The Fourth Law of Robotics

“This is the vital clue. I had the revolving door removed and had it weighed. The entire unit weighs two hundred and thirty kilos. I then had the computer estimate the force needed to get it to reach this speed in this time for varying amounts of pressure. Watch the green computer trace now. This is the maximum pressure that can be exerted by a fifty-kilo woman working her hardest.”

The green trace appeared in the air—ending well behind the image of the moving door.

“Interesting,” Dr. Calvin observed. “Voice or not, that was not a woman. “

“Exactly. Now the blue trace you see coming up would be that of a seventy-five-kilo man. Next the orange trace of a hundred-kilo man of exceptional strength. “

This trace, like all of the others, ended well behind the image of the moving door, being pushed around by the hand of the bank robber. I actuated the controls again and a red trace appeared that swung out fat ahead of the others and ended at the moving door.

“The red trace,” she said. “Tell me about it.”

“That trace represents the amount of energy needed to accelerate that door from a zero-motion state to the speed it reached to permit the thief to exit with the money in the time observed. I can give you the foot-pounds or meter-kilograms if you wish—”

“Just roughly. How much energy?”

“Enough to lift that desk—and you as well—one meter into the air. “

“I thought so. As strong as an hydraulic ram. And well beyond the abilities of a human being.”

“But well within the abilities of a robot.”

“Point taken—and proven, Dr. Donovan. So what do you suggest that we do next?”

“Firstly—I suggest that we do not inform the police.”

“Withholding information from the authorities is a crime.”

“Not necessarily. So far we have only assumptions and no real evidence. We could take this guesswork to the police if that is your decision. Then we must consider the fact that we are making public information that might be considered derogatory toward the public image of U.S. Robots and Mechanical Men, Inc., information that would affect the price of its stocks, affect our bonuses and retirement plans—”

“There is no need to go on. We will keep this development quiet for the moment. Now what do we do next?”

“That’s a good question. Since all robots manufactured by us are leased and not sold, we could try to trace this one. “

Dr. Calvin’s eyebrows climbed skyward at this rash assumption.

“Isn’t that a rather rash assumption?” she asked. “Do you know how many robots we have manufactured—that are still functioning? And all of our production for the past two decades—except for special-function units—are roughly equivalent in bulk to a human being.”

“All right, so we scratch that idea,” I muttered testily. “Maybe we are barking up the wrong drainpipe. The bank robber might be just a very strong man—and not a robot at all. After all, the robber did threaten the teller’s life—a violation of the First Law of Robotics. A robot may not injure a human being, or, through inaction, allow a human being to come to harm.”

She shook her head firmly. “There were no threats involved. As I recall it the thief just stated facts like, this is a hand grenade, I have pulled and discarded the pin. No threats or danger implied. Try again.”

“I will,” I said through tight-clamped teeth. Like her namesake aunt she was a giant of logical thought processes. “The Second Law then. A robot must obey the orders given it by human beings except where such orders would conflict with the First Law. “

“No orders were given that I recall. It all went smoothly and quickly—so quickly that the teller had no time to speak. And I think that you will agree that the Third Law is not relevant, either. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law. I think it might be said that we are back at square A. Any more suggestions?”

She asked this ever so sweetly but there was a steel gauntlet in her voice inside the velvet glove.

“I’ll think of something,” I muttered, although my brain was as empty of ideas as a vacuum flask.

“Might I make a suggestion?”

“Of course!”

“Let us turn this problem on its head. Let us stop asking ourselves if this was a robot and how or why the crime was done. Let us assume there is a criminal robot at large. If this is true we must find it. We cannot take our problem to the police, for the moment, for the reasons Just discussed. Therefore we must take this to a specialist—”

She frowned demurely as the desk annunciator buzzed, stabbed down the button angrily. “Yes?”

There is a gentleman here who says you are expecting him. He says that he is a specialist in clandestine investigations.

My own jaw echoed the gasping drop in hers. “Send him in,” she murmured weakly.

He was tall, well-built, his handsome face tanned to a teak finish. “Jim diGriz is the name,” he said. “I am here to help you people with your problem.”