## LESSWRONGLW

Contrast this to the notion we have in probability theory, of an exact quantitative rational judgment. If 1% of women presenting for a routine screening have breast cancer, and 80% of women with breast cancer get positive mammographies, and 10% of women without breast cancer get false positives, what is the probability that a routinely screened woman with a positive mammography has breast cancer? 7.5%. You cannot say, "I believe she doesn't have breast cancer, because the experiment isn't definite enough." You cannot say, "I believe she ...

3papetoast4mo
Only responding to this part. I'm sure you have multiple possible model of the system. If you have accounted for the possibility that your model is incorrect, then it will not be an assumption, it will be something that can be approximated into a distribution of confidence.
3Liliet B3y
Prior probabilities with no experience in a domain at all is an incoherent notion, since that implies you don't know what the words you're using even refer to. Priors include all prior knowledge, including knowledge about the general class of problems like the one you're trying to eyeball a prior for. If you're asked to perform experiments on finding out what tapirs eat - and you don't know what tapirs even are, except that they eat something apparently, judging by the formulation of the problem - you're already going to assign a prior of ~0 of 'they eat candy wrappers and rocks and are poisoned by everything and anything else, including non-candy-wrapper plastics and objects made of stone', because you have prior information on what 'eating' refers to and how it tends to work. You're probably going to assign a high prior probability to the guess that tapirs are animals, and on the basis of that assign a high prior probability to them being either herbivores, omnivores or carnivores - or insectivores, unless you include that as carnivores - since that's what you know most animals are. Priors are all prior information. It would be thoroughly irrational of you to give the tapirs candy wrappers and then when they didn't eat them, assume it was the wrong brand and start trying different ones. For additional clarification on what priors mean, imagine that if you didn't manage to give the tapirs something they actually are willing to eat within 24 hours, your family is going to be executed. In that situation, what's the rational thing to do? Are you going to start with metal sheets, car tires and ceramic pots, or are you going to start trying different kinds of animal food?

My point isn't that it is unreasonable to use symmetric (/antisymmetric) wavefunctions until we discover something that requires us to use a more complicated model. My objection is to an error in thinking that holds that such potential future discoveries are a-priori impossible. I'm with philosopher Bob on this one.

That is a great explanation. Thanks

I think quantum physicists here are making the same mistake that lead to the Gibbs paradox in classical phyiscs. Of course, my textbook in classical thermodynamics tried to sweep the Gibbs paradox under the quantum rug, and completely missed the point of what it was telling us about the subjective nature of classical entropy. Quantum physics is another deterministic reversible state-machine, so I don't see why it is different in principle from a "classical world".

While it is true that a wavefunction or something very much like it must be what the...

I have a counter-hypothesis: If the universe did distinguish between photons, but we didn't have any tests which could distinguish between photons, what this physically means is that our measuring devices, in their quantum-to-classical transitions (yes, I know this is a perception thing in MWI), are what is adding the amplitudes before taking the squared modulus. Our measurers can't distinguish, which is why we can get away with representing the hidden "true wavefunction" (or object carrying similar information) with a symmetric wavefunction. If ...

1nshepperd8y
If we had a destructive measurement device that reacted in the exact same way to photon type A vs photon type B, it would be an information-destroying irreversible process. Which would, I believe, require a drastic rewrite of much of physics due to the CPT theorem.
0hairyfigment8y
This seems like a great example of a theory that Occam's Razor should slash, or assign low probability. Though our best formal definition of the Razor is wrong [http://lesswrong.com/lw/jti/the_problem_with_aixi/].

(I don't claim to be using my notes to any great effect, but this is what I do with them):

To me, I've noticed that I seldom actually use my notes as a reference. When I need to refer to something, I go to a place in a book somewhere. Rather, during a lecture, my notebook for the class seems to function more as a way to keep me paying attention to the lecturer, and to run various complicated pieces of information (equations, etc) across my mind. (Okay, I do sort of refer to these during exam study, but the books tend to be more legible).

I also do a lot of m...

I've never understood why explaining the Born Rule is less of a problem for any of the other interpretations of QP than it is for MWI. Copenhagen, IIRC, simply asserts it as an axiom. (Rather, it seems to me that MWI is one of the few that even tries to explain it!)

0n4r98y
As I understand, it's less of a problem for a hardline Copenhagen interpretation because no definite ontological status is assigned to the wavefunction, or indeed the collapse of the wavefunction. CI can roughly be paraphrased as "Consider this set of rules for predicting experimental outcomes. Look how well it works! Of course, we're not asserting anything about actual reality here". One of those rules is the Born rule. Another is the fact that physical transformations correspond to unitary maps on the Hilbert space. All of them are postulated, and their correctness is a matter of experimental falsification/verification. Conversely, MWI assigns definite reality to the wavefunction, but denies that collapse is a real process, and does not postulate any rules about predictions of experimental outcomes. Instead, the claim that a process of measurement inevitably results in a single result being recorded - with probability given by the square amplitude of the wavefunction - must be derived from the pre-existing structure of the theory (possibly with some reasonable assumptions about gambling commitments). A conceivable alternative to MWI might have the Born rule as an additional postulate, supported only by experiment rather than following from the structure of the theory. I feel that this would be much less appealing to many of its advocates.
2The_Duck8y
I think the Born rule falls out pretty nicely in the Bohmian interpretation.

The problem that I've always had with the "utility monster" idea is that it's a misuse of what information utility functions actually encode.

In game theory or economics, a utility function is a rank ordering of preferred states over less preferred states for a single agent (who presumably has some input he can adjust to solve for his preferred states). That's it. There are no "global" utility functions or "collective" utility measures that don't run into problems when individual goals conflict.

Given that an agent's utility fu...

2[anonymous]8y
I think the misunderstanding here is that some of you interpret the post as a call to change your values. However, it is merely a suggestion for the implementation of values that already exist, such as utilitarian preferences. The idea is clearly never going to be attractive to people who care exactly zero about the SWB of others. But those are not a target group of effective altruism or any charity really.

Hmm. In a certain sense, is these sufficient conditions to actually define an organization with boundaries?

I don't think many of us have ever seen the outside of that university. :-P