The Forever Engine by Frank Chadwick

slats, arranged like louvers in a door.
    “Go ahead and touch them,” he told me. “They’re real enough. Only touch the top surfaces, though, unless you want the skin stripped off your fingers.”
    I knelt on the catwalk, reached out, and ran my fingers lightly along an upper edge.
    “Are they always so hot?”
    “No. As we ascend, their temperature increases. We don’t know why the temperature rises when they climb and drops as they descend, but my theory is it has to do with potential energy. A good trimsman keeps the climb shallow enough to avoid thermal distortion. The angle of the plane of the wood with respect to the center of mass of the world determines the amplitude of lift.”
    I sat on the catwalk, leaned my back against one of the steel ribs of the hull, and looked at the rows of louvers, their positions controlled by an elaborate array of brass and steel gears and thin control cables running up to and through the overhead. As I watched, the louvers adjusted slightly, two here, five over there, keeping the flyer in trim.
    Thomson and the others had figured out I was from a different future right away, but they’d done a good job of keeping it to themselves. It had been obvious to them once I talked about our “amazing” space-exploration program, which had finally put an unmanned rover on Mars in the twenty-first century. That’s why he hadn’t wanted me to tell Tesla about our space program—it would have let him in on the secret as well. Men from this world had been visiting Mars since 1870!
    And they had liftwood. It grew on Mars.
    “Back at the hospital I felt a downdraft when one of these things went over. I thought maybe it had big fans inside or something. Instead it’s got these wood slats, but when we took off I noticed a lot of wind underneath. So how do these things work?”
    “There is some controversy over that. The panels clearly do not block the effects of gravity. Since there are lifting panels between us and the ground, we would not feel the gravitational pull of the Earth below us, or would feel it with reduced effect. Nevertheless, we clearly do feel it.
    “The accepted explanation is that the louvers exert a repulsive force on whatever they come in contact with, but only do so parallel to the axis of strongest proximate gravitational attraction. The mechanism of this repulsion, and the source of the energy which produces it, remains a mystery, but it is one to which I believe you may have provided the answer.”
    “Me?” I said. “What does time travel have to do with it?”
    “Not time travel,” he answered, “but rather your explanation of matter in terms of small particles, particularly those—what are they called? Bosons? Those bosons which carry force and are exchanged.
    “The difficulty with the standard explanation of liftwood’s function is that it seems to allow for violation of conservation of matter, energy, and momentum. If you float something heavy and then drop it, you generate a good deal of kinetic energy at the impact point, and appear to do so for free.”
    “Nothing’s free,” I said.
    “Quite right, and there is some historical evidence from Mars’s past that in fact the entire momentum of the system is preserved. I now believe that liftwood does not actually repel matter which comes in contact with it, but rather exchanges momentum with it.”
    “What momentum? The air isn’t moving.”
    “Of course it is,” he said. “It is spinning around the Earth’s axis and hurtling through space as the Earth revolves around the sun. Each particle of air has enormous momentum. What remains a puzzle is why, or how, liftwood is able to selectively borrow the momentum parallel to the pull of gravity, but organic constructs are extraordinarily sophisticated. We cannot even begin to explain how a chameleon’s skin can so quickly react to its surroundings and duplicate them as a form of visual camouflage. Your time has extraordinarily advanced computing