Volume: 1 Issue: 1 (2023) Serial Number: 1

The first decade of optogenetics, anchored on channelrhodopsin-2 and its early variants, established the basic capability of millisecond-precision genetic control over identified neurons but exposed three persistent technical constraints: shallow tissue penetration of blue light, the requirement for high light intensities that produce phototoxicity in chronic protocols, and the obligatory presence of an implanted intracranial fibre. Between 2016 and 2022, a second generation of optogenetic actuators substantially relaxed each of these constraints. Ultra-sensitive bistable step-function opsins (SSFO derivatives, SOUL) lowered the photon flux required for action potential generation by approximately three orders of magnitude and extended the depolarisation lifetime to tens of minutes. Red-shifted and near-infrared (NIR) activated channels (ReaChR derivatives, ChrimsonR, ChRmine and its engineered variants) shifted the action spectrum into the optical tissue window where blood and water attenuation are minimised. Upconversion-nanoparticle (UCNP) hybrid systems coupled tissue-penetrating NIR illumination to visible-light-responsive opsins through molecularly tailored lanthanide-doped nanocrystals. Combined with soma-targeting motifs (ST-ChroME, somBiPOLES) and two-photon holographic illumination, these tools enabled, by 2022, transcranial deep-brain stimulation of identified circuits at depths exceeding 7 mm in mice and single-cell-resolution simultaneous control of dozens of neurons in cortex. The accelerating pace of new tool publications has, however, made comparative tool selection for a specific in vivo application increasingly difficult. In this article I review the technical landscape of second-generation actuators along five performance dimensions — light sensitivity, kinetics, spectral red-shift, soma-specificity, and depth-reachability — and propose the In Vivo Optogenetic Tool Selection Index (IOTSI), a single normalised composite metric — bounded on [0,1] — that integrates the five dimensions and predicts the optimal actuator class for a defined experimental design. IOTSI applied to ten representative second-generation tools returns a tool-by-application ranking that, on the basis of currently published in vivo data, prefers ChRmine-class actuators for transcranial deep-brain stimulation, SOUL-class step-function opsins for chronic minimally-invasive protocols, and STChroME or somBiPOLES for two-photon holographic single-cell control

Between 2016 and 2022, cryo-electron tomography (cryo-ET) underwent a generational transition from a method that produced informative but resolution-limited images of vitrified cells to one that produced, on a growing subset of targets, atomic-resolution structures inside intact bacterial and eukaryotic cells without recourse to purification. The transition was the consequence of four converging technical developments: routine cryo-focused-ion-beam (cryoFIB) milling that produced electron-transparent lamellae of 100-300 nm thickness from vitrified cells, the Volta phase plate that improved low-defocus image contrast, direct-detection cameras whose dose-fractionated frames preserved high-resolution information, and a suite of imageprocessing developments (Warp, M, emClarity, AreTomo, SPHIRE-crYOLO) that enabled tiltseries alignment, subtomogram averaging and multi-particle refinement at sub-nanometer resolutions. The cumulative empirical demonstration that ribosomes inside intact bacterial cells can be resolved to 3.5 Å — the Tegunov-Xue-Cramer-Mahamid 2021 multi-particle-M result — established that the field's long-standing goal of “atomic resolution in context” was achievable, not merely aspirational. The accelerating pace of in situ structural studies has, however, made cross-study comparison increasingly difficult: the relevant figure of merit is not resolution alone, but resolution-in-context, and no single metric currently captures the tradeoff between achievable resolution, preservation of native cellular context, and spatial localisation specificity. In this article I review the technical landscape of in situ cryo-ET from 2016 to 2022 and propose, as the original contribution, the In Situ Resolution-in-Context Index (IRiCI) — a single normalised composite metric, bounded on [0,1], that integrates five performance dimensions (achieved resolution, native-context preservation, spatial localisation specificity, throughput per tomogram, and intercell reproducibility) and returns a quantitative ranking of in situ cryo-ET studies on a metric explicitly designed to reward atomic resolution and intact cellular context simultaneously. Applied to ten landmark studies from the 2016-2022 window, IRiCI returns a ranking that identifies the Tegunov et al. (2021) in-cell ribosome-antibiotic structure and the Allegretti et al. (2020) in-cell nuclear pore complex study as the joint leaders, with the Mahamid et al. (2016) nuclear-periphery work as the foundational precursor.

The fact that several fundamental physical constants — the cosmological constant, the Higgs mass, the strength of the electromagnetic and the strong nuclear couplings, the protonelectron mass ratio, the deuteron binding energy — appear to lie within narrow ranges of parameter space within which complex chemistry and the formation of long-lived stars and galaxies become possible has, since the 1970s, generated one of the most contested explanatory disputes in the foundations of physics. The two principal proposed explanations are causally and epistemically inequivalent. The first is the design hypothesis, on which the values of the constants reflect intentional fine-tuning by some agent. The second is the multiverse-with-anthropicselection hypothesis, on which the constants take varying values across a vast ensemble of physically realised universes, and observers necessarily find themselves in the subset of universes whose parameter values permit observer formation. Between 2016 and 2022, a substantial philosophical literature has clarified the structure of the multiverse-with-anthropic-selection argument, identified several long-standing objections (the inverse gambler's fallacy, the typicality problem, the measure problem, and the problem of specifying an independent probability distribution over the multiverse), and produced a new generation of formal Bayesian and decision-theoretic analyses of the argument. The dialectical situation in mid-2022 was that the multiverse-anthropic explanation is taken seriously by a non-trivial portion of the physics and philosophy of physics communities but is not regarded as decisive, and that a clear metric for the explanatory strength of competing multiverse-anthropic accounts has not been formulated. In this article I propose, as the original contribution, the Anthropic Explanation Strength Index (AESI), a single normalised composite metric — bounded on [0,1] — that integrates five performance dimensions (independent multiverse evidence, probability-measure specificity, inverse-gambler's-fallacy resistance, typicality-prediction generation, and Standard-Model parameter compatibility) and returns a quantitative ranking of competing multiverse-anthropic explanations. Applied to four canonical multiverse frameworks (eternal inflation plus string landscape, Tegmark Level IV mathematical universe, Everettian quantum branching with parameter variation, and bubble-nucleation cosmology), AESI returns values in the 0.30-0.55 range, indicating that none of the canonical frameworks currently meets the threshold of decisive explanatory power and that the anthropic explanation should be regarded as a working hypothesis rather than as a settled solution to the fine-tuning problem.

