The Edge of Science' 



By Sanborn C. Brown 



Associate Dean, Graduate School, Massachusetts Institute of Technology 



It is very seldom in the life of a scientist that a whole new vista of 

 knowledge opens up, vast and challenging before him. But this has 

 really occurred in what has come to be called plasma physics. 



In physics a plasma is defined as a neutral collection of electrons and 

 positive ions (atoms that have been stripped of their electrons) which 

 move around in random thermal motion. We have discovered that 

 this is the most common form in which matter is found in the universe. 

 If you go out into the far reaches of so-called empty space, or to the 

 stars or the solar system, or almost anywhere in the galaxy except our 

 peculiarly cold bit of dust which we call the Earth, you will find 

 matter in this ionized state, the plasma state. Nearly all of the matter 

 in the universe is in this state, and yet it is only within the past 10 

 years or so it has been recognized as a common state of matter. The 

 whole subject of what we call plasma physics has excited a great frac- 

 tion of the scientific community. 



To bring order into a fairly chaotic collection of phenomena, I refer 

 you to a plot in which the nature of matter is defined in terms of two 

 variables : the density of electrons per cubic meter and the temperature 

 at which these electrons are to be found. The diagram shows the vari- 

 ous areas covered by plasma physics. 



To start our discussion we begin in the lower left corner of this 

 diagram. If we get to very cold electrons and to very transparent 

 matter, we are in what is called interstellar space, including any nebulae 

 we find in a study of the sky. It has not been long since all our infor- 

 mation about the interstellar space came from visual telescopes. Col- 

 lections of charged particles such as electrons and hydrogen nuclei, 

 which are dancing around in space, but which are still held together 

 by their mutual gravitational attraction, are not necessarily visible 

 optically but may be visible by radio telescopes. "We call these collec- 



1 This article Is based on Professor Brovrn's remarlrs at the Alumni Symposium on 

 "Engineering, Science, and Education for Tomorrow," held in Newarlf, N.J., April 18, 

 1964, and Is reprinted by permission from the Technology Review, vol. 66, No. 9, July 

 1964. 



766-74I&— <65— — 30 401 



