Unlike any other scientific topics, consciousness—the first-person awareness of the world

around—is truly in the eye of beholder. I know I am conscious. But how do I know that you are？

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 pup pets. Extend it to other creatures, and uncertainty grows. Is a dog conscious？ An elm？ A rock？

"We don't have the mythical consciousness meter," said Dr. Chalmers, a professor of philosophy and director of the Center for Consciousness Studies at the University of Arizona. "All we have directly to go on is behavior." So without even an elementary understanding of what consciousness is, the idea of instilling it into a machine—or understanding how a machine might evolve consciousness—becomes almost unfathomable①.

The field of artificial intelligence started out with dreams of making thinking or conscious machines, but to debate, its achievements have been modest. The field has evolved to focus more on solving practical problems like complex scheduling tasks than on imitating human behavior.

But many believe that the original goals of artificial intelligence will be attainable within a few decades.

Some people, like Dr. Hans Moravec, a professor of robotics at Carnegie Mellon University in Pitts burgh, believe a human being is nothing more than a fancy machine, and that it will be possible to build a machine with the same features, that there is nothing magical about the brain and biological flesh. "I'm confident we can build robot with behavior. that is just as rich as human being behavior," he said. "You could quiz it as much as you like about its internal mental life, and it would answer as any human being." To Dr. Moravec, if it acts consciously, it is conscious. To ask more is pointless.

Dr. Chalmers, regards consciousness as an unutterable trait, and it may be useless to try to pin it down. "We've got to admit something here is irreducible," he said. "Some primitive precursor conscious ness could go all the way down" to the smallest, most primitive organisms, he said. Dr. Chalmers too sees nothing fundamentally different between a creature of flesh and blood and one of metal, plastics and electronic circuits. "I'm quite open to the idea that machines might eventually become conscious," he said, adding that it would be "equally weird". And if a person gets into involved conversations with a robot about everything from Kant to baseball, "We'll be as practically certain they are conscious as other people," he said. "Of course, that doesn't resolve the theoretical question".

But others say machines, regardless of how complex, will never match people.

The arguments can become mysterious. In his book Shadows of the Mind, Dr. Roger Penrose, a mathematician at Oxford University, enlisted the incompleteness theorem in mathematics. He uses the theorem, which states that any system of theorems will invariably include statements that cannot be proven, to argue that any machine that uses computation—and hence all robots—will invariably fall short of the accomplishments of human mathematicians. Instead, he argues that consciousness is an effect of quantum mechanics in tiny structures in the brain that exceeds the abilities of any computer②.

According to the passage, ______ may be the most reliable touchstone for consciousness.

A．behavior

B．logical deduction

C．laboratory experiment

D．mental testing