Hi Roel:
Well, to be honest, I don't think you theory would be given a second thought by physicists. However, the following statement you made is most insightful, so let's look at it:
I think the more "active" an object or a person is, the faster it disappears from a point in time. So if one would be able to travel back in time for lets say an hour, a rock would still be there but any living tissue would be gone.
What you are discussing here is the PERSISTENCE of various forms of matter. The mechanism that determines the persistence of a given form of matter is actually chemical in nature. A rock does not chemically interact with its surroundings, and so it lasts longer than human tissue, which will chemically react with microbes and bacteria to break it down.
However, it is worth exploring your concept from the standpoint of how different forms of life (or non-life) PERCEIVE the flow of time. I pointed out a similar example in an earlier post, where if you ignored clocks, the average human would think time passed more quickly if they were busy...i.e. if they had a lot of "Matter in Motion" going on. On the flipside, a person who was simply sitting in a chair, with nothing to do or read, would think time passed more slowly. Now let's apply this concept to the difference between humans and trees. We know that trees have MUCH longer lifespans than humans do. We also know that trees are MUCH less mobile (have lower measures of matter in motion) than humans do. Therefore, if we assume that trees have some form of rudimentary perception (and experiments show they do), then it would be likely that they would perceive the passage of time MUCH more slowly than we do. What we call a year would seem more like a second in their lifespans. Now compare a human and a rock, and you see a MUCH larger disparity still!
If you accept this premise (and agree that Matter in Motion is really what helps us determine passage of time) then the conclusion would be that the flow of time is variable, and subjective (relative) to the observer's situation. So even though we may define what a "second" is to an extreme level of accuracy, it would likely mean nothing to an alien species, especially if they had much longer lifespans than we do....or, if they lived on a planet whose period around its sun was much longer than ours.
This sort of thinking, while it may not validate your theory that time is the smallest particle of matter, does help us realize that our limited human senses are NOT the "universal authority" on how things REALLY work. Time is likely not linear, but we pronounce it to be so simply because we believe that our senses tell us the whole truth.
Kind Regards,
RainmanTime
