Intuitive Special Relativity - Time Is Relative
In this post I am going to attempt to explain in an intuitive sense that time is relative.
There is no absolute time and by this I mean that events will be seen differently by observers moving at different speeds.
I hope to do this in a simple and intuitive manner. Let's see how it goes.
But first you may want to read my first three posts leading up to this one:
Intuitive Special Relativity (A Tough Concept Simply Explained)
Intuitive Special Relativity - What Is Time?
Intuitive Special Relativity - Time Dilation
Figure 1. Events as seen by a stationary observer.
(Image credit: Me, icons taken from CC0 creative commons sources)
The Setup
Let's say we have two train cars. One stationary (Figure 1) and one moving (Figure 2). There is an observer on each train (the red dot in the center).
Two bolts of lightning strike near the ends of the cars when the moving train is even with the stationary train.
The Stationary Observer
In Figure 1 above we have an observer on a stationary train car. As said above, at some point two lightning bolts hit near the ends of the car at the same time (time t = 0).
The signals of these events (the light) move towards the observer (time t = 1) and each signal reaches the observer simultaneously (t = 2).
So far so good.
Figure 2. Events as seen by a moving observer.
(Image credit: Me, icons taken from CC0 creative commons sources)
The Moving Observer
In Figure 2 above we have an observer on a moving train car. The same two lightning bolts as discussed above hit near the ends of the car at time t = 0.
The signals of these events (the light) move towards the observer (time t = 1) but the observer is also moving from left to right. This means that in t = 1 the right hand signal reaches the moving observer first.
In time t = 2, the left hand signal finally catches up with the moving observer.
The Implication
- The two observers see the same two lightning bolts.
- The stationary observer sees the two lightning strike events at the same time. This observer says the two events happened at the same time.
- The moving observer sees the right hand lightning strike first and the left hand lightning strike second. This observer says the two events happened at different times.
- Both observers are correct. Time is relative and your experience of time depends on your frame of reference.
Thank you for taking the time to read my post.