[{"content":" The history of the universe is a tug-of-war between the attractive force of gravity and the repulsive push of dark energy. While galaxies and clusters are defined by chaotic mergers and rapid gravitational growth, cosmic voids are the emptiest regions of space and the first places where gravity loses this battle. This makes them a unique window into exactly how and when cosmic expansion takes over.\nTo uncover this transition, we utilized state-of-the-art cosmological simulations to trace the life cycle and evolution of these underdense regions across 12.5 billion years of history. By categorizing voids based on their relative rank within their population rather than their absolute physical size, we successfully mitigated the selection biases introduced by galaxy formation that otherwise can lead to counterintuitive results. Through this relative framework, we discovered that void evolution is not a continuous process of emptying out. Instead, once the universe reaches a certain age, these structures settle into a calm and stable state, passively following the expansion of the cosmos.\nThis stabilization is clearly visible in the image above. While the dark matter densities on the left side show an expected evolution, with densities inside voids decreasing as matter evacuates and accumulates at their boundary, the densities of halos (our proxies for visible galaxies) on the right remain remarkably stable over time. Moreover, we also discovered that the expected evolution of dark matter densities can be reliably predicted with simple linear growth theory. Small deviations still persist, but these may point toward interpreting voids as \u0026lsquo;separate universes\u0026rsquo; that exhibit a naturally earlier and more potent dark energy onset.\nUltimately, these stable voids offer an exquisite and reliable window into the nature of dark energy, paving the way for more accurate measurements of the accelerated expansion of the cosmos.\n","date":"May 1, 2026","externalUrl":null,"permalink":"/publications/voids-pristine-evolution/","section":"Publications","summary":" The history of the universe is a tug-of-war between the attractive force of gravity and the repulsive push of dark energy. While galaxies and clusters are defined by chaotic mergers and rapid gravitational growth, cosmic voids are the emptiest regions of space and the first places where gravity loses this battle. This makes them a unique window into exactly how and when cosmic expansion takes over.\nTo uncover this transition, we utilized state-of-the-art cosmological simulations to trace the life cycle and evolution of these underdense regions across 12.5 billion years of history. By categorizing voids based on their relative rank within their population rather than their absolute physical size, we successfully mitigated the selection biases introduced by galaxy formation that otherwise can lead to counterintuitive results. Through this relative framework, we discovered that void evolution is not a continuous process of emptying out. Instead, once the universe reaches a certain age, these structures settle into a calm and stable state, passively following the expansion of the cosmos.\n","title":"Frozen in Time: Voids as Pristine Laboratories of Physics","type":"publications"},{"content":" The recent explosion in generative AI and Large Language Models (LLMs) offers a powerful opportunity to accelerate software development and create new tools, such as interactive scientific visualizations. Yet this also introduces a significant risk: the tendency for AI to \u0026ldquo;hallucinate\u0026rdquo; or simplify scientific laws to satisfy coding tasks or context limits. Moreover, these LLMs often lack the specialized intuition needed to distinguish between a functional script and a rigorously sound model, showcasing the need for expert guidance.\nTo address this risk, we developed the \u0026ldquo;Scientist-AI-Loop\u0026rdquo; (SAIL) framework, a workflow that keeps the researcher at the helm of the development process. SAIL structurally decouples domain logic and scientific concepts from the code syntax, allowing researchers to serve as strict project \u0026ldquo;Architects\u0026rdquo; while delegating code implementation to AI. By maintaining this human-in-the-loop oversight, scientists can verify that their software adheres to fundamental principles while still benefiting immensely from AI assistance.