Half Life of Knowledge

I belong to the Institute of Electrical and Electronic Engineers (IEEE). We give lots of talks on careers and jobs. In our last talk in Denver, we had about 30 folks. All were electrical engineers in their 40s and 50s. They were going through a career transition. Their key questions were:

What is hot right now?
How do I position my career to what's hot?
How can I get a job?

All great questions? However, the key thing for technical professionals is to keep current. It doesn't matter if the professional is in medicine, engineering, computer science, or architecture. These are all technical disciplines where the amount of knowledge is doubling every 5 or so years.
We call this the half life of knowledge - the amount of time knowledge is doubling. In some technical disciplines, the rate of change is more than drastic such as computer science, where I've heard it's more like 2 to 3 years.

Phenomenal.

This means that a professional does not retread then he or she is toast - unemployable or outsourceable. Tough thoughts in this economy.