Something from "nothing" - the Casimir Effect.

As promised, I'm taking a small break from introductory quantum mechanics, and discussing a topic that has some very real consequences in real life. This is one of the more strange predictions of quantum theory, so hold on. Ever heard of zero point energy? If you have it's related to the Casimir effect.



One of the most foundational rules of physics is that energy cannot be created or destroyed. This is known as the first law of thermodynamics, and was first stated by Rudolf Clausius in 1850. Essentially, you can change the form of energy, (e.g., from kinetic energy to potential energy), but you can't add more energy into the universe. Albert Einstein showed that this goes even farther than was originally though when he formulated his special theory of relativity. Einstein postulated that matter (what makes up everything we see) can be equated to energy - that the two are inescapably linked. Now, everything in the universe can be described in one way or another as energy. Einstein's theory was proven with the advent of nuclear theory, and since then, time and time again we have observed the conversion of mass into energy. The strangest part of this story starts back to the Heisenberg uncertainty principle once more, this time written slightly different way.

The delta E stands for the uncertainty in energy, and the delta t roughly corresponds to the time it takes for a system to change [1]. How can we interpret this? Well, it roughly means the given a process that lasts a short enough time, energy conservation can be briefly violated. Surely, you say, this must be incorrect. As it turns out, this is not incorrect and has been experimentally verified. Back in the 1940s, several physicists were trying to formulate the laws of quantum mechanics that were consistent with the strange predictions of traditional quantum mechanics, and with Albert Einstein's theory of relativity. This theory, now know as quantum electrodynamics, was finally able to make real predictions after years of formulation. The interesting part of the theory, and why I bring this up in the first place, is that calculations can be made in this theory by first drawing little diagrams of what happens.

 

This is known as a Feynman diagram. This diagram shows an electron interacting with an anti-electron. When this happens, a photon (light) is created. After this the photon turns back into an electron and an anti-electron once more. This is a process that has been at least partially observed. The truth is, all we can actually see in an experiment is what goes in, and what comes out. In the middle, where the squiggly line is (the photon), many other things could have happened, and must be taken into account in the calculations.

Here's the same thing, but different stuff happens in the center. In quantum electrodynamics, the contributions from each of these little pictures must be added up to get the complete picture. How do we know this? We get the wrong answer if we don't. The particles in the middle of the diagram are called virtual particles. The strange part about them is they are allowed to, and very option do violate conservation of energy! We cannot directly observe them, but we can prove their existence. How? Through the Casimir effect.

Several years after this theory was formulated, Hendrik Casimir calculated that given two parallel metal plates that are very close together and that have nothing but empty space (vacuum) between them, there would be an attractive force between them. This sounds very strange, but it was experimentally verified in 1997. What does this mean? The significance of this discover is that even in the vacuum of space, tiny virtual particles are popping in and out of existence, thumbing their noses at the 1st law of thermodynamics.

Well, I think all of this is cool, but I'm a physicist, why should you care? Well, the more technology advances, the smaller it becomes, delving into the nano-scale! Speaking of nano-scale, you should visit Nano Nook and It's a Small World for more information on nano technology! Say I'm creating a nano-scale device. It's constructed of tiny pieces of metal. It start to bring two pieces close together, but oh no! They start attracting! This has started to pose a problem for nano technology  manufacturers. Not only has it been a problem, but engineers are trying to figure out ways of using the Casimir effect to benefit nano technology. Read this article posted by The Economist on the Casimir effect for more information!

Another cool part, though it is perhaps a dead end, is that the Casimir effect admits the existence of NEGATIVE energy. Why do I find this interesting? As it turns out, negative energy density is an essential ingredient for wormholes, at least, according to Einstein's theory of relativity. I don't know about you, but the possibility of something like a wormhole really fascinates me.


Some people have postulated that the Casimir effect could be used to extract energy from empty space, but thus far, no one has been able to devise a way to do this. The energy is there, but whether or not it can ever be extracted has yet to be proven.

If you have any input on the Casimir effect, or wish to point out mistakes (which I surely have made) in this post, please feel free to comment! I have one more surprise post, then we'll return to our regular study of quantum mechanics.