Negative Mass

1. Negative Mass by Robert Nemiroff Michigan Tech

2. Physics X: About This Course • Officially "Extraordinary Concepts in Physics" • Being taught for credit at Michigan Tech • Light on math, heavy on concepts • Anyone anywhere is welcome • No textbook required • Wikipedia, web links, and lectures only • Find all the lectures with Google at: • "Starship Asterisk" then "Physics X"  • http://bb.nightskylive.net/asterisk/viewforum.php?f=39

3. Negative Mass: What it is not Negative mass is not: • dark energy • antiparticles (of positive mass particles) • demanded by any grand unification theory • detected in any abundance whatsoever • prohibited by GR • thought to occur as point particles

4. Negative Mass: Classical Effects Three attributes of a negative mass point particle: • inertial mass • momentum opposite of motion • acceleration opposite of force • "active" gravitational mass • repels positive mass • "passive" gravitational mass • is attracted to positive mass • this is part of the equivalence principle

5. Negative Mass: Classical Effects F = m a  still holds since m is now negative. F = - G M m / r2 between a positive mass M and negative mass m so the equivalence principle still holds. Note that the negative inertial mass makes this different from how charges act in electric force equations.

6. Negative Mass: Runaway Pairs Say you have a positive and negative mass right next to each other.  How do they interact gravitationally? • The positive mass would attract the negative mass. • The negative mass would move toward the positive mass • The negative mass would repel the positive mass. • The positive mass would move away from the negative mass • Together the two would "run away" in the direction of the positive mass

7. Negative Mass: Runaway Pairs A positive and negative mass side-by-side will  • continue to accelerate toward the positive mass • forever (or until they hit something) • the pair will soon achieve near-light speed • momentum (total) = 0 • because the negative mass' momentum is negative and cancels out the positive mass • Energy (total) = 0 •  same deal

8. Negative Mass: Runaway Pairs Runaway pairs are the basis for R. Forward's Diametric Drive which could propel spacecraft across the universe. It is unclear how to create a rigid connection between a positive and negative mass. Even if masses have unequal magnitudes, they will still move so that energy and momentum are conserved.

9. Negative Mass: Cosmological Voids Although the universe is mostly uniform, low density regions do exist, the largest known as "voids."   Voids act in some ways as if they have negative mass, even though they have positive mass. Voids do not follow the equivalence principle, however, and repel surrounding matter and accelerate away from high (positive mass) density.

10. Negative Mass: Lensing Searches Negative masses have been searched for in astronomical surveys of gravitational lensing. • They are expected to dim objects that pass behind them. • No dimming effects have ever been uniquely identified with negative mass. • A limit on the number density of point-like negative masses can be obtained

11. Related Exotic Matter Dark energy typically has a repulsive gravitational effect on normal matter, but has a positive mass-energy.  This is  because they exhibit a negative pressure.  Examples include cosmic strings, domain walls, and a pervasive cosmological constant.  A local variant is created by the Casimir effect. Some virtual particles can be thought of as having negative mass while being protected from being individually undetectable by the uncertainty principle. Faster-than-light normal matter formally has an imaginary amount of mass.