SR is that nothing can move faster than light

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Discussion Overview

The discussion revolves around the principles of Special Relativity (SR), particularly the assertion that nothing can move faster than the speed of light. Participants explore the implications of this principle, particularly in relation to simultaneity and the behavior of light signals in different reference frames.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the apparent contradiction between the principle that nothing can exceed the speed of light and the mathematical treatment of simultaneity involving observers in different frames, specifically regarding the speed of approach being $c + v$.
  • Another participant asserts that while no single body can exceed the speed of light, the distance between two bodies moving towards each other can close at a rate greater than $c$, suggesting a nuanced interpretation of relative motion.
  • A further contribution introduces an experiment involving light signals and a moving target, questioning whether the derived speed $c - u$ aligns with classical velocity addition, indicating a potential overlap with classical mechanics without invoking special relativity.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the speed of light limit and the behavior of moving bodies. There is no consensus on the interpretations or the mathematical formulations presented, indicating ongoing debate and exploration of the concepts.

Contextual Notes

Some participants reference classical mechanics and its relationship to special relativity, highlighting the need for clarity on assumptions and definitions in the context of velocity addition and simultaneity.

nieuwenhuizen
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Can somebody explain my error to me?

1. The base of SR is that nothing can move faster than light, c + v == c,
c - v = c

2 The next step many authors do is proving non-existence of simultaneity by
on observer at the platform versus one in a fast train. Flash from the
front, to be received at the tail, which is. they say "racing toward the
rays". Conclusion: Speed of approach is $c+v$ so that
$$ ( c + v ) \cdot \Delta t = L $$
Combination with a forward flash [ c - v ] leads to

$$ \frac{1}{c+v} + \frac{1}{1-v} = \frac{1}{c^2 - v^2 } $$

Why does this not contradict the base - statement 1 ?

Thanks to the one that does.

Nieuwenhuizen, J.K.
2009-02-16T15:36
 
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nieuwenhuizen said:
Can somebody explain my error to me?

1. The base of SR is that nothing can move faster than light, c + v == c,
c - v = c

2 The next step many authors do is proving non-existence of simultaneity by
on observer at the platform versus one in a fast train. Flash from the
front, to be received at the tail, which is. they say "racing toward the
rays". Conclusion: Speed of approach is $c+v$ so that
$$ ( c + v ) \cdot \Delta t = L $$
Combination with a forward flash [ c - v ] leads to

$$ \frac{1}{c+v} + \frac{1}{1-v} = \frac{1}{c^2 - v^2 } $$

Why does this not contradict the base - statement 1 ?

Thanks to the one that does.

Nieuwenhuizen, J.K.
2009-02-16T15:36
I am new to this and this is only to find how a reaction is handled. Sorry
 


nieuwenhuizen said:
Can somebody explain my error to me?

1. The base of SR is that nothing can move faster than light, c + v == c,
c - v = c

2 The next step many authors do is proving non-existence of simultaneity by
on observer at the platform versus one in a fast train. Flash from the
front, to be received at the tail, which is. they say "racing toward the
rays". Conclusion: Speed of approach is $c+v$ so that
$$ ( c + v ) \cdot \Delta t = L $$
Combination with a forward flash [ c - v ] leads to

$$ \frac{1}{c+v} + \frac{1}{1-v} = \frac{1}{c^2 - v^2 } $$

Why does this not contradict the base - statement 1 ?

Thanks to the one that does.

Nieuwenhuizen, J.K.
2009-02-16T15:36

No body can travel at greater than c, but there's no problem with the distance between two moving bodies closing at more than c. Two bodies approaching each other, each at nearly c in the observer's frame, will close distance at nearly 2c. Of course, in the frame of reference of one of the bodies, the distance is closing at nearly c, not nearly 2c, because all of the motion is in the other body, which cannot travel faster than c.
 


nieuwenhuizen said:
Can somebody explain my error to me?

1. The base of SR is that nothing can move faster than light, c + v == c,
c - v = c

2 The next step many authors do is proving non-existence of simultaneity by
on observer at the platform versus one in a fast train. Flash from the
front, to be received at the tail, which is. they say "racing toward the
rays". Conclusion: Speed of approach is $c+v$ so that
$$ ( c + v ) \cdot \Delta t = L $$
Combination with a forward flash [ c - v ] leads to

$$ \frac{1}{c+v} + \frac{1}{1-v} = \frac{1}{c^2 - v^2 } $$

Why does this not contradict the base - statement 1 ?

Thanks to the one that does.

Nieuwenhuizen, J.K.
2009-02-16T15:36
Consider please the following experiment performed in an inertial reference frame in the limits of Newton's mechanics. A source of light S located at the origin O emits successive light signals in the positive direction of the x-axis at constant time intervals t(e). The light signals
illuminate a target that moves with speed u in the positive direction of the x axis. When the first signal is emitted the target is located in front of the source. We impose the condition that the second emitted signal illuminates the target at a time t(r) i.e.
c[t(r)-t(e)]=ut(r).
where from
t(r)=ct(e)/[c-u]
Special relativity is not involved so far. Is c-u the result of a classical sddition law of velocities? That is the way in which the classical Doppler Effect formula is derived.
 

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