So who's right? They all are, in their own way. The key isn't to argue or fight over what "nothing" truly is, but to accept and understand these definitions as people use them. It's paramount to not confuse one meaning for another, or to get into a squabble over why it's wrong to use a word in a particular manner. Instead, when someone — particularly a scientist — says the word "nothing," try and understand which meaning they're using, and what the phenomenon is that they're trying to explain. For as far as our imaginations can take us, the only true form of knowledge we can hope to have concerning anything at all relies on putting it to the test in our own physical reality. Everything else, no matter how logically sound, is merely a construct of our minds.