Some people like to suggest nes-nisayon theory for the creation of the earth. In other words, even though everything appears to be 15 billion years old, it is in fact only 6000 years old, but was created fully formed. As to why G-d would pull such a stunt, the answer is that it makes logical sense that the world would be created fully formed. There is even a makor for this in the gemarah which tooks about adam being created as a 20 year old. Many people have a problem with this approach, because they don't like to think of G-d playing tricks and creating fakery, such as fake dinosuar bones, fossils and cave paintings.
Nes-nisayon gets even more shverre when you get to the mabul. The scientific evidence for there being no possibility whatsoever of a global flood, and no local flood covering more than a relatively small area, and for the fact that there has been continous human habitation of many varied areas of the earth going back 10 or 20 thousand years (if not more), and that biologically we cannot possibly be all descended from one person 5000 years ago, is solid. Not to mention the impossibility of all animals fitting in a small boat, and then being dispersed across the globe.
Therefore, to propose nes-nisayon as the answer to the mabul, requires us to say that not only was the flood in itself a completely miraculous event, but also that after the flood had finished, G-d miraculously wiped away all evidence. But even more than that, after the evidence was wiped away, G-d changed signs of human habitation, geology, biology and a host of other things to make it appear beyond a shadow of doubt that no such flood ever occurred.
Now, I can understand why G-d might want to create a completed world, there is a certain logic to that. But why would G-d remove all evidence showing that a flood had occurred ? And not only that, but go so far as to also plant fake evidence to show beyond a shadow of doubt that no flood ever did occur ? This has no relevance to any 'completed world' theory, and would have to involve an incredible amount of 'fakery' to create such an unbelievable nisayon.
The nes part I can understand. We have always thought of the mabul as a nes.
But this would truly be a strange nisayon.