Last Thursdayism is a criticism of the omphalos hypothesis created by Philip Henry Gosse in 1857. Wikipedia describes it as follows:
The omphalos hypothesis is one attempt to reconcile the scientific evidence that the universe is billions of years old with the Genesis creation narrative, which implies that the Earth is only a few thousand years old. It is based on the religious belief that the universe was created by a divine being, within the past ten thousand years (in keeping with flood geology), and that the presence of objective, verifiable evidence that the universe is older than approximately ten millennia is entirely due to the creator introducing false evidence that makes the universe appear much, much older.
Last Thursdayism is an attempt to criticize such a view of creation:
Though Gosse's original omphalos hypothesis specifies a popular creation story, others have proposed that the idea does not preclude creation as recently as five minutes ago, including memories of times before this created in situ. This idea is sometimes called Last Thursdayism by its opponents, as in "the world might as well have been created last Thursday."
Wikipedia also notes that Last Thursdayism is impossible to test scientifically:
The concept is both unverifiable and unfalsifiable through any conceivable scientific study—in other words, it is impossible even in principle to subject it to any form of test, by reference to any empirical data, because the empirical data themselves are considered to have been arbitrarily created to look the way they do at every observable level of detail.
Since there is nothing to observe and since Last Thursdayism does not originate from within physics itself (like the big bang), it requires no physical explanation any more than would Russell's teapot or the Flying Spaghetti Monster.
However, it does encourage skeptical questioning, perhaps unwittingly, about how real physical laws are. Are physical laws discoveries about nature as it really is or are they inventions of our minds that happen to work even if the universe has been around for billions of years?
Wikipedia contributors. (2019, August 4). Omphalos hypothesis. In Wikipedia, The Free Encyclopedia. Retrieved 14:57, August 19, 2019, from https://en.wikipedia.org/w/index.php?title=Omphalos_hypothesis&oldid=909247454