Main Menu /Magnetism
By Ed Perley
Magnetism and gravity. They are two forces we experience daily. At first thought, you might think the force that attracts metal to a magnet is not that much different from the force that holds the earth together and us on it. Actually, the two forces are much different, and exist for much different reasons.
The force of gravity, defined by Isaac Newton, is really quite simple in concept. All things with mass have an attraction to each other. The force pulling them together is determined by the total mass of the two objects. This force is noticeable only if one or both of the bodies has a very large mass, like the earth. If the total mass of two bodies is small--for instance, a couple of marbles, there is gravitational attraction there, but it is neglible.
Albert Einstein helped us to understand why gravity exists. According to his General Theory of Relativity, gravity results from the tendency of anything with mass to distort the space and time around it. This distortion produces "sinks" that other things with mass tend to gravitate to.
But now look at magnetism. It is much more selective and directional--and it is not as dependent on mass. It is not unusual for a magnet to have an attractive force many times stronger than it's weight. The earth, with an iron core thousands of miles in diameter, on the other hand has a magnetic field so weak we need a compass needle to detect it. Objects can be attracted, repelled, or left uneffected by a strong magnet. Clearly, Einstein's idea of mass distorting space and time can't work here. We have to look elsewhere.
To understand magnetism, we must leave the world of Newton's laws and Einstein's Law of Relativity, and look at the physics of very tiny things, specifically the electrons trapped in atoms and molecules. Here, the laws of Quantum Physics apply. It is a world where something can be nowhere and everywhere simultaneously. It's a world where all states of existance are multiples of integers, and 1/2 is the only fraction possible. In this world, an electron can and will jump from from one location and/or energy level to another without going in between. If we could do such a thing with large objects, we would be able to build starships able to to instantly pop in and out anywhere in our galaxy. Maybe some day.....
Electrons held in atoms and molecules are trapped in a regions of space called orbitals. An atomic or molecular orbital, which normally contains two electrons, is not anything like a planetary orbit. It is more a like a standing wave of mass/energy. Each electron is spread out everywhere at once within the limits of it's orbital. One electron has a spin quantum number of +1/2, and the other has a spin quantum number of -1/2, giving a total spin of 0.
Magnetism in iron is caused by a particular kind of orbital, known as a d orbital, that contains only one electron instead of the usual pair. In iron, and some other metals, atomic and crystal symmetries of the iron make it impossible for this electron to pair with any other ones. All it can do is try to align itself with adjacent d orbitals with opposite spin as much as it can.
A d orbital with an unpaired electron behaves, actually, like a very tiny magnet. As such, it has a north and south pole. Also, like a magnet, it tends to line itself a certain specific way in a magnetic field. One end can be attracted or repelled by the end of the d orbital on a nearby atom, just like with a magnet. If the iron is melted and cooled in a strong magnetic field, a significant majority of the unpaired d orbitals are forced to point permanaently in the same direction. The result is a magnet. The higher the per cent of unpaired d orbitals pointing the same direction, the more powerful is the magnet.
Another principal of quantum physics is that an orbital does not have a distinct outer boundary. Therefore, a very small part of the electron's existance can be found at great distances from the atom or molecule it is held in. It is this property that allows for the presence of a magnetic field extending far beyond the the atom. Of course, the magnetic field of one unpaired d orbital is extremely weak. But if a large proportion of atoms in a chunk of metal are pointing in the same direction, as in a magnet, the magnetic fields add together to build a magnetic field more than strong enough for us to detect. You are in effect creating a highly magnified d orbital with properties resembling that of a single object from quantum physics, an unpaired d orbital.
Take the north pole of a bar magnet, and move it around the north pole of another magnet. Feel how the two magnets are repelled. You are actually experiencing the shape and feel of an event in quantum physics, two unpaired d orbitals pushing against each other. Feel the stiff, elastic feel of an atomic orbital. Even though quantum physics normally involves things completely beyond the limits of our perceptions, the common magnet clearly demonstrates that it and the d orbitals it postulates must be real.