Hi Travis,

Wow! It’s very nice to hear we’re in agreement about both the framing of the problem and what the solution must look like. Apart from a single word, I’m also in agreement with:

“…it [had] better turn out that the boundary conditions on S’ *imply*, via the application of the basic dynamical postulates of the theory, the same sort…[Read more]

Hi Travis,

There are many aspects of the measurement problem, but I think the one that is hardest for retrocausal theories is that there should be no difference between an *interaction* and a *measurement*, since one can’t define a hard distinction between the two. Standard QM of course has this problem. It incorporates mere interactions into…[Read more]

Ian; the multiverse isn’t a BW, which points to hidden variables. But one doesn’t need the sort of HV’s that bother you: all you need is that the *future* is a hidden variable, hidden from our knowledge, and you can have a BW theory that is fundmanentally stochastic. Surely you don’t have a problem with treating future events (events that lie…[Read more]

Hi Dustin; Thanks for the kind words!

As for giving the Wood-Spekkens argument too much credit… If there was an existing retrocausal model they were attacking, that gave the right probabilities already, I’d certainly agree with you. But they’re framing it as an argument against trying to develop such a model in the first place. And since…[Read more]

> I cannot make any sense of your reference to “which aspect of Bell’s theorem doesn’t go through” somehow associated with “statistical independence of the allowed histories”. Would you care to clarify?

I have a detailed but very simple toy-Ising model showing how statistical independence can fail at the level of allowed histories in [Read more]

As I see it, the biggest pressing problem is how to make sense of QM and GR in the same consistent framework. (I’m not sure if this counts as a “practical purpose” in most people’s accounts, but it does in mine.) Certainly, many people don’t think we need to wait for an ability to collect empirical evidence in situations where both QM and GR are…[Read more]

Ian: if you are just referring to the “Block” itself, see my #2711 above.

If you’re talking about classical randomness, or stochastic theories, another way to think about it is this: Most people’s trouble with the Block Universe has to do with the *future*. Very few people have trouble imagining a Block-year-1999. (Do you?) So any randomness…[Read more]

Thanks, Bob – I have a pretty clear idea of where our paths diverge now.

Still, I happen to think that far more clarity is gained than lost when thinking about the CH framework choice as a hidden variable. (It’s certainly “hidden” at first, right?) Specifically, when thinking this way, it becomes far clearer which aspect of Bell’s theorem d…[Read more]

Hi Ian! Yes, I’m looking forward to talking about this in person…

I wouldn’t say that the Block Universe is particularly motivated by retrocausality — it’s best motivated by general relativity! (So yes, it does imply some ontological status of spacetime, modulo diffeomorphisms, etc.)

And curiously, many people interested in retrocausality…[Read more]

Hi Larry,

Thanks for posting this; I don’t think your ideas are getting their deserved attention from the wider quantum foundations community, and as you know am trying to inform people about them in my own work.

In my piece here in this forum, I talk about your one-particle model and conclude that it is effectively retrocausal. (The future…[Read more]

Hi Travis and Dustin,

Thanks for the interesting discussion! I thought I’m chime in with a few points of my own…

Travis, on your point #2, you never mentioned another aspect of locality (really, a pre-requisite!): restricting models to those that have exclusively spacetime-local beables. To me, *that’s* the important thing that…[Read more]

All good questions about the cause/correlation issues… Do you have a classical example in mind as an answer to your last question?

Still, you can’t carefully address these questions without comparing your definition of causation to some *other* definition of causation. Even if you don’t want to bring in other causation accounts, where your…[Read more]

Hi Nathan,

I think you’re almost exactly right about what should be considered a “good” variable, but I’ll throw one suggested change at you: Instead of taking the log of the number of possible ontic *states*, what about the log of the number of possible ontic *histories*? This associates “entropy” with regions of spacetime rather than…[Read more]