Under what condition will you and a friend share the same realm of spacetime? When will you not share the same realm?

Solution 10RQ Introduction: Space-time is a model that combines space and time into a single interwoven continuum. So, the “realm of space-time” refers that the domain of space and time. Step 1: The realm of space and time will be same if and only if you and your friend are at same frame of reference. So, if time changes, the time related to both of you will change. If position changes, it is applicable to both. If the frame containing you and your friend is moving with constant speed, it will be same for both of you. If it accelerates, the acceleration also will be same for both. If you and your friend are at different frames of references, then the position and time will be different. Sometimes, one will move with a constant velocity. There is a chance of accelerated motion too. If anything like these happened, the space and time coordinates will change and it will not be same for both. So, the realm of space and time will be different if you and your friend are at different frames of references. Conclusion: You and your friend will share the same realm of space time only if both of you are in same frame of reference. If both of you are in different frame of reference, then the realm of space and time will be different.