They said that the world and humanity have no real existence, and their entire reality is only an appearance. We perceive ourselves as if we are in a world, and we perceive ourselves with our senses, and we perceive the world with our senses. It turns out [according to this opinion] that all of existence of humanity and the world is only a perception and not in true reality, for it is impossible for anything to exist in true reality, since He fills all the worlds.

Shlomo Elyashiv