The lights are on
The PS4 will not be compatible with any previous Playstation. The PS2 was of course compatible with PS1 discs, and the first generation of PS3's were compatible with both PS1 and PS2 discs. Of course as you know the current gen of PS3's are only compatible with PS1 games (I only have about 20 or so and they all work, not sure about the 100's I don't have being compatible cause I know there has to be a title or two not compatible). But Sony has already stated that they will not be backward compatible, cmdrredd is correct.