# Simulate Free Fall Suppose that the pilot of a [Flight Simulator](Flight%20Simulator.md) aims the simulated aircraft vertically upwards at high speed and then switches off the engines. The aircraft should continue to rise until its upward momentum is exhausted, and then begin to fall back with increasing speed. The whole motion is called free fall, even though the aircraft is traveling upwards at first, because it is moving under the influence of gravity alone. When an aircraft is in free fall its occupants are weightless and can float around the cabin like astronauts in orbit. Weight is restored only when an upward force is again exerted on the aircraft, as it soon must be, either by aerodynamics or by the unforgiving ground. Free-falling aircraft are used to give astronauts weightlessness training before they go into space. A real aircraft could be in free fall for a couple of minutes or more, because it has several kilometers in which to go up and down. But a flight simulator on the ground can be in free fall only for a moment, while its supports let it ride up to their maximum extension and then drop back. Flight simulators (present-day ones, at least) cannot be used for weightlessness training: one needs real aircraft. Could one remedy this deficiency in flight simulators by giving them the capacity to simulate free fall on the ground? Not easily, for the [The Laws of Physics](The%20Laws%20of%20Physics.md) get in the way. Known physics provides no way other than free fall, even in principle, of removing an object’s weight. The only way of putting a flight simulator into free fall while it remained stationary on the surface of the Earth would be somehow to suspend a massive body, such as another planet of similar mass, or a black hole, above it. Even if this were possible [In Principle](In%20Principle.md) (remember, we are concerned here not with immediate practicality, but with what the laws of physics do or do not permit), a real aircraft could also produce frequent, complex changes in the magnitude and direction of the occupants’ weight by maneuvering or by switching its engines on and off. To simulate these changes, the massive body would have to be moved around just as frequently, and it seems likely that the speed of light (if nothing else) would impose an absolute limit on how fast this could be done. You could image crudely trying to approximate the experience of weightlessness such as training underwater with a weighted suit so as to have zero buoyancy. Or being strapped into a harness that is moved through the air via computer control in order to mimic weightlessness. But these methods will always be crude. You will inevitably feel the surfaces of support on your skin, and the sensation of falling, experienced through the sense organs of the inner ear, is not rendered at all. Stated generally, the problem is this: To override the normal functioning of the sense organs, we must send them images resembling those that would be produced by the environment being simulated. We must also intercept and suppress the images produced by the user’s actual environment. But these image manipulations are physical operations, and can be performed only by processes available in the real physical world. Light and sound can be physically absorbed and replaced fairly easily. But as I have said, that is not true of gravity: the laws of physics do not happen to permit it. The example of weightlessness seems to suggest that accurate simulation of a weightless environment by a machine that was not actually in flight might violate the laws of physics. But that is not so. Weightlessness and all other sensations can, in principle, be rendered artificially. Eventually it will become possible to bypass the sense organs altogether and directly stimulate the nerves that lead from them to the brain. So, we do not need general-purpose chemical factories or impossible artificial-gravity machines. When we have understood the olfactory organs well enough to crack the code in which they send signals to the brain when they detect scents, a computer with suitable connections to the relevant nerves could send the brain the same signals. Then the brain could experience the scents without the corresponding chemicals ever having existed. Similarly, the brain could experience the authentic sensation of weightlessness even under normal gravity. And of course, no televisions or headphones would be needed either. --- Date: 20241213 Links to: [First Principles Thinking](First%20Principles%20Thinking.md) [Virtual Reality](Virtual%20Reality.md) Tags: References: * []()