…The reason physicists have been skeptical about wormholes comes down to a problem with energy. To hold the throat of a wormhole open, you would need something called exotic matter. In physics, ordinary matter (stars, gas, you, your coffee) always has a positive energy density which corresponds to positive mass. Exotic matter would have negative energy density, essentially “negative mass.” We have never observed anything like that in nature. Most wormhole solutions that physicists have found over the decades require this exotic matter to exist, which is why wormholes have stayed firmly in the category of “mathematically possible but physically unlikely.” Today’s paper offers a way around this problem.