Light Black Holes from Light

Álvarez-Domínguez et al. [Phys. Rev. Lett. 133, 041401 (2024)PRLTAO0031-900710.1103/PhysRevLett.133.041401] have suggested that "it is not possible to concentrate enough light to precipitate the formation of an event horizon. We argue that the dissipative quantum effects coming from the self-interaction of light (such as vacuum polarization) are enough to prevent any meaningful buildup of energy that could create a black hole in any realistic scenario," and "the dissipation of energy via Schwinger effect alone is enough to prevent the formation of kugelblitze with radii ranging from 10^{-29} to 10^{8} m." I agree that, with the very restrictive assumption of Álvarez-Domínguez et al. of an adiabatic influx of electromagnetic energy, it is indeed highly implausible that black holes will form mainly from light in our actual Universe, either naturally or by any foreseeable human activity. However, if instead a rapidly changing influx is allowed, there are many idealized theoretical processes (though probably not occurring naturally or possible for humans to engineer) for forming black holes of any size down to near the Planck length (about 10^{-35} m) purely from photons, such as from colliding approximately plane-wave pulses, with only a small fraction of the energy escaping the black hole as scattered light or electron-positron pairs.