Viewers tonight may have anticipated disappointment, that there was no physics to blog about in this evening’s episode. But of course physics is everywhere.
Tonight our friends Leonard, Sheldon, Raj and Howard acquire a “Lord of the Rings” ring. The “One Ring”, we’re told, to bind the Rings of Power of the land of Middle Earth. At least they had a replica of it. None of them ever tried the ring on, but had they done so — if it were the real ring — it would have rendered them invisible. Invisibility is one of the principle powers of the ring. Oh, and world domination, too.
Physicists today are working on creating invisibility. Not having access to the Fires of Mordor or Elven blacksmiths, we instead have turned to Maxwell’s Equations. These are the four elegant equations that describe all of electricity, magnetism, and light. Because of James Clerk Maxwell and his four equations, we know that light is made from electric and magnetic fields.
Maxwell’s Equations were developed over many decades of the 19th century by physicists studying electricity and magnetism, among them many great minds: Gauss, Ampère, Faraday. But it was Maxwell who found the linchpin, the term that bound them all, and summarized the result in those four beautiful equations. At my own university, UCLA, as at most others, understanding Maxwell’s equations is the pinnacle of the first-year course in physics. Starting with balls rolling down an inclined plane and step-by-step understanding more and more physics, undergraduates are able to understand all of Maxwell’s equations after just one year of study, and thus understand perhaps one of the greatest intellectual achievements of all time.
The received wisdom about popular science writing is that with every equation I will lose half my readers. So I will skip the “equations” and just describe Maxwell’s four “rules” that have stood the tests of time by experiments:
#1. Electrons and protons create electric fields.
#2. There are no magnetic charges.
#3. Changing magnetic fields create loops of electric fields.
#4. Moving electric charges OR changing electric fields create loops of magnetic fields.
Now, what do these four rules mean for everyday living? A lot.
Rule #1 describes why you receive a shock in the winter after handling your fleeces. When rubbing fabric, you build up an excess of electric charge in your body. By this rule, an electric charge creates an electric field, which means it creates two points in space with different voltages. You are now resting at a higher voltage than, say your doorknob. A voltage difference will drive currents and can do anything from toast bread to run your television. When you touch the doorknob, current flows and … Zing! By the way, “voltage” has no meaning on its own. Only differences in voltages ever matter. So when you see a sign that says “Danger: Ten Thousand Volts”, it really should say “Danger: Ten Thousand Volts Relative to YOU”. If you touch something 10,000 Volts different than you, current will flow and for a few seconds you become the toaster.
Rule #2 was the subject of the boys’ Arctic expedition.
Rule #3: tells us how electric generators work. Move a magnet through a metal loop and you will set up a voltage difference that will drive a current, making a generator. If you reverse the situation, and drive a current in the loop then you can move a magnet and you’ve made a motor. Every motor is a generator and every generator is a motor. These basic building blocks of our technology were not invented by someone saying: “We need a way to make electricity” nor by saying “Is there a way I can use an electrical current to move things?” Rather, they were the by-product of the basic research of the day, into the elemental nature of electricity and magnetism. Curiosity, not necessity, is the mother of invention.
Rule #4 : The first part tells you how to make a magnet by running a current through a loop of wire. Even a refrigerator magnet works because electrons in the magnet are moving in circles and making magnetic fields.
Now for the second part of Rule #4: “Changing electric fields make loops of magnetic field”. Discovery of this last piece is Maxwell’s genius. Maxwell wondered why, if a changing magnetic field could produce loops of electric field, why could not the converse be true as well? He guessed that changing electric fields would produce loops of magnetic fields.
Indeed they do. Very small, almost inperceptably, but they do. So most remarkably, even in a perfectly empty space, changing electric fields will produce changing magnetic fields that will produce changing electric fields and so on, forever and ever. Maxwell noticed by combining equations #3 and #4 he could make a wave, a wave that turned out to travel at precisely the speed of light. The wave is created by changing electric and magnetic fields creating one another forever according to rules #3 and #4. The fact that he could predict the wave traveled the speed of light led Maxwell to conclude that light is an electromagnetic wave. (The conclusion was correct, but by accident. We now know many things, not just light, that travel near or at the speed “of light”. Had he known about all these other he could not have concluded so quickly that his waves were light waves. Sometimes a little ignorance is bliss.)
Now, over 100 years later engineers are designing materials to interact with the electric and magnetic properties of light. These materials can cause light to bend in ways that no naturally occuring material can, and are thus called meta-materials. Light entering a meta-material can be made to bend completely around an object effectively making a cloaking device.
The tricky part is that you must fabricate electrical components smaller than the size of one wave oscillation. Pieces less than an inch have been shown to effectively bend radio and microwaves (which are a type of light) around objects. Visible light would require elements 100,000 times smaller. But techniques are getting closer all the time!
(Easter-egg alert: Metamaterials featured prominently on the whiteboards of a previous episode: “The Creepy Candy Coating Corollary”, S0305.)
So our heroes don’t really need some Dark Lord to make them a silly invisibility ring. To the lab!!