\nThis workflow is illustrated through our two case studies, including the gravitational lensing visualization depicted above. While this image displays distortions from a point mass lens, the tool also models complex structures like cosmic voids. You can try both visualizations here. These tools successfully balance high-performance rendering with physical fidelity. More importantly, by establishing a framework to identify and fix AI \u0026ldquo;failure modes\u0026rdquo;, such as an algorithm naively inverting mass distributions to model voids, scientists across all disciplines can ensure their code remains robust throughout rapid development.\nConsequently, the SAIL methodology allows researchers to condense development time from months to days. It empowers experts to independently build interactive applications, fundamentally changing how we share and communicate scientific concepts and discoveries.\n","date":"March 1, 2026","externalUrl":null,"permalink":"/publications/sail-ai-visualization-tools/","section":"Publications","summary":" The recent explosion in generative AI and Large Language Models (LLMs) offers a powerful opportunity to accelerate software development and create new tools, such as interactive scientific visualizations. Yet this also introduces a significant risk: the tendency for AI to “hallucinate” or simplify scientific laws to satisfy coding tasks or context limits. Moreover, these LLMs often lack the specialized intuition needed to distinguish between a functional script and a rigorously sound model, showcasing the need for expert guidance.\n","title":"SAIL: A Framework for Rigorous AI-Assisted Scientific Coding","type":"publications"},{"content":" Cosmic voids are among the most powerful tools we have for mapping the universe, but they come with a high computational cost. To accurately predict their sizes and densities, researchers traditionally have to run massive, time-consuming simulations for every single variation of the universe’s physical parameters and laws.\nTo solve this, we developed a set of \u0026ldquo;emulators\u0026rdquo; based on neural networks. By training these algorithms on thousands of gravity-only simulations, we created an AI capable of predicting void statistics almost instantly by learning how these statistics depend on the physical parameters of the universe. This allows us to bypass the need for brute-force computation, enabling much faster and more reliable cosmological parameter estimation.\nThe image above highlights the impressive reliability of these emulators, maintaining high performance across diverse data sets. We proved that these emulators remain accurate even when applied to simulations with different resolutions or the added complexity of \u0026ldquo;messy\u0026rdquo; gas and star formation physics. Ultimately, this approach turns cosmic voids into a robust probe, allowing us to measure the universe\u0026rsquo;s fundamental ingredients with great efficiency.\nThese findings demonstrate that neural network emulators can successfully maintain accuracy despite the absence of \u0026ldquo;messy\u0026rdquo; gas and star formation physics in the training process, highlighting that voids are a highly reliable probe for extracting cosmological information.\n","date":"January 1, 2026","externalUrl":null,"permalink":"/publications/voids-neural-network-emulators/","section":"Publications","summary":" Cosmic voids are among the most powerful tools we have for mapping the universe, but they come with a high computational cost. To accurately predict their sizes and densities, researchers traditionally have to run massive, time-consuming simulations for every single variation of the universe’s physical parameters and laws.\nTo solve this, we developed a set of “emulators” based on neural networks. By training these algorithms on thousands of gravity-only simulations, we created an AI capable of predicting void statistics almost instantly by learning how these statistics depend on the physical parameters of the universe. This allows us to bypass the need for brute-force computation, enabling much faster and more reliable cosmological parameter estimation.\n","title":"Predicting Cosmic Voids with AI","type":"publications"},{"content":" The visible universe is shaped by violent astrophysical processes, from star formation to supermassive black holes driving gas out of galaxies. However, when physicists model the universe on a computer, they often simulate only dark matter and its gravity, as these other baryonic processes are incredibly complex and computationally expensive. While this shortcut leads to inaccuracies when predicting the properties of densely packed galaxies, we wanted to know if and how much these messy baryonic effects also disrupt the quiet, vast expanses of cosmic voids.