Reality, No Matter How You Slice It by Ken Wharton

Ken---

Superb job, one of a few essays I consider the very best I've read so far. I'll comment more on points of agreement later, but for now just want to record the way in which I'm engaged with these sorts of ideas, in part through your work and Huw Price's, in part through Matthew Leifer and Rob Spekkens, in part just from my own thinking. I tend to agree that the Bell correlations needn't worry one so much ... the absence of a "story" allowing one to get rid of them by conditioning on stuff in the intersection of the past light cones of the correlated events doesn't upset me. I am attracted to trying to understand this through a more "instrumentalist" account of what quantum theory does for us than the one you are suggesting for in this essay, but I tend to think that in the end the "instrumentalist" and "realist" approaches to "How to stop worrying and learn to love quantum correlations" (as I am thinking of titling a paper on the subject...) end up with something like the histories formulation. I'm not sure how the "no-dynamics" approach fits in... I tend to view any constraints between the events that comprise possible histories, as "substantive physics" and not care so much whether it's called "kinematics" or "dynamics". (I still need to read Rob Spekkens' winning essay from last year on exactly that subject...) And I see that you end up with a histories picture too. I view both an instrumentalist histories approach, and a micro-histories approach, as realist---just realist about different things. The thing I worry about is that *both* approaches may be committed to some level of "decoherence" arising from choosing a particular set of histories. It's the question of "what's the ontology". Even if it's a micro-ontology, it may generate decoherence. Now, maybe that's more likely on "standard" histories stories in which the "events" about which histories concern themselves are statements like "the particle is in this phase space cell" (or possible fuzzified, continuum versions that are more sophisticated...). Whereas the more sophisticated "microrealists" who wish to abandon Bell-like causality restrictions without worries, may have in mind more exotic kinds of "underlying reality", including, as Terry Rudolph likes to say, a reality that is not described in spacetime terms at all. Although it seems to me you may not want to go there! But then I wonder about getting the theory to avoid decoherence at a level that might be refuted by observation.

Possibly related is a certain similarity in my mind, which others in this thread (and elsehwere) have also drawn attention to, between "retrocausal" and "conspiratorial" explanations. I realize you have said they're not similar. But I'm not so sure. In situations like your description the two-slit experiment, the "retrocausal" influence seems to be coming from the different final measurement apparatus. Not sure how you would deal with a "which-way" measurement very near the slits (I guess you could put lenses there, too). But this seems almost as conspiratorial... the thing is that whatever determines some big macroconfiguration, determines the possible histories. And surely we *do* think we can predict, with high probability, that macroconfiguration from stuff in its past light cone... There is probably something I'm not understanding here, different in your explanation than in the conspiratorial one. It is likely in *just exactly what* the macronconfiguration is affecting: putting a different, and somehow less objectionable, kind of constraint on the set of histories in your case than in the conspiracy case. But I'd love to see an explanation of this that is as clear as what you've written on other points in this paper.

Just to be clear, again, this is not intended as criticism... just as a reaction. You wrote a paper that made me go back to what I've been thinking on these issues, and think about it some more... which is another sign of a good paper. Again, outstanding!

Cheers,

Howard

Hi Ken,

I finally got to your essay and gave it the best mark.

One minor criticism. A definition of dynamics would have helped less sophisticated readers like myself.

I invite you to visit my essay and see how I "give up dynamics", If you visit please be critical..... There is too much agreement around here.

Thanks,

Don Limuti

Dear Ken,

This is miles better!

First of all, I'm glad that you don't think acceleration resolves the twins paradox. But I do wonder why you would use 'acceleration' rather than saying something like 'the boosted twin', especially since acceleration has been wrongly thought by many to resolve the paradox.

But now to important stuff. I was talking with someone yesterday about my concerns with using verbs to describe space-time points, events, all of space-time, etc. What I learned was that a B-theorist uses the word "exist" non-existentially. Personally, I consider it nonsense to use language that doesn't actually apply to things by redefining words in such a convoluted way. Moreover, I think it leads to a lot of confusion, especially because it's so hard to not fall into the trap of thinking of these non-existential things that 'exist' as *existing*. (As an example, when you read what you wrote, don't you find it hard to not think of a *static* block? I think it's really hard to think of the block as a temporally singular, non-existential thing. I honestly can't make sense of "a thing that doesn't exist." Then I also have a tough time not thinking of existence *and* motion along the block when you write "updating is performed by a 3D agent over time"). And finally, I think if what's being proposed is so nonsensical that it can't even be properly described because the language comes to mean something else entirely, that's a pretty good indicator that it really is just nonsense.

