Einstein for Everyone - Bryan Bartnick

 

• What is the relativity of simultaneity? What is it not? In Special Relativity, is time unreal?

Norton explains that there can be a significant difference between perception and reality of events. From my previous background knowledge, I know that there are two critical assumptions that must be made for special relativity to hold: there is no preferred reference frame, and that the speed of light is independent of the speed of the source that is emitting that light.

According to Norton's "Spacetime, Tachyons, Twins, and Clocks," a change in perception from a nonmoving object to a moving object (or the other way around) will stretch spacetime, which can be diagrammed with space on the horizontal axis, and time on the vertical. Any motion of an object can be plotted on this diagram between space and time. 

In Norton's "Relativity of Simultaneity," he uses an example of a platform to illustrate what the relativity of simultaneity is. In this example, he proves that relativity of simultaneity means that the perspective of an observer can skew their perception of the time that events actually occurred, where the takeaway would be that the universe has neither an absolute sense of time or simultaneity, and each breaks down the further two objects are from one another.

As a more clear example that is similar to his platform example, imagine that you are in a rocket ship traveling a third of the speed of light being that you cannot exceed the speed of light (except for tachyons). The true reality is that there are two incredibly large lightning bolts that strike at the same time on opposite sides of the world (which happen to be perceivable from your rocket ship), and they are each the same distance away from you when they occur. Let's call the lightning bolt that is in the opposite direction that you are traveling "A," and the other "B." The lightning bolt "B" will appear to occur first because it will reach you, the observer, first. This means that the relativity of simultaneity completely depends on your frame of reference and that two events that occur at the same time, in reality, may not occur at the same universally because it depends on the frame of reference.

Norton does caution us to avoid grouping the "relativity of simultaneity" with "appearance simultaneity" because "appearance simultaneity" is the correctional process our sensations do to shape our perceptions. For example, if we see two flashes of light that we see at the same time, one faint and small and the other vibrant and large if we knew they were supposed to be the same time we would assume that the vibrant one occurred afterward but was closer to us than the fainter one since we saw them at the same time. The "relativity of simultaneity" only arises for events that occurred after we have corrected for the oddities already, and that there are still discrepancies in the perception of space and time.

Based on this, I actually still retain that there is still a "real" form of time. I believe that the fact that we hold each of these examples on the basis that there is a "reality," time must exist. We cannot say that events actually happened at the same time in all of these examples if time was unreal. I believe that if light theoretically did not have speed, then we would always have our perception of separate events with respect to one another be accurate. This ties into the fact that there is always a before, during, and after series, and these events will always be accurate if it was independent of the property of velocity.