Understanding Simultaneity in Relativity: Common Doubts Addressed

In summary, the conversation discusses the concept of relativity of simultaneity and how it relates to the synchronization of clocks. The example of two light sources and two tennis balls is used to explain how the observer's frame of reference affects their perception of time and simultaneity. The key takeaway is that simultaneity is relative and depends on the observer's frame of reference, as explained by the theory of relativity.
  • #1
novice2000
3
0
Hi everyone,

I got interested in physics recently and started reading a book called "relativity simply explained " by martin gardener. when i was going through the book i got some doubts in relativity of simultaneity.

my problem is described below

o>>> ---------------------------<< 0
1---------------B-------------------2
----------------C --> V
Point 1 and 2 are light sources equidistant from observer B . There are clocks at point 1 and 2 each.The moment the light is sent from point 1 clock at point 1 is set to zero and the moment the light is sent from point2 clock at point 2 is set to zero.

B receives the light from both point1 and point 2 simultaneously. Can he conclude that clocks at 1 and 2 are synchronized ?

C is an observer moving w.r.t to B Can he actually see that light from both sources reaching B at same time??


I have a few more queries

hoping to get a reply soon
 
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  • #2
novice2000 said:
B receives the light from both point1 and point 2 simultaneously. Can he conclude that clocks at 1 and 2 are synchronized ?
It depends on whether those clocks are moving with respect to B or not. If the clocks are not moving, then he can conclude they are synchronized. (Assuming they are working properly.)

C is an observer moving w.r.t to B Can he actually see that light from both sources reaching B at same time??
If you mean will a moving observer C agree that the light from both sources reached B at the same time: Yes. All observers will agree on that.
 
  • #3
Doc Al thanks for the reply

As you have mentioned the clocks are not moving w.rt to B and he concludes that clocks are synchronized.

Observer C sees that light from both sources reaches B at the same time.

o>>> ---------------------------<< 0
1---------------B-------------------2
----------------C --> V


the observer C is moving to the right with a speed V. He observes that light from 2 has to travel more distance and since speed of light is same in both directions he is forced to conclude that clock at 2 is set ahead of clock at 1

is my conclusion correct?
 
  • #4
Yes, that is correct.
 
  • #5
Oh great!



if i repeat the same experiment with two tennis balls instead of light source. ie i will release two tennis balls from both 1 and 2 with same speed say "w".

the two balls will arrive observer B at the same moment and he will conclude that clocks are synchronized. right?

C will see that both balls arrive observer B at the same moment.

o--> w--------------------- w<----- 0
1---------------B--------------------2
C --> V


if i take speed of ball from 1 as w-v ( relative speed . is this correct?)

and speed of ball from 2 as w+V .

is'nt it possible for observer C to back calculate and conclude that both clocks are synchronized??


i know there is some error. But can't figure out


Please help
 
  • #6
novice2000 said:
if i take speed of ball from 1 as w-v ( relative speed . is this correct?) and speed of ball from 2 as w+V ... i know there is some error. But can't figure out
Hi novice2000,

The error is just that you need to use the http://www.math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html" formula, not the Gallilean one.
 
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  • #7
novice2000 said:
if i repeat the same experiment with two tennis balls instead of light source. ie i will release two tennis balls from both 1 and 2 with same speed say "w".

the two balls will arrive observer B at the same moment and he will conclude that clocks are synchronized. right?
Right.

C will see that both balls arrive observer B at the same moment.
Right.

o--> w--------------------- w<----- 0
1---------------B--------------------2
C --> V


if i take speed of ball from 1 as w-v ( relative speed . is this correct?)

and speed of ball from 2 as w+V .
No, as DaleSpam already pointed out, this is not correct. You must combine speeds relativistically to get the correct answer. (That's why relativity thought experiments always use light beams--they always go at the same rate in any frame. Much easier to switch from one frame to another.)

is'nt it possible for observer C to back calculate and conclude that both clocks are synchronized??
The transformation of velocities that you used to get w-v and w+v is only true in Newtonian physics, not Einsteinian. (That transformation is called Galilean relativity, after Galileo.) Using that transformation, you would be able to conclude both clocks are synchronized: But that's no surprise--in the Newtonian world time is the same for any frame.

If you used the proper relativistic transformation (see DaleSpam's link), you'd find--once again--that simultaneity is relative.
 

FAQ: Understanding Simultaneity in Relativity: Common Doubts Addressed

What is simultaneity in relativity?

Simultaneity in relativity refers to the concept that the timing of events can be relative, depending on the observer's frame of reference. This means that two events that appear to happen at the same time to one observer, may not appear simultaneous to another observer in a different frame of reference.

How does the theory of relativity explain simultaneity?

The theory of relativity, specifically the special theory of relativity, explains simultaneity by taking into account the constant speed of light and the relativity of time. Time is not absolute and can vary depending on the observer's frame of reference. This means that the timing of events can also vary, leading to the concept of relative simultaneity.

Why is understanding simultaneity important in relativity?

Understanding simultaneity is important in relativity because it challenges our everyday understanding of time and events. It also has implications for how we perceive and measure time, as well as how we understand the universe and its fundamental laws.

Can there be absolute simultaneity in relativity?

No, according to the theory of relativity, there is no such thing as absolute simultaneity. This means that there is no universal concept of "now" that applies to all observers in all frames of reference. Simultaneity is relative and can vary depending on the observer's frame of reference.

What are some common misconceptions about simultaneity in relativity?

Some common misconceptions about simultaneity in relativity include the belief that time is absolute, that there is a universal "now" for all observers, and that events must be simultaneous in all frames of reference. These misconceptions stem from our everyday understanding of time and can be corrected by studying the principles of relativity.

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