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Cosmologists Show Negative Mass Could Exist In Our Universe
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.
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 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 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...
http://www.geoffreylandis.com
Someone on Wikipedia put together a nice image showing frequency and sensitivity of a couple different kinds of detectors and upcoming upgrades to them. There are some high frequency microwave interferometers not shown on there that could measure in the GHz range, with sensitivities to much smaller characteristic strains than on that chart. (You kind of need to multiply the strain by frequency to get something more comparable to say amplitude of EM waves, which is part of why higher frequency is more sensitive on that scale).
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").
http://www.geoffreylandis.com
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.
HAND.
Dark Matter and Dark Energy are two completely unrelated issues. Dark Matter is the unaccounted mass that is leading candidate as to why the rotational speed of galaxies is not matching observed matter and is definitely creating gravitational lensing in empty space. Dark Energy is the unexplained force driving galaxies apart, even faster than light in some cases. This is related to the expansion of space.