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2 + 1 is not always 3

multi-body effect

The many-body effect specifically prevents the normally linear addition of forces.


Ankara (Turkey). When multiple forces act on an object, their effects usually add up. Researchers have now demonstrated a case in which this is not the case. Under certain conditions, the interactions between three particles in an emulsion are anything but linear. And right now, 2 + 1 no longer equals 3. As the researchers reported, this so-called many-body effect is important, for example, for the construction of micromachines within nanotechnology.

The researchers were able to measure the spheres in the Casimir effect by alternately holding them with “laser tweezers”.


Usually 2+1 equals 3

It doesn’t matter whether in physics or mathematics, the simple calculation 1+2 usually always results in 3. These fundamental physical interactions are additive from gravitation to electromagnetism, as Giovanni Volpe and his colleagues at the University of Ankara explain . The two forces that are exerted by two electrical charges, for example, and a third charge, also result in the sum of the two individually measured forces.

Particles are held together by a “rubber band”.

Therefore, it should actually be assumed that this simple addition principle should also have an effect on the smallest particles. But whether this is actually the case was tested by Volpe and colleagues using the Casimir effect. The Casimir effect causes small insoluble particles to attract each other under certain conditions in a liquid mixture.

Similar to the van der Waals force that holds a gecko to a wall, interactions between the two particles also occur here. It seems as if they are connected with an invisible rubber band and that is the Casimir effect. This effect can also be observed in a vacuum with two parallel plates. You just get squeezed by it.


Glass beads in an emulsion

But what actually happens when three instead of just two articles interact within the liquid? Starting from the normal, the Casimir effect should now add up, as can also be observed with other forces. But that is exactly not the case here. For the experiment, the researchers prepared a mixture of water 2.6 lutidine, a liquid that forms an emulsion like water and oil.

Tiny glass beads were then added to this liquid, which served to determine the Casimir effect between two and three active beads. Among other things, this was achieved through the use of fine laser beams, which served as optical tweezers and fixed one sphere at a time and measured the reaction of the other spheres. Only two beads behaved as expected, so that the Casimir effect started at a certain temperature .

Differently than thought

However, when the third bead was added, something strange happened: the total force that two particles exerted on the third bead resulted in a completely different value than the individually added measured forces of the two articles together. It can now be said that the forces do not add up linearly, as do the forces in our everyday lives.

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