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I have a simple question. I hope I don't get a stupid answer. Where does the magnetic field of a permanent magnet comes from AND why is it permanent (are we dealing with perpetual motion)?

This is what wiki is saying: "The spin of the electrons in atoms is the main source of ferromagnetism, although there is also a contribution from the orbital angular momentum of the electron about the nucleus. When these tiny magnetic dipoles are aligned in the same direction, their individual magnetic fields add together to create a measurable macroscopic field."

What the wiki is saying is correct, but we have to think further or go one step further... So put your head out of the box:

THIS IS NOT THE ANSWER I WANT TO HEAR. Because then I can ask why is the electron spinning (or what is the origin of spin) and that for an infinit time (CRAZY)? This is of course a physics question......We are missing an important energy source, unless you know where this form of energy is coming from and why it is permanent.

Thank you very much!

Edit:

Wikipedia says: "Truly isolated systems cannot exist in nature..." Just be aware of this, before you are answering. (So before you are answering or commenting ==>THINK!)

user1843090
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    a look through the wiki article on ferromagnets will enlighten you http://en.wikipedia.org/wiki/Ferromagnetism – anna v Feb 14 '13 at 18:46
  • No, wiki is not enough – user1843090 Feb 14 '13 at 18:56
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    If it is not enough, can you say what level is your academic background in physics? Conservation of angular momentum even classically ensures that no energy is needed for an isolated spinning object in space to keep spinning , like earth for example as @joshhysics states in his answer. – anna v Feb 14 '13 at 19:32
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    for "permanent" look at Curie temperature in the wiki article that is not enough. – anna v Feb 14 '13 at 19:38
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    Maybe you do not know what physics is. Physics is the data base of enormous number of observation of nature together with the mathematical forms that can describe and predict those observations in the simplest way possible. In the end there are some elementary building blocks deduced, the electron is one of them. Physics does not tell us "why the electron" it can tell us "given the electron and the physics laws then...." . That the electron has a spin and a dipole moment is a given experimental fact. – anna v Feb 14 '13 at 20:18
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    I don't like dogmas :) I can alway ask why! And also in physics, just because you don't know the answer doesn't mean I am not allowed to ask why? – user1843090 Feb 14 '13 at 20:23
  • You should maybe go to a metaphysics site to get an answer on why at the level of elementary particles – anna v Feb 14 '13 at 20:39
  • I don't need metaphysics because I or someone else will solve this issue in physics :) – user1843090 Feb 14 '13 at 20:45
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    @user1843090 I'm confused about what you question actually is given the discussion thus far. The issue has been solved in physics. If you accept that the electron has been demonstrated to possess an intrinsic magnetic moment, and if you understand that the quantum mechanical property spin is responsible for this moment, then perhaps you'd like to know how spin emerges from something more "fundamental" or some such thing? – joshphysics Feb 14 '13 at 21:25
  • "perhaps you'd like to know how spin emerges from something more fundamental?" yes, modern physics is not saying where this energy, which "produces" this "phenomenon" of spin, comes from – user1843090 Feb 14 '13 at 23:11
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    To be very frank a poster unwilling to accept the observed truth as an answer to a physics question suggests that the question is not in fact one in the field of physics. You are welcome to believe anything you want, of course, but your beliefs are not going to help you to make correct prediction about the way the universe works, which is after all the business of science. – dmckee --- ex-moderator kitten Feb 15 '13 at 02:03
  • @user1843090 Now I don't agree with the people saying "where does the electron spin come from" isn't physics (for shame!), still, if modern physics doesn't answer the question, I don't understand what you expect from this website exactly? Maybe come back in a hundred years :-) – Retarded Potential Feb 15 '13 at 17:44
  • @RetardedPotential Thank you very much, your comment means a lot to me... – user1843090 Feb 15 '13 at 17:52

3 Answers3

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You write

Because then I can ask why is the electron spinning and that for an infinit time (CRAZY)?

You have a misunderstanding about the nature of spin. When we say that an electron has spin, we do not mean that it is literally spinning; spin is a quantum mechanical property of the electron.

See another related physics.SE question How do you fit a dipole in an electron?

As a side note (that is frankly not particularly relevant to ferromagnetism), in the context of classical mechanics, if you were to put a rigid, spinning object into space (where it is isolated from interactions with any other body) then the object would continue spinning without any "energy source." This can be justified by noting that angular momentum for a classical mechanical system is conserved in the absence of external torques.

