That something might physically exist, it should be present in our world for some time. There can be no object without the length, width and height, as well as the object can not be without the "duration" - "instant" object, that is, one that does not exist at least some amount of time does not exist at all.
According to the universal nihilism, the past and the future do not take the time in the present. In addition, it is impossible to quantify the duration, which we call "real time": any amount of time you would call "real time" can be divided into parts - past, present and future.
If this lasts, say, second, this second is divided into three parts: the first part will be the last, the second - this third - the future. One-third of a second, which we now call this can also be divided into three parts. I'm sure you already understand the idea - so you can continue indefinitely.
Thus, this does not really exist, because it does not last over time. Universal nihilism uses this argument to prove that there is nothing at all.