# Nico Schuster, Cosmologist

> Personal academic website of Nico Schuster, a cosmologist (postdoctoral
> researcher at CPPM, Marseille) working on cosmic voids: the large,
> underdense regions of the cosmic web. His research covers the theoretical
> modelling of void statistics and their sensitivity to fundamental physics
> — dark energy, modified gravity, and massive neutrinos — using both
> cosmological simulations and galaxy-survey data.

Website: https://nicoschuster.org/

## Background
- Current position: postdoctoral researcher at the Centre de Physique des Particules de Marseille (CPPM), in Alice Pisani's group (since 2024). Previously a postdoc at LMU Munich (2023-2024).
- PhD in Physics, LMU Munich (2020-2023), thesis "Unique Characteristics of Voids in a Complex Universe", supervised by Nico Hamaus and Jochen Weller.
- Research interests: cosmic voids and the large-scale structure of the Universe; the modelling of void statistics and their sensitivity to dark energy, modified gravity, and massive neutrinos; cosmological inference from galaxy surveys and simulations.
- Surveys and collaborations: DESI, Euclid, the Vera C. Rubin Observatory (LSST), and the Wide-Field Spectroscopic Telescope (WST).

## Key pages
- [About](https://nicoschuster.org/about/): Short introduction to Nico Schuster and his research.
- [CV](https://nicoschuster.org/cv/): Academic background, positions, and experience.
- [Publications](https://nicoschuster.org/publications/): Research papers, each with a plain-language summary.
- [Tools](https://nicoschuster.org/tools/): Interactive cosmology visualizations and public codes.
- [Outreach & Media](https://nicoschuster.org/outreach/): Popular-science writing, press coverage, and public talks.


## Publications

### Frozen in Time: Voids as Pristine Laboratories of Physics
Full title: Why cosmic voids matter: pristine evolution
Link: https://nicoschuster.org/publications/voids-pristine-evolution/ · https://arxiv.org/abs/2509.07092
Summary: The universe is constantly changing, making it notoriously difficult to track how structures evolve over time. To understand how voids grow and age, this paper uses cosmological simulations to track their evolution across 12.5 billion years of cosmic history. The results show that once the universe is old enough, voids settle into a calm and predictable state, passively following the expansion of the cosmos. That steadiness makes voids exceptionally reliable tools for testing dark energy and offers a clean laboratory for studying fundamental physics.
Keywords: cosmic voids, void evolution, large-scale structure evolution, Magneticum simulations, hydrodynamical simulations, halo tracers, void density profiles, linear growth theory, separate universe, dark energy, relative binning

### SAIL: A Framework for Rigorous AI-Assisted Scientific Coding
Full title: Setting SAIL: Leveraging Scientist-AI-Loops for Rigorous Visualization Tools
Link: https://nicoschuster.org/publications/sail-ai-visualization-tools/ · https://arxiv.org/abs/2603.18145
Summary: How can scientists use AI to create trustworthy code quickly? The SAIL framework solves this by putting researchers and AI coding assistants together in tight collaborative loops. By pairing human scientific expertise with AI code generation, fundamental principles stay rigorously verified while development speed accelerates.
Keywords: AI-assisted coding, large language models, scientific software, human-in-the-loop, gravitational lensing visualization, large-scale structure, science communication, cosmic web explorer

### Predicting Cosmic Voids with AI
Full title: Cosmological Inference with Cosmic Voids and Neural Network Emulators
Link: https://nicoschuster.org/publications/voids-neural-network-emulators/ · https://arxiv.org/abs/2502.05262
Summary: Extracting statistics from cosmic voids usually requires running slow and expensive simulations. To bypass this, we built fast AI emulators that near instantly predict what cosmic voids look like across different theoretical universes. This allows us to extract far more information from the full void population, measuring the universe's ingredients faster and more accurately, while remaining completely independent of the messy physics of normal matter.
Keywords: cosmic voids, neural network emulators, void size function, void density profiles, void-galaxy cross-correlation, Quijote simulations, cosmological inference, LCDM parameters, baryon-independent probe