\nTo find out, we utilized state-of-the-art hydrodynamical simulations to track both normal matter and dark matter, comparing them directly to standard dark-matter-only (gravity-only) simulations. The results were incredibly reassuring: cosmic voids are fundamentally robust, and their overall properties are virtually untouched by the complex physics of normal matter.\nHowever, looking closely at the mass around these voids reveals a subtle but clear difference, as seen in the image above. Because normal matter (dotted lines) interacts not only through gravity but also experiences pressure and explosive feedback, it gets smoothed out and pushed into the interiors of voids, leading to slightly higher inner densities. Meanwhile, cold dark matter (dashed lines), interacting solely through gravity, clumps much more sharply at the void boundaries.\nBy demonstrating that messy astrophysics barely alters voids, we establish that we can safely rely on straightforward, gravity-only simulations to generate robust statistics for comparison against measurements from next-generation cosmological surveys. Furthermore, the higher densities of gas found inside these voids might provide a crucial key to ultimately locating the missing baryons in our universe.\n","date":"August 1, 2024","externalUrl":null,"permalink":"/publications/voids-baryonic-physics/","section":"Publications","summary":" The visible universe is shaped by violent astrophysical processes, from star formation to supermassive black holes driving gas out of galaxies. However, when physicists model the universe on a computer, they often simulate only dark matter and its gravity, as these other baryonic processes are incredibly complex and computationally expensive. While this shortcut leads to inaccuracies when predicting the properties of densely packed galaxies, we wanted to know if and how much these messy baryonic effects also disrupt the quiet, vast expanses of cosmic voids.\n","title":"Do messy baryons spoil cosmic voids?","type":"publications"},{"content":" While denser regions of the cosmic web, like massive galaxy clusters, are dominated by complex gravitational forces, gravity behaves more gently in the emptiest regions of space, offering cleaner physical environments. Cosmic voids are actively expanding, pushing matter outward in a highly organized way that avoids the messy physics found elsewhere in the universe.\nUsing state-of-the-art hydrodynamical simulations (which include additional physics alongside standard gravity) across a vast range of scales, we investigated exactly how matter and galaxies move around these underdense regions. Surprisingly, we discovered that these motions can be described exquisitely well by the simple equations of linear mass conservation.\nAs shown in the image above, this holds true even for incredibly small, individual voids on scales of just a few megaparsecs, a regime where we would normally expect the physics to become highly nonlinear. Yet, the measured velocities of galaxies (dotted lines) match the simple theoretical predictions (solid lines) very well.\nThis confirms that despite the complexity of the surrounding cosmic web, voids provide a uniquely clean and mathematically predictable laboratory for precision cosmology.\n","date":"May 1, 2023","externalUrl":null,"permalink":"/publications/voids-nonlinear-structure-linear-dynamics/","section":"Publications","summary":" While denser regions of the cosmic web, like massive galaxy clusters, are dominated by complex gravitational forces, gravity behaves more gently in the emptiest regions of space, offering cleaner physical environments. Cosmic voids are actively expanding, pushing matter outward in a highly organized way that avoids the messy physics found elsewhere in the universe.\nUsing state-of-the-art hydrodynamical simulations (which include additional physics alongside standard gravity) across a vast range of scales, we investigated exactly how matter and galaxies move around these underdense regions. Surprisingly, we discovered that these motions can be described exquisitely well by the simple equations of linear mass conservation.