So, you may or may not know that there a 5 states of matter with 3 of them being quite well known. They are solid, liquid and gas. A good way to think of these states is by their physical properties. Solids have a fixed volume and shape, liquids have a fixed volume and unfixed shape, and gases have an unfixed volume and shape. What about the uncommon ones? The first one is known by a few and that is plasma. Plasma is an ionized gas that consists of positively charged ions and negatively charged subatomic particles known as electrons; an example being lightning. Now what about this 5th state of matter and what does it have to do with negative mass?
The 5th state of matter is referred to as Bose-Einstein condensate and it is really, really cool; literally. The way in which this state is formed in labs is by cooling the element known as rubidium. The rubidium is cooled to a fraction of absolute zero; around -273 degrees celsius. As the atoms are cooled, they start to move incredibly slow, almost coming to a standstill but not quite. Once at this incredibly frosty temperature, all of the atoms of rubidium start to act as a single atom and can flow or move without losing any energy; becoming a superfluid. This is when we start to manipulate it into experiencing negative effective mass.
Using lasers, scientists start to alter the normal spin and rotation of the atoms. When the atoms were released from the influence of the lasers, some of them started to behave weirdly; in a way that isn’t very intuitive to Newton’s Second Law of Motion which you can display right now! Put an object like your phone on the table next to you and push it. When you apply force to a mass it starts to accelerate away from the side that the force is applied; making it slide forward. Negative effective mass doesn’t do this. If something experiences negative effective mass and you try to push it away from you, it doesn’t move in the expected way cause a kind of anomaly.
You might be wondering of the real world applications for this new technique for the creation of negative effective mass. Scientists say that the information gathered from further investigation could lead to an increased understanding of incredibly large cosmological phenomena like black holes, dark energy and dark matter; but they’re not positive. See what I did there?