I agree SIA is non-martingale (common thirder property). I think one thing you are saying is that if we agree with “simple Bayes” we can’t have probabilities over personal histories, and a big motivation for SIA is simple Bayes, so SIA-ers will tend to not assign consistent probabilities over personal histories; I’d agree there.
I feel that it probably has timeline inconsistencies, such as assigning a different size to the universe at different moments, without any observations to update on.
This is standard thirding. In standard Sleeping Beauty, between Sunday → Monday, Beauty gets no non-trivial observations. Yet her epistemic state changes, in the following sense: Usually, you should move your ‘current time’ beliefs forward according to a clock (assuming you have a good internal clock). However, from Sunday → Monday, Beauty should assign some probability to “it is Tuesday” which is not updating according to an internal clock. (Actually, halfers agree here, that upon awakening, she should consider it plausible that it’s Tuesday.). Thirders correspondingly assign more probability to Tails in a non-Martingale fashion (and this is not so counter-intuitive if you account for the internal clock issue). This is a probability for an objective event that happened in the past predictably changing. It violates Martingale, yet Dutch book arguments suggest that violating Martingale here is necessary to avoid sure losses (assuming CDT, which is the common background Dutch book assumption).
Analogous case for universe size: Number of times Beauty wakes up depends on how scientists measure size of universe on Monday (on Sunday no one knows what the size is).
That’s standard Sleeping Beauty; I crafted duplicate Sleeping Beauty so that there was no memory-loss issue. Sleeping Beauty always knows what day it is.
Are you saying that SIA+SSSA suffers from these problems?
SSSA+SIA does not assign consistent probabilities over full personal histories. (It assigns probabilites over centered worlds and some amount of personal history probability can be derived from that, yet won’t satisfy assumptions of OP for personal probabilities, e.g. won’t consider to be exhaustive.)
In standard Sleeping Beauty there is no memory loss from Sunday → Monday. This is part of David Lewis’s argument for single-halfing (using Martingale assumption). So violating Martingale even when your mind hasn’t been messed with in the intervening time is standard thirding.
With duplicate Sleeping Beauty we have analogous Dutch book arguments for thirding. If you assign to Heads on Sunday then you must assign to Heads on Monday if you are a CDT to avoid sure losses. Sure loss for 1⁄2 Heads on Sunday, 1⁄2 heads on Monday is: on Sunday, the bookie, who has no info advantage on Beauty, offers “-$6 if Heads, +$7 if Tails”, which Beauty accepts; then on Monday the bookie, who has also been split so he doesn’t know which room it is, offers “+$5 if Heads, -$4 if Tails”; the total shared account has -$1 if Heads, -$1 if Tails, since the Monday bet happens twice if Tails.
(One can appeal to utility function re: shared accounts, however, if it’s a shared account for an altruistic fund, which all copies of Beauty care about equally, we still have a problem)
Someone can hold “I don’t buy Dutch book arguments at all, I think Martingale can be supported on other assumptions”, however historically, diachronic Dutch book arguments have been a significant argument for Martingale.
I agree SIA is non-martingale (common thirder property). I think one thing you are saying is that if we agree with “simple Bayes” we can’t have probabilities over personal histories, and a big motivation for SIA is simple Bayes, so SIA-ers will tend to not assign consistent probabilities over personal histories; I’d agree there.
This is standard thirding. In standard Sleeping Beauty, between Sunday → Monday, Beauty gets no non-trivial observations. Yet her epistemic state changes, in the following sense: Usually, you should move your ‘current time’ beliefs forward according to a clock (assuming you have a good internal clock). However, from Sunday → Monday, Beauty should assign some probability to “it is Tuesday” which is not updating according to an internal clock. (Actually, halfers agree here, that upon awakening, she should consider it plausible that it’s Tuesday.). Thirders correspondingly assign more probability to Tails in a non-Martingale fashion (and this is not so counter-intuitive if you account for the internal clock issue). This is a probability for an objective event that happened in the past predictably changing. It violates Martingale, yet Dutch book arguments suggest that violating Martingale here is necessary to avoid sure losses (assuming CDT, which is the common background Dutch book assumption).
Analogous case for universe size: Number of times Beauty wakes up depends on how scientists measure size of universe on Monday (on Sunday no one knows what the size is).
That’s standard Sleeping Beauty; I crafted duplicate Sleeping Beauty so that there was no memory-loss issue. Sleeping Beauty always knows what day it is.
Are you saying that SIA+SSSA suffers from these problems?
SSSA+SIA does not assign consistent probabilities over full personal histories. (It assigns probabilites over centered worlds and some amount of personal history probability can be derived from that, yet won’t satisfy assumptions of OP for personal probabilities, e.g. won’t consider
In standard Sleeping Beauty there is no memory loss from Sunday → Monday. This is part of David Lewis’s argument for single-halfing (using Martingale assumption). So violating Martingale even when your mind hasn’t been messed with in the intervening time is standard thirding.
With duplicate Sleeping Beauty we have analogous Dutch book arguments for thirding. If you assign
(One can appeal to utility function re: shared accounts, however, if it’s a shared account for an altruistic fund, which all copies of Beauty care about equally, we still have a problem)
Someone can hold “I don’t buy Dutch book arguments at all, I think Martingale can be supported on other assumptions”, however historically, diachronic Dutch book arguments have been a significant argument for Martingale.
Yep!
I suppose it’s back to my old conclusion—decision theory is more fundamental that probability theory. https://arxiv.org/abs/1110.6437
Just finished up a post on probabilities over centered worlds.