\n","title":"Simple dynamics inside the emptiest places","type":"publications"},{"content":" Neutrinos are the lightest massive particles that we know of, but their exact mass is still one of the biggest unknowns in particle physics. Unlike regular matter, neutrinos move too fast to be trapped by the gravitational pull of typical galaxies and their dark matter halos, meaning they naturally flow into the nearly empty regions of space, cosmic voids, potentially altering them in the process.\nThrough dedicated simulations, we investigated how these lightweight particles affect the properties of voids. By analyzing the clustering bias of these voids, a measure of how voids are distributed relative to the overall matter in the universe, we found that void properties are highly sensitive to the total sum of neutrino masses.\nOur research shows that by categorizing voids based on their minimal density and average density ( \\( \\Delta_\\mathrm{h}\\) in the image above), we can isolate distinct neutrino signatures. For example, in cosmologies with massive neutrinos, we find more voids at smaller and larger average densities, while voids with densities around the mean ( \\( \\Delta_\\mathrm{h}=0 \\) ) become rarer.\nThese unique signatures highlight that the largest empty spaces in the universe can be used as a precision scale to weigh its lightest known particles.\n","date":"December 1, 2019","externalUrl":null,"permalink":"/publications/voids-massive-neutrinos/","section":"Publications","summary":" Neutrinos are the lightest massive particles that we know of, but their exact mass is still one of the biggest unknowns in particle physics. Unlike regular matter, neutrinos move too fast to be trapped by the gravitational pull of typical galaxies and their dark matter halos, meaning they naturally flow into the nearly empty regions of space, cosmic voids, potentially altering them in the process.\nThrough dedicated simulations, we investigated how these lightweight particles affect the properties of voids. By analyzing the clustering bias of these voids, a measure of how voids are distributed relative to the overall matter in the universe, we found that void properties are highly sensitive to the total sum of neutrino masses.\n","title":"Weighing neutrinos with cosmic emptiness","type":"publications"},{"content":" CPPM, Marseille I\u0026rsquo;m a cosmologist with a focus on cosmic voids: the enormous nearly empty spaces that fill most of our Universe. I\u0026rsquo;m a Postdoctoral Researcher at CPPM in Marseille, where I investigate the theoretical modelling of void statistics and their sensitivity to fundamental physics (e.g. dark energy, neutrino masses, theories of gravity), working with both simulations and galaxy survey data.\nJump to a section:\nAbout — a short introduction to me and my work. CV — my academic background and experience. Publications — my research papers, each with a jargon-free summary. Tools — interactive cosmology visualizations and public codes. Outreach \u0026amp; Media — popular-science writing, media, and outreach. ","date":"May 1, 2026","externalUrl":null,"permalink":"/","section":"Home","summary":" CPPM, Marseille I’m a cosmologist with a focus on cosmic voids: the enormous nearly empty spaces that fill most of our Universe. I’m a Postdoctoral Researcher at CPPM in Marseille, where I investigate the theoretical modelling of void statistics and their sensitivity to fundamental physics (e.g. dark energy, neutrino masses, theories of gravity), working with both simulations and galaxy survey data.\n","title":"Home","type":"page"},{"content":"A selection of papers I have made a major contribution to, each with a short, plain-language summary. Click any title, here or in the sidebar, to read a jargon-light explanation, see a key figure, discover my collaborators, and find the official abstract and a link to the paper.\nFor my complete, up-to-date publication list, see my arXiv author page or ORCID.\n","date":"May 1, 2026","externalUrl":null,"permalink":"/publications/","section":"Publications","summary":"A selection of papers I have made a major contribution to, each with a short, plain-language summary. Click any title, here or in the sidebar, to read a jargon-light explanation, see a key figure, discover my collaborators, and find the official abstract and a link to the paper.\nFor my complete, up-to-date publication list, see my arXiv author page or ORCID.