To me the time is defined by an increase of entropy and thus pertains to the irreversible processes. In some sense it reflects the transition from reversible state to the irreversible one. In other words the time "kills" the present states of everything surrounding us. Some believe that irreversibility is defined by quantum processes where you can never determine the speed and location of the electron simultaneously which is commonly known as a Geisenberg principle.

That is taking place because the fact of observation changes the observable itself meaning that by simply looking at the world we alter it irreversibly. Our measuring devices break into the matter of the nature making it to respond and thus shifting it to another state of being. Furthermore there is another thing known as a random event. It is the one which has no pre-history behind it. Radioactive decay would be an example of those. There is no evident cause leading to that, it just happens at certain circumstances and no one can ever predict where it might go. The opposite kind of events are predetermined ones and they do have the underlying reasons to happen. Physical laws make our world pre-determined so by knowing them we can predict the events and avoid randomness at least to some extent. Say gravity forces pre-determine our bodies to be pulled down to the Earth and we can not change that law but we are able to predict that outcome and use our legs to not fall. On the contrary we are not capable to predict the tiny particles being born and disappearing out of a physical vacuum which is happening all the time randomly. It is like a mutational process in biological systems. It can change the future dramatically still being almost unnoticeable. But it turns us towards a chaos theory though which is another long story.