The Maldacena conjecture and Rehren duality

We analyse the implications of the fact that there are two claims for a dual to N=4 superconformal SU(N) Yang-Mills theory (SCYM), the Maldacena conjecture and the theorem of Rehren. While the Maldacena dual is conjectured to be a non-perturbative string theory for large string coupling gs and small N , the Rehren dual is an ordinary quantum field theory on AdS5 for all values of the parameters. We argue that as a result, if we accept the Maldacena conjecture, one of the following statements must be true: 1) SCYM does not satisfy the axioms of algebraic quantum field theory for finite N because its observables do not obey the causal structure of conformal Minkowski space;. 2) String theory on AdS5×S 5 is not a quantum theory of gravity in 10 dimensions because it is dual to an ordinary quantum field theory on AdS5 whose causal structure remains fixed for all values of its couplings; or 3) there is no consistent quantisation of string theory on AdS5 × S 5 for finite string scale ls and gs. In evaluating the evidence for each of these conclusions we point out that many of the tests of the Maldacena conjecture can be explained by a weaker form of an AdS/CFT correspondence.