13,174 research outputs found
A glance beyond the quantum model
One of the most important problems in Physics is how to reconcile Quantum
Mechanics with General Relativity. Some authors have suggested that this may be
realized at the expense of having to drop the quantum formalism in favor of a
more general theory. However, as the experiments we can perform nowadays are
far away from the range of energies where we may expect to observe non-quantum
effects, it is difficult to theorize at this respect. Here we propose a
fundamental axiom that we believe any reasonable post-quantum theory should
satisfy, namely, that such a theory should recover classical physics in the
macroscopic limit. We use this principle, together with the impossibility of
instantaneous communication, to characterize the set of correlations that can
arise between two distant observers. Although several quantum limits are
recovered, our results suggest that quantum mechanics could be falsified by a
Bell-type experiment if both observers have a sufficient number of detectors
Return of the Boltzmann Brains
Linde in hep-th/0611043 shows that some (though not all) versions of the
global (volume-weighted) description avoid the "Boltzmann brain" problem raised
in hep-th/0610079 if the universe does not have a decay time less than 20 Gyr.
Here I give an apparently natural version of the volume-weighted description in
which the problem persists, highlighting the ambiguity of taking the ratios of
infinite volumes that appear to arise from eternal inflation.Comment: 7 pages, LaTe
A signature of anisotropic bubble collisions
Our universe may have formed via bubble nucleation in an eternally-inflating
background. Furthermore, the background may have a compact dimension---the
modulus of which tunnels out of a metastable minimum during bubble
nucleation---which subsequently grows to become one of our three large spatial
dimensions. When in this scenario our bubble universe collides with other ones
like it, the collision geometry is constrained by the reduced symmetry of the
tunneling instanton. While the regions affected by such bubble collisions still
appear (to leading order) as disks in an observer's sky, the centers of these
disks all lie on a single great circle, providing a distinct signature of
anisotropic bubble nucleation.Comment: 10 pages, 5 figures; v2: crucial error corrected, conclusions revise
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