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The journey of a photon through a hydrogen molecule is the shortest event ever timed

The time it takes for a single particle of light to pass through a hydrogen molecule is now the shortest duration ever measured.

This interval was about 247 zeptoseconds, or trillions of billionths of a second, the researchers report in the October 16 issue of the journal Science. For comparison, there are as many zeptoseconds in a second as there are seconds in 2,500 times the age of the universe, which is about 13.8 billion years old. The new observation allowed physicists to witness matter-light interactions with a whole new level of detail.

Physicists shone X-ray light particles on hydrogen molecules in a gas. When each light particle, or photon, crossed an H2 molecule, it tore off an electron from one hydrogen atom and then the other. Because electrons can exhibit wave-like behavior (SN: 5/3/19), the two expulsion events shook waves of electrons that spread and fused, similar to ripples formed by a stone jumped twice over a pond. . The overlapping ridges and pipes of these waves created an interference pattern, which the researchers observed using an instrument called a reaction microscope (SN: 11/5/10).

If the electronic waves were formed simultaneously, the interference pattern would be symmetrical around the center of the H2 molecule. But because one electronic wave formed slightly earlier than the other and had more time to spread, the pattern shifted toward the second wave, says study co-author Sven Grundmann, a physicist at Goethe University in Frankfurt, Germany.

This change allowed researchers to calculate the 247-zeptosecond delay between the emission of the two electronic waves. This matched the team’s expectations based on the speed of light and the known diameter of a hydrogen molecule.

Previous experiments have observed particle interactions as short as atoseconds (SN: 3/12/10), which are 1,000 times longer than zeptoseconds.

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