How Big is a Photon?

I think photon is a bogus term, generated by an attempt to explain something we don't understand....I don't think a photon has size, only different qualities...Just look at all the different terms used to measure light...

It's like trying measure a shower of water where the water has 10 different levels of wetness, from 0 wetness to extreme wetness...you measure a spot over time for wetness and get an average, but in real time it tells you nothing...

I think the takeaway from this video is that the EM field energy is continuous. It can be any value. But to measure it, it has to interact with matter by a quantum amount that is proportional to frequency.

If the laser has been attenuated to the point where it takes a second for a quantum of energy to pass by, the energy somehow accumulates until it is absorbed by a detector atom where the intensity of the field is high.

You don't see an interference pattern of a single "photon" detection. The interference pattern is a record of many detections, each occurring independently.

I don't know whether or not there is a flaw in this reasoning. I'm curious whether it can be used to explain quantum puzzles like the delayed-choice quantum eraser experiment.

I look at it like light is radiation like heat, now you can measure heat by BTU's, but you wouldn't ask how big is a BTU...you might ask though how many BTU's are in this space of 1 m³ , but you are measuring the effect of the radiation...Light is hard enough to describe in detail, why add to the confusion with made up terms and imagined qualities...

Actually you can use same measurements for shower water, if you replace "light" with "water".

You missed out Nits, One nit is equal to one candela (one candlepower) per square meter (1cd/m2)

I really found the video interesting, but I'm not convinced that the experiment says much about the size of a photon.

Assuming that a beam of light is made up of discrete photons, then no matter how much we attenuate the beam, it is still made up of discrete photons. If photons are indeed discrete, then a beam splitter does not split any photon into two pieces, but rather sends some fraction of the photons off to the side, allows another fraction of the of the photons to pass on through straight ahead, and probably absorbs a third (hopefully small) fraction of the initial photons.

Since the now split beams travel different distances, but at the same speed, before striking the target, they will do so in different amounts of time. Thus any pair of photons causing the interference pattern must have been emitted at different times, with the photon traveling the longer distance having been emitted well before the photon that followed a straight path.

I do NOT believe this experiment shows that a single photon can interfere with itself.

Comments?

Well things can be true and not true at the same time, that is a paradox of logic....

I really found the video interesting, but I'm not convinced that the experiment says much about the size of a photon.

I would say the size of a photon, or how close two photons have to be to show interference, depends on the coherency of the source (temporal and spatial).

Temporal coherency (purity of sine wave) determines the length of the photon, and spatial coherency (degree of collimation) determines the width.

For example, for a good coherent source like a single mode HeNe laser with a coherence length of 100 meters would have a photon length of 100 meters. (Most sources have a much shorter coherency length, e.g., a diode laser might only be coherent for about a millimeter.) The coherency length is the difference in path length in an interferometer that there will be interference.

The mirrors inside a laser cause the light to be highly collimated resulting in a narrow beam with low divergence when it exits the laser. Light from a distant star, or even more so, a distant quasar would be extremely collimated. Interference could be detected from two detectors far apart.

So if the laser light in the experiment is highly attenuated so that only a single photon is in the interferometer at any time, the photon can be up to 100 meters long due to the temporal coherency of the HeNe laser and can interfere with itself inside the interferometer.

When it is detected, the photon makes a single dot on the detector screen. The position of this dot is controlled by the self interference, a fact that is not obvious until multiple photons have been detected and the pattern is evident.

The universe does not carry an obligation for the observer to understand it.

https://www.caltech.edu/about/news/quantum-entanglement-of-photons-doubles-microscope-resolution

It get's weirder than that. You can detect an object with zero photons, sometimes...

Without reading in detail all the erudite contributions, I would say to an order of magnitude, it's the same as the wavelength of the radiation.