Are object oriented languages more powerful than declarative programming languages? By powerful I mean are they able to solve a class of problems that any program written in a declarative programming language can't?
Personally I don't think so. There exists a set of problems for which it is easier to write a program using an object-oriented language, but I think those problems could be solved using declarative languages too (albeit it might be harder to so)
Would like to hear more views on this one.
Go read up on Turing completeness. It basically means any turing complete language can solve any problem a turing machine can.
And most languages are turing complete. (I doubt you'd ever use a non turing complete language).
Alternatively you can think of it as you can solve any problem with Ook! even though it's a very silly language.