"But how did you do it?"
"I don't know how much knowledge you have of physics," the Brain said slowly. "The explanation is a bit technical for the untrained man to understand. However, I'll explain it as simply as I can.
"Matter, as you probably know, is made up of tiny electrified bodies called electrons. When measurements were made it was found that the whole mass of the electron is due to its electrical charge. The inevitable conclusion is that the material universe is not the substantial, objective thing it was formerly thought to be. Matter is a completely spectral thing with no actual substance. The idea of substance must be replaced by that of behavior.
"Thus, opening the 'door' became a problem of controlling that behavior in such a way as to create a refraction of the matter separating worlds. That is not as simple as it may sound because a mind, to be able to do it, must possess a thorough understanding of the forces it deals with. It must have a tremendous capacity for concentration, and its logic must be entirely uninfluenced by emotion. I believe it is safe to say that no other mind, before mine, has ever combined these qualities in sufficient degree to accomplish the deed."
Strangely Ostby was not too surprised by this revelation. The makers of the capsule residing in the flesh of his left forearm had concluded, as a result of their studies, that the "door" might be the product of mind power. Their greatest mistake had been that it would take the combined power of at least eight brilliant minds to achieve the necessary matter refraction.
Here, then, lay the end of his search, Ostby knew. He regretted that its conclusion must entail the death of the Brain.
Somewhat as a form of apology he said, "It probably won't surprise you too much to know that I have decided to continue my fight on the side of the people of Earth. I am not going to let the accident of ancestry blind me to the justice of their cause. Also, regardless of my personal feelings, I must do whatever is necessary to attain my end. Do you see what I am trying to say?"
"I do," the Brain answered. "Your next question is, will I consent to close the 'door' voluntarily. My answer will be no, and then you will say that you must kill me. Am I right?"
Ostby nodded. "Tell me," he said, "are you not afraid to die?"
"The instinct of self-preservation is as strong in me as it ever was."