Inertial & Non-Inertial Frames: Light Wavelengths

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Discussion Overview

The discussion revolves around the effects of rotation on the wavelength and frequency of light signals exchanged between a rotating body and a central body, specifically in the context of inertial and non-inertial frames. Participants explore the implications of relativistic effects on light propagation without the influence of gravity or body size.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant claims that when a rotating body sends a light signal to a central body, the wavelength received by the central body is longer by a factor of 1/γ, while the central body sending a signal to the rotating body results in a wavelength that is shorter by a factor of γ.
  • Another participant agrees that the wavelength is longer but suggests it is by γ times, and states that the frequency of light is slower by a factor of 1/γ. They also assert that the wavelength received by the rotating body is shorter by 1/γ times, with the frequency being γ times faster.
  • One participant questions the repetition of the topic, referencing a previous thread where a similar question was discussed.
  • A participant acknowledges the semantic nature of the disagreement but expresses a sense of agreement on the core ideas presented.
  • Another participant provides a mathematical basis for their claims, referencing the relationship between frequency, wavelength, and the factor γ, while also noting the complexity of previous discussions.

Areas of Agreement / Disagreement

Participants express differing views on the factors by which wavelength and frequency change, indicating a lack of consensus on the precise relationships. Some agree on the general effects but differ in the specific factors involved.

Contextual Notes

There are unresolved aspects regarding the definitions of terms and the mathematical steps involved in deriving the relationships discussed. The discussion also reflects a dependency on the assumptions made about the system being analyzed.

HALON
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When neglecting gravity and body size, if a body rotating at uniform angular velocity about a central body sends a light signal to the central body, the central body will receive the wavelength as longer by [itex]1/γ[/itex]. Conversely, if the central body sends a signal to the rotating body, the rotating body will receive the wavelength as [itex]γ[/itex] times shorter. Is this correct?
 
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HALON said:
When neglecting gravity and body size, if a body rotating at uniform angular velocity about a central body sends a light signal to the central body, the central body will receive the wavelength as longer by [itex]1/γ[/itex].
The wavelength is longer but I would say by [itex]γ[/itex] times. Or you could say the frequency of the light is slower by a factor of [itex]1/γ[/itex].

HALON said:
Conversely, if the central body sends a signal to the rotating body, the rotating body will receive the wavelength as [itex]γ[/itex] times shorter. Is this correct?
Again, it is shorter but I would say by [itex]1/γ[/itex] times and the frequency is [itex]γ[/itex] times faster.

But this may just be semantics.
 
Didn't we already talk about this exact same thing in a previous thread of yours? You asked literally the same question in https://www.physicsforums.com/showthread.php?t=762176 and got the same answer ghwellsjr gave you above.
 
ghwellsjr said:
The wavelength is longer but I would say by [itex]γ[/itex] times. Or you could say the frequency of the light is slower by a factor of [itex]1/γ[/itex].


Again, it is shorter but I would say by [itex]1/γ[/itex] times and the frequency is [itex]γ[/itex] times faster.

But this may just be semantics.

I see your point about the semantics, but essentially we are in agreement.

[EDIT] I began with [itex]γ=(1-v/c)^{1/2}[/itex] for an instant of angular velocity, then [itex]f_{orbit}=f_{central}/γ[/itex], which is simply [itex]1/γ[/itex]
Using [itex]c=fλ[/itex]
we get Orbit's view of light as [itex]c=(1/γ*f)(γλ)[/itex]
And the reciprocal is Central's view of light [itex]c=(γf)(1/γ*λ)[/itex]


WannabeNewton said:
Didn't we already talk about this exact same thing in a previous thread of yours? You asked literally the same question in https://www.physicsforums.com/showthread.php?t=762176 and got the same answer ghwellsjr gave you above.
Yes but... it was the last question I posted on that thread and I didn’t receive your reply. You implicitly answered it earlier in a very detailed (and for me complicated) way, which I took as agreement. Indeed my last question there was also rather longwinded. So I condensed the question (without all the equations) to seek clarification and confirmation.

If ghwellsjr is correct then it satisfies me and this thread may be closed.
 
Last edited:

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