1,769 research outputs found
Prediction and explanation in the multiverse
Probabilities in the multiverse can be calculated by assuming that we are
typical representatives in a given reference class. But is this class well
defined? What should be included in the ensemble in which we are supposed to be
typical? There is a widespread belief that this question is inherently vague,
and that there are various possible choices for the types of reference objects
which should be counted in. Here we argue that the ``ideal'' reference class
(for the purpose of making predictions) can be defined unambiguously in a
rather precise way, as the set of all observers with identical information
content. When the observers in a given class perform an experiment, the class
branches into subclasses who learn different information from the outcome of
that experiment. The probabilities for the different outcomes are defined as
the relative numbers of observers in each subclass. For practical purposes,
wider reference classes can be used, where we trace over all information which
is uncorrelated to the outcome of the experiment, or whose correlation with it
is beyond our current understanding. We argue that, once we have gathered all
practically available evidence, the optimal strategy for making predictions is
to consider ourselves typical in any reference class we belong to, unless we
have evidence to the contrary. In the latter case, the class must be
correspondingly narrowed.Comment: Minor clarifications adde
Anthropic reasoning in multiverse cosmology and string theory
Anthropic arguments in multiverse cosmology and string theory rely on the
weak anthropic principle (WAP). We show that the principle, though ultimately a
tautology, is nevertheless ambiguous. It can be reformulated in one of two
unambiguous ways, which we refer to as WAP_1 and WAP_2. We show that WAP_2, the
version most commonly used in anthropic reasoning, makes no physical
predictions unless supplemented by a further assumption of "typicality", and we
argue that this assumption is both misguided and unjustified. WAP_1, however,
requires no such supplementation; it directly implies that any theory that
assigns a non-zero probability to our universe predicts that we will observe
our universe with probability one. We argue, therefore, that WAP_1 is
preferable, and note that it has the benefit of avoiding the inductive
overreach characteristic of much anthropic reasoning.Comment: 7 pages. Expanded discussion of selection effects and some minor
clarifications, as publishe
Molecular tweezers and chiral reagents: Synthesis of noval disubsituted 5,6,8,9-tetrahydrodibenz[a,j]anthracenes
Thesis (B.S.) in Chemistry -- University of Illinois at Urbana-Champaign, 1990.Includes bibliographical references (leaves 18-19)Microfiche of typescript. [Urbana, Ill.]: Photographic Services, University of Illinois, U of I Library, [1990]. 1 microfiche (24 frames): negative.s 1990 ilu n
Self-Modification of Policy and Utility Function in Rational Agents
Any agent that is part of the environment it interacts with and has versatile
actuators (such as arms and fingers), will in principle have the ability to
self-modify -- for example by changing its own source code. As we continue to
create more and more intelligent agents, chances increase that they will learn
about this ability. The question is: will they want to use it? For example,
highly intelligent systems may find ways to change their goals to something
more easily achievable, thereby `escaping' the control of their designers. In
an important paper, Omohundro (2008) argued that goal preservation is a
fundamental drive of any intelligent system, since a goal is more likely to be
achieved if future versions of the agent strive towards the same goal. In this
paper, we formalise this argument in general reinforcement learning, and
explore situations where it fails. Our conclusion is that the self-modification
possibility is harmless if and only if the value function of the agent
anticipates the consequences of self-modifications and use the current utility
function when evaluating the future.Comment: Artificial General Intelligence (AGI) 201
Credible threat: Perceptions of pandemic coronavirus, climate change and the morality and management of global risks
Prior research suggests that the pandemic coronavirus pushes all the “hot spots” for risk perceptions, yet both governments and populations have varied in their responses. As the economic impacts of the pandemic have become salient, governments have begun to slash their budgets for mitigating other global risks, including climate change, likely imposing increased future costs from those risks. Risk analysts have long argued that global environmental and health risks are inseparable at some level, and must ultimately be managed systemically, to effectively increase safety and welfare. In contrast, it has been suggested that we have worry budgets, in which one risk crowds out another. “In the wild,” our problem-solving strategies are often lexicographic; we seek and assess potential solutions one at a time, even one attribute at a time, rather than conducting integrated risk assessments. In a U.S. national survey