Relativity: Observer's Perspective - Am I Getting it Right?

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SUMMARY

The discussion centers on the observer's perspective in relativity, specifically regarding a hypothetical experiment involving two lasers placed 599,584,916 kilometers apart in a gravity-free environment. The original poster posits that an observer equidistant from both lasers would perceive the light from both lasers meeting at the center after 500 seconds, while each laser would see the light from the other taking 1,000 seconds to meet. However, participants clarify that there is no valid reference frame for light and emphasize the need for clearer definitions of the experiment's parameters, such as the direction of the lasers and the nature of their emission.

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  • Understanding of Einstein's theory of relativity
  • Familiarity with the concept of light speed (299,792,458 km/s)
  • Knowledge of reference frames in physics
  • Basic principles of laser operation and emission
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  • Explore the concept of simultaneity in special relativity
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Vincent Vespa
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Hello, all. I'm trying to wrap my mind around relativity, and I just wanted to make sure I'm not getting it wrong. I'd really appreciate it if anyone were to take the time to chime in on this hypothetical that I think explains it.

Say someone was to put two lasers (in a "gravity free" environment) 599,584,916 kilometers apart and fired them at the exact same time. Imagining that the two laser points are observation points and that the person running the experiment was in the center of these two points (299,792,458 km from either laser), we get three relative perspectives. For the observer in the middle, the two points would appear to meet in the center (taking 500 seconds). For either of the laser points they should appear to meet at the opposite laser (taking 1,000 seconds), since the stationary (from the view of the experimenter) lasers would be moving at the speed of light relative to the laser point.

Do I have this right? I don't really have anyone else to ask... I'm not a student or anything, just curious.
 
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Vincent Vespa said:
Do I have this right? I don't really have anyone else to ask... I'm not a student or anything, just curious.

Did you mean 1000 seconds and 2000 seconds? Light takes 1000 seconds to cover 299,792,458 km.

But even after making that correction, the answer is no, as there is no such thing as the reference frame of light, or the world as viewed by a beam of light. There's some discussion of this in the FAQ at the head of this page.

https://www.physicsforums.com/showthread.php?t=511170
 
Last edited:
Vincent Vespa said:
Hello, all. I'm trying to wrap my mind around relativity, and I just wanted to make sure I'm not getting it wrong. I'd really appreciate it if anyone were to take the time to chime in on this hypothetical that I think explains it.
I think a lot of us would like to chime in but your scenario is very confusing. Here are some questions you need to answer:
Vincent Vespa said:
Say someone was to put two lasers (in a "gravity free" environment) 599,584,916 kilometers apart and fired them at the exact same time.
1) Which direction are the lasers pointed in? Are they aimed at each other or in some other direction?

2) When you say "fired", do you mean they both emit a short burst of laser light or do you mean they are turned on and stay on?
Vincent Vespa said:
Imagining that the two laser points are observation points and that the person running the experiment was in the center of these two points (299,792,458 km from either laser), we get three relative perspectives.
3) Are these two laser points moving or stationary?

4) Are these two laser points the emitted laser light from a burst?

5) Are these two laser points a place where the laser light is shining, making a bright dot or point?

6) Are there two observers located wherever these two laser points are?

7) Is the person running the experiment moving or stationary?

8) Is the person running the experiment located in line with the two lasers?

9) Are the two lasers aimed at the person running the experiment?

10) Does the person running the experiment fire the lasers?
Vincent Vespa said:
For the observer in the middle, the two points would appear to meet in the center (taking 500 seconds). For either of the laser points they should appear to meet at the opposite laser (taking 1,000 seconds), since the stationary (from the view of the experimenter) lasers would be moving at the speed of light relative to the laser point.
I can't make any sense of these statements. Maybe after you answer the above 10 questions you will understand how to rephrase the rest of your scenario.
Vincent Vespa said:
Do I have this right? I don't really have anyone else to ask... I'm not a student or anything, just curious.
 

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