Nostalgia for a Physical Thing That No Longer Exists

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The discussion revolves around the concept of physical entities that can be perceived but no longer exist, focusing on photons and astrophysical phenomena. While photons are stable particles that do not decay, the conversation highlights that light from distant quasars and proto-galaxies allows us to see objects that have since ceased to exist due to the finite speed of light. The analogy between optical telescopes and the human eye emphasizes how both detect light through diffraction patterns. The conversation also hints at a riddle-like quality to the topic, prompting further contemplation. Ultimately, the discussion explores the intriguing relationship between perception and the existence of physical entities.
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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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