In teaching science, I believe there are two distinct types of wonder. The first might be called “touch wonder” and the second “think wonder.” An interesting conversation today got me thinking about the ways to link these two distinct types of wonder.
Touch wonder I call this. Hold a magnet near a common science center device called a ring thrower. (My friend Jeff Shapiro of Science Kinetics sells just such a device. Here’s a picture of one from his website.)
When you push the button, an aluminum ring goes flying into the sky. At the same time, the magnet in your hand shakes back and forth, yet isn’t touching anything other than your hand. You’ve just discovered an invisible thing called a magnetic field!
Think wonder is this: you are starstuff. The elements that make up your body – carbon, oxygen, nitrogen – were forged inside a giant star billions of years ago. Those same atoms have been moving in and out of molecules, perhaps part of a rock, or a drop of water, or a potato, before finding themselves inside your body, becoming what you call “you.”
But are these two types of wonder really different? Can we forge a connection from one to the other?
Let’s go back to the ring thrower. That invisible magnetic field you just felt is the force behind radio, television, cell phones, and all other manner of wireless devices. Not only that, but the discovery that electricity can make magnetism (and vice versa), the discovery that makes the ring thrower do what it does, is also the driving force behind electric motors and electric generators. Every time motion changes into electricity (what the power company’s doing right now to allow me to type this) and every time electricity changes into motion – in your can opener, your ceiling fan, the hands on your clock, and the disk spinner in my Wii, to which I’m now totally addicted:) – this strange connection is there.
It was Michael Faraday who first discovered that moving magnets could make electricity. This simple, informal man, a self-taught scientist, made his discovery by trying, observing, and thinking about what he saw. His discovery, one late night in his laboratory, would change the world forever. Can you imagine that?
But there’s more. The connection between electricity and magnetism was well-studied for nearly a century before anyone had any idea why these two different forces should be linked. The connection finally came from another scientific hero of mine, Albert Einstein.
The way electricity and magnets link gives a clue to the source of the connection. Isaac Newton tells us there’s nothing particularly special about motion. Motion in a straight line at a constant speed is supposed to be just like standing still. There’s no real difference between the two.
Yet along come the 19th century scientists like Hans Oersted, Andre Ampere, Faraday, and James Clerk Maxwell to tell us that when it comes to electricity and magnets, suddenly motion does matter. Here’s how.
Suppose you have a long, straight wire. Send an electric current through the wire. Set an electric charge (called a “test charge”) beside the wire. It feels nothing. But set the test charge in motion alongside the wire, and suddenly that test charge feels a magnetic field. It is either attracted toward or pushed from the wire.
How can that be, if motion in a straight line at constant speed is no different from standing still? Einstein gives us the answer.
It turns out that with every step you take, you change your universe. Both space and time warp, convulse, change every time we change our motion relative to the rest of the universe. In particular, a moving electric charge next to a current-carrying wire sees something very strange. If the wire and charge are stationary relative to one another, then the positive charge and the negative charge in the wire look to the test charge like they’re perfectly balanced. Even though electric charge is moving through the wire, there’s just as much charge “moving in” as “moving out” and so the test charge feels nothing.
But set the test charge in motion. Now the electric charge through the wire looks unbalanced. Suppose the test charge is positive. If negative charge is moving opposite the test charge, and positive charge moving with the test charge, length contraction (curtesy the Special Theory of Relativity) causes a greater density of negative charge and a smaller density of positive charge. The test charge is attracted to the wire!
If, on the other hand, the positive charge moves opposite the test charge (you switch the wires on the battery), then the test charge “sees” a greater density of positive charge. The test charge is repelled! Now we see where that weird velocity term comes from in magnetic physics. Magnetism is nothing more (and nothing less!) than the application of Special Relativity to the real, everyday world of electric currents and moving magnets!
So lurking within that magnet shaking so frantically in your hand is one of the deepest secrets of the universe. With your every movement, you change the shape of the world. Wonderful!