed lose their magnetism past a "Curie temperature" which can be somewhere between 250 and 600 deg. C, depending on the substance. See:
            http://www.geo.umn.edu/orgs/irm/hg2m/hg2m_b/hg2m_b.html
In principle, you might be able to bake pieces of iron into pottery and then magnetize them, although they do have very different coefficients of expansion.

    Instead I would encourage you to look into pottery materials which are naturally magnetic. I don't know how magnetic you want your pottery to be (or your reasons for making it magnetic) but many ceramic materials are naturally magnetic. Some of the strongest magnets made commercially are ceramic--although, admittedly, they have very special compositions.

    But even ordinary ceramic materials exhibit some magnetism: I have read, for instance, where brick buildings were found useless for magnetic observatories, because their bricks were too strongly magnetic, having absorbed the Earth's magnetic field when they cooled down from being fired.

    Meanwhile, if you have a local university with a geophysics department or with a physics department where some members specialize in solid state physics, you might ask there.

    Even if your pottery material can hold permanent magnetism, you still need to magnetize it. You might ask at the university--perhaps they have instruments for magnetizing materials, and that would be the safest way. You may or may not create a sufficient magnetizing field by wrapping around your sample a thick insulated electric wire (e.g. house wiring, no. 14 gauge) and touching its ends briefly to a car battery. It's a short circuit and sparks of hot metal may fly because of the heat (also, it's bad for the battery) so the touch should be VERY brief, with appropriate precautions. Also wear glasses and leather gloves. Even then, the field may or may not be strong enough to magnetize--get some engineering help on this, someone who can calculate the field ahead of time (and you can also experiment first with a small sample).

    Suppose you put a big sheet of thick soft iron (of the appropriate kind) next to a magnet. The magnetic field on the other side will be very weak, but there will exist a strong force between the magnet and the shield itself.

    I suspect there will also be strong forces with a sheet of soft iron between two magnets. Sorry.

  Shielding magnetic fields--(B)

    At the temperature of liquid helium, 4 degrees above absolute zero--and in some more recent materials, up to tens of degrees above that--certain materials become ideal conductors of electricity. They have no resistance, and if you induce an electric current in a ring of such material and check it hours later, the current is still flowing. It is a quantum phenomenon, and has been applied where large currents are needed to create strong magnetic fields--in large particle accelerators, magnetic levitation trains and in medicine, in some magnetic resonance imaging (MRI).

    An ideal conductor makes sure the voltage on it is everywhere the same (like, zero). If the voltage is the same, any wave, which involves an oscillating voltage, cannot work its way through it That's why metals block light, and if polished, can reflect it back.

    You can try the following experiment: take a small portable battery-operated radio--with no antenna, or with a short one--and tune it on to some station, so that the sound is loud and clear. Then take aluminum foil, the kind used in the kitchen, and wrap everything in it, including antenna. The sound should stop, because the radio signal cannot get through the conducting aluminum. Then unwrap it and you will get the sound back.

    The real question you should ask is--why is clean salt water a conductor of electricity, but transparent. Or, why is a chinaware dish (as is used for food) an insulator but not transparent?

A question on radioactive heating of the earth's core - you mention potassium and U238.

I was a tour pilot to Kilauea and Mauna Loa back in the early 80s and came VERY close to the lava fountains and flows. I recall no mention of danger from radioactivity, so am wondering if radioactivity is only occurring at depths way below that of issuing magma.

Can you please clarify

REPLY

    The energy release is actually very diffuse: the problem is that it is difficult for the heat to escape. Look at it this way. If you are standing on a square foot of ground, imagine a wedge-shaped chunk of the Earth below you, going all the way to the center of the Earth. Assuming a spherical symmetry of materials in the Earth, all the heat generated by radioactivity in that wedge has no other place to escape except that square foot you are standing on! Therefore, even if the rate at which heat is generated (per unit volume) is very, very small (as it is), an appreciable heat flow may be necessary to get rid of it.

    Two corrections may be added here. One, most of the heat is generated in the upper 100 miles of the Earth, in the crust. And two, while this heat flow can be observed by specially designed heat probes almost anywhere on Earth (it is greater in volcanically active regions, where hot springs also exist), there also exist "hot spots" where the heat flow is much larger than average, and comes from greater depth.

    I am from traditional Hindu family in Nepal where there is a tradition/superstition (whatever, I am poor in English!) that one should not sleep, mostly at night, having his/her body aligned north-south with head to the north. Generally, sleeping with head towards northward is thought to cause bad dreams and/or luck. Is there any relation of body parts with the geo-magnetism that might have such effects?

REPLY

I am sorry, but I cannot find any scientific phenomenon which will support the belief you describe. My guess is that it came from China, from the ancient beliefs of "geomancy" whose practitioners used a magnetic compass to determine "lucky" or "good" directions. You will find more on the web site

        http://witcombe.sbc.edu/earthmysteries/EMGeomancy.html

The human body seems unable to sense magnetic forces: to do so it needs to contain either magnetic materials or large electric currents, and we have no evidence for either (certain animals, such as homing pigeons, may have organs sensitive to the field, but not people).

    All of the information I have found reports the weakening of the dipole and a possible reversal date of about 1300 yrs in the future. My questions are:

1) The information on the web sites seems to date from 1993, 1995, and possibly 2001. Is there any current, ongoing research on this subject? Are there any new findings in the last 5 to 10 yrs?

2) Does the weakening of the dipole appear linear, or is the rate changing?

