If a photon leaves a source 4,2 light years away how far apart will it be from a similar photon it was adjacent to (say less than 10^3 wavelengths) when it departed. Does the inverse square law mean that individual photons get further apart and stay the same size or do they occupy a larger space (area). I assume relativity (special or general, I do not really understand) stops photons dispersing in three dimensions. Why? How do the photons line up in space behind each other? If we do not know how do we find out? I then tried to make a single photon telescope but was deterred by a number of issues. The stability of the tripod carrying the device. It would need to would maintain its position to better than 2,8 e-17 arcsec, for at lest a few seconds, just to look at the planet 4,2ly away. I suspect that the earth wobbles more than this and certainly the telescope mount. I was aiming to look for an artificial source of protons considerably smaller than the size of the planet. The smallest pin hole I found was 12,7 μmm that, if mounted at 43º gives a 857 nmm elipse on the detector. Thus the question how big is a photon? Can the photons from the distant source find a way through the pin hole? As of the time writing the only SPAD device that I have found requires a helium compressor. I go back to the days when if we wanted a photo diode we used a germanium transistor and scraped the paint off. I was planing to buy an avalanche diode from RS. I could take a broad approach and use the earths inherent gravitational wobble to scan larger parts of the universe with my avalanche diode, with the paint scraped off. A bit of Fourier to filter out the noise and still find the occasional photon streaming from now distant planets and having signatures just a bit different to the background but I need a few thousand of them. My crude calculation shows the photon density from a 1000 Watt/m^2 source 4,2 light years away is small 1/10^20 m^2. What does a photon do when it encounters a pin hole of ten wavelengths diameter after it has been isolated by the inverse square law and travelled 4.2 light years? I am encouraged by the thought that should I capture one photon I should see several behind it if I can get the quenching circuit to reset the diode fast enough. How far behind are they? I am now looking for the slightest encouragement and help to refine the calculations before placing the order with RS.