The Relativity Of Simultaneity

The Relativity Of Simultaneity

In my previous post we discussed time dilation (time slowing down) as a consequence of the speed of light being an invariant. (Check out that post if you haven't seen it already)
http://alexdoesphysics.blogspot.com/2018/08/how-to-slow-down-time-time-dilation.html

Reading that post will help you understand analyzing events from different reference frames (perspectives).

In this post we’ll discuss another consequence of special relativity relating to time. We will realize that what two observers consider to be simultaneous can change and that idea of an absolute time doesn't exist. 

This means if North Korea and the US both got hit by a nuke at the same time according to one observer. Another observer moving differently may claim the US got hit first and a third may claim North Korea got hit first.

Formula Derivation

This equation tells us that the time difference according to the stationary observer depends on the speed and length of the train. If we think more generally it can tell us more interesting things about time.

• A fast-moving observer will not agree on whether two events happen at the same time with a stationary observer. 
• Depending on the direction of the movement, the order of the events can change. Since velocity is a vector if we have a negative velocity we get a negative time difference. This means that the events happen the other way round. In the case of the train, it means the train moves to the left and hits the right side first. 
• Two events very far apart will appear to happen at different times even if the velocities are quite low. 
• All observers agree on simultaneity if the two events happen at the same point in space,

This idea that simultaneity is relative goes completely against our normal understanding of time. To get a deeper understanding of how time works you have to look at the universe as being 4-dimensional space-time rather than a space where time progresses gradually (later I will do a post talking about space-time).

A question you may ask is what happens if two events are casually related? 

If man A shoots man B can a moving observer claim that man B got hit by the bullet before man A even shot? 

No. Special relativity is strange, but precedence order is always preserved. A man can't get shot before the bullet is even shot. In a later post I will also discuss cause and effect in special relativity.

Thanks for reading. If you enjoyed this post or any of my others, follow and subscribe to my blog. Feel free to discuss anything related to this post or ask questions in the comments below.

Check out my other posts on special relativity! (Link to all the posts)

How To Slow Down Time (Time Dilation)

How To Travel To The Future

How Galilean Relativity And The Lorenz Maxwell Equations (The 2 Postulates) Contradict

The Postulates Of Special Relativity


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