The question of whether the world that we observe around us is real, has been asked for a long time. It has been asked before Descartes, and after him; and it has been asked by all of us at some point in time.
Descartes hit upon the question, in a profound way. How can we make certain that the world surrounding us, exists the way we imagine it to exist? It takes more than measurement--using the scientific method--to give us an indisputable answer. It takes our sense of "presence" in the context of our environment to fully believe that our world exists--in not only a scientific way--but in an authentic way (immersed in everyday existence). Even our connection to the presence of everything outside of us and the ideas within our minds is based on faith that we do perceive ourselves and everything around us in an accurate way. It is a "vivid belief" that we are connected to a world, and universe, that we can understand.