Omphalos is the Greek word for navel.
According to the ancient Greeks, Zeus sent out two eagles to fly across the world to meet at its center, the "navel" of the world. Omphalos stones to denote this point were erected in several areas surrounding the Mediterranean Sea, the most famous of those was at the oracle in Delphi.
The omphalos hypothesis was named after the title of an 1857 book, Omphalos by Philip Henry Gosse. In this book Gosse argued that in order for the world to be "functional", God must have created the Earth with mountains, canyons, trees with growth rings, Adam and Eve with hair, fingernails and navels, and that therefore no evidence we can see of the presumed age of the earth and universe can be taken as reliable.
The idea has seen some revival in the twentieth century by some modern creationists, who have extended the argument to light that appears to originate in far-off stars and galaxies, although many other creationists reject this explanation and also cantankerously believe that Adam and Eve had no navels.
Bertrand Russell, influenced by Gosse, discussed the ramifications of such a theory in his 1921 work, The Analysis of Mind, stating:
"There is no logical impossibility in the hypothesis that the world sprang into being five minutes ago, exactly as it then was, with a population that 'remembered' a wholly unreal past. There is no logically necessary connection between events at different times; therefore nothing that is happening now or will happen in the future can disprove the hypothesis that the world began five minutes ago."
Jorge Luis Borges, in his 1940 work, Tlön, Uqbar, Orbis Tertius, describes a fictional world in which some essentially follow as a religious belief a philosophy much like Russell's discussion on the logical extreme of Gosse's theory:
"One of the schools of Tlön goes so far as to negate time: it reasons that the present is indefinite, that the future has no reality other than as a present memory."
Last Thursdayism (sometimes Last Tuesdayism or Last Wednesdayism) is a whimsical version of omphalism. It is the idea that the world was created last Thursday, but with the appearance of age: people's memories, history books, fossils, light already on the way from distant stars, and so forth.
This parody has been taken further, with claims that the Universe was created Last Thursday by Queen Maeve the housecat, who would destroy the world Next Thursday, keeping a Heaven of sorts for those who were nice to cats and damning evildoers to the Hell of the the never-cleaned Eternal Litterbox.
Such navel gazing is probably no more illogical a belief than the complex modelling required to show that the Big Bang created time and space. Though admittedly, we are still eagerly awaiting the mathematical proofs for omphalism and its derivatives.