On the Non-Existence of Nash Equilibrium in Games with Resource-Bounded Players

TL;DR

This paper demonstrates that in certain sequences of computational games, Nash equilibria may not exist when players are resource-bounded, highlighting fundamental limitations of equilibrium concepts in such settings.

Contribution

It proves the non-existence of polynomial-time Nash equilibria in sequences of resource-bounded games assuming one-way functions, and shows that computational constraints can prevent equilibrium existence.

Findings

No polynomial-time Nash equilibrium exists under certain conditions.

Resource bounds can prevent the existence of Nash equilibria.

Examples illustrate limitations of equilibrium concepts with computational constraints.

Abstract

We consider sequences of games $\mathcal{G}=\{G_1,G_2,\ldots\}$ where, for all $n$, $G_n$ has the same set of players. Such sequences arise in the analysis of running time of players in games, in electronic money systems such as Bitcoin and in cryptographic protocols. Assuming that one-way functions exist, we prove that there is a sequence of 2-player zero-sum Bayesian games $\mathcal{G}$ such that, for all $n$, the size of every action in $G_n$ is polynomial in $n$, the utility function is polynomial computable in $n$, and yet there is no polynomial-time Nash equilibrium, where we use a notion of Nash equilibrium that is tailored to sequences of games. We also demonstrate that Nash equilibrium may not exist when considering players that are constrained to perform at most $T$ computational steps in each of the games $\{G_i\}_{i=1}^{\infty}$. These examples may shed light on competitive settings where the availability of more running time or faster algorithms lead to a "computational arms race", precluding the existence of equilibrium. They also point to inherent limitations of concepts such "best response" and Nash equilibrium in games with resource-bounded players.