3) The reversal, when it happens, is expected to take 1000 yrs or more. How will we know when it is happening? What indicators would we look for? Could we now be in the early stages of a reversal?

I'm still reading from link to link through your site.

REPLY

    You ended your message with ".. I'm still reading from link to link through your site." The "questions and answers" collection contains many questions about reversals (there were more, but not all are included), and you might find them interesting, too.

    If your patience holds out, look up the review "A Millennium of Geomagnetism" on my web site, which tells more about dynamos and reversals. One article cited there is about the work by Coe, Glatzmeier et al. (1999), who actually simulated reversals on a computer..

To answer your questions:

1. The variation of the Earth's magnetic field is slow, so little changes over one decade. The main advances are in paleomagnetism--tracing of fossil magnetism from congealed lavas (and some deposits)--and in theory. Coe's report suggests a new approach using computer simulations, but please realize, they are currently are just similar to the Earth's, the actual range of parameters for the Earth is different, and to use them would take more computing power than we now have.

   (LI> From 1840 to 1970 the weakening rate seemed to be 5% per century, but after that it might have speeded up to 7%. The transition ("geomagnetic jerk") was rather abrupt, apparently taking just a few years.

2. As far as I know, the decline of the dipole field is balanced by the growth of other modes of the Earth's central field, with the total magnetic energy changing little. (However, the field we observe on the surface weakens, because other modes decline faster with distance from the Earth's core.)

    Such balance is not essential. Rather little energy is lost to resistive heating, but some could be absorbed by being converted into kinetic energy, by speeding up some flows. However, if it holds, when the main dipole field "goes to zero" the Earth's field does not vanish, it just gets complex--you may have for a while 4, 6 or more magnetic poles, and a somewhat weaker field.

    The present trend, reaching zero in perhaps 1300 years, but it may change. Studies of magnetism in ancient lavas, and also the simulations, show that "excursions" happen where the magnetic field declines and then rises again; I am not sure how fast these events are.

Love this site! Really interesting reading. Hope to hear from you soon!

REPLY

    Depends on what you mean by "levitation." Strong magnets are hung from cranes in scrap-yards and are used to lift scrap iron from pile to pile, or from a pile to a waiting truck, but I do not think that's what you had in mind, Very strong magnets also keep experimental "maglev" trains hovering a tiny distance above a special tack--they exist in Japan and Shanghai, I believe one is in Germany, too.

    My question is,.... well, I know the earth's magnetic field blocks high energy radiation/protons from the sun, but why does it not block all radiation ie: visible light, UV light, infrared? also, does the ability to block different wavelengths/energy levels depend on the strength of the field?

REPLY

    The reason, of course, is that the two are quite different. The bullets are chunks of matter, and to let them through, the matter of the armor has to give way, something it strenuously resists. The sound is a wave: the bullets make the armor oscillate and propagate the wave through it, without breaking its integrity.

    Similarly with particles and radiation from the Sun (or from any source outside Earth): they are completely different. Particles carry an electric charge, and a moving electric charge is in somewhat equivalent to an electric current. Electric currents react to magnetic forces--in fact, magnetism may be viewed as interactions between electric currents--so it's no wonder charged particles get deflected, sometimes even trapped.

    What IS important is that the Earth's core is metal, because metals conduct electricity. Also, that the metal is molten, and therefore can flow. Something indeed causes it to flow--some source of energy, still debated, creates heat which flows outwards, to the mantle and ultimately away from Earth. It is THIS flow, which interacts in a complicated way (similar to what was modeled by some computers) and creates the magnetism as a by-product.

    Because flows can vary, this also explains why the magnetic field of Earth is slowly changing (the main north-south "bar magnet" is weakening by 5-7% per century), and has in the past even reversed.

    Are there any courses or universities that offer a curriculum that might be preferred? Is it possible, after taking some basic courses, to work with scientists already studying the field?

REPLY

In other words: a tough field for making a living.

    I gather that you are about to choose your university education. Areas related to the Earth's magnetism can be of interest--and if you are really interested, you may look for summer jobs in them--but in general, you start with broad studies and specialize only gradually. Studying computer applications, applied math, electronics and physics is a reasonable start, and choosing a university with a strong program is important (also, can be expensive), as are good textbooks.

    Once you are enrolled, see that you get good grades and a good grasp on the subject. Keep notes--they help you understand (you will not write down what you don't understand, but try to make sense of it first). And ask for advice--from teachers, colleagues, professionals.

    We were watching the Apocalyptic drama "The Core" in science today. In case you haven't seen it, it's about the Earth's outer core stopping. As a result, all electronics stop working, there are giant electric storms as the magnetic field cuts out, and when the field is gone, the earth is fried. So some scientists drill to the core of the Earth to start a huge explosion to get the outer core moving again.

    I was wondering: is any of this possible? Could the outer core stop moving, and if it did, would all our electronic devices shut down? Why? Would there be so many violent static superstorms? And would the earth be completely fried by the solar winds if its magnetic field disappears?

REPLY

    The Earth's magnetism appears to be due to the slow flow of billions of tons of molten iron in its core, and you cannot change such flows abruptly. Currently the main north-south field is decreasing at 5-7% per century, and even this does not seem to be a real loss of magnetic energy, just a shift of patterns--as the north-south field gets weaker, the less regular parts of the field are growing stronger, the energy is almost unchanged. Magnetic records in ancient lavas, etc., suggest that this rate is typical,

That is a very difficult thing to explain at 6th grade level!