One of the most important lessons the Christian ought to learn when faced by atheists claiming that the Christian worldview is mistaken is the idea that observation is theory-laden. To put it in terms more familiar to many Christians, this is the idea that each human has their own worldview, and their worldview commitments influence the way in which they perceive and interpret the evidence.
According to W.O. Quine, observation is “theory-laden” in the following way:
“Theory-ladenness of observation holds that everything one observes is interpreted through a prior understanding of other theories and concepts. Whenever we describe observations, we are constantly utilizing terms and measurements that our society has adopted. Therefore, it would be impossible for someone else to understand these observations if they are unfamiliar with, or disagree with, the theories that these terms come from.
An example of this could be given for determining an object’s acceleration. If someone is to understand the measurement of 2 miles per second squared, he needs an understanding of the concepts of distance, time, and velocity. Our observation of how much something is increasing in speed depends on our previous knowledge of these theories. As a result, such an observation is said to be theory-laden.”
Thomas Kuhn and Paul Feyerabend were also important thinkers in articulating the manner in which observation is theory-laden rather than purely objective. All scientists come to the table with their own biases. No one is completely objective. Thomas Kuhn articulated three specific manners in which observation could be theory-laden:
K1. Perceptual Theory Loading. Perceptual psychologists, Bruner and Postman, found that subjects who were briefly shown anomalous playing cards, e.g., a black four of hearts, reported having seen their normal counterparts. e.g., a red four of hearts. It took repeated exposures to get them to say the anomalous cards didn’t look right, and eventually, to describe them correctly. (Kuhn 1962, 63). Kuhn took such studies to indicate that things don’t look the same to observers with different conceptual resources. If so, black hearts didn’t look like black hearts until repeated exposures somehow allowed the subjects to acquire the concept of a black heart. By analogy, Kuhn supposed, when observers working in conflicting paradigms look at the same thing, their conceptual limitations should keep them from having the same visual experiences (Kuhn 1962, 111, 113–114, 115, 120–1). This would mean, for example, that when Priestley and Lavoisier watched the same experiment, Lavioisier should have seen what accorded with his theory that combustion and respiration are oxidation processes, while Priestley’s visual experiences should have agreed with his theory that burning and respiration are processes of phlogiston release.
K2. Semantical Theory Loading: Kuhn argued that theoretical commitments exert a strong influence on observation descriptions, and what they are understood to mean (Kuhn 1962, 127ff). If so, proponents of a caloric account of heat won’t describe or understand descriptions of observed results of heat experiments in the same way as investigators who think of heat in terms of mean kinetic energy or radiation. They might all use the same words (e.g., ‘temperature’) to report an observation without understanding them in the same way.
K3. Salience: Kuhn claimed that if Galileo and an Aristotelian physicist had watched the same pendulum experiment, they would not have looked at or attended to the same things. The Aristotelian’s paradigm would have required the experimenter to measure
…the weight of the stone, the vertical height to which it had been raised, and the time required for it to achieve rest (Kuhn 1992, 123)
and ignore radius, angular displacement, and time per swing (Kuhn 1962, 124).
These last were salient to Galileo because he treated pendulum swings as constrained circular motions. The Galilean quantities would be of no interest to an Aristotelian who treats the stone as falling under constraint toward the center of the earth (Kuhn 1962, 123). Thus Galileo and the Aristotelian would not have collected the same data. (Absent records of Aristotelian pendulum experiments we can think of this as a thought experiment.)
Thus, the production of data, both when it comes to the design of the experiment and its execution, are all heavily influenced by the background assumptions of the scientist. Oftentimes, these include theoretical or philosophical commitments of the scientist, which may lead them to ignore evidence that inconveniently does not fit their theory, and focus on the evidence which presumably does support it.
“For example, in order to obtain data on orgasms in female stumptail macaques, one researcher wired up females to produce radio records of orgasmic muscle contractions, heart rate increases, etc. But as Elisabeth Lloyd reports, ‘… the researcher … wired up the heart rate of the male macaques as the signal to start recording the female orgasms. When I pointed out that the vast majority of female stumptail orgasms occurred during sex among the females alone, he replied that yes he knew that, but he was only interested in important orgasms (Lloyd 1993, 142). Although female stumptail orgasms occuring during sex with males are atypical, the experimental design was driven by the assumption that what makes features of female sexuality worth studying is their contribution to reproduction’ (Lloyd 1993, 139).”
Researchers do not always use narrative to articulate their observations. Sometimes they use audio recordings, photographs and drawings. their devices maybe used to create pictorial images, graphs, number tables, and various other non-sentential records. These resources can heavily bias the observations they record. Graphs and other non-sentential pieces of data may be read differently, for example. A dark spot on a micrograph may mean one thing to one anatomist, and another thing to another. A blip on a Geiger counter may refer either to the sort of radiation a scientist wants to record, or an arbitrary surge of ambient radiation that is confounding the results of the experiments. This sort of bias is known as “semantic loading.”
Another potential confusion among scientists is differing operationalizations. According to the philosophy of science known as operationalism, what humans mean by concepts is the way in which they are measured. Thus, two scientists may claim to have observed oxygen, but they may operationalize oxygen in distinct manners. One may measure it according to bubbles in a chamber whereas others measure it in terms of particles. It is important for the scientist to make explicit how he is measuring the objects of his observations and how he is defining these measurements.
It is possible that perception is itself theory-laden. In other words, different scientific witnesses to an event in a lab may report different observations under these same conditions. Either expectations or perceptions themselves may have altered their interpretation.
“Furthermore proponents of incompatible theories often produce impressively similar observational data. Much as they disagreed about the nature of respiration and combustion, Priestley and Lavoisier gave quantitatively similar reports of how long their mice stayed alive and their candles kept burning in closed bell jars. Priestley taught Lavoisier how to obtain what he took to be measurements of the phlogiston content of an unknown gas. A sample of the gas to be tested is run into a graduated tube filled with water and inverted over a water bath. After noting the height of the water remaining in the tube, the observer adds “nitrous air” (we call it nitric oxide) and checks the water level again. Priestley, who thought there was no such thing as oxygen, believed the change in water level indicated how much phlogiston the gas contained. Lavoisier reported observing the same water levels as Priestley even after he abandoned phlogiston theory and became convinced that changes in water level indicated free oxygen content (Conant 1957, 74–109).”
Bogen, Jim, “Theory and Observation in Science”, The Stanford Encyclopedia of Philosophy (Summer 2014 Edition), Edward N. Zalta (ed.), URL = <plato.stanford.edu/archives/sum2014/entries/science-theory-observ….