What’s the Smallest Particle in the Universe?

image via New Scientist

September 4, 2025, 6:00 PM

• •Subatomic particles don't have a measurable size.
• •Fundamental particles are those that cannot be broken down further.
• •Massless particles, like photons, are candidates for the "smallest."
• •The answer to 'smallest' depends on how the question is asked.

The article explores the question of what constitutes the smallest particle in the universe, delving into the complexities of defining "small" in particle physics. It highlights the distinction between a particle's mass and physical size, and the differences between fundamental and nonfundamental particles. The text explains that fundamental particles, according to the Standard Model, have no size, and the concept of size becomes almost meaningless. Ultimately, the article suggests that the answer depends on how the question is approached, with photons and neutrinos being strong candidates for the smallest particles.

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