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?
  f39

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.