The discussion centers on the visibility of a single photon or ray of light in an infinitely large space devoid of particles or energy fields. It concludes that light is only visible when it interacts with a detector, such as the human eye, and that in a hypothetical empty space, a photon would not be visible from all angles. The visibility of light is contingent upon scattering, which occurs in the real world due to particles like dust and air molecules redirecting light towards observers. Therefore, without such interactions, light remains undetectable.
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Allen_Wolf said:If we introduce a single photon or a single ray of light, will it be visible from all angles?
You could put it stronger than that, I think. It can only be said to 'exist' when it interacts with something. On the way from the source to the target, the light is best regarded as a wave (or probability density variation, if you want to do it the hard way) and where the energy will turn up (your eye, for example) is never predictable until it actually happens. Diffraction always limits the precision with which you can predict where an individual photon will turn up.mfb said:To be "visible", a photon has to interact with some sort of detector. Only at the place of this interaction it will be visible. For a ray of light you get some volume where you can detect the light - namely this ray.
How can we have a detector when there are no particles to make it out of?Allen_Wolf said:IMAGINE an infinitely large space where there exists no particles or energy fields at all. If we introduce a single photon or a single ray of light, will it be visible from all angles?
Allen_Wolf said:IMAGINE an infinitely large space where there exists no particles or energy fields at all. If we introduce a single photon or a single ray of light, will it be visible from all angles?
In this model, it would be the scattering particle that has to be regarded as the detector - it has interacted with the photon,pixel said:In the real world, you may see the path of a ray of light (consisting of many photons) because the light is scattered from dust and air molecules. Generally this scattering will redirect the light in all directions, including your eye, and what you see is the volume of space the light is scattered from. It would be hard to see a single photon in the real world as that would be scattered in one particular direction that would likely miss your eye, and besides it would just be a single blip of light. In your hypothetical empty space, there would be nothing to scatter or redirect the light to your eye so it would not be visible.