Here is the background and then my theory.
Often when you are modelling, you drop a part on the floor - well I do it all the time!
I am sure that you have all observed that to go looking for a small part immediately is often a waste of time. Give it a few minutes and there it is. Now, my wife has theories about this, mostly to do with impatience and incompetent looking.
My theory is this. We can prove the existence of time travel by the process described above. What actually happens is that, by falling off the table - along with the plastic content of the part, the likelihood of being able to replace it if lost, and the correlation of the plastic colour with that of the floor covering - the part will actually disappear - albeit, just a few minutes but none the less disappear. This is proven by the fact that the part will not be visible for that few minutes.
My theory is that the part is actually travelling through time and will just re-appear once we catch up with it. There can be no other rationalisation!