It is only the interface that matters to an observer. A lump of metal that has been left out is just being a lump of metal, until you look at where this lump of metal contacts the air- and you discover that the process of oxidation is going on.
Another way of looking at it would be this: If a tree falls in a metaphysical forest where there is nothing for it to land on, fall through, or in any other way effect, does it matter? No. The falling tree only matters because it disturbs air particles, breaks through branches, and crushes mimes.
This is a consequentialist view point. The relative importance of something is determined by what impact it has on other somethings.
On a side note, I'm reading Toy Soldiers, the book that lead to a forgettable but enjoyable movie starring none other than the infamous Wil Wheaton. It's bad- oh so bad. I estimate the reading level is around fifth-gradeish, and it's got that style that's so common in political intrigue thrillers. I rate it slightly higher than Clive Cussler, who I have had the misfortune to stumble through twice- the first time because it was novel, the second time because I thought the first time wasn't too bad. That and I was 10.