When to take one box, when to take two: A concrete analysis of Newcomb's problem
Abstract
Fifty-seven years of debate have not led to a consensus on Newcomb's problem. I argue that this failure comes from not viewing the problem in concrete terms, for which common-sense intuitions are clearly applicable. If near-perfect predictions are not required - only predictions good enough that Evidential Decision Theory (EDT) recommends taking only one box - Newcomb scenarios without any fantastic elements are actually feasible. I give a detailed account of such concrete scenarios, in which the decision-maker has varying amounts of information about the prediction process. I argue that in these scenarios it is rational to take both boxes, as Causal Decision Theory (CDT) recommends. To make this more convincing, I introduce a simpler impersonal Newcomb problem, also with a concrete realization, to help bridge causal intuitions from everyday decisions to the standard Newcomb scenario. I also argue that Newcomb's problem with nearly perfect predictions can only be realized by a (currently fantastic) process in which the Predictor accurately simulates the thoughts of a Participant. In a functionalist view of consciousness, this simulation will be a conscious entity, whose experience will not be distinguishable from that of a ``real'' person. In this scenario, CDT recommends taking one box. I conclude that when Newcomb's problem is properly analysed in concrete terms, CDT gives the correct answer in all scenarios.
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BibTeX
@misc{neal2026when,
title = {{When to take one box, when to take two: A concrete analysis of Newcomb's problem}},
author = {Radford M. Neal},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.28825},
eprint = {2608.28825},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28825},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - When to take one box, when to take two: A concrete analysis of Newcomb's problem
AU - Radford M. Neal
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2608.28825
UR - https://arxiv.org/abs/2608.28825
AB - Fifty-seven years of debate have not led to a consensus on Newcomb's problem. I argue that this failure comes from not viewing the problem in concrete terms, for which common-sense intuitions are clearly applicable. If near-perfect predictions are not required - only predictions good enough that Evidential Decision Theory (EDT) recommends taking only one box - Newcomb scenarios without any fantastic elements are actually feasible. I give a detailed account of such concrete scenarios, in which the decision-maker has varying amounts of information about the prediction process. I argue that in these scenarios it is rational to take both boxes, as Causal Decision Theory (CDT) recommends. To make this more convincing, I introduce a simpler impersonal Newcomb problem, also with a concrete realization, to help bridge causal intuitions from everyday decisions to the standard Newcomb scenario. I also argue that Newcomb's problem with nearly perfect predictions can only be realized by a (currently fantastic) process in which the Predictor accurately simulates the thoughts of a Participant. In a functionalist view of consciousness, this simulation will be a conscious entity, whose experience will not be distinguishable from that of a ``real'' person. In this scenario, CDT recommends taking one box. I conclude that when Newcomb's problem is properly analysed in concrete terms, CDT gives the correct answer in all scenarios.
ER -