I think you want to ask about P(maps|discover) / P(no maps|discover). Unless both wikipedia and my intuition are wrong.

Does catching you in this error relieve me of the responsibility of answering the question? I hope so. Because I would want to instead argue using something like P(maps|discover) vs P(maps|not discover). That doesn't take you all the way to P(discover), but it does at least give you a way to assess the evidential weight of the map evidence.

A false theory, by contrast, is simply false, it has no connection to reality. How do you assign anything other than an arbitrary probability to something that simply cannot be?

Intrade knows that one! At the Higgs boson bet over 200 people think they know how to assign a probability to the issue.

http://www.intrade.com/jsp/intrade/common/c_cd.jsp?conDetailID=622297&z=1224442713385

1: By using the counterfactuals in the Tegmark Level IV multiverse.

2: By giving it a probability of 0. If T is falsified, that means P(D|T)=0 - we obtained data that T claims is impossible. In this case, Bayes' theorem sets P(T|D)=0. Bayesianism includes all correct thinking tools, including Popperian epistemology.

But is P(D|T) really 0? We could have made a mistake and not recorded the correct data. Certainly scientists in the past have done so, and thought that they falsified theories that they didn't falsify. In this case, P(D|T) is very small but nonzero, and so is P(T|D) (unless p(D|~T) is also very small.)

3: You cannot avoid giving a probability. Because of Cox's theorem, which says we must use probability theory to reason about uncertainty (although I must confess that the assumption that we must use a single real number to reason is rather strong.)

Counterfactuals of the sort of theory that Perplexed describe do exist in a Quantum Multiverse; why not assign them probabilities?

Anyway, why would you want to make your entire epistemology contingent on a particular theory of physics? It sounds like the CR would collapse if Copenhagen turned out to be correct.