# Can Bohm’s Pilot go backwards through time to maintain locality?

I’m starting to think this idea would defy the Bohm interpretation enough to be distinct. Can I call it Retropilot? I’m thinking the pilot wave can be modified in a way that maintains both locality and causality. I’m sure this idea has been discussed here and it’s likely I’m missing some obvious flaw.

So when an entangled photon is measured, nothing happens superluminally. Instead, the pilot wave travels backwards through time along the same path as the photon and at the same speed. When it reaches the time and place of the origin of the entangled photons, the spin gets set. In the case of electrons, the pilot wave travels at the same speed as the electron but in the opposite direction through time and space.

To think about this relativisticly, if the measurements of entangled photons are out outside of each other’s light cones, then there’s no way to determine which measurement came first. Both measurements cause a pilot wave to return back to the origin and they reach the origin at the same time, which is when the photons were emitted.

Some think of positrons as electrons traveling backwards through time. Feynman used retrocausality in his diagrams. You don’t know what will happen to that positron in the future without measuring it. So the system stays deterministic. The same can be said about the pilots as well. So if I have this right, this modified Bohm interpretation keeps both locality and causality.

Sure.

You simply replace the wave function with a positive and negative time solution.

Let's say we have two spatially separated and vertically aligned polarisers and an entangled source between them. When one entangled photon arrives at the polariser it has a 50 percent chance of passing through, but at this point it does not know whether to pass through and be detected without knowing the position of the other polariser that its entangled partner goes through. Now we rewind the universe (same as sending a wave back in time) and at the source the two backward waves meet and have sufficient information to have a predetermined orientation that is compatible with the predetermined future. Note that the universe can not continue to run forward until we resolved whether the photons are detected or not if there is only a single universe. With multiple universes the universe can split into four different versions accounting for all the possible permutations but then we are going into the MWI version. This means when we set the universe going forward again there is no random probability of passing through the polarisers, but a certainty. Now let us say that the positions of the polarising analysers are determined by Alice and Bob. Each time we rerun the universe Alice and Bob make the exact same decision on which way they orientate their analysers. The implication of the backwards wave is that the universe is completely deterministic and this extends to the decisions of humans like Alice and Bob, removing all possibility of free will. Do we want to go there? Well, whether we like it or not, if that is how the universe works then we have to accept it. However, I think there fundamental problems with removing randomness, especially in quantum theory and I think the laws of thermodynamics requires it too.

Secondly, I would be interested if anyone can articulate the difference between the pilot wave theory and the transactional interpretation, or are they the same thing?

Secondly, I would be interested if anyone can articulate the difference between the pilot wave theory and the transactional interpretation, or are they the same thing?

The differences lye in the wave function, and how the collapse is performed. In all honesty, we can see things that look like random collapses in the Bohmain Interpretation. But the wave function was determined at the big bang, so what we see in this theory is the wave function following pilot waves. The transactional interpretation is when you take a wave form and make one wave come from the past (an offer wave) and a wave from the future (an echo wave). They meet in the present time, and form a transaction, which has all the appearance of a collapse.

Thenewmans,
Something like this has already been done by Rod Sutherland:
http://arxiv.org/abs/quant-ph/0601095
Fantastic! I haven’t read much of it yet. (I have to work on my paying job.) From what I’ve read so far, it all matches the image in my head! He says that retrocausality can be used to explain the nonlocality in Bell’s theorem. Explain it? It solves it. That leaves me with 3 questions.

1 – What other interpretations maintain locality? I don’t think MWI does. (Yuiop, what do you think?)

2 – Does this interpretation break causality? I don’t think so. At least, it manages to skirt causality issues since this pilot wave is not an observable. Even if it was an observable, it can’t tell you anything additional about the future. You can’t measure it twice and expect the same result. In this way, it’s similar to imagining a positron as just an electron going back through time.

3 – If locality and causality are maintained, what principal does this interpretation break? In Wikipedia, I read that Bell’s theory proves an interpretation must violate either locality or “Counterfactual Definiteness”.

DrChinese
Gold Member
1 – What other interpretations maintain locality? I don’t think MWI does.

...

3 – If locality and causality are maintained, what principal does this interpretation break? In Wikipedia, I read that Bell’s theory proves an interpretation must violate either locality or “Counterfactual Definiteness”.

1: MWIers assert that locality is maintained.

3: It is sometimes asserted that Counterfactual Definiteness is violated in retrocausal interpretations as there is still no existence of unmeasured non-commuting observables.

Fantastic! I haven’t read much of it yet. (I have to work on my paying job.) From what I’ve read so far, it all matches the image in my head! He says that retrocausality can be used to explain the nonlocality in Bell’s theorem. Explain it? It solves it. That leaves me with 3 questions.

1 – What other interpretations maintain locality? I don’t think MWI does. (Yuiop, what do you think?)

2 – Does this interpretation break causality? I don’t think so. At least, it manages to skirt causality issues since this pilot wave is not an observable. Even if it was an observable, it can’t tell you anything additional about the future. You can’t measure it twice and expect the same result. In this way, it’s similar to imagining a positron as just an electron going back through time.

3 – If locality and causality are maintained, what principal does this interpretation break? In Wikipedia, I read that Bell’s theory proves an interpretation must violate either locality or “Counterfactual Definiteness”.

1 - The MWI does, but only if can be shown to be an empirically adequate interpretation of QM to begin with. And I don't think it is.

2 - It doesn't break statistical causality (i.e. that operators corresponding to physical observables commute at spacelike separations), but it does break Bell's local causality criterion (see Bell's papers, "La Nouvelle Cuisine" and "Free Variables and Local Causality", for a clear explication, or one of Travis Norsen's papers on Bell's Local Causality criterion.).

3 - See 2.

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1: MWIers assert that locality is maintained.
OK then, maybe I should attempt an argument for MWI is not local and see who counters it. I’m not that up on MWI but I’ll try. Let’s say Alice and Bob are spatially separated and Alice takes a measurement but Bob does not. At what point in time does Bob divide into 2 worlds because of Alice’s measurement? You can’t say at the moment Alice takes the measurement. That would imply a preferred inertial frame of reference. If the photons are shot in opposite directions through a vacuum, then both photons are always outside of the other’s past and future light cone. So Bob could take a measurement anywhere along the path of his photon and the result must match Alice’s.