Physicists are often asked why the image of an object, such as a chair, appears reversed left-to-right rather than, say, top-to-bottom when viewed in a mirror. Their answer is simply that an image viewed in a mirror appears reversed about the axis around which the viewer rotates his or her field of sight about a vertical axis, mirror images usually appear reversed left-to-right. This is the field-of-sight explanation.
However, some physicists offer a completely different explanation of what mirrors “do,” suggesting that mirrors actually reverse things front-to-back. If we place a chair in front of a mirror we can envision how its reflected image will appear by imagining another chair in the space “inside” the mirror. The resulting reflection is explanation treats it as though it were as real and three dimensional as the original chair.
This explanation appeals strongly to many people, however, because it is quite successful at explaining what a mirror does—to a point. It seems natural because we are accustomed to dealing with our mental constructs of objects rather than with the primary sense perceptions on which those constructs are based. In general, we our eyes; rather, we look into them, with our focal lengths adjusted into the imagined space.
In addition to its intuitive appeal, the front-to-back explanation is motivated in part by the traditional desire in science to separate the observer from the phenomenon. Scientists like to think that what mirrors do should be explainable without reference to what the observer does (e.g., rotating a field of sight). However, questions longer addressing images and appearances, because an image entails an observer and a point of view.
What this question is testing
Your task
Identify why the author included the referenced detail at that point in the passage — its function, not its content.
Common trap
Answers that merely repeat or summarize the topic of the detail instead of describing the role it plays.
Winning move
Ask what job the detail does for the paragraph, then for the passage's broader point.
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