Now, implosion has to be explained in the movie for the Manhattan Project portions of the film to have any scientific drama, but why is Teller the one explaining it? Why not Tolman (who initially proposed it at Berkeley), Serber (who looked into it a bit afterwards and popularized the concept through the Los Alamos Primer), Neddermeyer (who quickly grabbed onto the implosion problem and ran the relevant experiments at Los Alamos for a year, and as a result is sometimes mistakenly credited with originating the implosion idea in the first place), or Teller's compatriot von Neumann (who made some calculations that put implosion on a solid theoretical foundation that it had been lacking before)? It's true that Teller worked with von Neumann on the above calculations, but that doesn't strike me (personally) as such a major role in the process that he must be the one to explain implosion to Oppenheimer, if that's indeed what this scene is showing. Perhaps Nolan is intentionally inflating Teller's role in the implosion problem (nobody has been confirmed to be playing von Neumann yet) to contrast with Teller's later refusal to do implosion calculations because of his intense interest in the Super (a refusal which, by the way, led to a certain Klaus Fuchs being brought in to work on implosion, so maybe that link will be in the film too). I guess giving Teller a large role in the implosion subplot will give the audience more familiarity with his character as he becomes more important later on.