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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.
As I understood it with my very limited knowledge of physics, there are perceivable phenomena that did not quite make sense because it was an either/or situation.
In that case, Occam's Razor makes way for Sherlock Holmes' "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
A model that allows for more of the perceived phenomena than previous models must be taken under more scrutiny.
As we better understand the universe, we find gaps between reality and our understanding. We then try to extend our understanding to better match reality, and that means filling in those gaps. Sometimes it takes many tries to fill in a gap, or at least make it smaller.
Negative mass is one of those attempts, and it's worth noting that they aren't clinging to the concept, they're simply suggesting that it's one possibility that can be tested. In other words, they actually are using Occam's Razor. In this realm, nothing is simple, which makes the Razor harder to use.
The living have better things to do than to continue hating the dead.
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
Before I read the article, I'd have been predisposed to agree with the poster who called this "The crackpot cosmology theory Du Jour". However the article does note that not only does negative matter possibly explain the current lack of detection of gravitation waves but (presumably unlike many other phenomena) predicts that if there is negative matter, we WOULD be able to detect gravitational waves but only above a certain frequency:
"the evidence that could back it up would be the discovery of the threshold frequency above which the waves do propagate"
If anyone who can read and understand the actual paper could tell us non-cosmologists when our improving technology might be able to detect gravitational waves above the cut-off frequency I would appreciate it. I mean is it technology that is (very roughly) 10 years away, 25 years, a century or basically only when we have god-like powers. I seem to remember that NASA was going to launch a space based interferometer with "arms" (free floating platforms) in a triangle 5 million km on a side. Would that be able to detect them? The whole point now isn't just to prove the existence of gravity waves but also negative matter (and the possibility of warp drives, yay!).
Actually, since (if I am reading the article correctly) they are looking for "higher frequencies", doesn't that mean the detectors should be smaller? ("arm" length shorter?) Shouldn't they be increasing the sensitivity instead? Or is the sensitivity increased by making the detector larger? I'm so confused!
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 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.
An excellent question, and as yet we don't have an answer.
There are actually two apparently unrelated phenomena we call mass - inertia and "gravitational charge", and last I heard we don't even have any substantial hypotheses as to why the two always seem to appear in the same ratio. The properties of a "negative mass object" would vary wildly depending on whether one or the other, or both properties were negative.
Negative gravitational mass only would mean you have an object that behaves as normal, but would presumably be repelled from normal gravitational matter (and then there's the question of how it would react to other negative matter - a naive hypothesis would be mutual attraction - rather like electrostatics except that like charges attract and dislike charges repel.
Negative inertial mass would likely mean that acceleration would be in the opposite direction of applied forces - push on a chunk and it would move towards you (basis for a cool "reactionless" drive?). This would also be repelled from normal mass, but for a different reason - gravitational forces would pull on it just like normal matter, but the resulting acceleration would be in the opposite direction.
If both are negative then you get stuff that acts like normal matter so long as only gravity is affecting it - gravitational forces would repel it from normal matter, but since the inertial mass is negative the resultant acceleration would be toward the gravitational source. All other forces would still result in backwards acceleration.
--- Most topics have many sides worth arguing, allow me to take one opposite you.