The universe was created last Thursday. It probably wasn't. But can’t you prove me wrong if I were to say that it was. This insane theory is known as last Thursdayism (alternately Last Tuesdayism or Last Wednesdayism). 


Last Thursdayism is the idea that the universe was created last Thursday, but with the physical appearance of being billions of years old. It's also a counter to the creationism theory. Under Last Thursdayism, books, fossils, light already on the way from distant stars, and literally everything (including your memories of the time before last Thursday) were all formed at the time of creation (last Thursday) in a state such that they appear much older.


Last Thursdayism functions both as a philosophical point on how our observations may not match with "reality" and a Reductio ad absurdum (Reductio ad absurdum is a method of proving the falsity of a premise by showing that its logical consequence is absurd or contradictory) of the young-Earth creationist idea of omphalism (the Omphalos hypothesis is a creationist idea asserting that the universe was created to appear very, very old despite being created not that long ago). If the world was, hypotheticly, created 6,000 years ago with the appearance of being made billions of years ago, what is there to stop us from claiming it was made Last Thursday?


Last Thursdayism is what's known as an unfalsifiable fallacy, anything you attempt to say to prove it wrong, I could simply disprove by saying it was part of the creation that happened last Thursday, every movie, every book, every textbook of historical events that have happened in the past, I could simply say was created last Thursday. 


The debate on whether Last Thursdayism is true has raged on ever since the creation of the universe last Thursday.