Cosmologists Show Negative Mass Could Exist In Our Universe 214
KentuckyFC (1144503) writes The idea of negative mass has fascinated scientists since it was first used in the 16th century to explain why metals gain weight when they are oxidized. Since then, theoretical physicists have shown how it could be used to create exotic objects such as wormholes and the Alcubierre warp drive. But cosmologists' attempts to include negative matter in any reasonable model of the cosmos have always run into trouble because negative mass violates the energy conditions required to make realistic universes with Einstein's theory of general relativity. Now a pair of cosmologists have found a way around this. By treating negative mass as a perfect fluid rather than a solid point-like object, they've shown that negative mass does not violate the energy conditions as had been thought, and so it must be allowed in our universe. That has important consequences. If positive and negative mass particles were created in the early universe, they would form a kind of plasma that absorbs gravitational waves. Having built a number of gravitational wave observatories that have to see a single gravitational wave, astronomers might soon need to explain the absence of observations. Negative mass would then come in extremely handy.
We've observed and created antiparticles (Score:2, Informative)
The summary makes mention that we haven't noted any substantial signs of this material, but how is that any different from, say, antimatter, which we know can exist?
Not too long ago, I think we even created an anti-hydrogen atom.
Negative mass? Not so much (yet).
Negative mass- not antimatter, but odd (Score:5, Informative)
Negative mass is very diferent from antimatter. Antimatter is opposite to normal matter in charge and quantum numbers (such as baryon number, etc.), but still has positive mass.
Negative mass reacts oppositely to both gravity and intertia. Oddly, that means that negative mass still falls down in a gravitational field: The gravitational force is opposite, but negative mass responds negatively to force (a=F/m, where both F and m are negative). So negative mass particles repel each other gravitationally, but are attracted to positive mass objects.
This has peculiar consequences. One consequence is that, for objects of negative mass, gravity and electrostatic charge switch. For normal mass objects, gravity is attractive, but like electrical charges repel. For negative matter, gravity is repulsive, but like electrical charges attract.
I wrote about this [nasa.gov] once, in the AIAA Journal of Propulsion and Power-- not a journal that physicists usually read, I'm afraid. If you have access to AIAA online, it's here: http://arc.aiaa.org/doi/pdf/10... [aiaa.org]
Re:OMG! A (possibly) testable theory! (Score:2, Informative)
Negative mass is weird (Score:5, Informative)
What am I missing?
Nothing. Negative mass is weird.
What you're pointing out -- that a positive mass and a negative mass would chase each other-- was pointed out in 1957 in Bondi's paper about negative mass, "Negative Mass in General Relativity". Rev. Mod. Phys. 29 (3). Robert Forward, in 1990, then extended that analysis even further and pointed out that negative mass is even weirder than that.
A negative mass chasing a positive mass accelerates forever... but it doesn't violate conservation of energy, because the faster a negative mass moves, the more negative the kinetic energy, so the positive kinetic energy and the negative kinetic energy cancel out, leaving energy conserved.
There are weirder things than that, too.
If you think this is so weird that bulk negative mass can't exist... well, that's what Einstein thought (the "positive energy condition").
Yes, they're separate (Score:4, Informative)
Dark matter conerns the "missing" (i.e. never observed directly) mass in the universe, which has despite its "invisibility" been observed indirectly; for example look up Bullet Cluster on Wikipedia.
Dark energy concerns what it is that is causing the expansion of space-time (and consequently) the universe itself.
Re:Dark energy is negative (Score:5, Informative)
Re:Negative mass is weird (Score:5, Informative)
Okay, as long as I've got you on the line... :)
What's supposed to happen when negative and positive mass collide?
If I throw a tennis ball at a wall, it bounces off (and the wall recoils imperceptibly). If I throw a negative tennis ball at a wall -- or throw it away, causing it to move toward the wall, whatever -- what happens when it hits? It seems like it would try to "recoil" in the same direction it was traveling, maybe even giving the wall a "tug" instead of a "push" when it hit. \
Well, I already said negative matter is weird.
Robert Forward proposed that when positive matter and negative matter touch, they cancel each other out, and vanish:
(+) + (-) --> 0 (vacuum)
The mass cancels, and you're left with nothing there.
Unfortunately, we know that this can't happen, because if it did, then the opposite reaction could occur:
0 --> (+) + (-)
--vacuum spontaneously generating pairs of positive and negative mass. If this could happen, it would happen, everywhere, all the time. But it doesn't. So there are rules (presumably conservation laws) forbidding this from occurring.
But it can't move forward, because presumably negative and positive matter can't simply interpenetrate -- or can they?
Of course they can interpenetrate. The reason that you can't walk through a brick wall is because of Pauli exclusion [physlink.com]: the electrons in your body can't occupy the same place (the same quantum state) as the electrons in the wall. But, whatever negative matter is, it's not electrons (nor any of the other particles that make up "solid" matter). So, yes, it would pass right through ordinary matter.