Physicists observe 'negative mass'
bbc.co.uk
bbc.co.uk
"It is easy to see that the mass of a particle cannot be negative. For, according to the principle of least action, the integral
\[ S=\int_1^2 \frac{1}{2} m v^2 dt \]
has a minimum for the actual motion of the particle in space from point 1 to point 2. If the mass were negative, the action integral would take arbitrarily large negative values for a motion in which the particle rapidly left point 1 and rapidly approached point 2, and there would be no minimum."
Isn't Hamilton's principle also valid in quantum mechanics?
https://news.ycombinator.com/item?id=14093860
From the top comment ...
> The headline is deeply misleading.
> This article is not about classical negative mass or exotic matter – which would be major breakthroughs.