I got the idea of Kartye Tree from an image I dreamt one night. Imagine a pogo stick, where you leap on it, and it springs you off in a new direction. In modern medical science, we've already applied that concept to prosthetics, where handicapped runners wear modified limbs to gain both distance and height, and in the process, outdistance their opponents. All it takes is the energy of the human body, and the modified limbs multiply it by a variable factor to create more thrust than otherwise possible.
How much thrust would 100,000 people be able to generate if you could apply it all at once? That's what Kartye Tree does, accumulates all the energy in each step taken by each person on board the tree, and at a pivotal moment, it releases it, thrusting the ship forward in a mighty leap, and in the process, it builds momentum in the long trip among the stars.
We already use this principle in our current level of technology. Look at the simple self-winding watch. Our arms move, the springs self-wind, and then in small bursts of released energy, the hands are flung around the dial. Then what about hybrid cars? The very act of braking stores energy that we can later release to increase our speed. It's fabulous! If we can do this now, what will we accomplish in a thousand years?
We know now our current energy reserves are far vaster than thought only a few decades ago, but what if we didn't need them at all? Kartye tree has been forced to rethink every existing technology to survive in a situation where no energy source is accessible, except that one that is inexhaustible: the human body.
Hybrid cars? Self-winding watches? They're just the tip of the iceberg! Look at what the people of Kartye Tree were able to do!