So what's my point: I do understand what you've written here, insofar as every time you say "I'm" you're really speaking non-existentially about what you "are". I'm actually pretty okay with the description until the last paragraph, because I don't think you're being too cavalier with your use of non-existential verbs until that point. But in the last paragraph, I think you're getting a bit carried away when you use three in a row ("updating is performed") in a way that tends to give the impression that you're not only talking of the block as something that 'exists' but doesn't really exist, but also of a sequence of updates that move up the world line.

Alternatively, you could say (with the use of single quotation marks to indicate non-existential use of verbs) "The whole 4D block 'exists'. My world-line 'exists' in it. At each point along my world-line, I 'have' some knowledge of the entire 4D block; i.e., as I may 'know' something about past, present, and future events at each point of my world-line. At 'later' times, my knowledge of the block is more complete than at 'earlier' times." (I know "earlier" and "later" are adjectives, but I think it's good to still use the single quotes there). Maybe you could sum that up by saying, "one's incomplete knowledge of the 4D block 'is' a monotonically increasing function of one's worldline, where at each point along the worldline, that incomplete knowledge 'is' 4D".

I think we're now on the same wavelength about what you want to describe, and I think the description of 'subjective updating', if stated carefully in this way, making sure to note the non-existential meaning of 'exist', etc., is about the best you can do. But then I simply have to wonder why you want it to be that way anyway. One reason, from our discussion above, might be that you don't like quantum non-locality. But I have a tough time seeing how a fear of existence in a world in which magic happens, can lead one to want to 'live' in a world where one doesn't actually *live* at all; where one doesn't actually *exist*. I think it's better to try to sort out our problems than just give in to unrealistic implications--and I honestly think a realistic version of quantum theory, or really quantum gravity, will come about after we've taken the more immediately necessary step of properly interpreting and understanding relativity.

I guess that brings the discussion back to the one we were having above. Would it be at all possible to take that up again now? I think I've shown an ability to really understand this position that I think needs to be rejected, being very open to thoughtful consideration of its meaning and implications. I think you'll find if you do read what I wrote there, that I've given the same thoughtful consideration in coming to my own position on the matter.

One more thing I wanted to say before I quit, in relation to the point you made early on about symmetry, is this: last night at the summer school on physics and philosophy of time that I'm attending, Stephan Hartmann gave a talk about the No-Alternatives Argument, which basically runs as, "Physicists have identified certain constraints, C, and have a set of data, D, that they want to use to construct a quantum gravity. To date, only string theory seems to meet all of C and D. Given the amount of effort that's been put into the construction of an alternative, we can be optimistic to some extent that there reall are no alternatives." The "some extent" is evaluated using Bayesian analysis.

My objection to this entire line of reasoning comes in at the very beginning. It's true that having identified C, the usual goal is to try to construct a theory that adds C explicitly into the framework. But we know of cases in history, where ideas have been rejected for a long time just because they were naively thought to be at-odds with some constraint or other that people thought necessary to hold onto. For instance, given a butterfly's ability to easily flutter about, or even the fact that the Earth retains its atmosphere, people felt quite strongly for a long time that the Earth has to be fixed at the centre of the solar system, and this constraint was violently held onto (e.g., Bruno). But then Galileo showed (with a simple thought experiment that didn't even need to be conducted) that butterflies can flutter around just as well in the cabin of a ship, as they can when it's back at harbour, and it was realised that this constraint wasn't necessary to the realisation of the data, and the Solar System could, for all that constraint had mattered, be heliocentric. In light of what I've written about symmetry above, I would like you to consider that perhaps the standard symmetry constraint of modern physics maybe is being made too explicitly, for all the observed symmetries that must be reconciled.

