Michio Kaku on Extraterrestrial Civilizations: “How Advanced
Could They Possibly Be?”

To quote:

Although it is impossible to predict the precise features of such advanced civilizations, their broad outlines can be analyzed using the laws of physics. No matter how many millions of years separate us from them, they still must obey the iron laws of physics, which are now advanced enough to explain everything from sub-atomic particles to the large-scale structure of the universe, through a staggering 43 orders of magnitude.

…

Physicist Freeman Dyson of the Institute for Advanced Study estimates that, within 200 years or so, we should attain Type I status - a truly planetary one, which has mastered most forms of planetary energy. Type 1 energy output may be on the order of thousands to millions of times our current planetary output.They also have enough energy to alter the course of earthquakes, volcanoes, and build cities on their oceans. In fact, growing at a modest rate of 1% per year, it would take only 3,200 years to reach Type II status, and 5,800 years to reach Type III status.

Full article here:

http://www.dailygalaxy.com/my_weblog/2007/12/michio-kaku-on.html