 Maudlin’s challenge to the transactional interpretation has been met with a range of responses (see P. Lewis 2013 and the entry on  action at a distance in quantum mechanics  for more discussion of possible responses). The responses generally fall into two types (P. Lewis 2013). The first type of response attempts to accommodate Maudlin’s example within the transactional interpretation. Berkovitz (2002) defends the transactional interpretation by showing that causal loops of the type found in Maudlin’s experiment need not obey the assumptions about probabilities that are common in linear causal situations. Marchildon (2006) proposes considering the absorption properties of the long distance boundary conditions: if the universe is a perfect absorber of all radiation then a confirmation wave from the left will always be received by the radioactive source at the time of emission and it will encode the correct probabilistic information. Kastner (2006) proposes differentiating between competing initial states of the radioactive source, corresponding to the two emission possibilities, that together characterize an unstable bifurcation point between distinct worlds, where the seemingly problematic probabilities reflect a probabilistic structure across both possible worlds.