The transactional interpretation of quantum mechanics John Cramer’s transactional interpretation of quantum mechanics (TIQM) is billed as resolving the fuzzy agnosticism of the Copenhagen interpretation while avoiding the alleged ontological excesses of the Many Worlds Interpretation. Yet it has a low profile.
Is this because no-one care anymore about ontology in physics, or is there something about TIQM which undermines belief in it?
 A: It's a combination of all these things and more. Most importantly, the TIQM interpretation is nonsense and all the positive words you hear about it are just unjustifiable hype promoted purely by John Cramer himself.
Ontology - or "realism", as it is technically called in quantum mechanics - has been falsified in physics in the mid 1920s and it can never be "unfalsified" again. It's established that objects don't possess well-defined properties before they're measured. This insight continues to be hard to swallow for many people - however it doesn't mean that there is anything questionable about it.
The TIQM merges all the usual misconceptions about the "real wave function" with some very special inconsistencies such as retrocausality - the influence of the future on the past - that is obtained by a bizarre interpretation of the Feynman-Wheeler theory, a theory that turned out to be incorrect by itself (although it helped to stimulate Feynman and others to find the right rules of quantum field theory). Concerning the Feynman-Wheeler theory, its historical role, and some of its problems, see

Wheeler-Feynman theory, QED without fields, vacuum polarization

A: I have come across a very simple question or critique of the Transactional Interpretation in an article "Nine formulations of Quantum Mechanics". The multiple authors of this 2002 AMJ paper are QM physics teachers.
They ask how "two particle" transactional handshakes work: are there "two handshakes across spacetime" or "one handshake across Configuration Space"? Without an answer to this question they are unable to "report on how the TI differentiates between bosons and fermions".
A: I have a new approach to TI which is discussed in my forthcoming book for CUP.
It will be available in fall 2012.  I don't think the basic transactional picture
has any problem accounting for quantum phenomena including multiparticle states, but the ontology of my version is different from Cramer's. I will look into Shor's algorithm, but I don't see why this would constitute a challenge for TI because TI has no problem with quantum computation that I know of. Any quantum system can be modeled in the transactional picture. The only situations regarded as challenges are contingent absorber experiments such as Maudlins; this issue is addressed and resolved in the book and a preview is here: http://philsci-archive.pitt.edu/8963/
Some recent papers on TI are on my website: rekastner.wordpress.com; some of this material is in the book.
Thanks for your interest.
A: Nobody has explained to me how Shor's quantum factorization algorithm works under the transactional interpretation, and I expect this is because the transactional interpretation cannot actually explain this algorithm. If it can't, then chances are the transactional interpretation doesn't actually work. (I have looked at some of the papers that purport to explain the transactional interpretation, and have found them exceedingly vague about the details of this interpretation, but assuming this interpretation is actually valid, maybe somebody else with more determination could figure these details out.)
A: I suspect a problem people have with TIQM is that Wheeler-Feynman absorber is woven into this.  The advanced potentials and the rest are a bit much for many to swallow.  