\n","title":"Publications","type":"publications"},{"content":"I am Nico Schuster and I currently work as a Postdoctoral Researcher at the Centre de Physique des Particules de Marseille (CPPM) in Alice Pisani\u0026rsquo;s research group. I am active within several current and upcoming cosmological surveys: DESI, Euclid, the Vera C. Rubin Observatory (LSST), and the Wide-Field Spectroscopic Telescope (WST).\nIn my research, I explore the underlying properties of our Universe by using cosmic voids, the expansive, low-density regions between galaxies, to test fundamental physics. My research focuses on the theoretical modelling and interpretation of matter and galaxy distributions in and around voids, with the goal of sharpening cosmological constraints and establishing rigorous models for the next generation of galaxy surveys. In parallel, I study the imprints of dark energy, modified gravity, massive neutrinos, and other physical theories on cosmic voids, developing new observables tailored to disentangle their respective signatures.\nBefore Marseille I completed my PhD at LMU Munich, where I studied the fundamental properties of cosmic voids and advanced the modeling of their statistics to increase the potential of voids as cosmological probes. This PhD project was supervised by Nico Hamaus and Jochen Weller.\nAlongside my research, I build interactive visualization tools that serve the public and the cosmology community, bridging the gap between teaching, outreach, and research by making complex ideas accessible to everyone. You can try them on the Tools page.\nFor more details on my education, research experience, and selected work, please see my CV page. My public codes are available on my GitHub, and all of my papers are accessible through arXiv.\n","externalUrl":null,"permalink":"/about/","section":"Home","summary":"I am Nico Schuster and I currently work as a Postdoctoral Researcher at the Centre de Physique des Particules de Marseille (CPPM) in Alice Pisani’s research group. I am active within several current and upcoming cosmological surveys: DESI, Euclid, the Vera C. Rubin Observatory (LSST), and the Wide-Field Spectroscopic Telescope (WST).\nIn my research, I explore the underlying properties of our Universe by using cosmic voids, the expansive, low-density regions between galaxies, to test fundamental physics. My research focuses on the theoretical modelling and interpretation of matter and galaxy distributions in and around voids, with the goal of sharpening cosmological constraints and establishing rigorous models for the next generation of galaxy surveys. In parallel, I study the imprints of dark energy, modified gravity, massive neutrinos, and other physical theories on cosmic voids, developing new observables tailored to disentangle their respective signatures.\n","title":"About","type":"page"},{"content":"","externalUrl":null,"permalink":"/categories/","section":"Categories","summary":"","title":"Categories","type":"categories"},{"content":"A short web CV. A more detailed publication list lives on the Publications page and on ORCID.\nResearch experience # Postdoctoral Researcher — Centre de Physique des Particules de Marseille (CPPM), Oct 2024 – present. Postdoctoral Researcher — Ludwig Maximilian University (LMU) of Munich, Oct 2023 – Sep 2024. Education # PhD in Physics — LMU Munich, 2020 – 2023. Thesis: Unique Characteristics of Voids in a Complex Universe. Supervisors: Nico Hamaus and Jochen Weller. MSc in Physics — LMU Munich, 2015 – 2018. Thesis: Influence of massive neutrinos on cosmic voids. BSc in Physics — LMU Munich, 2012 – 2015. Thesis: Der Blandford-Znajek Prozess. Surveys \u0026amp; collaborations # I am an active member of:\nDESI — the Dark Energy Spectroscopic Instrument Euclid the Vera C. Rubin Observatory (LSST) the Wide-Field Spectroscopic Telescope (WST) I have also co-authored consortium papers with Euclid, eROSITA, and CosmoVerse.\nSelected publications (first author) # Why cosmic voids matter: pristine evolution, JCAP (2026), arXiv:2509.07092. Setting SAIL: Leveraging Scientist-AI-Loops for Rigorous Visualization Tools (preprint, 2026), arXiv:2603.18145. Why cosmic voids matter: mitigation of baryonic physics, JCAP (2024), arXiv:2312.11241. Why cosmic voids matter: nonlinear structure \u0026amp; linear dynamics, JCAP (2023), arXiv:2210.02457. The bias of cosmic voids in the presence of massive neutrinos, JCAP (2019), arXiv:1905.00436. Awards # 1st prize, best poster — XIV Tonale Winter School on Cosmology (2021). Cosmology course I taught (as TA) voted Best Lecture in the LMU Physics Master\u0026rsquo;s program (2022). Talks # Over 45 presentations to date, including 14 invited talks.