> Does anyone assert that any photon carries information about what it interacted with in the past? Does a photon have any information content other than its en

> Does anyone assert that any photon carries information about what it interacted with in the past? Does a photon have any information content other than its energy/wavelength? So "each one carries a bit of the image of whatever it hits" is total (ok, be nice now) poetic blarney. An analogy to how we perceive things seems appropriate. The light from some source (i.e the sun) hits an object, the light rays are then reflected/transmitted/refracted through the surface based on various material properties. Your eye, acting like a pinhole camera, captures all the light rays from that surface, and then projects it onto the sensor reception surface (I think the retina?) creating the 'image' that we see. So the specific way the light rays interacts with the surface is what creates the 'information content'. For example, we perceive a blue-colored surface because the surface properties (i.e roughness) will specifically reflect wavelengths associated with blue. A specular surface will reflect light back to the eye, creating a 'shiny' surface. A very cool demonstration of how light conveys information is in dual photography: https://www.youtube.com/watch?v=p5_tpq5ejFQ https://www.youtube.com/watch?v=p5_tpq5ejFQ And the original paper: https://graphics.stanford.edu/papers/dual_photography/https://graphics.stanford.edu/papers/dual_photography/ https://graphics.stanford.edu/papers/dual_photography/https:.... They shine a light source onto an object, take a picture, and then by processing the light rays in the photo, are able to generate the same scene but from the perspective of the light source. It's really astounding when you see it. They can do this reconstruction because the flow of light rays from the light source to the object, that is then reflected to the camera can be reversed (it follows Helmhotz Reciprocity - light ray that is reflected off an object is the same as the light ray that hits the surface that creates the reflected ray). So by processing the light rays in the camera image, they can reverse it, and calculate how the light source would have "perceived" the original scene. In the case of the blackhole, I wonder if it's just that the light that enters the blackhole might loop around multiple times, but if it doesn't hit a surface, then the light that they can process/interpret would literally show what it reflected off before it entered the blackhole, which would be an image from the past.