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One tiny push for some Beryllium ions, one big leap forward for Physics…


Researchers at the National Institute of Standards and Technology in Boulder, Colorado, have measured the smallest force ever – a few yoctonewtons. 

That’s 10-24N, a mind blowingly tiny number by anyone’s standards. It’s also several orders of magnitude smaller than the previous record, which stood at a comparatively huge attonewton (10-18N). This sizeable difference between the previous lowest measurement and the new one is due to the different materials used: old methods involved small wires and paddles, but this time researchers used something much, much smaller. 

The group were able to measure such a small force using a cluster of just 60 Beryllium ions. The ions weighed in at around 0.1 yoctokilograms themselves, and their size was key to being able to make such a tiny measurement. During the experiment the ions were held in a Penning trap, a device that holds charged particles in place using a combination of magnetic and electric fields. These traps are well suited to making precision measurements on groups of ions, in fact many of the highest precision mass measurements, including the mass of an electron and proton, come from Penning traps. They’re also good at storing other charged particles. Indeed, antiprotons at CERN are stored in Penning traps. 

Penning Trap

A Penning Trap: The electric field is shown in blue, and the magnetic field in red. An ion is shown, trapped in a vacuum at the centre of the trap.


An electric field was used to nudge the ions, as they remained held in the trap. The force on the ions during the push was measured indirectly, by shining a laser on the ions and looking at the change in the light when it was reflected back. 

The group think that by decreasing the number of ions they use, it would be possible to measure even smaller forces in the future. Small measurements using this method could be used to get some very precise measurements of fundamental forces, such as gravity, as well as imaging materials’ surfaces in greater detail than ever before. 

Paper available as a preprint at: arxiv.org/abs/1004.0780v2 

Image Credit: Arian Kriesch Akriesch


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