\nTeaching \u0026amp; Supervision # Teaching assistant at LMU Munich for Cosmology and Statistics (Master\u0026rsquo;s level), and for Astrophysics, Quantum Mechanics, and Theoretical Electrodynamics (Bachelor\u0026rsquo;s level). I taught two lectures and ran two hands-on workshops at the MUSI undergraduate summer school at CPPM in June 2026.\nGuided graduate research across multiple institutions, including the co-supervision of PhD students at CPPM and 5 Master\u0026rsquo;s theses projects at LMU Munich, and serving as the primary supervisor for a Master\u0026rsquo;s project at CPPM.\nService \u0026amp; leadership # Referee for A\u0026amp;A, ApJ, MNRAS, JCAP, and The Astronomy and Astrophysics Review. Support Observing Scientist for DESI at the Mayall 4-m Telescope (Kitt Peak). Lead organiser and co-chair, Voids@CPPM 2025 workshop. Coordinator and co-chair of the weekly Voids@CPPM group meeting. Dark Energy manager (CN-4) for the Excellence Cluster ORIGINS (2024). Outreach # Public interactive tools (Cosmic Web Explorer, Lensing visualization) and public talks, including a full-dome public talk at the ESO Supernova Planetarium. More on the Outreach \u0026amp; Media page.\nSkills # Python, Jupyter, LaTeX, Git, Bash; the VIDE void finder. Languages: German (native), English (C2), French (B1).\n","externalUrl":null,"permalink":"/cv/","section":"Home","summary":"A short web CV. A more detailed publication list lives on the Publications page and on ORCID.\nResearch experience # Postdoctoral Researcher — Centre de Physique des Particules de Marseille (CPPM), Oct 2024 – present. Postdoctoral Researcher — Ludwig Maximilian University (LMU) of Munich, Oct 2023 – Sep 2024. Education # PhD in Physics — LMU Munich, 2020 – 2023. Thesis: Unique Characteristics of Voids in a Complex Universe. Supervisors: Nico Hamaus and Jochen Weller. MSc in Physics — LMU Munich, 2015 – 2018. Thesis: Influence of massive neutrinos on cosmic voids. BSc in Physics — LMU Munich, 2012 – 2015. Thesis: Der Blandford-Znajek Prozess. Surveys \u0026 collaborations # I am an active member of:\n","title":"CV","type":"page"},{"content":" Legal notice # This is a personal, non-commercial website run by Nico Schuster. Published and maintained by Nico Schuster — schuster@cppm.in2p3.fr.\nHosting: Cloudflare, Inc. (Cloudflare Pages), 101 Townsend Street, San Francisco, CA 94107, USA — cloudflare.com.\nPrivacy # This site is designed to respect your privacy. It sets no cookies and does not track you across the web.\nFor basic, aggregate visitor statistics (such as page-view counts), this site uses GoatCounter, a privacy-friendly analytics service. GoatCounter does not use cookies, does not collect or store personal data, and does not build visitor profiles. Counting is based on anonymised, aggregated information only; no individual visitor can be identified.\nBecause no personal data is collected, there is nothing to request, correct, or delete. If you have any questions about this site, you can reach me at the address above.\nLast updated: July 2026.\n","externalUrl":null,"permalink":"/legal/","section":"Home","summary":"Legal notice # This is a personal, non-commercial website run by Nico Schuster. Published and maintained by Nico Schuster — schuster@cppm.in2p3.fr.\nHosting: Cloudflare, Inc. (Cloudflare Pages), 101 Townsend Street, San Francisco, CA 94107, USA — cloudflare.com.\nPrivacy # This site is designed to respect your privacy. It sets no cookies and does not track you across the web.\n","title":"Legal \u0026 Privacy","type":"page"},{"content":" Interactive Outreach Tools # Beyond traditional outreach and both scientific and public writing, a major part of my science communication involves building interactive visualizations for the cosmology community to use.\nMy browser-based simulations of the cosmic web and gravitational lensing are publicly available and actively used by colleagues worldwide for teaching and public engagement. For more details on these tools and to explore them live, go here.