630 research outputs found
Energy and Information Near Black Hole Horizons
The central challenge in trying to resolve the firewall paradox is to
identify excitations in the near-horizon zone of a black hole that can carry
information without injuring a freely falling observer. By analyzing the
problem from the point of view of a freely falling observer, I arrive at a
simple proposal for the degrees of freedom that carry information out of the
black hole. An infalling observer experiences the information-carrying modes as
ingoing, negative energy excitations of the quantum fields. In these states,
freely falling observers who fall in from infinity do not encounter a firewall,
but freely falling observers who begin their free fall from a location close to
the horizon are "frozen" by a flux of negative energy. When the black hole is
"mined," the number of information-carrying modes increases, increasing the
negative energy flux in the infalling frame without violating the equivalence
principle. Finally, I point out a loophole in recent arguments that an
infalling observer must detect a violation of unitarity, effective field
theory, or free infall.Comment: 25 pages, 3 figures. v2: minor clarifications, references added;
published versio
Asymptotic states of the bounce geometry
We consider the question of asymptotic observables in cosmology. We assume
that string theory contains a landscape of vacua, and that metastable de Sitter
regions can decay to zero cosmological constant by bubble nucleation. The
asymptotic properties of the corresponding bounce solution should be
incorporated in a nonperturbative quantum theory of cosmology. A recent
proposal for such a framework defines an S-matrix between the past and future
boundaries of the bounce. We analyze in detail the properties of asymptotic
states in this proposal, finding that generic small perturbations of the
initial state cause a global crunch. We conclude that late-time amplitudes
should be computed directly. This would require a string theory analogue of the
no-boundary proposal.Comment: 20 pages, 7 figures. v2: reference adde
Probabilities in the landscape: The decay of nearly flat space
We discuss aspects of the problem of assigning probabilities in eternal
inflation. In particular, we investigate a recent suggestion that the lowest
energy de Sitter vacuum in the landscape is effectively stable. The associated
proposal for probabilities would relegate lower energy vacua to unlikely
excursions of a high entropy system. We note that it would also imply that the
string theory landscape is experimentally ruled out. However, we extensively
analyze the structure of the space of Coleman-De Luccia solutions, and we
present analytic arguments, as well as numerical evidence, that the decay rate
varies continuously as the false vacuum energy goes through zero. Hence,
low-energy de Sitter vacua do not become anomalously stable; negative and zero
cosmological constant regions cannot be neglected.Comment: 18 pages, 13 figures, Mathematica notebooks available from the
authors. v2,v3: typos and omissions fixe
Anthropic Explanation of the Dark Matter Abundance
I use Bousso's causal diamond measure to make a statistical prediction for
the dark matter abundance, assuming an axion with a large decay constant f_a >>
10^{12} GeV. Using a crude approximation for observer formation, the prediction
agrees well with observation: 30% of observers form in regions with less dark
matter than we observe, while 70% of observers form in regions with more dark
matter. Large values of the dark matter ratio are disfavored by an elementary
effect: increasing the amount of dark matter while holding fixed the baryon to
photon ratio decreases the number of baryons inside one horizon volume. Thus
the prediction is rather insensitive to assumptions about observer formation in
universes with much more dark matter than our own. The key assumption is that
the number of observers per baryon is roughly independent of the dark matter
ratio for ratios near the observed value.Comment: 10 pages; v3: published version, references adde
Precursors, Gauge Invariance, and Quantum Error Correction in AdS/CFT
A puzzling aspect of the AdS/CFT correspondence is that a single bulk
operator can be mapped to multiple different boundary operators, or precursors.
By improving upon a recent model of Mintun, Polchinski, and Rosenhaus, we
demonstrate explicitly how this ambiguity arises in a simple model of the field
theory. In particular, we show how gauge invariance in the boundary theory
manifests as a freedom in the smearing function used in the bulk-boundary
mapping, and explicitly show how this freedom can be used to localize the
precursor in different spatial regions. We also show how the ambiguity can be
understood in terms of quantum error correction, by appealing to the
entanglement present in the CFT. The concordance of these two approaches
suggests that gauge invariance and entanglement in the boundary field theory
are intimately connected to the reconstruction of local operators in the dual
spacetime.Comment: 25 pages, 6 figure
Bubble, Bubble, Flow and Hubble: Large Scale Galaxy Flow from Cosmological Bubble Collisions
We study large scale structure in the cosmology of Coleman-de Luccia bubble
collisions. Within a set of controlled approximations we calculate the effects
on galaxy motion seen from inside a bubble which has undergone such a
collision. We find that generically bubble collisions lead to a coherent bulk
flow of galaxies on some part of our sky, the details of which depend on the
initial conditions of the collision and redshift to the galaxy in question.
With other parameters held fixed the effects weaken as the amount of inflation
inside our bubble grows, but can produce measurable flows past the number of
efolds required to solve the flatness and horizon problems.Comment: 30 pages, 8 figures, pdftex, minor corrections and references adde
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