Nostalgia for a Physical Thing That No Longer Exists

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Discussion Overview

The discussion revolves around the concept of physical entities that can be perceived visually but no longer exist. Participants explore the implications of visibility and existence in the context of light and astronomical phenomena.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that photons are a physical thing that can be seen but do not exist in a stable form after being absorbed by the eye.
  • Another participant argues that photons are stable particles and questions the initial claim, introducing the idea of quasars and proto-galaxies as examples of entities that can be seen but no longer exist due to the finite speed of light.
  • A later reply emphasizes the relationship between visible light and photon absorption, noting that once a photon is absorbed, it ceases to exist.
  • Some participants express curiosity about the nature of the discussion, questioning whether it is intended as a riddle.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the existence and stability of photons, as well as the interpretation of visible phenomena. The discussion remains unresolved with multiple competing views presented.

Contextual Notes

There are assumptions regarding the definitions of existence and visibility that are not fully explored, particularly in relation to the nature of photons and astronomical objects.

pedong
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is there a certain physical thing that you can see with your naked eyes, but it doesn´t exists anymore.
 
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Photons.
 
cmos said:
Photons.

I was under the impression that photons exist and that they were completely stable particles that did not decay. On the other hand, if you consider astrophysical phenomena, quasars and proto-galaxies that can be seen in the distant reaches of space no longer exist but can be seen because of the finite speed of light. I know that these bodies are not observed with the naked eye, but optical telescopes and the camera on the Hubble telescope are, in many ways, analogous to the human eye because they are all diffraction pattern sensors.
 
Clearly we can see visible light. But to see visible light your eye has to absorb a photon. Once absorbed, that photon ceases to exist. :smile:
 
Brilliant. I never thought of that.
 

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