Photon wavelengths and frequencies

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Discussion Overview

The discussion revolves around the concept of solar sails and the potential for creating a mechanism that could amplify the momentum generated by photons. Participants explore theoretical ideas about reflecting versus absorbing light and the implications for momentum transfer in the context of propulsion systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose the idea of creating a sail that generates an opposite force to push off photons, suggesting this could theoretically double the momentum.
  • Others argue that using a perfect mirror would be the most effective way to achieve maximum momentum transfer, as it reflects light rather than absorbing it.
  • A participant suggests that an active push could be achieved by shining a laser off the back of the sail, although this raises concerns about the efficiency of lasers.
  • Another viewpoint is that to gain more momentum than a perfect mirror would provide, the sail would need to emit something, effectively turning it into a photon rocket, which may not be efficient.
  • One participant mentions the idea of using a thermal mass at the focal point of a parabolic mirror/sail as an alternative approach to enhance propulsion.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the mechanisms of momentum transfer in solar sails, with no consensus reached on the most effective approach or the feasibility of the proposed ideas.

Contextual Notes

Participants discuss various assumptions about the efficiency of different propulsion methods, the nature of light interaction with sails, and the theoretical implications of their proposals, but these assumptions remain unresolved.

Quarinteen
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Hello guys. I was thinking about solar sails and was wondering if it was possible to instead simply create a sail that is pushed by photons create something that creates an opposite force that pushes off the photons. If you did this in theory would you not be able to double the momentum? An opposite wavelength that won’t cancel out the push but amplified it?
 
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Do a google search for solar sails.
 
Quarinteen said:
Hello guys. I was thinking about solar sails and was wondering if it was possible to instead simply create a sail that is pushed by photons create something that creates an opposite force that pushes off the photons. If you did this in theory would you not be able to double the momentum? An opposite wavelength that won’t cancel out the push but amplified it?
I think we call this a mirror.
 
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Quarinteen said:
Hello guys. I was thinking about solar sails and was wondering if it was possible to instead simply create a sail that is pushed by photons create something that creates an opposite force that pushes off the photons. If you did this in theory would you not be able to double the momentum? An opposite wavelength that won’t cancel out the push but amplified it?
You could have a solar sail that reflected the light instead of absorbing it. That would passively double the change in momentum compared to one that absorbed. If you wanted to add an active "push" then you could just shine a laser off the back in addition.
 
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The only way you could get more momentum out of a light sail than using a perfect mirror, as phyzguy proposes, is if the sail actually emits something. And that's just making it a photon rocket - probably not a particularly efficient one.
 
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Dale said:
You could have a solar sail that reflected the light instead of absorbing it. That would passively double the change in momentum compared to one that absorbed. If you wanted to add an active "push" then you could just shine a laser off the back in addition.
Great minds think alike, I see. :biggrin:
 
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Dale said:
You could have a solar sail that reflected the light instead of absorbing it. That would passively double the change in momentum compared to one that absorbed. If you wanted to add an active "push" then you could just shine a laser off the back in addition.

Lasers aren't terribly efficient : what about just a thermal mass of sorts : sub-critical atomic pile at the focal point of a parabolic mirror/sail.
 
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hmmm27 said:
Lasers aren't terribly efficient : what about just a thermal mass of sorts : sub-critical atomic pile at the focal point of a parabolic mirror/sail.
That is basically the way the Pioneer anomaly works.
 
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