Ripples in the Dark: Wave Physics and the Cosmic Web

by Aoibhinn Gallagher (Maynooth University)

Thursday Oct 23, 2025, 2:15 PM → 3:45 PM Europe/Berlin

D6-135 (UHG)

In this talk I will present a coherent narrative from the foundations of cosmic structure formation to new insights arising from wave-based descriptions of dark matter, culminating in the main results of my recent work (here).
I will begin by outlining the standard ΛCDM picture of how small primordial density fluctuations grow under gravity into the sheets, filaments, and haloes of the cosmic web, and how simple approaches such as the Zel’dovich approximation capture aspects of this nonlinear evolution. I will then introduce wavelike (or ultra-light scalar) dark matter, highlighting its theoretical basis, its distinctive scale-dependent behaviour due to a macroscopic de Broglie wavelength, and the advantages of the Schrödinger–Poisson formalism as an alternative to traditional fluid or N-body methods. Building on this framework, I will discuss how classical fluid analogies, such as pressure, viscosity, and Reynolds numbers, can be meaningfully applied to such wave systems, drawing on results from our recent study (mentioned above). I will show when these analogies hold, where they fail, and what they reveal about the physics of wavelike dark matter and the growth of cosmic structure, before concluding with prospects for future analytical and numerical developments.

2025-10-23_Aoibhinn_Gallagher.pdf