Needing a basic clarification with SR

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Discussion Overview

The discussion centers around the concept of the speed limit in special relativity (SR), particularly regarding how velocities are perceived in different frames of reference. Participants explore the implications of velocity addition and the foundational principles that govern these observations.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant expresses confusion about why objects cannot be moving at the speed of light in certain frames of reference, questioning if two objects moving at c/2 in opposite directions could be perceived as moving at c from each other's perspective.
  • Another participant suggests looking up velocity addition, implying that there are established rules governing how velocities combine in relativity.
  • A later reply emphasizes that the equations for velocity addition are based on the postulate that all observers measure the speed of light as c, regardless of their frame of reference, rather than solely on time dilation.

Areas of Agreement / Disagreement

The discussion reflects a lack of consensus, with some participants providing references and clarifications while others express confusion about the underlying principles of special relativity.

Contextual Notes

There are unresolved assumptions regarding the participants' understanding of the foundational concepts of special relativity, particularly the implications of the speed of light and velocity addition.

jam.muskopf
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I am new to understanding the concepts in SR and GR, and one of the main concepts i am having difficulty with is the speed limit. I don't understand why things can't already be moving at the speed of light in certain frames of reference. For instance, from the Earth's frame of reference, isn't it possible for something to be traveling c/2 in one direction and something else to be traveling at c/2 in the exact opposite direction, making the velocity from either object's frame of reference c?
 
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No, look up velocity addition in wikipedia.
 
Thanks!
 
These equations on velocity addition are based off time dilation, correct?
 
jam.muskopf said:
These equations on velocity addition are based off time dilation, correct?

No, they are based on the postulate (or empirical observation) that all observers measure the speed of light to be c, regardless of their frame of reference.
 

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