### Do messy baryons spoil cosmic voids?
Full title: Why cosmic voids matter: mitigation of baryonic physics
Link: https://nicoschuster.org/publications/voids-baryonic-physics/ · https://arxiv.org/abs/2312.11241
Summary: Ordinary matter (gas, stars) is notoriously difficult to model and can easily muddy cosmological measurements. To determine if these messy 'baryonic' effects also infect the emptiest regions of space, we measured them using high-resolution simulations both with and without gas physics. The answer: voids remain almost completely untouched, with changes occurring only on tiny scales. This confirms cosmic voids as some of the cleanest and most robust probes in modern cosmology.
Keywords: cosmic voids, baryonic physics, astrophysical processes, hydrodynamical simulations, dark-matter-only simulations, gravity-only simulations, Magneticum simulations, void density profiles, void-galaxy cross-correlation, void size function, void properties, weak lensing, missing baryons, cosmological probes, void modeling, baryon-independent probe

### Simple dynamics inside the emptiest places
Full title: Why cosmic voids matter: nonlinear structure & linear dynamics
Link: https://nicoschuster.org/publications/voids-nonlinear-structure-linear-dynamics/ · https://arxiv.org/abs/2210.02457
Summary: While most of the cosmic web is defined by messy, complicated dynamics, this paper shows that the movement of matter and galaxies around cosmic voids remains beautifully simple. Detailed simulations across a huge range of scales reveal that these motions follow linear theory all the way down to small scales of 1 Mpc, making void environments exceptionally easy to model.
Keywords: cosmic voids, watershed voids, linear dynamics, void size function, void properties, radial velocity profiles, void density profiles, void-galaxy cross-correlation, Magneticum simulations, tracer sparsity, void merging, precision cosmology, void modeling

### Weighing neutrinos with cosmic emptiness
Full title: The bias of cosmic voids in the presence of massive neutrinos
Link: https://nicoschuster.org/publications/voids-massive-neutrinos/ · https://arxiv.org/abs/1905.00436
Summary: Neutrinos are particles with a tiny but unknown mass. Because they flow easily into cosmic voids, voids are unusually sensitive places to look for their effect, which could help us finally weigh them. This paper studies how the total mass of neutrinos changes the clustering of voids in simulations, and finds a clear, measurable signal that survives even when we use realistic galaxy-like tracers
Keywords: cosmic voids, massive neutrinos, neutrino free-streaming, void bias, DEMNUni simulations, void-halo bias, weak lensing, sum of neutrino masses, void physics sensitivity

## Tools & interactive visualizations
Interactive tools created and maintained by Nico Schuster (details: https://nicoschuster.org/tools/):
- Cosmic Web Explorer — a real-time, interactive browser simulation of how the cosmic web of voids and filaments forms (2LPT + quasi-N-body gravity, WebGL/WebGPU), with live void-finding and cosmology switching. Live: https://nicosmo.github.io/cosmic_web_explorer/ - Code: https://github.com/nicosmo/cosmic_web_explorer
- Gravitational Lensing Visualization — an interactive demo of how galaxy clusters and voids bend the light of background galaxies. Live: https://nicosmo.github.io/lensing_visualization/ - Code: https://github.com/nicosmo/lensing_visualization
- Void Profile Analysis Toolkit — a Python code for measuring density and velocity profiles around cosmic voids. Code: https://github.com/nicosmo/void_profile_analysis
Both browser visualizations were built with the SAIL (Scientist-AI-Loop) framework: https://arxiv.org/abs/2603.18145

## Selected outreach & writing
- "Exploring What DESI Measures: An Interactive Cosmic Web in Your Browser" — guest blog post for the DESI collaboration introducing the Cosmic Web Explorer (July 2026): https://www.desi.lbl.gov/2026/07/03/exploring-what-desi-measures-an-interactive-cosmic-web-in-your-browser/
- "The Emptiest Places in the Universe Might Contain Its Best Secrets" — Wired feature (May 2026): https://www.wired.com/story/cosmic-voids-might-contain-universes-best-secrets/
- Full-dome planetarium talk at the ESO Supernova (Garching) for the "Kosmisches Kino" series.
More: https://nicoschuster.org/outreach/

## Contact
- Email: schuster@cppm.in2p3.fr
- GitHub: https://github.com/nicosmo
- ORCID: https://orcid.org/0000-0001-5620-8554
- arXiv: https://arxiv.org/search/astro-ph?searchtype=author&query=Schuster,+N