96 research outputs found
The state of Hawking radiation is non-classical
We show that the state of the Hawking radiation emitted from a large
Schwarzschild black hole (BH) deviates significantly from a classical state, in
spite of its apparent thermal nature. For this state, the occupation numbers of
single modes of massless asymptotic fields, such as photons, gravitons and
possibly neutrinos, are small and, as a result, their relative fluctuations are
large. The occupation numbers of massive fields are much smaller and suppressed
beyond even the expected Boltzmann suppression. It follows that this type of
thermal state cannot be viewed as classical or even semiclassical. We
substantiate this claim by showing that, in a state with low occupation
numbers, physical observables have large quantum fluctuations and, as such,
cannot be faithfully described by a mean-field or by a WKB-like semiclassical
state. Since the evolution of the BH is unitary, our results imply that the
state of the BH interior must also be non-classical when described in terms of
the asymptotic fields. We show that such a non-classical interior cannot be
described in terms of a semiclassical geometry, even though the average
curvature is sub-Planckian.Comment: Replaced to agree with the published version. Added explanation
On the Entropy of Strings and Branes
We show that the entropy of strings that wind around the Euclidean time
circle is proportional to the Noether charge associated with translations along
the T-dual time direction. We consider an effective target-space field theory
which includes a large class of terms in the action with various modes,
interactions and corrections. The entropy and the Noether charge are
shown to depend only on the values of fields at the boundary of space. The
classical entropy, which is proportional to the inverse of Newton's constant,
is then calculated by evaluating the appropriate boundary term for various
geometries with and without a horizon. We verify, in our framework, that for
higher-curvature pure gravity theories, the Wald entropy of static neutral
black hole solutions is equal to the entropy derived from the Gibbons-Hawking
boundary term. We then proceed to discuss horizonless geometries which contain,
due to the back-reaction of the strings and branes, a second boundary in
addition to the asymptotic boundary. Near this ``punctured'' boundary, the
time-time component of the metric and the derivatives of its logarithm approach
zero. Assuming that there are such non-singular solutions, we identify the
entropy of the strings and branes in this geometry with the entropy of the
solution to all orders in . If the asymptotic region of an
-corrected neutral black hole is connected through the bulk to a
puncture, then the black hole entropy is equal to the entropy of the strings
and branes. Later, we discuss configurations similar to the charged black
p-brane solutions of Horowitz and Strominger, with the second boundary, and
show that, to leading order in the expansion, the classical entropy
of the strings and branes is equal exactly to the Bekenstein-Hawking entropy.
This result is extended to a configuration that asymptotes to AdS.Comment: 47 pages, 1 figure, 1 table, 1 appendix, published versio
What Makes a Language Easy to Deep-Learn?
Neural networks drive the success of natural language processing. A
fundamental property of language is its compositional structure, allowing
humans to produce forms for new meanings systematically. However, unlike
humans, neural networks notoriously struggle with systematic generalization,
and do not necessarily benefit from compositional structure in emergent
communication simulations. This poses a problem for using neural networks to
simulate human language learning and evolution, and suggests crucial
differences in the biases of the different learning systems. Here, we directly
test how neural networks compare to humans in learning and generalizing
different input languages that vary in their degree of structure. We evaluate
the memorization and generalization capabilities of a pre-trained language
model GPT-3.5 (analagous to an adult second language learner) and recurrent
neural networks trained from scratch (analaogous to a child first language
learner). Our results show striking similarities between deep neural networks
and adult human learners, with more structured linguistic input leading to more
systematic generalization and to better convergence between neural networks and
humans. These findings suggest that all the learning systems are sensitive to
the structure of languages in similar ways with compositionality being
advantageous for learning. Our findings draw a clear prediction regarding
children's learning biases, as well as highlight the challenges of automated
processing of languages spoken by small communities. Notably, the similarity
between humans and machines opens new avenues for research on language learning
and evolution.Comment: 32 pages, major update: improved text, added new analyses, added
supplementary materia
Generating Benchmarks for Factuality Evaluation of Language Models
Before deploying a language model (LM) within a given domain, it is important
to measure its tendency to generate factually incorrect information in that
domain. Existing factual generation evaluation methods focus on facts sampled
from the LM itself, and thus do not control the set of evaluated facts and
might under-represent rare and unlikely facts. We propose FACTOR: Factual
Assessment via Corpus TransfORmation, a scalable approach for evaluating LM
factuality. FACTOR automatically transforms a factual corpus of interest into a
benchmark evaluating an LM's propensity to generate true facts from the corpus
vs. similar but incorrect statements. We use our framework to create two
benchmarks: Wiki-FACTOR and News-FACTOR. We show that: (i) our benchmark scores
increase with model size and improve when the LM is augmented with retrieval;
(ii) benchmark score correlates with perplexity, but the two metrics do not
always agree on model ranking; and (iii) when perplexity and benchmark score
disagree, the latter better reflects factuality in open-ended generation, as
measured by human annotators. We make our data and code publicly available in
https://github.com/AI21Labs/factor
- …