Defining progress of any kind is a difficult proposition. When attempted systematically and quantitatively (as in the case of scientific progress), it becomes nearly impossible. As such, an argument for the definition of scientific progress is best presented in a familiar and appropriate framework for the subject area – a model. It is fitting that something like scientific progress is presented in such a format, as the methods and language of sciences such as chemistry and physics lend themselves to the discussion at hand.
In physics, vectors are a very simple yet important concept. A vector, by definition, is any quantity that has both a magnitude and a direction. Progress exemplifies this; it is not accurately defined without a direction in which it is moving (toward what objective), and at what rate (self-explanatory). However, this notion leads to an intrinsic conundrum in the context of the physical science metaphor: motion is relative, depending on arbitrary points as defined by an observer. One could argue endlessly on the beginning of scientific progress, and argue just as long where it may end. When all is said and done, the definition of scientific progress is only valid if the points of reference are valid as well.
There is corollary to this model which comes from insights gleaned by mathematical chemists only recently, which has become known as "Schrodinger's Cat". It relates to quantum mechanics, which can be expressed very simply as follows: at its smallest, most basic level, energy cannot be subdivided infinitely; instead, it moves up and down a ladder of discrete states, having a probability of existing at any given state at any given time. A system has only a probability of existing at a given state because observing a system causes the characteristics of the system to become dynamic, and therefore immeasurable. Schrodinger's Cat is a thought experiment designed to explain the decidedly probabilistic nature of quantum mechanics.
In this experiment, a cat is in a tightly sealed box. There is also a mechanism in this box that measures the state of a certain particle which only exists in two states. If the particle is in one state, the mechanism releases a poison that kills the cat. If it is in another state, the cat remains alive. The point of the above thought-experiment is that the cat is simultaneously alive and dead, at least until an observer opens the box.
This thought experiment provides the answer to the age old question, "If a tree falls in a forest, and no one is around to hear it, does it make a sound?" The answer is simultaneously yes and no, until someone tries to measure or observe it. That is also true in the case of progress. Progress doesn't become a real, tangible thing until an observer measures it, as per the quantum mechanics metaphor, and then defines it relative to something else, as per the vector metaphor. Simply put, scientific progress is a construct of the viewpoint, limited knowledge, and bias of a historian.
A/N: Didn't see that coming, did you?