11. So electrons near the top of the valence band behave like they have negative mass . 12. :: : We have a negative mass article, which has some discussions about its properties. 13. By contrast, the hypothetical exotic matter has a negative mass and the energy-momentum equation is 14. :Negative mass ( if it existed ) would not cause an upward dent in space. 15. Rather, negative mass would cause there to be less space in the middle, instead of more. 16. Sometimes they predict absurdities like subatomic particles with negative masses or even negative probabilities of existing. 17. Such materials would possess qualities like negative mass or being repelled rather than attracted by gravity. 18. In considering negative mass , it is important to consider which of these concepts of mass are negative. 19. Negative mass would possess some strange properties, such as accelerating in the direction opposite of applied force.20. This method can even work for objects with holes, which can be accounted for as negative masses .