Cheers,

Daryl

Dr. Wharton

Richard Feynman in his Nobel Acceptance Speech (http://www.nobelprize.org/nobel_prizes/physics/laureates/1965/feynman-lecture.html)

said: "It always seems odd to me that the fundamental laws of physics, when discovered, can appear in so many different forms that are not apparently identical at first, but with a little mathematical fiddling you can show the relationship. And example of this is the Schrodinger equation and the Heisenberg formulation of quantum mechanics. I don't know why that is - it remains a mystery, but it was something I learned from experience. There is always another way to say the same thing that doesn't look at all like the way you said it before. I don't know what the reason for this is. I think it is somehow a representation of the simplicity of nature."

I too believe in the simplicity of nature, and I am glad that Richard Feynman, a Nobel-winning famous physicist, also believe in the same thing I do, but I had come to my belief long before I knew about that particular statement.

The belief that "Nature is simple" is however being expressed differently in my essay "Analogical Engine" linked to http://fqxi.org/community/forum/topic/1865 .

Specifically though, I said "Planck constant is the Mother of All Dualities" and I put it schematically as: wave-particle ~ quantum-classical ~ gene-protein ~ analogy- reasoning ~ linear-nonlinear ~ connected-notconnected ~ computable-notcomputable ~ mind-body ~ Bit-It ~ variation-selection ~ freedom-determinism ... and so on.

Taken two at a time, it can be read as "what quantum is to classical" is similar to (~) "what wave is to particle." You can choose any two from among the multitudes that can be found in our discourses.

I could have put Schrodinger wave ontology-Heisenberg particle ontology duality in the list had it comes to my mind!

Since "Nature is Analogical", we are free to probe nature in so many different ways. And you have touched some corners of it.

With regards,

Than Tin

Dear Ken,

Kindly indulge me. Probably no better place to clarify things with the experts than this forum.

Is it being implied by the relational view of space and as suggested by Mach's principle that what decides whether a centrifugal force would act between two bodies in *constant relation*, would not be the bodies themselves, since they are at fixed distance to each other, nor the space in which they are located since it is a nothing, but by a distant sub-atomic particle light-years away in one of the fixed stars in whose reference frame the *constantly related* bodies are in circular motion?

You can reply me here or on my blog. And please pardon my naive view of physics.

Accept my best regards,

Akinbo

Dear Ken,

Thank you so much for your posts. It means an awful lot knowing that you feel you've benefitted from this exchange, as I certainly have. Honestly, I really hope we can continue to agree to disagree, because for me it's all about getting things right, and being precise and careful at every step is such a huge part of that. In that regard, I don't know if it could be more beneficial than to have an opponent who truly understands and can appreciate both sides of the argument for what they are.

I have some specific responses to what you wrote. Copying isn't working on my phone, so I'll only quote a few words.

>if there is a cosmic rest frame...

Is a whole 3d space that exists any more non-local than a 4d block that 'exists'? Also, Shelly Goldstein sure gave a persuasive argument last night in favour of Bohmian mechanics.

>And it would seem to be rather convoluted...

Do you have Hawking and Ellis handy? Can you flip to the section on spherically symmetric gravitational collapse? It refers to observers O and O', and there's an E-F diagram... Consider the implicit definition of time that's being used--I.e. the variable they use to refer to time's passage. You know I think there's an objective time variable for the whole universe. It's not the E-F advanced time parameter. In any case, I think we both agree that descriptions of actual temporal passage are inconsistent with einsteinian notions of the relativity of simultaneity, which is what they're implicitly assuming--I.e. they give a dynamical account of temporal passage while assuming a physical definition of simultaneity that's inconsistent with that.

Now look at the statical coordination of de sitter space in the images I posted above. The r coordinate becomes imaginary at the coordinate singularity. It's simply no good after that, for all t. I talked about this with Gordon Belot today, and he thought Felix Klein showed that this was the right way of interpreting the line element. I actually think the Schwarzschild 'event horizon' is also such a coordinate singularity. Remember, I think space-time is globally hyperbolic at a fundamental level.

Now, to get back to the E-F description. Do you have Kip Thorne's black holes and time warps? He recalls a conversation with Lipschitz, where he called Finkelstein's paper a revelation that lifted a fog (or something like that). It was what convinced Wheeler that black holes exist, etc.

