Transactional Interpretation of Quantum Mechanics

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Schrödinger equation as part of a monument in front of Warsaw University's Centre of New Technologies. Halibutt / Wikimedia Commons / CC-BY-SA 3.0

The transactional interpretation of quantum mechanics is an approach to understanding the physical meaning of quantum mechanics which attempts to explain the results of quantum mechanics in a way that is fully consistent with relativity, and which preserves causality.

The transactional interpretation of quantum mechanics was developed by physicist John G. Cramer of the University of Washington, first published in 1986 in the journal Reviews of Modern Physics.

One of the issues Cramer was trying to deal with was that presented by quantum entanglement, such as presented in the EPR paradox. When a measurement is made of the entangled system, the entire system collapses into a state to match the result, no matter how far the different parts of that system are.

The problem with the traditional Copenhagen interpretation of quantum mechanics is that it requires this information to somehow be "known" by the whole system instantaneously. This is the issue of nonlocality, which has been confirmed by experimental tests of Bell's theorem. And that causes problems with relativity, because no information should be able to travel faster than the speed of light.

In Cramer's interpretation, the information sent by the measurement of the system goes not merely out into the future at the speed of light, but also backward in time at the speed of light. This time-reversed wave of information comes into contact with the entire system when they were close together, back when they actually became entangled.

The theory is fully nonlocal, but it requires no violation of relativity. (Information traveling backward in time is not a violation of relativity. At least not in this case.)

The name comes from the idea that each collapse of the quantum wavefunction is a "transaction," where the emitting and absorbing particles are exchanging information.

It is these transactions that actually cause the continual creation of physical reality, according to the transactional interpretation.

Despite the belief that this approach resolves issues such as the EPR paradox and the Schroedinger's cat paradox, there are a number of issues that remain with the interpretation. It has not been widely adopted by the mainstream physics community, in large part because it suggests that there would be quantum states with negative energy, and so far scientists have never detected such states. However, it is the most widely-studied of a class of "retrocausal" interpretations of quantum mechanics that, though still extremely controversial, are gaining some measure of traction within theoretical physics circles.

It's possible that the mysteries of quantum mechanics may be explained by something that seems even weirder than the mysteries themselves.

Also Known As:

The transactional interpretation is sometimes referenced with the initials TI or TIQM (for "transactional interpretation of quantum mechanics").