New Frontiers in Physical Science Research Vol. 9,
6 March 2023,
The world is composed by events. We can sense the changes of events directly by our five senses or indirectly by using the measurement equipment and tools. If in a closed system including the observer no changes are sensed, no time passes and if even a very small change is sensed, time passes. It means that the time is not a real degree of freedom and can be only understood through the concept of changes in events. The events can be considered as relata and their mutual or multiple interactions can be considered as relation. Causality can be sensed if one relata creates a change in the other relata and in consequence the passage of time can be sensed. These two relates are connected to each other by a causal world line. If two relates are connected by a timelike curve theoretically, but they cannot make change in each other, one relata has only a priority in occurrence respect to other (time precedence), and in consequence, one can omit the past non-casual events from the casual world line. In addition, in causality relation, we should consider more than one causal world line due to the uncertainty principle of quantum mechanics and its probabilistic nature (superposition principle). Therefore, at Planck scale, more than one casual world line should be assigned to the relation between two casual events when we want to study the dynamic of spacetime. It means that no kinematic state can be considered at Planck scale and a quantum spacetime manifold (QSTM) should be only assigned to the casual world line, from beginning. The quantum field operators and the particles are assigned to the point of the QSTM in Planck scale and in consequence, the physical theories are background dependent at the scale.