The Universe, the perfect mind blower for those who love deep physics stuff. When we think about order of events, we often seek aid from the old 24 hours system to help our confused brains get trough the heavy content of time. In fact, humans are so confused about time that a single doubt about the existence of absolute time can lead us to get so many things twisted.
The image above is a sketch of a simple idea that someone told me once on YouTube. This is about how different reference frames describe event, and order of event in different ways, although describing the same thing.
There are 3 observers and three stars. Geometrically, the distance from observer 1 to 2 is the same as from 1 to 3, and distance from 2 to 3 is greater than the two first mentioned distances. Accordingly, the distance from observer 1 to star 1, star 4, and star 3 is relatively the same. It is important to notice that the distance from observer 2, and 3, to star 3, is also the same, and equal to that from observer 1 to star 3. Basically, star 3 is the center of a circumference that passes at all three observatories. However, distance from observer 2 to star 1 is relatively much less than all distances previously mentioned, and only equal to that from observer 3 to star 4. All distances here are measured in light years and time in billions of years considering the cosmic macro scale herein addressed.
Now imagine that light is emitted from star 1 and star 4 simultaneously, and emitted from star 3 billions of years later. Also, try to neglect the presence of other stars in between the observers and the three stars. That way, light from star 1 and star 4(light 1 and light 4), travelling the same distance with the same velocity, would reach observatory 1 at the same time. And only billions of years later, would light from star 3 (light 3) reach observatory 1. Thus, from observatory 1, the order of events would be as follows: light 1 and light 2; light 3.
Now here is an interesting question: