"Right!" Kim said. "But why was the _Starshine_ used by my revered great-grandfather to bring the first colonists to Alphin Three?" "Because--well--because you have to have a receiver for a matter-transmitter, and you have to carry it. Alphin Three was almost the last planet in the Galaxy to be colonized, wasn't it?" "Yes. Why do you have to carry a receiver? No, don't bother. But do answer this one. If two places are both too far to get to, what's the difference?" "Why, none." "Oh, there's a lot!" he told her. "The next star-cluster is too far away for the _Starshine_ with her present drive and fuel. To the next galaxy is no farther. But when I stopped trying to think of ways to stretch our fuel, and started trying to think of a way to get to the next galaxy, I got it." She stared. "Are we going there to live?" she said submissively. But her eyes were sparkling with mirth. He kissed her exuberantly. "My dear, I wouldn't put anything past the two of us together. But let me show you how it works." He spread out the drawings he had made from the construction-records while she searched the Pilot. He expounded their meaning enthusiastically and she listened and made admiring comments, but it is rather doubtful if she really understood. She was too much occupied with the happy knowledge that he was again confident and hopeful. But the idea was not particularly complicated. Every fact was familiar enough. Space-ships, in the old days, and the _Starshine_, in this, were able to exceed the speed of light by enclosing themselves in an overdrive field, which was space so stressed that in it the velocity of light was enormously increased. Therefore the inertia of matter, its resistance to acceleration, or its mass, was reduced by the same factor, y. The kinetic energy of a moving space-ship, of course, had to remain the same when an overdrive field was formed about it. Thus when its inertia was decreased by the field, its velocity had to increase. Mathematically, the relationship of mass to velocity with a given quantity of kinetic energy is, for normal space, MV=E. In an overdrive field, where the factor y enters, the equation is M/y, yV=E. The value of y is such that speeds up to two hundred times that of light result from a space-ship at normal interplanetary speed going into an overdrive field. A matter-transmitter field, as everyone knows now, simply raises the value of y to infinity. The formula then becomes M/infinity, infinity V=E. The mass is divided by infinity and the velocity multiplied by infinity. The velocity, in a planet-to-planet transmitter, is always directly toward the receiver to which the transmitter is tuned. In theory, then, a man who enters such a transmitter passes through empty space unprotected, but his exposure is so exceedingly brief--across the whole First Galaxy transit was estimated to require .0001 second--that not one molecule of the air surrounding him has time to escape into emptiness.