Sony has send a statement:
“We are working on utilizing PS2 emulation technology to bring PS2 games forward to the current generation,” a Sony representative told WIRED via email. “We have nothing further to comment at this point in time.”
Very similar to the Xbox One’s backwards compatibility, the PS4 emulator will work similar to the PS2 system. This will enable the PS4 to play PS2 games. It is not yet confirmed if PS2 disks will work on the PS4. It is also uncleared if the emulator will allow the PS4 play PS2 titles from the PlayStation Network.