Trillions of cosmic particles stream through human bodies every second, mostly undetected
An estimated 100 trillion neutrinos pass through each person per second, along with muons and other particles from cosmic ray interactions, but pose virtually no health risk.
What happened
According to physicist Michael Pravica at the University of Nevada, Las Vegas, approximately 100 trillion neutrinos pass through each human body every second. These neutrinos originate primarily from nuclear fusion reactions in the sun, though some come from distant galaxies. Nearly all neutrinos pass through matter without interaction due to lacking electrical charge and having almost no mass, earning them the designation "ghost particles." Additionally, cosmic rays—highly energetic particles traveling at near light speed from across the universe—strike Earth constantly; when they collide with the atmosphere, they generate secondary particles including muons, with roughly one to two muons passing through a human hand each second. Scientists detect and estimate cosmic particle frequencies using specialized observatories like the IceCube Neutrino Observatory in Antarctica, which records the rare interactions between neutrinos and atomic nuclei in ice.
Context
The passage of these particles highlights an underlying physical reality largely imperceptible to human awareness. Neutrino interactions with human bodies are extremely rare—an individual would expect no more than roughly one interaction over an entire lifetime, according to physicist Lu Lu at the University of Wisconsin-Madison, with virtually no biological effect. Cosmic radiation exposure from secondary particles like muons and neutrons contributes approximately 0.4 millisieverts per year to the average person, comparable to a few chest X-rays annually and representing a small fraction of total natural background radiation exposure. The detection methods employed—such as using light sensors to observe Cherenkov radiation in ice—depend on extremely small sample sizes and statistical extrapolation to estimate the total flux of particles passing through Earth and its inhabitants.