experiment in which participants were randomly assigned to coronavirus or climate change surveys (N = 3203) we assess risk perceptions, and whether risk perception “hot spots” are driving policy preferences, within and across these global risks. Striking parallels emerge between the two. Both risks are perceived as highly threatening, inequitably distributed, and not particularly controllable. People see themselves as somewhat informed about both risks and have moral concerns about both. In contrast, climate change is seen as better understood by science than is pandemic coronavirus. Further, individuals think they can contribute more to slowing or stopping pandemic coronavirus than climate change, and have a greater moral responsibility to do so. Survey assignment influences policy preferences, with higher support for policies to control pandemic coronavirus in pandemic coronavirus surveys, and higher support for policies to control climate change risks in climate change surveys. Across all surveys, age groups, and policies to control either climate change or pandemic coronavirus risks, support is highest for funding research on vaccines against pandemic diseases, which is the only policy that achieves majority support in both surveys. Findings bolster both the finite worry budget hypothesis and the hypothesis that supporters of policies to confront one threat are disproportionately likely also to support policies to confront the other threat.publishedVersio
The Genetic Component of the Forced Diving Bradycardia Response in Mammals
We contrasted the forced diving bradycardia between two genetically similar (inbred) rat strains (Fischer and Buffalo), compared to that of outbred rats (Wistar). The animals were habituated to forced diving for 4 weeks. Each animal was then tested during one 40 s dive on each of 3 days. The heart rate (fH) was measured before, during, and after each dive. Fischer and Buffalo exhibited marked difference in dive bradycardia (Fischer: 120.9 ± 14.0 beats min−1 vs. Buffalo: 92.8 ± 12.8 beats min−1, P < 0.05). Outbred rats showed an intermediate response (103.0 ± 30.9 beats min−1) but their between-animal variability in mean dive fH and pre-diving resting fH were higher than the inbred strains (P < 0.05), which showed no difference (P > 0.05). The decreased variability in fH in inbred rats as compared with the outbred group indicates that reduced genetic variability minimizes variability of the diving bradycardia between individuals. Heritability within strains was assessed by the repeatability (R) index and was 0.93 ± 0.05 for the outbred, 0.84 ± 0.16 for Buffalo, and 0.80 ± 0.12 for Fischer rats for fH during diving. Our results suggest that a portion of the mammalian diving bradycardia may be a heritable trait
An Infrared Divergence Problem in the cosmological measure theory and the anthropic reasoning
An anthropic principle has made it possible to answer the difficult question
of why the observable value of cosmological constant (
GeV) is so disconcertingly tiny compared to predicted value of vacuum
energy density GeV. Unfortunately, there is a
darker side to this argument, as it consequently leads to another absurd
prediction: that the probability to observe the value for randomly
selected observer exactly equals to 1. We'll call this controversy an infrared
divergence problem. It is shown that the IRD prediction can be avoided with the
help of a Linde-Vanchurin {\em singular runaway measure} coupled with the
calculation of relative Bayesian probabilities by the means of the {\em
doomsday argument}. Moreover, it is shown that while the IRD problem occurs for
the {\em prediction stage} of value of , it disappears at the {\em
explanatory stage} when has already been measured by the observer.Comment: 9 pages, RevTe
The spherical probe electric field and wave experiment
The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed
Parathyroid hormone 1-34 and skeletal anabolic action: The use of parathyroid hormone in bone formation
Intermittently administered parathyroid hormone (PTH 1-34) has been shown to promote bone formation in both human and animal studies. The hormone and its analogues stimulate both bone formation and resorption, and as such at low doses are now in clinical use for the treatment of severe osteoporosis. By varying the duration of exposure, parathyroid hormone can modulate genes leading to increased bone formation within a so-called ‘anabolic window’. The osteogenic mechanisms involved are multiple, affecting the stimulation of osteoprogenitor cells, osteoblasts, osteocytes and the stem cell niche, and ultimately leading to increased osteoblast activation, reduced osteoblast apoptosis, upregulation of Wnt/β-catenin signalling, increased stem cell mobilisation, and mediation of the RANKL/OPG pathway. Ongoing investigation into their effect on bone formation through ‘coupled’ and ‘uncoupled’ mechanisms further underlines the impact of intermittent PTH on both cortical and cancellous bone. Given the principally catabolic actions of continuous PTH, this article reviews the skeletal actions of intermittent PTH 1-34 and the mechanisms underlying its effect
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