A four dimensional signal would not boom in from some external balcony of spacetime. It would arrive as a pattern in the same three dimensional fields and particles already mapped by physics, folded into the fabric of what detectors routinely record.
In modern theory, matter and radiation are described by quantum field theory, where electrons, photons and other particles are excitations of underlying fields spread through three dimensional space. Any higher dimensional agent trying to inject information must still couple to these fields, altering charge distributions, spin states or local energy density. The interaction would show up as a disturbance in the electromagnetic field, a shift in a quantum superposition or a tweak in the stress energy tensor, not as a separate, exotic channel hovering outside ordinary space.
That constraint follows from locality and conservation laws embedded in current models of spacetime. If extra spatial dimensions exist, standard model fields appear effectively confined, so any cross dimensional influence must project down into the allowed degrees of freedom. To observers inside three dimensions, the origin of the disturbance would be opaque, but its footprint would look like an unusual, yet still lawful, configuration of familiar particles and forces. The message, in other words, would be indistinguishable from a cleverly arranged fluctuation in the physics already under study.
