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Cosmologists Show Negative Mass Could Exist In Our Universe 214

Posted by Unknown Lamer
from the beam-me-up dept.
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.
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Cosmologists Show Negative Mass Could Exist In Our Universe

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  • 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?

    • by Anonymous Coward

      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).

      • Not only have we created them, we have small stores at CERN and a few other facilities for experimentation on.

      • by Geoffrey.landis (926948) on Thursday July 17, 2014 @10:33AM (#47474705) Homepage

        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]

        • by gstoddart (321705)

          So, I will happily demonstrate my complete lack of understanding on this topic ...

          Is this similar to, unrelated to, part of, dissimilar, orthogonal, integral, or in any way linked to Dark Matter?

          Because I (and probably most of us) don't understand that either.

          • by ColdWetDog (752185) on Thursday July 17, 2014 @11:33AM (#47475187) Homepage

            Almost, but not quite, entirely unlike Dark Matter.

          • 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.

            • by gstoddart (321705)

              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)

              Wait ... dark matter and dark energy are separate things now? Are they related? Or totally separate things?

              Honestly, are you guys just fucking with us? ;-)

              You're in good company! If you did understand it, you could publish, and you should be getting a phone call from Stockholm soon.

              Oh, good, I'm not supposed t

              • by warrax_666 (144623) on Thursday July 17, 2014 @12:16PM (#47475571)

                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.

              • by Bengie (1121981) on Thursday July 17, 2014 @12:20PM (#47475607)
                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.
                • by Immerman (2627577)

                  I thought the anomalous galactic rotational curve had been almost entirely explained a year or two ago by repeating the analysis using the far more computationally expensive Relativity theory rather than the known-flawed Newtonian theory of gravity. There's still the gravitational lensing anomalies, bullet cluster, etc. supporting the existence of DM, but the while galactic rotation was the impetus for postulating it's existence, it's no longer a strong supporting argument.

              • by suutar (1860506)

                My way of remembering it is this: Dark matter is why large structures (galaxies) don't fly apart. Dark energy is why even larger structures (the universe) does.

        • by cuby (832037)
          I don't know very little about the subject, but I have a question and a speculation.
          The question is what would happen in an encounter of 2 objects with symmetrical masses?
          The speculation is about negative mass and antimatter... What if, somehow, negative mass was more attracted to antimatter? Could that explain why there is so little antimatter around?
        • 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.

          Aw dammit, I was hoping we could build antigravity vehicles from this stuff...or at least some negative mass body panels to lighten up my car :-(

          • If it exists, we can do something so much better - we can build Alcubiere Drives - that is, the real version of what Star Trek called "Warp Drives".

            (This reference is not accidental - Star Trek inspired Alcubiere's research as he himself pointed out in an e-mail to Shatner - he wanted to test if Star Trek's loophole was really possible, and he found out it is at least theoretically possible, but only if negative mass exists).

        • 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.

          Trying my best to ignore my intuition, which is heavily biased toward "all mass is positive":

          A negative mass would fall down in a gravitational field (generated by a positive mass) -- it would experience a force directed away from the positive mass, and it would respond to that force by moving toward the positive mass.

          However, the negative mass would repel the positive mass gravitationally -- effectively, exert a force directed away from itself -- correct?

          It seems to me that if you had two equal but opposit

          • by Geoffrey.landis (926948) on Thursday July 17, 2014 @12:11PM (#47475525) Homepage

            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").

            • 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. But it can't move forwa

              • by Geoffrey.landis (926948) on Thursday July 17, 2014 @02:39PM (#47477055) Homepage

                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.

                • Out of interest, if there were pair creation events of involving particles of negative mass/gravity how would we detect them?

                  I'm not being critical, I'm curious - how would a particle accelerator, or a bubble chamber or whatever, look different with a negative mass particle?

                  • Out of interest, if there were pair creation events of involving particles of negative mass/gravity how would we detect them?

                    You're asking a lot, since we don't really know what the property of the particles are. A negative mass particle would curve in electric and magnetic fields (the usual way to determine what a particle is) just like a positive mass particle of the opposite charge. However, since negative mass particles also have negative kinetic energy, conservation of energy means that the remaining particles will have more energy coming out of the collision than they did going into it.

                    I'm not being critical, I'm curious - how would a particle accelerator, or a bubble chamber or whatever, look different with a negative mass particle?

                    Positive mass particles emit positiv

                • Ah, the

                  Pauli exclusion

                  principle. IANA physicist, but I've never been happy with this here thingy. As the article states, "Wolfgang Pauli gave physics his exclusion principle as a way to explain the arrangement of electrons in an atom. His hypothesis was that only one electron can occupy a give quantum state." This is a principle without an explanation. It's one of those physics things that you have to take on faith, and because nothing works without it. AFAIK there's never been any real explanation of _why_ this pr

                  • 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 [utexas.edu]-- worked out.

