Nostalgia for a Physical Thing That No Longer Exists

[pedong]

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

 

[cmos]

Photons.

 

[jarmour3]

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.

 

[cmos]

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.

 

[Defennder]

Brilliant. I never thought of that.

 

[russ_watters]

Clever, if this is a riddle. Is it...?