The difference between a brain and a computer can be expressed in a single word:complexity.
Even the most complicated computer man has yet built can't compare in intricacy with the brain. Computer switches and comportents number in the thousands rather than in the billions.What's more, the computer switch is just an on-off device,whereas the brain cell is itself possessed of a tremendously complex inner structure.
Can a computer think? That depends on what you mean by "think". If solving a mathematical problem is "thinking", then a computer can "think" and do so much faster than a man. Of course, most mathematical problems can be solved quite mechanically by repeating certain straightforward processes over and over again. Even the simple computers of today can be geared for that.
Surely, though, if a computer can be made complex enough, it can be as creative as we are. If it could be made as complex as a human brain, it could be the equivalent of a human brain and do whatever a human brain can do.
But how long will it take to build a computer complex enough to duplicate the human brain? Perhaps not as long as some think. Long before we approach a computer as complex as our brain, we will perhaps build a computer that is at least complex enough to design another computer more complex than itself. This more complex computer could design one still more complex and so on and so on and so on.
In other words, once we pass a certain critical point, the computers take over and there is a "complexity explosion". In a very short time thereafter, computers may exist that not only duplicate the human brain--but far surpass it.