Personally, I find all of this convoluted. I think you can only have my sense of existence or your sense of 'existence' and neither admits of the dynamical emergence of black holes in the universe. I think it's entirely inconsistent.

>I'll note without comment...

Ah, but I'm allowed to conduct my thought experiments assuming absolute simultaneity in the Earth's rest-frame due to the principle of relativity. The important thing in assuming a cosmic rest-frame is whether the empirical evidence supports that. Right?

>Finally, I will caution... (whole paragraph)

:) Can I say I feel justified to be just a little snobbish about these things, insofar as I personally think a non-existential definition of "exist" (and all other verbs) is a convoluted and misleading way of speaking, which has led to a mountain of confusion (by the way, a good chunk of my essay is devoted to discussing this)?

Again, thank you so much for discussing all of this. I can't tell you how much it means to have the opportunity to debate with you. It's been very clarifying. By the way, do you think Greene is really thinking non-existentially about the block? It seems to me in the quote I posted below, that he's really emphasizing the block's existence.

Best regards,

Daryl

Dear Ken,

Replying to post on physical basis for introduction of principle of least action (dated Jul. 13, 2013 @ 10:41 GMT)

Having (time x change), or (time x energy) comes naturally by way we introduce the principle of least action. But this introduction is done on the level of effective systems, i.e. not at fundamental level at all. The bigger picture, with places to introduce spacetime as one piece on both low and effective levels, is painted in http://www.fqxi.org/community/forum/topic/1597 Notice there that notion of time is connected to the system, i.e. it is not a global time (can we call it local time?). And since it is not a global time, a little special place of time in Lagrangian method does not produce global problems, which none of us want :) .

De facto, when we look for a new theory (i.e. suggesting new Lagrangian), we watch out not to have bad things like negative energy. And, although it is beautiful to have complete time-space (t-x) symmetry, we avoid certain theories specifically based on this aspect of time being experimentally a little different.

Sincerely,

Mikalai

Hi Ken,

OK, a little more in the way of a response to your response:

1. I'm still not sure that what Eddington is talking about is unphysical. He's just talking about probability theory. Chains of probabilities are naturally asymmetric. It's just the way they are. Which leads me to...

2. Again, I think relativity is mis-interpreted. The arrow of time is built into it via the very fact that the sign of time in the metric is opposite that of space. It's easier to see if you work through relativity graphically using diagrams, but once you see it you can't "unsee" it, as they say. The only way to make time perfectly symmetric in relativity is to either drop the basic notion of cause and effect or allow for things like complex-valued masses and strange things like that. So, in short, I think it's incorrect to say that all the laws of modern physics are time-symmetric. They're not.

Ian

Hi Ken (and Howard),

As an addendum to the things I mentioned above, what occurred to me while reading Howard's comments was that, in a nutshell, I think we're overcomplicating things by missing the obvious. I know the retrocausal approach has become quite popular, but, again, it seems to be based on a certain set of notions that we seem to be clinging to for dear life --- the time-symmetric nature of modern physical theories, the absolute correctness of the Standard Model, etc. --- and I have no idea why. Again, I don't think the Standard Model needs replacing. I just see it like I see most theories: it is a highly accurate description of a limited set of phenomena. [And for the sake of people who don't want to go digging for my other comments, relativity is simply not time-symmetric. There's a neat little gedankenexperiment that you can do with a type of light clock that shows that if you run it backwards you don't get the Minkowski metric. You only get it if you run it forward in time.]

Ian

*Lifshitz. Sorry. I think it was him and not Landau, but he was talking about Landau as well, I believe. It's been a while since I read that, though. By the way, I'm not thinking of geodesic incompleteness, anymore than there is geodesic completeness past the coord singularity in dS space, described in those coords.

Hi Wharton,

I like the trend that this essay encompasses about not dwelling on the spacetime view of things and also its emphasis on returning to the big picture. It put some critical controversies in history in a more viewable, and relate-able, light.

Thanks,

Amos.

Dear Professor Wharton

Do you have opinion about my essay?

Yuri