Assigning probabilities to metaphysical ideas

Take all the metaphysical models of the universe that any human ever considers.

Say there are n number of mutually-incompatible ones. I don’t have a good definition of this, so our estimates will vary by orders of magnitude.

Start with 1:1 odds, or a 50% chance that one of them is correct, and a 50% chance that none were correct.

0.5/​n is the prior for a given individual metaphysical model.

You might have opinions about “50%”. Maybe you think humans are actually way less likely than that to ever think of the “right” one. Maybe you think we’re almost guaranteed to, for some reason. I started with a very general, unimposing prior of 1:1 odds. We can generalize this to p/​n, for whatever you think p is.

How big is n? I don’t know but I ran a Twitter poll asking people to pick a rough order of magnitude. I would like a number. It’s easy to lie with numbers, but it’s even easier to lie without them.

Updates away from the base rate can be made based on the complexity of the idea. This mechanism is very general, and it should apply even in this domain to some extent. Some religions are crazy complicated, so probability mass should be gouged from those. Though, estimating “complexity” is going to be very hard. The lady down the road is a witch, she made the universe. Still, do we have zero information about such complexity comparisons? I doubt that.

I have seen smart people say there is no way to assign probabilities to metaphysical ideas. They then express opinions about many worlds interpretation, the simulation argument, and others. They’ll do it with even less informative, more nebulous terms than a probability. Such as “I am skeptical”, or “seems really likely”. As a forecaster I have also seen some wildly overconfident claims made by some smart people. Many orders of magnitude above a cloud of reasonable base rate estimates. I know they don’t have that much information and aren’t calibrated.

I thought it would help to give a simple base rate template. So here is one.