# Non linear interpretations of QM and string theory?

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## Main Question or Discussion Point

Are interpretations that are non linear with respect to the wave function (eg. GRW, transactional) compatible with string theory?

## Answers and Replies

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PeterDonis
Mentor
2019 Award
All interpretations make the same actual predictions, so they are all equally compatible with string theory. How compatible that actually is is an open question: nobody has derived the standard math of QM from string theory, although it is widely believed that it can be done.

bhobba
All interpretations make the same actual predictions, so they are all equally compatible with string theory. How compatible that actually is is an open question: nobody has derived the standard math of QM from string theory, although it is widely believed that it can be done.
When I asked Lubos Motl, he told me that interpretations that are non linear with respect to the wave function are not compatible with string theory.

PeterDonis
Mentor
2019 Award
When I asked Lubos Motl, he told me that interpretations that are non linear with respect to the wave function are not compatible with string theory.
Did he explain why? Did he say that such interpretations make different physical predictions from standard QM? If they do, they're not interpretations, they're different theories.

Did he explain why? Did he say that such interpretations make different physical predictions from standard QM? If they do, they're not interpretations, they're different theories.
He said that they do. But the GRW interpretation is the only one that makes different predictions. The transactional interpretation makes the same predictions as QM (as I've been told) but just adds the backwards in time wave which breaks the linearity.

He said that they do. But the GRW interpretation is the only one that makes different predictions. The transactional interpretation makes the same predictions as QM (as I've been told) but just adds the backwards in time wave which breaks the linearity.
So I guess that the transactional interpretation is compatible even though it's non linear, because it still makes the same predictions (again at least what John Cramer says)

PeterDonis
Mentor
2019 Award
I guess that the transactional interpretation is compatible even though it's non linear, because it still makes the same predictions
That's what I would say, yes.

Demystifier
Gold Member
The transactional interpretation makes the same predictions as QM (as I've been told) but just adds the backwards in time wave which breaks the linearity.
I don't think that backwards in time wave, as such, breaks the linearity. In transactional interpretation linearity is broken by absorption, not by backwards propagation.

That's what I would say, yes.
I don't think that backwards in time wave, as such, breaks the linearity. In transactional interpretation linearity is broken by absorption, not by backwards propagation.
The original quantum state according the transactional interpretation is linear. But linearity with the shrodinger equation breaks when the confirmation wave is generated. But it still makes the same predictions as standard QM.
However, according to the interpretation, spacetime together with its metric structure emerges by way of transactions, so this can be a theory of quantum gravity.
So can it still be compatible with string theory?