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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).
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
What ever happened to Occam's Razor?
It competes with the totalitarian principle, "everything that is not forbidden is compulsory."
http://www.geoffreylandis.com
It was used by William of Ockham in the late middle ages to argue against the species theory of perception -- the idea that everything you can see constantly emanate images of themselves in every direction. It states (in scholastic Latin) "Do not multiply entities beyond necessity."
It was then stripped of its context somewhere halfway through the previous century, became a rallying cry of pretty much every self-proclaimed skeptic, and erroneously believed to say "the simplest explanation is usually right"
That is what happened to Ockham's razor, and I wish it had stayed in the 13th century, along with all the other idiotic arguments for and against realism about universals.
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!
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).
Is this similar to, unrelated to, part of, dissimilar, orthogonal, integral, or in any way linked to Dark Matter?
It's unrelated to dark matter (which has positive mass- that's how we know it's there), but dark energy is gravitationally negative (it causes expansion to accelerate: it's gravitationally repulsive)
Because I (and probably most of us) don't understand that either.
You're in good company! If you did understand it, you could publish, and you should be getting a phone call from Stockholm soon.
http://www.geoffreylandis.com
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.
Man who doesn't understand the science, the math, or the data, calls theory crackpot. News at 11.
The Kruger Dunning explains most post on
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.
Actually yes. Copernicus discarded geocentricism and found that the heliocentric model greatly simplified things, but he retained circular orbits with the planets moving at uniform speeds which still required epicycles to match observation. (in fact, it would have required an infinite number of epicycles to exactly match observation).
Kepler took the next step with elliptical orbits and so was able to predict planetary motion with unprecedented accuracy.
Ah, the
Pauli exclusion
principle. IANA physicist, but I've never been happy with this here thingy.
Fortunately, your happiness is not relevant to whether physics works.
...
Oh, BTW - this is just one of many examples where science does, in fact, depend on pure faith.
No, this is one of the many examples where science depends on pure observation. The Pauli exclusion principle was first arrived at from observations, and only somewhat later was the theoretical basis-- the spin-statistics theorem-- worked out.
http://www.geoffreylandis.com