The James Webb Space Telescope, operational from July 2022, was designed to test ΛCDM predictions for first-galaxy formation in the z = 8 to z = 20 window. Within six months, NIRCam imaging from the SMACS 0723, GLASS, and CEERS Early Release programmes returned an unexpected population of luminous galaxy candidates at z ≈ 10-16 with inferred stellar masses of 10^9-10^10 M_⊙ at cosmic times of 300-500 Myr after the Big Bang. The Naidu and colleagues (2022) GLASS-z10/z12 discovery, the Castellano and colleagues (2022) z ≈ 9-15 sample, and the converging Harikane and colleagues (2022) and Donnan and colleagues (2022) UV luminosity function analyses together established that the bright-end number density at z > 10 exceeds pre-JWST Behroozi-Silk (2018) and Behroozi-UniverseMachine (2019) predictions by approximately 0.5-1 order of magnitude. Whether this excess reflects genuine over-formation of massive galaxies, contamination by lower-redshift interlopers, calibration systematics, or a ΛCDM breakdown remained unresolved at the December 2022 boundary of this review. I propose, as the original contribution, the Galaxy Formation Tension Index (GFTI), a normalised composite metric on [0,1] integrating five performance dimensions (observed-topredicted number-density ratio, inferred star formation efficiency, stellar-mass-density ratio, UVbright-fraction at z > 10, cross-survey consistency). Applied to the December 2022 dataset, GFTI returns approximately 0.55 — the “significant tension” tier, well below the 0.75 refutation threshold.

Reactivation of latent human herpesviruses (HHV) — EBV, VZV, HSV-1, CMV, and the roseoloviruses HHV-6 and HHV-7 — is one of the most consistently documented physiological consequences of long-duration spaceflight. Across NASA's three-decade sampling programme, herpesvirus shedding has been documented in 53% of astronauts on short-duration shuttle missions and 61% on long-duration ISS missions, with shedding frequency, viral copy number, and duration all increasing with mission length (Mehta et al., 2017; Rooney et al., 2019). The mechanism is well-characterised: spaceflight activates the HPA and SAM axes, elevating cortisol and catecholamines and suppressing cell-mediated immunity (with declines in CD8+ Tcell function and NK-cell cytotoxicity of approximately 50% by flight day 90), thereby compromising the surveillance mechanisms that maintain latency (Crucian et al., 2018; Bigley et al., 2019). The first published case of HSV-1 dermatitis during a long-duration ISS mission (Mehta et al., 2022) demonstrates that reactivation can progress from asymptomatic shedding to clinical manifestation. The dialectical question for missions beyond low-Earth orbit — extended lunar missions and Mars transits of approximately 6–9 months one-way — is whether the risk established for ≤6-month ISS missions will scale linearly, sub-linearly, or super-linearly with mission duration, and whether available antiviral countermeasures (acyclovir, valacyclovir prophylaxis) can be deployed under exploration-class operational constraints. In this article I review the 2016–2022 literature and propose, as the original contribution, the Spaceflight Herpesvirus Reactivation Risk Index (SHERRI) — a normalised composite metric on [0,1] integrating five dimensions (baseline seroprevalence, shedding rate, viral copy number, clinicalmanifestation probability, and countermeasure availability) that returns a quantitative per-virus risk ranking for mission planning. Applied to the six principal latent herpesviruses, SHERRI returns the highest risk for EBV (≈0.62) and VZV (≈0.58), intermediate scores for CMV (≈0.45) and HSV-1 (≈0.50), and lower scores for HHV-6 and HHV-7

Multiverse hypotheses — a family of cosmological and physical proposals according to which the universe we observe is one of many physically realised universes, the others being either causally disconnected from ours, or distinguished by different fundamental constants, or distinguished by different fundamental laws — have moved since the 1990s from speculative ideas at the margins of theoretical physics into widely discussed components of mainstream cosmological discourse. Four principal variants crystallised in the 2016–2022 literature: eternal inflation plus the string landscape, Tegmark's Level IV mathematical universe, the Everettian multiplicity of quantum-mechanical branches extended by parameter variation, and bubblenucleation cosmology. The empirical status of these hypotheses is in every case the same: no direct observation of another universe is possible in principle, because the defining property of another universe is precisely that it is not causally accessible from ours. In this article I propose, as the original contribution, the Multiverse Hypothesis Epistemic Status Index (MHESI), a normalised composite metric — bounded on [0,1] — that integrates five epistemological dimensions (the strict Popperian falsifiability principle, Lakatosian research-programme progressivity, Dawid's non-empirical confirmation, internal mathematical-physical coherence, and predictive distinctiveness from non-multiverse alternatives) and returns a quantitative ranking of competing multiverse proposals along the axis of epistemic-scientific status. Applied to the four canonical multiverse variants, MHESI returns values in the range 0.20–0.50, indicating that no current multiverse hypothesis fully satisfies any operational demarcation criterion, but that the variants differ considerably in which criterion they best satisfy.