The Universe is all that is existent. All that’s existent is all that we can experience with our senses,detect using the technology and wise to consider the possibility of some of the existent remaining undetected even with the technology either because they can’t be detected at all or because of the need of advancement of technology in order to detect those;this means ourselves & every existent thing around us,near and far away are part of existence. In short , an individual & the entire world around her [experienced, detected,undetected and hence unknown] is the Universe.
Existence means Something and Non-existence means Nothing ! Logic preaches “something always has to be made of something”
All of the existent must have been made of something which in turn must have been made of something else and so on……the fact that all of the existent can be segmented (broken/divided) & till the stage of extremely small-sized pieces not only substantiates the claim of Logic,but also enlightens us that in reality,there is only a small-sized thing existent and not a big-sized thing , in fact all the big in this universe are made of small ones. These small ones constitute all the existent of the present day universe and can be simply termed ‘the stuff’.