  One of the key insights in the emerging field of non-Hermitian photonics is
that well-established concepts like the laser can be operated in reverse to
realize a 'coherent perfect absorber' (CPA). While conceptually appealing, such
CPAs are limited so far to a single, judiciously shaped wavefront or 'mode'.
Here, we demonstrate how this limitation can be overcome by time-reversing a
'degenerate cavity laser', based on a unique cavity that self-images any
incident light-field onto itself. Placing a weak, critically-coupled absorber
into this cavity, we demonstrate that any incoming wavefront, even a complex
and dynamically-varying speckle pattern, is absorbed with close to perfect
efficiency in a massively parallel interference process. Moreover, the coherent
nature of multi-mode absorption allows us to tune the degree of absorption over
a wide range. These characteristics open-up interesting new possibilities for
applications in light-harvesting, energy delivery, light control, and imaging.
