It's a three-part question. What is consciousness? Can you put it in a machine? And if you did, how could you ever know for sure?

Unlike any other scientific topics, consciousness -- the first-person awareness of the world around -- is truly in the eye of the beholder. I know I am conscious. But how do I know that you are?

Could it be that my colleagues, my friends, my editors, my wife, my child, all the people I see on the streets of New York are actually just mindless automatons who merely act as if they were conscious human beings?

That would make this question moot.

Through logical analogy -- I am a conscious human being, and therefore you as a human being are also likely to be conscious -- I conclude I am probably not the only conscious being in a world of biological puppets. Extend the question of consciousness to other creatures, and uncertainty grows. Is a dog conscious? A turtle? A fly? An elm? A rock?