Physicists have clocked the shortest time span ever

It’s how long it took a chunk of light to cross a hydrogen molecule

The shortest time span ever measured is 247 zeptoseconds. That’s how long it takes light to cross a hydrogen molecule.

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Physicists have measured the shortest span of time ever. It’s 0.000000000000000000247 second, also known as 247 zeptoseconds. And this period is how it takes a single particle of light to pass through a molecule of hydrogen.

Not familiar with zeptoseconds? Take all the seconds that have passed since the beginning of the universe. (The universe is about 13.8 billion years old.) Multiply that number by 2,500. That’s about how many zeptoseconds fit into just one second.

Researchers reported their new measuring feat in the October 16 Science. It should allow physicists to now study interactions between light and matter at a whole new level of detail.

To begin, the scientists shined X-ray light on hydrogen gas. Every hydrogen molecule contains two hydrogen atoms. Light particles are known as photons. Each is considered a quantum of light. When a photon crossed each molecule, it booted an electron — first from one hydrogen atom, then the other.

Those kicked-out electrons stirred up waves. That’s because electrons sometimes act like waves. These “electron waves” were similar to ripples that form by a stone skipped twice over a pond. As those electron waves spread out, they interfered with each other. In some places they made each other stronger. In other places, they cancelled each other out. The researchers were able to observe the ripple pattern using a special type of microscope.

If the electron waves had formed at the same time, the interference would have been perfectly centered around the hydrogen molecule. But one electron wave formed slightly before the other. This gave the first wave more time to spread out. And that shifted the interference toward the source of the second wave, explains Sven Grundmann. He’s a physicist at Goethe University in Frankfurt, Germany.

This shift let the researchers calculate the time delay between the creation of the two electron waves. That delay: 247 zeptoseconds. It matches what the team had expected, based on the speed of light and the known diameter of a hydrogen molecule.

Past experiments have observed particle interactions as short as attoseconds. One attosecond is 1,000 times as long as a zeptosecond.

Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.

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