✊As ʟɪɢʜᴛ ғʀᴏᴍ ᴀ sᴛᴀʀ sᴘʀᴇᴀᴅs ᴏᴜᴛ ᴀɴᴅ ᴡᴇᴀᴋᴇɴs, ᴅᴏ ɢᴀᴘs ғᴏʀᴍ ʙᴇᴛᴡᴇᴇɴ ᴛʜᴇ ᴘʜᴏᴛᴏɴs?☃️
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As ʟɪɢʜᴛ ғʀᴏᴍ ᴀ sᴛᴀʀ sᴘʀᴇᴀᴅs ᴏᴜᴛ ᴀɴᴅ ᴡᴇᴀᴋᴇɴs, ᴅᴏ ɢᴀᴘs ғᴏʀᴍ ʙᴇᴛᴡᴇᴇɴ ᴛʜᴇ ᴘʜᴏᴛᴏɴs?
Answer:
A photon typically has a definable (though not easily measurable) spatial extent. See, for example, Single Photon Hologram, which describes a way that the spatial (and temporal) extent can be measured -- as long as we have access to plenty of identical photons. Because the speed of light is the same for all frequencies/wavelengths, a photon propagating in the vacuum cannot spread out in its direction of propagation. However, it definitely spreads out in the directions perpendicular to its direction of propagation. In order to know if photons from a source can start out overlapping but at some distance no longer overlap, it would be necessary to know the details of the source and its size.
Note: "overlap" is a fuzzy concept in this context. If a contour surface could be drawn around the photon so that the surface enclosed a volume containing, say 99.99% of the photon's probability of being present, then we might for example agree to pretend the portion of the wavefunction outside the volume does not exist, and agree that in some cases the photons will not overlap. However, the wavefunction of a free photon has an at least extremely small but finite value everywhere, so in an absolute sense all the photons from the source will overlap (though no experiment is likely to be able to prove it).
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