Simultaneous events  special relativityby jaumzaum Tags: events, relativity, simultaneous, special 

#1
Feb1313, 10:07 AM

P: 246

I'm studying special relativity and I'm having difficulty in understanding somethings. I have 2 questions I'm confused about.
1) If I am moving in relation to you, when you observe me, I should be in slowmotion. but you are moving in relation to me, so when I observe you, will you be in slow motion too? 2) Consider the following experiment. Pam and Jim are moving in a 1dimensional space frame. Pam moves to the right with velocity v (in relation to me, I'm at rest at the origin), and Jim moves to the left with velocity v too. Both are hanging a 1 meter rule in the hands, pointing forward. They have always the same distance in relation to the origin. Consider the following events Event 1: the front of the Pam's rule touches Jim Event 2: the back of the Pam's rule passes Jim Event 3: the front of the Jim's rule touches Pam Event 4: the back of the Jim's rule passes Pam Δt(x,y) = time interval between event x and y measured by Pam Δt'(x,y) = time interval between event x and y measured by Jim Δt''(x,y) = time interval between event x and y measured by me For me, events 1 and 3, 2 and 4 should be simultaneous. But let's analyze Jim's frame of reference. For Jim, event 1 and 2 occur at the same place, so, Jim measures the proper time. Thereby Δt(1,2) > Δt'(1,2) Also, Δt'(3,4) > Δt(3,4) For symmetry, Δt(3,4)=Δt'(1,2), Δt(1,2)=Δt'(3,4) So Δt(1,2)>Δt(3,4) and the events should not be simultaneous to Jim, the same for Pam Is this right? 



#2
Feb1313, 10:18 AM

Sci Advisor
HW Helper
PF Gold
P: 4,108

Try drawing the diagrams that I suggested in this recent post
http://www.physicsforums.com/showpos...1&postcount=13 Often a geometric argument is more tangible than an algebraic calculation. [please report back if it is helpful] 



#3
Feb1313, 10:48 AM

PF Gold
P: 4,081

These diagrams show how the simultaneity is different when events are seen from three frames. I'm not sure if the labelling corresponds to yours.




#4
Feb1313, 11:30 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 38,879

Simultaneous events  special relativity 



#5
Feb1313, 02:55 PM

PF Gold
P: 4,521

I'm not just nitpickingthese are important distinctions. Jim and Pam can actually measure the Proper Times on each of their own clocks but they cannot measure the Coordinate Times or intervals of remote events. Rather, we calculate those times based on the selected Inertial Reference Frame. 


Register to reply 
Related Discussions  
Two Events in Special Relativity with on Time Dialation  Introductory Physics Homework  9  
[Special Relativity] Find frame K' in which events in K appear to be simultaneous  Introductory Physics Homework  4  
Special Relativity: Find the reference frame in which two events are Simultaneous  Introductory Physics Homework  10  
Special Relativity calculating a time period so simultaneous in all reference frames  Advanced Physics Homework  4  
Simultaneous events in SR...?  Special & General Relativity  12 