without getting too deep, it is worth while to note, that photons have length. I.e. the more well defined their energy is the more cycles they must contain and the less that can be said about the emission process due to the time energy precision limit of the uncertainty principle. For example, the green line photons from the northern lights are very precise in their energy - have so many cycles they are more than a meter long. And thus even "when" they were emitted is quite uncertain.
I have measured the length of some photons and shown one photon can in a classical sense be far (four feet) from itself! Here is how you do that:
Posting now below a crude "typed" drawing (in two parts):
Extended light source and lens making parallel beams (0nly one shown below) but each part of the source makes a beam at very slightly different angles:
*
*
*............()===== This beam enters beam splitter "a" shown below (this part of drawing separated for ease of construction.)
*
*
Ok, that is best I could do. (If I made lens () taller then parts of the light source, represented by some * , would be too far above or below lens.)
Below is one of the slightly divergent beams (only one shown), leaving the lens and going to first 45 degree beam splitter "a" and going straight thru with part (of same photon) going up to hit 45 degree mirror, b, too, which makes it again traveling parallel to the entering beam.
Sorry that these beam splitters and mirrors are not shown actually at 45 degrees - but that is best a "typed drawing" can do.
...........d
......b/======/======...This is the path of "self- rejoined" photon to the screen thru another lense one focal length from it.
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()===== / ======/c
Lens.....a
Optically an "extended source" with lens one focal lengh from it followed by a second lense one focal length from the screen, just images the source (up side down) on the screen. Inserting these beam splitters and mirrors does not change that. It only make it possible for slightly differing path "split photons" to arrive at the screen where they would have but now they "want" to get back in phase with them selves, and do so as best a they can. Leaving dark lines where if they can not become "particles" there as they would not exist there since their waves are 180 degrees out of phase with themselves there. Note almost all the time photons can be thought of as waves, but if detected / absorbed they "die as particles" in one spot - not spread out over miles as they can be when waves.
Note that the length of paths: abd and acd, are the same. I.e. when the separate SINGLE photo get back together with itself, after being at times in its flight it 4 feet from itself, it arrives at the screen, unified, at the same time, but some of the many slightly divergent beams arriving there are "out of phase" with themselves and cancel (make dark interference lines) on the screen. The diverse in angle beams following paths abd & acd are exactly the same length ONLY for paths with pairs of equal angle degree corners. (parallelograms or rectangles.)
I will not go into details, but it is well known that photons ONLY interfere with themselves (and proven by using such low intensity sources that most of the time not even one exist - long exposure film, still has an interference pattern on the developed film, etc.) This is why one only needs monochromatic light, but not coherent light, source to produce interference patterns.
Now here is what you do to measure the length of a photon: You rotate beam splitter a very slightly counter clockwise, so that the path ab passes to the left of mirror at b, but pull mirror b back to still be hit by that now tilted beam. You of course must also rotate mirror b slightly clockwise, so the beam leaving it follows the old path to beam splitter d again. Now the corner turned at b is not 90 degrees. Perhaps this adds 5 cm of extra length to path abd.
What one sees on the screen is that there is a little light where there was none. I. e. the interference pattern on the screen is a little "washed out." This slight twisting of a & b is increased and then the pattern is more washed out. I kept repeating this until with ~30 cm extra path length for abd, the screen was with uniform illumination.
Crudely speaking this implies that none of the part of the photon going via path abd had yet arrived at the screen before the full length of the part of the same photon going by path acd had already disappeared into the screen. I.e. my spectral line source was making photons that were about 30cm long.
PS I have Ph. D. in physics and would be more active here, but my first post about time were removed as like this one I told things most do not know. Hope you get to read this one before it is removed.
