Phenomenalism
Phenomenalism is the view that physical objects do not exist as things in themselves but only as perceptions or sensory stimuli (e.g. redness, hardness, softness, sweetness, etc.) situated in time and in space. In particular, phenomenalism reduces talk about physical objects in the external world to talk about bundles of sense-data. For a brief period, Bertrand Russell (1872–1970) held the view that all that we could be aware of was this sense data; everything else, including physical objects which generated the sense data, could only be known by description, and not known directly.
Read more about this topic: Simulation Hypothesis, Origins, Later Thinkers