Mary's room (also known as Mary the super-scientist) is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" (1982) and extended in "What Mary Didn't Know" (1986). The argument is intended to motivate what is often called the "Knowledge Argument" against physicalism — the view that the universe, including all that is mental, is entirely physical. The debate that emerged following its publication became the subject of an edited volume — There's Something About Mary (2004) — which includes replies from such philosophers as Daniel Dennett, David Lewis, and Paul Churchland.

Mary's Room is a proposed thought experiment that attempts to establish that there are non-physical properties and attainable knowledge that can be discovered through conscious experience. It attempts to refute the theory that all knowledge is physical knowledge. C. D. Broad, Herbert Feigl, and Thomas Nagel, over a fifty-year span, presented insight to the subject, which led to Jackson's proposed thought experiment. Broad makes the following remarks:
He [the archangel] would know exactly what the microscopic structure of ammonia must be; but he would be totally unable to predict that a substance with this structure must smell as ammonia does when it gets into the human nose. The utmost that he could predict on this subject would be that certain changes would take place in the mucous membrane, the olfactory nerves and so on. But he could not possibly know that these changes would be accompanied by the appearance of a smell in general or of the peculiar smell of ammonia in particular, unless someone told him so or he had smelled it for himself.
Roughly thirty years later, Feigl expresses a similar notion. He concerns himself with a Martian, studying human behavior, but lacking human sentiments. Feigl says:
...the Martian would be lacking completely in the sort of imagery and empathy which depends on familiarity (direct acquaintance) with the kinds of qualia to be imaged or empathized.
Nagel takes a slightly different approach. In an effort to make his argument more adaptable and relatable, he takes the stand of humans attempting to understand the sonar capabilities of bats. Even with the entire physical database at one's fingertips, humans would not be able to fully perceive or understand a bat's sonar system, namely what it's like to perceive something with a bat's sonar.