It is shown how a Doubly-Special Relativity model can emerge from a quantum cellular automaton description of the evolution of countably many interacting quantum systems. We consider a onedimensional automaton that spawns the Dirac evolution in the relativistic limit of small wave-vectors and masses (in Planck units). The assumption of invariance of dispersion relations for boosted observers leads to a non-linear representation of the Lorentz group on the (ω, k) space, with an additional invariant given by the wave-vector k = π/2. The space-time reconstructed from the (ω, k) space is intrinsically quantum, and exhibits the phenomenon of relative locality.The existence of a fundamental scale of length or mass, which can be identified with the Planck scale, is a ubiquitous feature of quantum gravity models [1][2][3][4][5][6][7]. The appearance of the minimum length P = G/c 3 is the result of combining the fundamental constants that characterize physical theories describing different scales: (quantum mechanics), c (special relativity), and G (gravity). The so-called Planck length P is commonly regarded as the threshold below which the intuitive description of space-time breaks down, and new phenomenology is expected. A natural hypothesis is that quantum features become crucial in determining the structure of space-time below the Planck scale, leading to a radical departure from the traditional geometric concepts. This perspective makes one wonder about the fate of Lorentz symmetry at the Planck scale. A possible way of tackling this question is to consider a theory with two observerindependent scales, the speed of light and the Planck length, as proposed in the models of Doubly-Special Relativity (DSR) [8][9][10][11][12][13]. All the DSR models share the feature of a non-linear deformation of the Poincaré symmetry that eventually leads to a modification of the quadratic invariantSuch deformed kinematics are especially interesting since they provide new phenomenological predictions, e. g. wavelength dependence of the speed of light and a modified threshold for particle creation in collision processes. Evidences for a violation of the Lorentz energymomentum dispersion relation (1) have recently been sought in astrophysics, see e. g. the thresholds for ultrahigh-energy cosmic rays [14,15], and in cold-atom experiments [16].A recent approach to a Planck scale description of physical kinematics is that of quantum cellular automata (QCAs) [17][18][19][20][21]. The QCA generalizes the notion of cellular automaton of von Neumann [22] to the quantum case, with cells of quantum systems interacting with a finite numer of neighbors via a unitary operator describing the single step evolution [23]. We assume that each cell x of the lattice corresponds to the local value ψ(x) of a quantum field whose dynamics is described by a QCA. From this perspective the usual quantum field evolution should emerge as a large scale approximation of the automaton dynamics occurring at an hypothetical discrete Planck scale. In Ref.[17] a QCA-cal...
It is shown that under reasonable assumptions a Drake-style equation can be obtained for the probability that our universe is the result of a deliberate simulation. Evaluating loose bounds for certain terms in the equation shows that the probability is unlikely to be as high as previously reported in the literature, especially in a scenario where the simulations are recursive. Furthermore, we investigate the possibility of eavesdropping from the outside of such a simulation and introduce a general attack that can circumvent attempts at using quantum cryptography inside the simulation, even if the quantum properties of the simulation are genuine.
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