How big is a visible photon?
Why Hacker News recommends it
HN recommends it as an approachable, intuitive explanation of why visible photons can be surprisingly large, from a channel known for practical optics.
What it is
Huygens Optics shows through a laser interference experiment that the question of a photon's size is really about coherence length. It argues that photons exist as energy exchanges between radiation and matter, not as little particles in free space.
Recommended by 3 HN commenters across 3 different months, 2021 to 2025.
What Hacker News said
Recommends NavinF · 2022-03 · on “First images from James Webb telescope exceed expectations”
Yeah I was also surprised to find that photons can be really big: [this video] Before I saw the experiments in that video, I assumed photons were about as wide as their wavelength.
Recommends jiggawatts · 2022-08 · on “Third-polarizing-filter experiment demystified (2004)”
I know it's not exactly Nature, but I like this one for the approachable and intuitive explanation: [this video] Fundamentally, you have to believe in nonsense such as kilometer-sized particles that are also infinitesimal if your point of view is that photons are particles. Many of the "mysteries" of Quantum Mechanics vanish if keep in the back of your mind that QM is just a bag of mathematical tricks that "work" in specific scenarios to solve practical problems, but aren't a model of "what actually occurs". Practically all of it is restricted to statistical predictions related to matter. Remove matter or remove statistics and then the models are no longer valid. I'm not making this up. Go dig up
Recommends somat · 2023-01 · on “Can a Human See a Single Photon?”
I am not a physicist but fun fact, In transit there is no such thing as a photon(electro magnetic waves can transit at any energy level) however light can only interact with matter at discrete energy levels, so the photon(a discrete energy level of light) only exists there, at the interaction with matter. For some very good practical optics you can do a lot worse than the Huygens Optics youtube channel. [this video]
Cites jiggawatts · 2021-10 · on “Conterintuitive facts in mathematics, CS, and physics”
It makes more sense if you think of the polariser sheets as fences with vertical bars, and light like a string going through between two bars and being wiggled. If the direction of the waves in the string are at right-angles to the slit, the wave can't propagate through the bars. If the wave is at an angle, then some of the wave gets through, with a maximum of 100% when the wave wiggles up and down in the same direction as the slit. In this model you can visualise how three 45-degree slits will allow some light to go through even though two 90 degree slits don't -- the light is transformed by its passage through the polarisers. Where QM people get themselves confused is that they assume that
Cites somat · 2025-08 · on “Double-slit experiment holds up when stripped to its quantum essentials”
My understanding is that a lot of the weirdness is that there may be no such thing as a photon, that is, what we call a photon is the em field interacting with matter(electrons really), in transit there is no such thing as a "single photon" That is, the em field is not quantized( or at least not quantized at the level of a photon) It is very possible to have your em field at "sub photon level" and the electrons at the far end will accumulate energy until a photon level is reached and presto a single photon experiment. What it is actually measuring I am not sure. [this video] (Huygens Optics -How big is a visible photon?)