Abstract: First-order phase transitions in the early Universe and inside neutron stars could leave observable imprints, including a stochastic gravitational wave background or characteristic waveforms in specific frequency ranges. Predicting these signals requires precise understanding of critical bubbles, often addressed using effective field theory or perturbation theory. In this talk, I will explain how the problem is tackled in the context of gauge/gravity duality, and show the explicit computation of (fully-backreacted) critical bubbles in a strongly coupled system. I will also discuss possible effective approaches to the problem, and compare the results of the different perspectives.