\nMedia, Press Coverage \u0026amp; Articles # DESI Collaboration Blog — Exploring What DESI Measures: An Interactive Cosmic Web in Your Browser (July 2026). A guest post I contributed to the DESI collaboration, introducing my browser-based Cosmic Web Explorer and showing how its structures line up with DESI\u0026rsquo;s galaxy maps, including the BAO mode that highlights the Baryon Acoustic Oscillation feature DESI is built to measure. Read the post The DESI acronym written into the simulated cosmic web, the preview image for the guest blog post. Wired.com — The Emptiest Places in the Universe Might Contain Its Best Secrets (May 2026). Interviewed for Becky Ferreira\u0026rsquo;s feature about the fundamental properties of cosmic voids, their use in cosmology, and their potential to resolve major cosmological tensions. Read the article\nCNRS France Press Release — DESI finishes initial Y5 survey (April 2026). The release featured a visualization of my Cosmic Web Explorer that compares its visual output with the distribution of galaxies as observed by DESI. Read the release (French only)\nOutput of the Cosmic Web Explorer vs. a slice of DESI Y5 galaxies. Public Talks \u0026amp; Engagement # Cosmic Emptiness: What can we learn from the space between galaxies? — ESO Supernova Planetarium in Garching, Germany (September 2024). Delivered an immersive full-dome presentation to an audience of over 100 in German for the \u0026ldquo;Kosmisches Kino\u0026rdquo; talk series, guiding the audience through explanatory slides paired with immersive full-dome videos of cosmological simulations and large-scale structure. View event page (German only)\nCommunity Outreach — Contributor to local and international science outreach events, including engaging the general public at the 4th Azores School on Observational Cosmology and representing the LMU physical cosmology group at prospective student events.\nLive under the dome at the ESO Supernova Planetarium for the \u0026ldquo;Kosmisches Kino\u0026rdquo; series. ","externalUrl":null,"permalink":"/outreach/","section":"Home","summary":"Interactive Outreach Tools # Beyond traditional outreach and both scientific and public writing, a major part of my science communication involves building interactive visualizations for the cosmology community to use.\nMy browser-based simulations of the cosmic web and gravitational lensing are publicly available and actively used by colleagues worldwide for teaching and public engagement. For more details on these tools and to explore them live, go here.\n","title":"Outreach \u0026 Media","type":"page"},{"content":"","externalUrl":null,"permalink":"/tags/","section":"Tags","summary":"","title":"Tags","type":"tags"},{"content":"Three projects live here:\nCosmic Web Explorer — A real-time, interactive browser simulation of how the cosmic web of voids and filaments forms. Gravitational Lensing Visualization — An interactive demo of how massive clusters and voids bend the light of background galaxies. Void Profile Analysis Toolkit — A Python code for measuring density and velocity profiles around cosmic voids. The two visualizations are fully interactable directly on this page. For a larger view on their own dedicated pages, use the Open in full window option below the embeds. Both were built using the SAIL framework (Scientist-AI-Loop). You can read more about this workflow on my publications page or directly in the paper.\nCosmic Web Explorer # Experience the formation of the universe\u0026rsquo;s large-scale structure right in your browser via this real-time, interactive simulation. Built as a pedagogical \u0026ldquo;2.5D\u0026rdquo; model, it combines second-order Lagrangian perturbation theory (2LPT) with a local, quasi-N-body gravity scheme, rendered via WebGL and WebGPU for high performance, to let you watch primordial fluctuations collapse into voids, filaments, and halos from redshift z=10 to the present day.\nWhile the physics are simplified compared to realistic N-body simulations to maintain interactive performance, the Cosmic Web Explorer includes a robust suite of genuine analysis features:\nReal-time void identification: Uses a custom-coded Voronoi-watershed algorithm in the spirit of VIDE/ZOBOV. Dynamic measurements: Live calculations of void density profiles, normalized density distributions, power spectra or correlation functions, redshift-space distortions, and more. Adjustable cosmologies: Switch seamlessly between \\( \\Lambda \\)CDM, \\(w \\)CDM, and \\(w_0 w_a \\)CDM models and change their parameter values to see how the cosmic web responds. Moreover, the tool also lets you export videos and snapshots, and you can even write your own text into the cosmic web (see the banner at the top of this page for an example). While the tool by default uses realistic initial conditions, it also has an additional \u0026ldquo;BAO Init.