The massive clash of cultures that lies at the heart of this excellent novel is shown through the Anglo-Indians and the Indians that are presented to us in the novel. The Anglo-Indians seem to invest all of their time and energy into creating a sort of mini-Britain out in the Raj, no matter how inappropriate or costly this exercise is. Note how Adela's first meal in India with the Anglo-Indians is described:
A dish might be added or subtracted as one rose or fell in the official scale, the peas might rattle less or more, the sardines and the vermouth be imported by a different firm, but the tradition remained; the food of exiles, cooked by servants who did not understand it.
The food in a way acts as a strong metaphor for the Anglo-Indians themselves. They, like the sardines and vermouth, have been imported into India and do not "fit" the culture and are not understood by the Indians. The Anglo-Indians are shown to spend all of their time and all of their energy in trying to maintain this sense of living in little-Britain, dressing for dinner and holding on to cultural practises back home. Adela is shocked by the lack of interest they have in India and Indians.
Indians are mostly shown to be fascinated observers of the Raj and its adherents. They appear, on the whole, to be endlessly patient with being treated in such a terrible way, as witnessed when Adela asks Dr. Aziz how many wives he has. The crucial difference is that they have their own culture, beliefs and practices, and the novel suggests that this cultural gulf is something that cannot be transcended no matter how earnest and eager both parties are to bridge the gap.