# antimatter and magnetism

Suppose I had a piece of iron made of anti-matter. Would it be attracted by a magnet made of regular iron? Could I magnetize my anti-matter iron? Would it then have poles, one of which would point north?

I know that no one can whip out a piece of anti-iron and check this out. But does anyone have an educated guess?

My educated guess is no, it would be repelled. The anti-matter magnet would be made of positron and and anti-protons, so it would have a reversed polarity. I may be getting a little “Doctor Who” here, but that’s my guess.

Anti-iron would behave exactly like iron, magnetically speaking (except possibly that the relationship between positronic orbital angular momentum and magnetic moment of the iron atom would be reversed–I need to go check my old solid state book).

Because there are no (as far as we have observed) particles with magnetic charge, all magnetic fields are of dipole or higher order. For your typical dipolar bar magnet, that means that there is a north and a south pole to the field–independent of whether it is generated by a bunch of electrons or a bunch of positrons.

So, if you put the south pole of your iron magnet near the north pole of your anti-iron magnet, be prepared for a little boom.

Rick

So, if you could theoretically have a magnet made of anti-iron, it would be attracted by a magnet composed of normal iron?

I find this quite difficult to believe if one of the most common scientific sayings is “For every action there is an equal and opposite reaction”. As far as this goes, wouldn’t an anti-magnet generate an anti-magnetic field which would neither repel nor attract a normal magnetic field, but would cancel the other one out.

Also, if there are no particles which transfer magnetic field, the WHAT IS a magnetic field? Is is a vibration in a higher dimentional plane, as some have postulated that gravity may be?

One final thing - I read about ‘magnons’ somewhere - do they have anything to do with this? I think they were described as a ‘quantum of magnetic energy’ but I really can’t remember…

“Now be quiet before I rather clumsily knight you with this meat cleaver” - Edmund Blackadder

Sorry, Rick, I’ve just re-read your post and I see what you mean about the opposite poles attracting between matter and antimatter magnets.

Although I’m still only at College and theoretical physics is merely an interest (hopefully to be involved in a career at a later date) of mine, I’m still not sure about this magnetic field idea (see my last post). Maybe you can answer my previous question(s)…

“Now be quiet before I rather clumsily knight you with this meat cleaver” - Edmund Blackadder

BIGmatt,

There are indeed no particles with “magnetic charge” in the same sense that there are particles with electric charge. Technically speaking, this means that magnetic fields are divergence-free–any (imaginary) closed surface has just as many magnetic field lines going into it as going out of it. Contrast this to the case of electric fields, where the difference between incoming and outgoing field lines is directly proportional to the charge enclosed by the surface (Gauss’ Law).

Electric and magnetic fields are closely related, however (hence the term electromagnetism used to describe the phenomena associated with them). In particular, electric fields that change with time (and moving electric charges, which amount to the same thing) generate magnetic fields, and vice-versa (see Maxwell’s Equations in any intorductory physics text for an idea of the relationships between electric and magnetic fields and charge/current. Electromagnetic fields are not associated with the vibration of any medium–the concept that light waves were carried by the “ether” was disproved by the Michelson-Morley experiment more than 100 years ago.

Currents and time-varying electric fields are not the only way to generate magnetic fields, however. Particles such as electrons, protons, and neutrons have intrinsic magnetic moments (i.e. they act like tiny bar magnets). Note that these are not magnetic charges, since the dipole fields still have zero divergence. The magnetism of the metals like iron, cobalt, and nickel comes from the orbital angular momentum of unpaired d-shell electrons (IIRC) which generates a dipole field like a little current loop (Did you ever make an electromagnet by winding a wire around a nail? It’s a little like that.).

As for magnons, I’m not sure, but I assume they are quantized magnetic flux excitations in a solid material. And you probably don’t want me to get into flux quantization (besides, it’s been about 10 years since I even looked at this stuff, so I’m extremely rusty). Any solid state physicists out there?

Rick

Sorry to followup to my own post, but I should add that both ‘electric’ and ‘magnetic’ forces are generated by the exchange of the mediating particle of the electromagnetic force: the photon.

Rick

Would a compass made with an anti-iron magnet point to the East & West Poles, instead of the North & South?

Anti-matter still has the same electromagnetic properties as matter, just with the opposite electric charge.

In other words, an anti-proton does not have anti-positive charge, it has negative charge. So, your magnet will behave the same except that the orientation of the magnetic field will be reversed, but there isn’t exactly a sign on an iron atom that says “My electrons spin this way”. You would not be able to tell by just the magnetic field whether an atom is iron or anti-iron.

Sorry folks, I’m on vacation and cannot check in often. RickG, notice that you said magnetism comes from “electron shells”. Other reference books I have read recently say stuff like magnetism comes from electrons in motion and spinning and revolving in atoms count.

This is the crux of my question. Is everyone being a bit careless with terminology when they say “electrons”? My instincts says anti-electrons (positrons) should work equally well. But I cannot find one reference source that agrees with my instinct. Furthermore, my instincts seem to suck on sub-atomic physics.