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Is it possible in nature to measure action values below $\hbar/2$? To make a long story, this is not possible. A new literature search showed that Bohr told about the "indivisibility" of the quantum of action $\hbar$ for many years, in all his seminars throughout the world. It then was a shock, with the discovery of spin, that the indivisible value was $\hbar/2$ and not $\hbar$. But the result remains. There is no action below $\hbar/2$. Already Bohr had told that all effects of quantum theory follow from this indivisibility. His Como lecture is an example. After the $spin/2$ shock, these arguments somwehow were not much used any more, out of fear that even smaller values would be possible. However, $\hbar/2$ really is the minimum value. > Arguments against: > - spin particles do exist; spin and action has the same dimension, > thus action values below $\hbar/2$ are possible. The action W is defined as $W= \int L d \phi,$ where L is the total angular momentum and $\phi$ the phase. The spin S enters in the total angular momentum together with orbital angular momentum. There is no way to have W smaller than $\hbar/2$ for a particle of spin that is composed, because the finite extension of such a particle always leads to a finite orbital angular momentum, and thus W is never . Spin could lead to a zero W only if the particle is point-like, ie, elementary. However, no elementary particles of spin are known. One is predicted to exist: the Higgs particle. The statement that $\hbar/2$ is the smallest action in nature thus implies that the Higgs is composed, not elementary. (We will see in 2008, when the LHC in Geneva is ready.) (Except if there might be another way out of the contradiction...) > I would be especially interested in getting more arguments *against* > the thesis. No other attempts arrived yet. Regards Christoph Schiller