No, it is not real . . . at least not the way it is shown in the movies. If it is fluid enough for you to sink in it, then it is fluid enough for you to float or tread water in it. The TV "Mythbusters" (Discovery Channel) did a segment on this. If the sand is dense, you don't sink; if it's liquid enough to sink, then you don't . . . the issue is how to get out . . .