Community
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joshphysics
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  • You say "where it is isolated from interactions with any other body" there is no such system :) No isolated systems exists in nature.............And I don't have a misunderstanding of spin, I am aware that spin is quantum mechanical property of the electron, but that does not change my question. – user1843090 Feb 14 '13 at 19:33
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    @user1843090 the earth needs no energy to keep on spinning – anna v Feb 14 '13 at 19:34
  • @anna: so then it is voodoo^^ Don't tell me about frictionless environment...the magma , oil and whatever is inside the earth produces friction enough, for at least getting slower – user1843090 Feb 14 '13 at 19:38
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    It is not voodoo except if you think that physics is voodoo. it is conservation laws coming out of the laws of mechanics as formed mathematically , and is due to Noether's theorem.http://en.wikipedia.org/wiki/Noether%27s_theorem – anna v Feb 14 '13 at 19:40
  • Conservation law say, if you have friction, which the earth has, then it mus slow down!..........Of course in general the math will be wrong if your physical understanding is wrong – user1843090 Feb 14 '13 at 19:42
  • friction is an extra interaction. All interactions might change the angular momentum by taking some away or adding some.even so the earth spins for a very long time, and a rigid body in space would spin for even much longer before the tiny interactions with the density in space would affect it. – anna v Feb 14 '13 at 20:11
  • highly speculative thoughts of yours.............I don't know how much you now about the earth, but the earth is definitely NOT a rigid body :) – user1843090 Feb 14 '13 at 20:17
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    @user1843090 Your concern was shared by physicists when they were trying to figure out the atom. Classical physics can't account for an electron in an orbit that doesn't radiate away its momentum the way a planet does (if I'm not mistaken). The reason it's possible for the electron to be in a stable orbit is "because" of its quantum character. Because the electron can only exist in fixed orbits about the nucleus, it can't radiate away infinitesimally tiny amounts of energy, so it can't radiate away energy except in discrete jumps. I personally don't know why there is a lowest orbit, though. – amr Feb 14 '13 at 20:41
  • @ amr lowest orbit is because of the Heisenberg uncertainty principle. – Árpád Szendrei Jul 13 '18 at 16:36
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The electron is spinning for an infinite time. Yup, it's crazy. Quantum theory does allow for persistent currents, not just electron spin.

In fact you can see this sort of quantum perpetual motion in action at everyday scales with superconductivity and superfluidity. A current flowing in a loop of superconducting wire persists indefinitely without a power source.

This is perpetual motion of what Wikipedia calls the "third kind", elimination of dissipative forces. It cannot be used as an energy source or to reduce entropy (first and second kind). So we are not "missing an important energy source" in that sense.

[Added:] I'll build on amr's comment to a different answer, which makes a relevant observation: you can say the same thing about the electron orbiting the nucleus. Its orbit should decay via electromagnetic radiation and it should spiral into the nucleus. But this is not what happens! Atoms are stable!

This is one of the very facts that lead to quantum theory in the first place. This isn't the place to give an introductory course to quantum theory (and I am not the person to do it), but it was proposed that some things can change only in discrete steps (quanta), not continuously, and the electron's angular momentum is one of them. And this proposal explains many many things that non-quantum explanations don't.

Retarded Potential
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  • No, I was not the one who downvotes! I appreciate every constructive answer. And i am not able to vote, because I created a new account. – user1843090 Feb 14 '13 at 20:54
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    clearly the Physics Establishment is trying to silence you, user1843090. in 100 years, textbooks will describe the battle that you, user1843090, faced against the entrenched ideologies of our current times. "many fought against the revolution brought on by user1843090, but ultimately for naught, for the vibrance of the ideas themselves cleaved a winding but successful path through the darkness of stubborn physicists." – amr Feb 14 '13 at 21:01
  • @user1843090 oh, my mistake! sorry. – Retarded Potential Feb 14 '13 at 21:06
  • thank you to both of you guys, appreciate your comments.... – user1843090 Feb 14 '13 at 21:17
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I'm commenting here until someone more knowledgeable comes along. This is my understanding:

Say you have two bars both made of the same exact material, except that one of the bars is a permanent magnet. If you add up the collective "magnetic power" of both materials, you will get the same result. Both materials are equally "magnetic."

The difference is that the permanent magnet has its atoms/molecules aligned in the same direction throughout the material (more accurately, its atoms/molecules are aligned in such a way that its magnetic field lines are aligned throughout the material), and this has a cumulative effect which creates a larger-scale field. On the other hand, in the non-magnet the tiny-scale magnetic fields are all pointing in random directions, so they conflict with each other and you don't get a large field. The same magnetic potential is still there, but they are too random to create a larger-scale effect.

The reason a permanent magnet has its individual magnetic fields aligned probably has to do with the particular manner in which the material cooled as it was released from the Earth. Imagine a molten material made of countless tiny magnets. Remember that magnets want to align with eachother (opposites attract, likes repel), and because the material is molten, the molecules are free to adjust into alignment as the material cools, provided that the atomic structure allows it.

That's probably what that wikipedia article calls "symmetry breaking," and it is not a clean process -- most likely there is cellular-automaton-like warfare between competing orientations before the overall material cools to one orientation. If the material cools too quickly, you won't have a large-scale magnetic field.

As a general note, there is a lot of variation and interesting behavior due to the rate at which various materials cool. For example, the different rates of cooling are partly responsible for why carbon may look like a charred husk in one case and a pristine diamond in another.

If your question is "where does magnetism come from?" then that's a different question. I think the shortest answer is probably "light."

You sound dissapointed that there are no relatable answers. You'll find that a lot of physics is strange and that in the boundaries of our knowledge we necessarily have phenomenological answers, not explicative ones.

amr
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    yes my qestion is where magnetism comes from. you say light? hmm...light sounds cool but I don't think so, because light needs energy to radiate....but thank you for your answer. I think physics is only strange if we don't have good explainations. Maybe I can ask my question in hundred years and I bet I get a much more appropiate answer. – user1843090 Feb 14 '13 at 20:39