Just a small example? (It can be extended as per will) A person (X) and his friend (Y) are sitting in a room that has a table placed in the centre. X says to his friend, 'Can you determine whether the table is in the exact centre of the room or not?' Y says, 'I go even further, this table is not there. It's only our brains that are programmed in such a way (by nature) that we can build a perception of this table. The table is here only from our view point otherwise it does not exist in the very first place.' Suddenly an alien comes there. He can't see (feel) the room, the table, the persons sitting in it. For him it's just emply space. He says to himself, '****, I can't trace any matter in this part of the universe also, despite our advanced technology that has a history of over a billion years, despite these highly advanced gadgets that I am carrying with me.' He just flies there to and fro and in the process passes through the friends, the table, and leaves the place. For him there is no trace of 'matter' for trillions of lightyears that he has travelled. Obviously, the friends are also unmindful of the alien's presence, though Y is saying exactly what is happening right in front of them. I could have put this scenario using popular terms like "different regions of space time" or "time travel" or using "very few words". But I like it this way only. Do you agree with Y and consequently with the alien? Why/Why not?