457 research outputs found
Observational Tests of Intergalactic Enrichment Models
We summarize recent results assessing the carbon and silicon abundances of
the intergalactic medium (IGM) using the `pixel optical depth' technique. We
briefly discuss the implications of these results for models of intergalactic
enrichment, focusing on distinguishing `early' z >> 4 enrichment by the first
generations of stars and objects from `late' enrichment by 2 < z < 5 Ly-break
galaxies. We then discuss the comparison of observed QSO spectra to simulated
spectra generated from cosmological simulations that self-consistently include
enrichment, and draw qualitative implications for the general picture of
intergalactic enrichment at z > 2.Comment: 6 pages, to appear in proceedings of IAU 199 conference, "Probing
Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menar
Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics
We study the quantum measurement problem in the context of an infinite,
statistically uniform space, as could be generated by eternal inflation. It has
recently been argued that when identical copies of a quantum measurement system
exist, the standard projection operators and Born rule method for calculating
probabilities must be supplemented by estimates of relative frequencies of
observers. We argue that an infinite space actually renders the Born rule
redundant, by physically realizing all outcomes of a quantum measurement in
different regions, with relative frequencies given by the square of the wave
function amplitudes. Our formal argument hinges on properties of what we term
the quantum confusion operator, which projects onto the Hilbert subspace where
the Born rule fails, and we comment on its relation to the oft-discussed
quantum frequency operator. This analysis unifies the classical and quantum
levels of parallel universes that have been discussed in the literature, and
has implications for several issues in quantum measurement theory. It also
shows how, even for a single measurement, probabilities may be interpreted as
relative frequencies in unitary (Everettian) quantum mechanics. We also argue
that after discarding a zero-norm part of the wavefunction, the remainder
consists of a superposition of indistinguishable terms, so that arguably
"collapse" of the wavefunction is irrelevant, and the "many worlds" of
Everett's interpretation are unified into one. Finally, the analysis suggests a
"cosmological interpretation" of quantum theory in which the wave function
describes the actual spatial collection of identical quantum systems, and
quantum uncertainty is attributable to the observer's inability to self-locate
in this collection.Comment: 17 pages, 2 figures; revised version to match published version,
including authorship change. Abstract is abridge
How Did the IGM Become Enriched?
The enrichment of the intergalactic medium with heavy elements is a process
that lies at the nexus of poorly-understood aspects of physical cosmology. We
review current understanding of the processes that may remove metals from
galaxies, the basic predictions of these models, the key observational
constraints on enrichment, and how intergalactic enrichment may be used to test
cosmological simulations.Comment: 12 pages; To appear in the proceedings of the CRAL-Conference Series
I "Chemodynamics: from first stars to local galaxies", Lyon 10-14 July 2006,
France, Eds. Emsellem, Wozniak, Massacrier, Gonzalez, Devriendt, Champavert,
EAS Publications Serie
Hurdles for Recent Measures in Eternal Inflation
In recent literature on eternal inflation, a number of measures have been
introduced which attempt to assign probabilities to different pocket universes
by counting the number of each type of pocket according to a specific
procedure. We give an overview of the existing measures, pointing out some
interesting connections and generic predictions. For example, pairs of vacua
that undergo fast transitions between themselves will be strongly favored. The
resultant implications for making predictions in a generic potential landscape
are discussed. We also raise a number of issues concerning the types of
transitions that observers in eternal inflation are able to experience.Comment: 15 PRD-style pages, 5 figures, expanded discussion of measures in
Sec. II, added reference
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