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DeVliegendeHollander comments on Beyond Statistics 101 - Less Wrong
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That works up until the point where you actually have to think about what it means to "causally interact" with something. Also questions like "does something that falls into a black hole cease to exist since it's no longer possible to interact with it"?
But there are trivially easy answers to questions like that. Basically you have to ask "Cease to exist for whom?" i.e. it obviously ceases to exist for you. You just have to taboo words like "really" here such "does it really cease to exist" as they are meaningless, they don't lead to predictions. What often people consider "really" reality is the perception of a perfect god-like omniscient observer but there is no such thing.
Essentially there are just two extremes to avoid, the po-mo "nothing is real, everything is mere perception" and the traditional, classical "but how things really really REALLY are?" and the middle way here is "reality is the sum of what could be perceived in principle". A perception is right or wrong based on how much it meshes with all the other things that can in principle be perceived. Everything that cannot even be perceived in theory is not part of reality. There is no how things "really" are, the closest we have to that what is the sum of all potential, possible perceivables about a thing.
I picked up this approach from Eric S. Raymond, I think he worked it out decades before Eliezer did, possibly both working from Peirce.
This is basically anti-metaphysics.
Does this imply that only things that exist in my past light cone are real for me at any given moment?
I don't know what real-for-me means here. Everything that in principle, in theory, could be observed, is real. Most of those you didn't. This does not make them any less real.
I meant the "for whom?" not in the sense of me, you, or the barkeeper down the street. I meant it in the sense of normal beings who know only things that are in principle knowable, vs. some godlike being who can know how things really "are" regardless of whether they are knowable or not.
I'd like to congratulate you on developing your own "makes you sound insane to the man in the street" theory of metaphysics.
Man on the street needs to learn what counterfactual definiteness is.
Ilya, can you give me a definition of "counterfactual definiteness" please?
Physicists are not very precise about it, may I suggest looking into "potential outcomes" (the language some statisticians use to talk about counterfactuals):
https://en.wikipedia.org/wiki/Rubin_causal_model
https://en.wikipedia.org/wiki/Counterfactual_definiteness
Potential outcomes let you think about a model that contains a random variable for what happens to Fred if we give Fred aspirin, and a random variable for what happens to Fred if we give Fred placebo. Even though in reality we only gave Fred aspirin. This is "counterfactual definiteness" in statistics.
This paper uses potential outcomes to talk about outcomes of physics experiments (so there is an exact isomorphism between counterfactuals in physics and potential outcomes):
http://arxiv.org/pdf/1207.4913.pdf
Sounds like this is perhaps related to the counterfactual-consistency statement? In its simple form, that the counterfactual or potential outcome under policy "a" equals the factual observed outcome when you in fact undertake policy "a", or formally, Y^a = Y when A = a.
Pearl has a nice (easy) discussion in the journal Epidemiology (http://www.ncbi.nlm.nih.gov/pubmed/20864888).
Is this what you are getting at, or am I missing the point?
No, not quite. Counterfactual consistency is what allows you to link observed and hypothetical data (so it is also extremely important). Counterfactual definiteness is even more basic than that. It basically sets the size of your ontology by allowing you to talk about Y(a) and Y(a') together, even if we only observe Y under one value of A.
edit: Stephen, I think I realized who you are, please accept my apologies if I seemed to be talking down to you, re: potential outcomes, that was not my intention. My prior is people do not know what potential outcomes are.
edit 2: Good talks by Richard Gill and Jamie Robins at JSM on this:
http://www.amstat.org/meetings/jsm/2015/onlineprogram/ActivityDetails.cfm?SessionID=211222
Well, this whole thread started because minusdash and eli_sennesh objected to the concept of accusal trade for being too metaphysical.
I just need to translate that for him to street lingo.
"There is shit we know, shit we could know, and shit could not know no matter how good tech we had, we could not even know the effects it has on other stuff. So why should we say this later stuff exists? Or why should we say this does not exist? We cannot prove either."
My serious point is that one cannot avoid metaphysics, and that way too many people start out from "all this metaphysics stuff is BS, I'll just use common sense" and end up with there own (bad) counter-intuitive metaphysical theory that they insist is "not metaphysics".
You could charitably understand everything that such people (who assert that metaphysics is BS) say with a silent "up to empirical equivalence". Doesn't the problem disappear then?
No because you need a theory of metaphysics to explain what "empirical equivalence" means.
To be honest, I don't see that at all.
Well, that's where it starts to break down; because what you can, in theory, observe is different from what I can, in theory, observe.
This is because, as far as anyone can tell, observations are limited by the speed of light. I cannot, even in principle, observe the 2015 Alpha Centauri until at least 2019 (if I observe it now, I am seeing light that left it around 2011). If Alpha Centauri had suddenly exploded in 2013, I have no way of observing that until at least 2018 - even in principle.
So if the barkeeper, instead of being down the street, is rather living on a planet orbiting Alpha Centauri, then the set of what he can observe in principle is not the same as the set of what I can observe in principle.