          • "all mass is positive":

            Well, in truth some mass is just not quite _sure_, but is willing to go along with the consensus.
            And some mass is on a downer, and just not the type to be 'up' all the time.

        • by geekoid (135745)

          You should do an ama.

        • by Immerman (2627577)

          >Negative mass reacts oppositely to both gravity and intertia.

          Well, that's one hypothesis. But as I recall there are several hypothesis for each of the three possible interpretations of "negative mass", and none of them have any supporting evidence for actually existing.

          • Would an opposite reaction to inertia mean that an object becomes easier to accelerate the more massive it becomes?

            • by Immerman (2627577)

              No, assuming you mean negative inertial mass it would probably just accelerate in the opposite direction. You push on it, it moves towards you instead of away, and you generate energy instead of expending it.

        • by rossdee (243626)

          It means that if you have 2 objects, one of negative mass and one of normal mass (and nothing else around) The negative mass object will fall toward the normal one, and the normal one will be repelled by the negative one. The negative mass chases the normal mass and accelerates.
          As the speed increases, the acceleration increases (once you get to a significant fraction of the speed of light)

          It makes a good 'space drive'.

          I wish I had patented the idea back in 1976 when I first thought of it when I was taking

      • by Dcnjoe60 (682885)

        But an anti-hydrogen atom still has mass.

      • by hAckz0r (989977)
        No, I think the next step is likely that someone will 'mathematically prove' that you can have anti-energy or something cruft like that, to explain away Dark Energy. Where the word 'prove' actually means 'infer' from some magical fantasy land mathematical contortions. Once you divest yourself from the physical reality you can twist equations around to do many impossible things. Why so many people invent fantasy to try and explain away actual evidence is beyond me. At least with anti-matter we have actual ev
        • by lgw (121541)

          Dark Matter certainly exists - as certain as anything in cosmology. We know a few things about it: it reacts normally to gravity, but it doesn't interact with light or electrons in any way (these things are true of neutrons as well, of course). Further, it has no analog to EM interaction that could produce friction in some other way - we know this because it doesn't clump like normal matter.

          How do we know this? There were many theories for the galactic rotation rate anomaly, but only the WIMP (dark matt

    • Of course it does exist. It was discovered by Dr. Cavor and is sold as Cavorite(TM).

    • by NotDrWho (3543773)

      The summary makes mention that we haven't noted any substantial signs of this material

      They're just pointing out that it CAN exist, like unicorns and the Loch Ness monster.

  • A goal for all those zero sized models and weight loss fanatics to aim for!

  • This kind of subject always leads to a cascade of stupid questions in my head that I can't answer, leaving me feeling even dumber than usual. Does negative mass necessarily imply negative weight? What about momentum and kinetic energy? If a lump of matter with negative mass hit something, would it actually absorb energy from it rather than imparting energy to it? Would a negative-mass planet have an anti-gravity field? Is it even meaningful to talk about matter with negative mass, or is some physicist going

    • You forgot the most important question:

      Can I use this to make a flying car and/or hoverboard?

    • by mikael (484)

      Given that negative mass atoms repel each other, a negative mass planet would never form. Even if one did form, it would disintegrate rather violently within seconds. Probably be fun too watch.

      So, negative mass atoms could only form thin gas clouds.

    • by Immerman (2627577) on Thursday July 17, 2014 @01:52PM (#47476657)

      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.

      • by Tx (96709)

        Glad I came back to look for later replies, thanks for that.

      • by HiThere (15173)

        FWIW, I believe that General Relativity is based on the idea that those aren't really two distinct things, but rather the two "ideas" of what mass is are two different ways of talking about the same basic reality. If you want to really consider them as separate things that just happen to be equal, then I think you need to replace General Relativity with something else...and there don't appear to be any good candidates.

  • Having built a number of gravitational wave observatories that have to see a single gravitational wave...

    If they must see that same single gravitational wave over and over again, why do we need to keep building more of them? Why don't we build some to see OTHER gravitational waves?

    ;-)

  • by wisebabo (638845) on Thursday July 17, 2014 @10:53AM (#47474877) Journal

    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!

    • Re: (Score:2, Informative)

      by Anonymous Coward
      Someone on Wikipedia put together a nice image [wikipedia.org] 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 sens
  • As I understand it (could certainly be wrong) the whole hypothesis for "dark energy" was created to explain the reason why the Universe's rate of inflation is increasing. Also, I believe we have, so far, been unable to prove its existence except through this increasing speed of inflation.

    Wouldn't negative gravity obviate the need for dark energy?
    • by geekoid (135745)

      The 'dark' in 'Dark energy', means we don't know what it is.
      It wouldn't obviate the need for dark energy, it would be dark energy.

  • find a way to make them in the lab. I want my anti-grav car.

  • He's my negative mass brother!
  • But there probably is less than a pound of it!

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