time is an obscure concept and linked to the propagation of light in matter. scientists have now clocked the shortest time measurement ever, expressed as 247 ‘zeptoseconds’, by observing the time it took for a photon (a particle of light) to travel across a hydrogen molecule. in this ultrafast timescale, a zeptosecond is equal to a trillionth of a billionth of a second.

shortest time period ever measured, 247 zeptoseconds!
schematic representation of zeptosecond measurement. the photon (yellow, coming from the left) produces electron waves out of the electron cloud (grey) of the hydrogen molecule (red: nucleus), which interfere with each other (interference pattern: violet-white). the interference pattern is slightly skewed to the right, allowing the calculation of how long the photon required to get from one atom to the next.
image by sven grundmann, goethe university frankfurt



the length of the hydrogen molecule was known already, as is the speed of light! before this real-time measurement, one could simply calculate that it takes a photon 247 zeptoseconds to pass through the molecule. a research group led by sven grundmann, a nuclear physicist at goethe university in frankfurt, germany have been using the PETRA III facility at the deutsches elektronen-synchrotron (DESY) in hamburg, germany. future experiments will manage to capture even smaller measurements of time.

shortest time period ever measured, 247 zeptoseconds!
measuring station P06 at the ring accelerator PETRA III
image © DESY / heiner müller-elsner