Our bodies, we are told, are 60% water. We are walking oceans, thinking Great Lakes. An MRI measures our water—specifically, water’s hydrogen—looking for eddies and pools: where it flows freely, where it’s bound up in dense tissue. But an MRI doesn’t “see” water; it listens. The machine listens to faint radio signals from the water inside us.

Before MRI, doctors had to cut into the body or use radiation—X-rays, CT scans—to get a detailed understanding of what was happening inside. MRIs can map the body’s interior without damaging it. They work at the quantum level, measuring the behavior of protons in hydrogen atoms. Imagine one of those protons as a spinning bar magnet. The MRI coaxes a tiny excess of those protons into alignment, using a magnetic field that is tens of thousands of times stronger than the Earth’s. It then knocks them out of line for a split second using a radio pulse and listens for the signals as they drift back into place.

Such language only crudely approximates the quantum physics involved. We have, over the past century, expanded our understanding of the material world in ways strange and fantastical compared to the Newtonian model. But our brain-mapping technologies still—still—do not explain how thoughts arise, or the nature of consciousness, or the ancient question of the soul. The better we get at mapping the physical brain—the more closely we listen to the water within—the more conspicuous become our unanswered questions.

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Links:

• How Does an MRI Machine Work? – National Institute of Standards and Technology, May 14, 2025

  
  

• The stuff that makes most physicists cringe: Quantum Approaches to Consciousness – Stanford Encyclopedia of Philosophy

  
  

• Essay about some of the human drama behind the invention of the MRI: “The ‘Indomitable’ MRI” by Julie Wakefield, Smithsonian Magazine, June 2000

  
  

• More human drama: “N.Y. scientist disputes medical Nobel choice” – Thomas H. Maugh II and Charles Piller, Los Angeles Times, October 12, 2003

  
  

This post is part of The American 250, a series featuring 250 objects made by Americans, located in America, in honor of the country's 250th anniversary. 250 words on 250 works, from January 1 to December 31, 2026.

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