I read last week about an article which claimed that negative mass has been discovered. Scientists doing the experiment at Washington State University discovered a fluid which when given acceleration moves in opposite direction of the acceleration.
Scientists cooled rubidium atoms to temperatures equivalent to absolute zero which resulted in a state called Bose-Eienstein condensate. At this stage atoms stated moving super slowly and behaved as super fluid.Scientists then used lasers to change the spin of atoms in the fluid and the atoms started behaving in different way. Normally when energy is given to atoms, they start vibrating to higher frequencies but in the superfluid they were slowing down. We have a general convention that when force is applied onto an object it accelerates in direction of force applied, where force acting on the particle is proportional to mass and acceleratioon on the object. This case showed that when force was given to rubidium atoms via laser, they should have accelerated in direction of force but they were not. What does this mean or does it make sense.
This could mean that the rubidium atoms were in state of negative mass by virtue of which they were trying to oppose the direction of force. But mass cannot be in physical terms or in reality be negative.Negative mass could mean a negative energy and it is not practicable.This meaning of negative mass can only be in mathematical terms to describe the state of the atoms.
Physics Forum 