A photon has no size (it has wavelength but that doesn’t dictate size), it is a discrete, massless unit of energy.
Every measurement we make about something comprises the transfer of a discrete ‘bit’ of energy, such as a photon wave function collapse.
When we look at the stars we see bright points and dark spaces, this lead to “Olbers’ paradox, which said more or less: if the universe is infinite, why the sky is not always bright, due to the infinite numbers of stars contained in it? The more common answer is that the universe is finite.”
There is another paradox, however, when we see a light point, we are registering a photon locally, at our eye, the implied direction of the point of light comes, presumably, from registering more photons with a particular ‘direction’. Perhaps this direction can only be implied statistically from multiple photons. How?
“this is diferent from Oblers paradox, because anywhere in space, you WILL in fact see light, and therefore photons are occupying that space”.
In other words, can you tell the origin of a light source from a single photon? Is it possible that space itself is made of photons, or more accurately that the limit of ‘unravelled space’ is photon like and that mass is a different or curled up spacial geometry? All this leads to the (actually quite commonplace notion) of event timelines as being the geometry of space itself. (I could imagine this looking like some kind of Fractal Tree, i.e. there is no continuous background space with constant axes).
“Since photons can start at any frequency (also for the value of other properties), there is no way to tell how far a photon has travelled just from its detection. By looking back along its path until you see something you may be able to find its origin.”
‘By looking back along its path until you see something you may be able to find its origin’ - circular argument.
Related: Why is water in a glass transparent? “Since the photon that comes out of glass is going in the exact same direction as the photon that went in, something very interesting is happening inside the glass. The photon reaches the glass and is immediately absorbed by an electron. Sometime later, the electron emits a new photon. The new photon is travelling in exactly the same direction as the old photon. The new photon is absorbed by the next electron, which later emits another photon, again travelling in the exact same direction. This process repeats billions of times until the final photon is ejected on the other side of the glass, still in the exact same direction, and goes on its way.”