Hi all,
Despite the holiday on Thursday, we have two talks scheduled this week:
On Wednesday Lefteris Tselentis will tell us about "The Möbius games and other Bell tests for relativity”. The talk will take place at 14:00 in HIT F12.
On Friday Gilles Brassard will tell us about "Probability and consequences of living inside a computer simulation”. The talk will take place at 14:00 in HIT F12.
See below for the abstracts.
Best, Ladina
************** Title: The Möbius games and other Bell tests for relativity
Abstract: We derive multiparty games that, if the winning chance exceeds a certain limit, prove the incompatibility of the parties' causal relations with any partial order. This, in turn, means that the parties exert a back-action on the causal relations; the causal relations are dynamical. For example, a general-relativistic violation of that inequality certifies change of curvature, in the same sense as a quantum-mechanical violation of a Bell inequality certifies a source of entanglement. We discuss these games as device-independent tests of spacetime's dynamical nature in general relativity. To do so, we design a relativistic setting where, in the Minkowski spacetime, the winning chance is bound to the limits. While we do not show the violation of these inequalities within the framework of general relativity, we find otherwise tame processes with classical control of causal order that win the games deterministically. These suggest a violation of the bounds in gravitational implementations. We obtain these games by uncovering a "pairwise central symmetry" of the correlations in question. This symmetry allows us to recycle the facets of the acyclic subgraph polytope studied by Grötschel, Jünger, and Reinelt in the mid-80s for combinatorial optimization. This abstract is based on the following work: https://arxiv.org/abs/2309.15752
************** Title: Probability and consequences of living inside a computer simulation
Abstract: The question of whether or not we are living inside a computer simulation has inspired a large amount of fiction (notably the novel Simulacron-3 and the movie The Matrix), but, unsurprisingly, not much serious research. Among the more reasonable and quantitative attempts, let us mention Nick Bostrom’s simulation argument: if societies do not tend to self-destruct before acquiring a technology sufficiently advanced to create simulations that are indistinguishable from reality, in which countless simulated beings strive, our probability of living inside such a simulation approaches unity. Elon Musk even declared in 2016 that "the odds we’re in base reality is one in billions". Was he right? Through a refinement of Bostrom's argument and the introduction of an equation reminiscent of the one Drake postulated to estimate the number of extraterrestrial civilisations in the universe, we come to the opposite conclusion: the probability that we live in base reality is rather high. Nevertheless, it is legitimate to wonder if we could use quantum cryptography to preserve our privacy against our overlords should we actually live in a computer simulation.