I don't claim to understand any of this, but it sure sounds like you are correct, looking at the terminology. Someone had already added the paper to the "Negat

I don't claim to understand any of this, but it sure sounds like you are correct, looking at the terminology. Someone had already added the paper to the "Negative mass" article, so I removed it: https://en.wikipedia.org/w/index.php?title=Negative_mass&diff=prev&oldid=775415593 https://en.wikipedia.org/w/index.php?title=Negative_mass&dif... ... And added it to the "Effective mass (solid-state physics)" article: https://en.wikipedia.org/w/index.php?title=Effective_mass_(solid-state_physics)&diff=prev&oldid=775415322 https://en.wikipedia.org/w/index.php?title=Effective_mass_(s... The bit I removed from the "Negative mass" article said: In April 2017, researchers at Washington State University claimed to have created a fluid with negative mass inside a Bose-Einstein Condensate. I expanded it ever so slightly to read: In April 2017, researchers at Washington State University claimed to have created a fluid with negative effective mass inside a Bose–Einstein condensate, by engineering the dispersion relation. Slightly awkward, but hopefully at least a slight improvement. PS: also added a "disambiguation" thingy at the top ("For negative mass in theoretical physics, see Negative mass."), now realizing it may be of dubious utility.