2009 Nobel Laureates in Physics

The 2009 Nobel Laureates in Physics have been announced! This year the award honors pioneers in information technology. Half the prize is going to Charles Kao (Standard Tel Labs), and the other half to Willard Boyle and George Smith (Bell Labs).

Charles Kao (left)  -  Willard Boyle and George Smith (right)

Charles Kao is being recognized for his foundational work in the development of optical fibers. Those fibers are now the veins and arteries of our electronic lives, allowing us to transmit data efficiently across long distances. They function on a very simple principle: light signals can be transmitted by bouncing light bouncing through a hair-thin glass tube.

However, the first optical fibers couldn't even transmit data across a football field -- the signal attenuated too quickly as it passed through the fibers. In the 60's, Kao was able to show that this attenuation was the result of the absorption and scattering of light, caused by metal ions in the glass. The problem was thus to figure out how to develop more pure glass fibers. Kao correctly argued that this could be done using silica. His research on the problem later led to the development of the super-efficient optical fibers we know today.

Boyle and Smith are being recognized for their invention of the Charged Coupled Device (CCD). That's the device that takes the place of photo-film in your digital camera. From the mid-60's up through the 70's, Bell Labs tried to develop and market an early video conferencing tool, called the Picturephone. The idea never took. But the CCD's developed along the way became central in our ability to take and transmit digital images.

In the semi-conductor department of Bell Labs, Boyle and Smith were asked to develop a semi-conductor memory device, on pain of losing funding in their department. After an hour's discussion, the two got the basic idea sketched on a chalkboard: to store a charge in a confined region using a metal-oxide semiconductor. The surface of the device is a matrix of little capacitors, or pixels. When light hits a pixel on the surface, it knocks out electrons that are stored in the capacitor. The lucky feature of this process is that the number of electrons is proportional to the intensity of light. (That's an essentially quantum phenomenon called the photoelectric effect, explained by Einstein in 1905.) So by recording the number of electrons ejected, you can get a reading on the intensity of light in each little region, and use this to produce a photo image.

Congratulations to Kao, Boyle and Smith!

Visualize a Wave Function

Can you visualize a normalized wave function on spacetime?

Let's try with a simple example. The role of a wave function is to assign a complex number to each point (x, t) in spacetime. This is central to a quantum description of the world. The complex number at each point is interpreted as an amplitude, which determines a probability -- the probability of measuring some physical quantity (like position or momentum) at that point.

But in the end, it's just a complex number, of unit length.

Now, a complex number lives on the complex plane -- a plane with the vertical axis representing a complex value, and the horizontal axis representing a real value. And the complex numbers of unit length live on a circle around the origin. So you can think of these numbers as readings on a circular meter -- like a speedometer or an altimeter -- except that the meter reads amplitudes instead of speeds or altitudes.

That means you can visualize the wave function ψ(x, t) as assigning a meter-reading to each point in spacetime. And if I fix a point in space -- like a spot on my kitchen floor -- then I can trace through the history of this wave function over time. The result will be a smoothly changing meter reading. For example, the meter arrow might just spin around clockwise over time.

Then it would look something like the following.

(Click to enlarge)

Challenge Question: How would you characterize the "time-reverse" of this description of the world? Tune in next post for a discussion...

Edit: The above account is not quite right -- see the post comments for more.