\u0026rdquo; mode, which places amplified rings from Baryon Acoustic Oscillations on top of the initial density field to highlight this cosmological feature in the resulting structures.\nCosmic Web Explorer Open in full window ↗ Source code: github.com/nicosmo/cosmic_web_explorer\nCredits: Initial concept by Simon Bouchard and Nico Schuster; developed by Nico Schuster; code generation assisted by Google Gemini and Claude. Thanks to Julien Zoubian and Dennis Frei for their contributions to the code, and to many colleagues for useful discussions and feedback.\nHow to cite: Schuster, N., Bouchard, S., Zoubian, J., \u0026amp; Frei, D. (2026). Cosmic Web Explorer (v1.1.0). Zenodo, doi:10.5281/zenodo.18915566. AGPLv3.\nGravitational Lensing Visualization # An interactive WebGL visualization of gravitational lensing that lets you bend and distort the light of background galaxies in real time. By dragging a massive foreground cluster or void across your screen, you can instantly see how gravitational fields warp the space around them and explore how changing the parameters of the lens affects the distortions.\nThe tool is built for intuition, utilizing inverse ray-tracing in a fragment shader under a thin-lens approximation, as well as amplified distortions to illustrate the core physical effects. To further isolate these effects, you can toggle between different backgrounds, such as a grid to visualize spacetime distortions, dots to observe magnification and shear, or even your own uploaded image. It allows you to actively switch between several models of mass distributions:\nMultiple cluster models: Test a simple point mass, an NFW dark-matter halo, or an elliptical lens with visible critical curves and caustics to explore effects of strong and weak lensing.\nRealistic void profiles: Visualize how underdensities act as diverging lenses, using both a simplified toy model and the realistic HSW profile.\nReal-time rendering: The fragment-shader implementation ensures smooth, immediate feedback as you reposition the lens and change its parameters.\nGravitational Lensing Visualization Open in full window ↗ Source code: github.com/nicosmo/lensing_visualization\nCredits: Concept and visualization by Nico Schuster and Andrés Salcedo; code generation assisted by Google Gemini. Thanks to Dennis Frei for his contributions to the code, and to many colleagues for useful discussions and feedback. The caustic and critical-curve algorithms build on the lenstronomy package.\nHow to cite: Schuster, N., Salcedo, A. N., \u0026amp; Frei, D. (2026). Visualizing Gravitational Lensing (v1.0.0). Zenodo, doi:10.5281/zenodo.18914869. CC0.\nVoid Profile Analysis Toolkit # A Python toolkit for measuring, saving, and stacking radial profiles around cosmic voids in cosmological simulations. The code computes the density and velocity profiles of tracers in spherical shells around void centers, stacks multiple voids to achieve high signal-to-noise measurements, and estimates uncertainties using Jackknife resampling. Built for efficiency, it processes profiles in parallel and natively integrates with the VIDE library when available (falling back to SciPy otherwise while maintaining periodic boundary conditions). This toolkit serves as the core analysis pipeline behind several of my publications.\nSource code: github.com/nicosmo/void_profile_analysis\nHow to cite: Schuster, N. (2025). Void Profile Analysis Toolkit (Software). Zenodo, doi:10.5281/zenodo.17967174.\nThis code implements methods from arXiv:2210.02457, arXiv:2312.11241, and arXiv:2509.07092, so check out their methods sections for more details.\n","externalUrl":null,"permalink":"/tools/","section":"Home","summary":"Three projects live here:\nCosmic Web Explorer — A real-time, interactive browser simulation of how the cosmic web of voids and filaments forms. Gravitational Lensing Visualization — An interactive demo of how massive clusters and voids bend the light of background galaxies. Void Profile Analysis Toolkit — A Python code for measuring density and velocity profiles around cosmic voids. The two visualizations are fully interactable directly on this page. For a larger view on their own dedicated pages, use the Open in full window option below the embeds. Both were built using the SAIL framework (Scientist-AI-Loop). You can read more about this workflow on my publications page or directly in the paper.\n","title":"Tools \u0026 Visualizations","type":"page"}]