Hidden under all this talk about the wave moving through time making changes is a more fundamental problem. As we noted, despite the many precautions Time Safari Inc takes, they are making changes to history. They are deflecting photons which are perceived by creatures in the past; changing airflow and energy levels; puncturing the dermal layers of the prey’s body; transporting small quantities of nitrogen from the future to the past. The changes they make are minimal, but they are changing the past. It is foolish to pretend otherwise.
Yet when Middleton changes the past by killing the butterfly, waves of change pass through the future, crashing into physical objects as they alter the universe.
What we have here is a distinction made between “minimal” and “meaningful” changes. That is, a “meaningful” change causes a visible wave to pass through time, but a change that is not “meaningful” does not. The complication is, how does the universe know the difference? At the moment the change happens, it cannot even be recognized as a change at all–for the universe to know that the altered path of photons or the death of the butterfly is a “change”, it must know what would have happened otherwise. It is difficult to explain the concept of a wave of change occurring without this aspect that it occurs when what would have happened does not happen as it did in the original history. Yet if what triggers the wave is that somethng changed, a wave should occur whenever anything changes. Every trip to the past should trigger waves.
This is awkward, because obviously they do not. Granted, a change that is minimal will not have the severe consequences, altering climate and speciation drastically. But it remains the case that the waves can be seen and can be felt, and even if all they are changing is the total amount of nitrogen in the atmosphere, we ought to be able to see and feel the waves.
Perhaps, though, a minimal wave peters out. If it’s only a bit of nitrogen, a scattering of light, and a slight localized temperature change, perhaps the waves created will be so weak that they will fade within a few years. This is contrary to what we observe, as the waves appear to become stronger as they advance through time, but it is a poorly understood and explained idea so it may be that we have it wrong. Yet that leaves the other problem. If the wave emanating from Middleton’s change made it impossible for Ryer to travel to the moment of Middleton’s arrival, then it would seem that smaller waves ought also have the same effect, such that once the scout has changed the world by scouting no one should be able to travel through those waves to reach the moment the scout was there. All trips make changes, therefore all trips generate waves, no matter how small; and if waves prevent time travelers from reaching the point from which the waves emanate, no time traveler can ever visit a location previously visited by another traveler.
The distinction of a “meaningful” change to history is not one that history itself can understand; it must generate waves for every change if it does so for any change. The waves must have the same qualities even if they are making what to humans seem insignificant changes. Waves should have been a common experience by the time the serious ones arrived.
There is, though, another problem with them.