Assume the universe consists of a single photon, a single atom of hydrogen and a spherical detector (like an encompassing shell) with a semi-infinite radius. The photon gets "absorbed" by the hydrogen atom. Moments after the photon is emitted. My question is the following: from the time the photon is emitted until it is detected, is it correct to say that the photon is everywhere* along a 2D spherical front? When it gets detected, will it show up as a point at a random location on the detector? *I get the nagging feeling that the word everywhere is not accurate. Also, does this example require more assumptions about the uncertainty in the electron/proton's momentum and position? Thank you.