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How big is a visible photon?

Huygens Optics · explainer · Watch on YouTube

Quantum physicsEveryday physics & science demos

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.

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.

  • 3 people recommended it
  • 3 different months
  • 0 strong recommendations
  • first 2021, last 2025

What HN commenters said

  1. “I was also surprised to find that photons can be really big”

    Experiments show photons can be surprisingly large.

    NavinF, 2022-03 · Recommendation · in “First images from James Webb telescope exceed expectations”

  2. “I like this one for the approachable and intuitive explanation”

    Approachable, intuitive explanation of photon size.

    jiggawatts, 2022-08 · Recommendation · in “Third-polarizing-filter experiment demystified (2004)”

  3. “For some very good practical optics you can do a lot worse than the Huygens Optics youtube channel.”

    Channel offers very good practical optics.

    somat, 2023-01 · Recommendation · in “Can a Human See a Single Photon?”

Excerpts from Hacker News comments, linked to the originals. Summaries and labels were written by a language model from those comments.

Topics: photons, coherence length, interference, optics, quantum

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