# A Note on Contingent Acceleration

I just saw an airplane turn on my walk home, and it dawned on me how strange it is that a machine can change its own velocity, which you could argue is a consequence of how I think about time. Specifically, I think about time as a set of possible outcomes along a discrete graph, simply because it’s a practical way to think about how a system can change, especially if you’re writing software to model its behavior. That is, if the system is in a given state, then there is some set of possible next states, and so on, which will produce a discrete graph. I happen to think that time is actually physically structured this way, but what’s relevant for this discussion, is that you can certainly model time as a discrete graph, as a practical matter.

Returning to the airplane, when it’s heading straight ahead, there will be some set of possible next states for the airplane’s motion at any given moment. But if the airplane were an ordinary projectile, this would not be the case, macroscopically, and instead, it would have a simple parabolic trajectory that would be unchangeable, absent intervention. So an ordinary projectile moving through space near Earth, doesn’t really have an interesting path through time, but is instead deterministic, at least at our scale of observation, absent intervention. In contrast, because an airplane can turn, increase velocity, or perhaps tilt, at any given moment, the next moment in time could always be some legitimately different state, leading to a multiplicity of possible paths through time, representing the future outcomes that are possible at any given moment.

As an example, let’s assume the plane is flying itself, which is realistic, and during the flight, the plane responds to some weather data, that causes it to change its course, turning the plane in a particular direction. Tracing the events that lead to this outcome, we have an exogenous event, which is the weather itself, then we have the systems within the airplane, receiving a signal representing the change in the weather, and then a response in the software piloting the plane, and ultimately the physical mechanisms of the plane itself, within the engines and the wings, responding to the software’s instructions.

It’s not as if any of this violates the conservation of momentum, since the plane is powered by fuel and electricity, to which there’s no magic, though the plane’s role in this set of facts requires electrical and mechanical energy to be already extant within the plane, in order for it to first receive the transmission, calculate the appropriate response, and then physically execute that response. However, what is in my opinion fascinating, upon reflection, is that the ability of systems of this type to respond to exogenous signals, allows these systems to have complex paths through time, that are contingent upon information that is exogenous to the system. In this case, even when piloting itself, the airplane can effectively decide to change directions, meaning that at any given moment, its path through time is very different from any ordinary, inanimate projectile.

All systems can of course be accelerated by exogenous momentum, which is typically a collision. But this is different: this is instead the case of a system that is ultimately accelerated by an exogenous piece of information. It is ultimately the ability to respond to information about an environment that makes the path of a system like this through time fundamentally different from any inanimate system. Though airplanes are obviously distinguishable from living systems, what I suppose I never fully appreciated, is that they arguably have more in common, in terms of their behavior through time, with living systems, than inanimate systems, since they are capable of acceleration that is contingent upon exogenous information.

To make it perfectly clear, we can distinguish between, for example, the position of the wheel of a car, and the information transmitted to the airplane: the position of a wheel is a physical state of the car itself, whereas the transmission regarding the weather is a representation of the state of an exogenous system, that is transmitted to the plane, that in turn causes a response within the plane itself. The point being, that a plane can respond to a representation of the state of an exogenous system, which really is the ability to autonomously respond to information, as opposed to being accelerated by some circumstance physically connected to the plane.