When light (photons) travel from a distant star, do individual photos get “spread out” so that there is space between photons as they race through the cosmos?
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Yes. You don’t need astronomical distances for this to happen. Distance between photons is what makes photographs look grainy in low light.
There’s a catch, because quantum physics is always tricky. Photons travel as waves but interact as particles. The light wave is everywhere at once, getting thinner as it spreads. In that sense the photons aren’t separate yet.
The photon particle appears somewhere that a wave peak intersects something else. Modern physics still has no idea how a wave “knows” how to produce only one particle, even as it spreads across the universe. But we are sure that waves can add up or cancel, yet they also conserve energy making just the right number of photons in the end.
Photons are actually waves (more specifically – propagating changes in electric and magnetic potential in the electromagnetic field), not objects, so yea the wave spreads out and covers more space as it moves, similar to how dropping a pebble in a pond, it starts at a localized point and spreads out throughout the lake.
Some xray space telescopes routinely view objects so faint and far away that they actually *count* individual photons as they hit the sensor. You might only detect one photon every couple of seconds from a given source.
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