Need Help with Playstation 3?

How come ps2 games don't work on the ps3? Is there a way to fix it?

Suggestion:

Syed don't answer ps3 questions if you don't know anything about the ps3. All ps3s with 4 USB ports except the 40 gb model play playstation 1,2, and 3 games. Also my friend thinks and so do I all playstations play ps1 games.