In 1986 John G Cramer published a new interpretation of quantum mechanics (QM), the Transactional Interpretation (TI). It is particularly relevant for understanding how light propagates. Imagine, he says, that light travels not just in the one direction we are used to from the source and forward in time but that there is additional 'acceptor' wave travelling backwards through time from the where the light is absorbed. It is by the transaction of both waves moving between source and where it is absorbed that the energy of the photon is transferred. This is a form of time travel that is hidden from the observer under all normal conditions but none the less is happening all the time. It would be the normal way that light propagates in nature, irrespective of any special conditions imposed on how it is emitted or absorbed. The development of TI grew out of an earlier idea first proposed by Wheeler and Feynman called Absorber Theory and worked on by Hoyle, Narlikar and Cramer in which they consider classical electromagnetic waves travelling both forwards and backwards in time.
An interpretation of QM is intended to give a concept of what is happening to the quanta, something that QM itself does not do as it is a statistical theory but interpretations do not make new predictions. Most physicists have not been persuaded to take TI seriously, the majority still follow the Copenhagen Interpretation (CI). In personal communications with other scientists, I have received some negative responses to TI. Nick Herbert has his doubts about it and Brandon Carter went so far as to describe it as 'dodgy'. Cramer is fighting a lonely battle, I compliment him for his courage and determination. In 2003 he reanalyzed a another new quantum mystery, the Ashfar Experiment, and claims that TI offers a betters explanation than either CI or The Many Worlds.
Now Cramer has taken the bold step of announcing that he will try by experiment to prove information can travel backwards through time but even if he succeeds it does not necessarily follow that physicists would accept it as evidence in favour of TI. There maybe other ways to understand the result. I have my own doubts about TI as I suspect that if we can use information sent back from the future, this discovery could go hand in hand with confirming that there are Many Worlds. TI as it is formulated at the moment is not a Many Worlds theory. I wonder if the insights it brings can be applied to a Many Worlds theory?