I admit to being hardly qualified to hold forth on this subject but...
In his book "The Fabric Of Reality", in discussing the odd results of the famous double slit experiment,
David postulates "shadow photons" which interact with the single photon to produce the interference result. He goes on to argue that there must be millions of these shadow photons. Since they don't interact with any known measurement device they must exist elsewhere... From this he postulates that they exist in other universes and from that assumption concludes that the "multiverse" exists.
Given the same experiment, my conjecture differs. It is "known" that the vacuum gives rise to "virtual particles" ( https://en.wikipedia.org/wiki/Virtual_particle ). Indeed, these can be measured, giving rise to the Casimir effect ( https://en.wikipedia.org/wiki/Casimir_effect ). Interactions between photons, especially in their wave-like characteristics, and virtual particles seems a more Occam's Razor solution.
Does the interaction of the wave-like photon and the "slot-space confinement" occupied with virtual particles affect and explain the result? What effect would virtual particles have on the photon wave? Indeed, do virtual particle interactions with "real" particles explain the measurement collapse problem?
To that point, what effect does a "slot" have for virtual particle generation / frequency / wavelength / etc.? Does virtual particle production change due to slot width? Do certain slot widths generate "virtual standing waves" that interact with particles? If the slots were "Casimir-width" does the double slit experiment outcome change? Perhaps "shadow photons" are just inducing "resonant virtual particles" to temporarily exist and affect the results.
The leap of faith from a double-slit result to a multiverse seems a bit too far for me to jump.
These virtual particles of which you describe appear to be of the particle being measured. So these aren’t just “some” virtual particles, they are THE particle you are trying to measure, only “ghosts” which react with nothing but themselves (so the particle only appears influenced by its own shadow particle, not those of others.
The multiverse conjecture does not necessarily conclude that whole, functional universes also exist (“out of phase” or something), it may be more like a dense plume of potential of which ours is a stable hyper dimensional manifestation. Ours may be the only one complete with stable laws of physics, where the other(s) are the vat of ghost particles refracting from whatever this manifest universe is doing.