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What's the smallest thing the human eye can see?

The Nobel Prize in Chemistry this year went to three scientists who figured out how to achieve sharper microscope images by manipulating fluorescence in the sample. (See :52 in the video for a more basic example of how fluorescent stains help distinguish objects in a microscope image.)

The methods that Eric Betzig, Stefan Hell and William Moerner invented pushed the boundary of what was believed to be the physical limits of microscopy. And that raises the question: What exactly is the smallest thing we can see?

It depends on what it means to "see" something. Human eyes can make out objects down to the diameter of a strand of hair. Light microscopes, also called optical microscopes, extend our vision to smaller things, like these red blood cells, captured by photographer Aurel Manea:


More than 10 red blood cells would fit on the tip of a human hair, but they're huge in relation to viruses. Almost all viruses are too small for optical microscopes to capture.

Electron microscopes (EM) can generate images of viruses and other nanoscale objects by shooting a beam of electrons into a sample and measuring the interactions that result. That's how Alex Zettl at the Lawrence Berkeley National Laboratory created this groundbreaking video of carbon atoms:

carbon atom graphene sheet

What this gif shows is carbon hexagons in graphene — an ultra thin material made of pure carbon — rearranging themselves in response to a hole punched in the material. Like x-rays or MRIs, EMs do not use the visible lightwaves that our eyes rely on. So this might not count as "seeing" carbon atoms, but it's the closest we can get.

Check out the video above for a 90-second tour of the tiny things at the edge of human vision.