Q: What’s the difference between anti-matter and negative-matter?

Physicist: Anti-matter is exactly the same as matter, but different.  If you, and everything else on the planet, were suddenly turned into anti-matter, you’d never know the difference.  While the “anti-” of anti-matter may seem to give it an air of mystery, it still acts just like ordinary matter in essentially every respect.  Specifically, anti-matter carries positive energy and mass, just like regular matter, while negative matter carries negative energy and mass.

Famously, when you bring matter and anti-matter together they annihilate.  All of their combined mass is converted into buckets of energy in an amount dictated by Einstein’s little-known equation, E=mc2.  For comparison, the largest nuclear device ever detonated, the USSR’s “Tsar Bomba”, is the yield you’d expect from about 1 kg of anti-matter (so about 2 kg of energy total, because it needs some mass to annihilate with).  A single atom of anti-matter (say, anti-carbon) annihilating in your ear would be just barely audible as a pop.  It’s the energetic equivalent of a ant stomping a foot (in anger!).

Negative matter, more commonly called “exotic matter”, has negative energy.  If you were to bring it into contact with ordinary matter you would see, not an awesome explosion, but an underwhelming and abrupt nothing.  When exotic matter in brought together with ordinary matter, the positive energy of the matter and the negative energy of the exotic matter cancel out entirely, leaving nothing at all behind.

Exotic matter is a freaking blank check for sci-fi writers.  Warp drives, worm holes, perpetual motion, and even time machines are possible if you allow for negative matter and energy.  In fact, Hawking proved that if you want to build a time machine smaller than the universe, negative energy/mass is a requirement.  Spacetime, as described by general relativity, is pretty limited by the fact that energy and matter seem to be strictly positive.  About the weirdest things you’ll see are black holes, which are pretty cool, but… time machines.  With a liberal peppering of exotic matter (often far more than the universe’s total stockpile of regular matter) you can really open up the flood gates of the weird.

However the big difference, arguably the biggest difference, between anti-matter and negative matter is that negative matter doesn’t exist.

There are some subtle physical laws that imply that the creation of negative energy, in the form of exotic matter or not, has limitations called “quantum interest“.  Anytime a bit of negative energy is generated (and the methods involved create, like, none), a larger, overwhelming pulse of positive energy must be created almost immediately.  In fact, we’ve never directly observed negative energy and it’s very, very likely that we’ll never be able to do more than infer that negative energy exists.

But anti-matter definitely exists, and can be created and stored (a few particles at a time) here on Earth.  Many particle accelerators today generate and use anti-protons all the time.  When you smash stuff together, or otherwise get a mess of energy in one place, new particles are generated; half matter and half anti-matter.  It’s basically annihilation in reverse.  Once you create a spray of new particles, you sort the matter and anti-matter apart, keep the anti-particles ionized, and store them (briefly) in a “magnetic bottle“.  If they ever becomes electrically neutral the magnetic bottle stops working, and they fall and annihilate with the ordinary matter at the bottom of the container.  Anti-particles are totally the hot potatoes of particle physics.

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7 Responses to Q: What’s the difference between anti-matter and negative-matter?

  1. steve says:

    What’s your take on a proposition by Christian Beck at the University of London and Michael Mackey at McGill University, which seems to indicate that following a phase transition, some zero-point photons below a frequency of about 1.7 THz, making them gravitationally active, whereas above that they are not? Supposedly this resolves the 120 order of magnitude problem which excludes zero point as a candidate for dark energy.

  2. The Physicist The Physicist says:

    Never heard about that idea.

  3. Pingback: Q: If you are talking to a distant alien, how would you tell them which way is left and which way is right? | Ask a Mathematician / Ask a Physicist

  4. Alexander Cooke says:

    Negative matter annihilating with matte breaks conservation of energy, the only way for them to have o momentum before annihilation is to being going in the exact same direction at the same speed.

  5. pingpong says:

    antimatter exists but negative matter does not

  6. Xerenarcy says:

    physics is full of funny coincidences… time only goes forward. mass-energy is always positive. gravity always attracts. speed always slows time, doesn’t reverse it. i think we are at a point where there are far too many equivalences implying a preferred energy ‘direction’ for them to be unrelated.

  7. Rob Heusdens says:

    Matter with the property of having negative mass has sure been hypothized and researched as an abstract concept. For example Bondi studied it.
    In fact one can think of two different kinds of negative mass. 1. Using the standard assumption that gravitational mass = inertial mass, or 2. Using the non-standard assumption that gravitational mass = -1 * inertial mass. [or: intertial mass = absolute value of gravitational mass]

    For assumption 1., the properties of negative mass are:
    - negative mass attrackts negative mass, but then (F=ma, inertial mass = gravitational mass) accelerates opposite to the force! Effectively then negative mass self repels.
    - positive mass is repelled from negative mass.
    - negative mass accelerates towards positive mass.

    For assumption 2., the properties of negative mass are:
    - negative mass attracts negative mass (and here: also accelerates in the same direction)
    - positive mass is repelled from negative mass (as in assumption 1.)
    - negative mass is repelled from positive mass.

    [Please note that assumption 2. is in fact unnecessary, because all that it does is interchange the concept of positive and negative, and therefore it would be just the same as negative mass matter in assumption 1.]

    Using assumption 1. and hypothezing that there is indeed negative mass matter (that is, we do not exclude it´s existence, although it has never been found directly) and see how it would behave if it exists in the universe like positive mass matter (from the big bang), for example created in equal amounts as positive mass matter.

    Positive mass matter would as in the big bang model form galaxies and stars. Negative mass matter however self repells and spread out. But since it accelerates still towards this positive matter clumps, it will surround the galaxies, and have influence on the rotation speed of the galaxy. Since it also self-repels, it would therefore not exist inside the galaxy but only around it.

    Another property is the electromagnetic properties of negative mass matter. Here the negative mass matter inverts attraction and repulsion as compared to positive mass matter. Positively charged negative mass matter will attrackt positively charged negative mass matter, that is like charges attrackt, unlike charges repell. For electromagnetic interactions between positive mass matter and negative mass matter, we can also find the interactions for the combinations of the two types of mass and two types of charge (which here for brevity I have left out, but which can easily be resolved).

    Now this is of course purely theoretical, and noone seen ever negative mass matter. Standard physics currently excludes the negative mass concept, and considers it unphysical. But then nobody ever saw dark matter either, in fact we still don’t know what it is, we can only say what it is NOT. It might be that negative mass is the only remaining candidate and can be shown to fit the data quite well.

    Although that is something seperate, previously also the concept of repulsive gravity and negative energy were thought of unphysical/impossible, but inflation just comes with this concept well thought out. This does not imply negative mass should be considered to be physical too solely on that basis, but then maybe it is not too far fetched to consider it physical, and see if that would somehow help explain somethings we currently do not know. Unless it can turn out to have explenatory power and consistentent with the other established framework of physics (or maybe large part do need to be rewritten), there is no use of assuming that it negative mass matter can exist.

    A very speculative thought, which ought to be further explored is if negative mass matter can fit the data we have about dark matter, and also fits the experimental data we have about the evolution of the universe. But we know the impact of this would be enormous, since it would involve many parts of physics, which partly need to be rewritten on the basis of physical existence of negative mass matter (if a case can be made it makes sense as candidate for dark matter and/or dark energy). It would be major paradigm change in physics, and maybe even opens the way to unifying gravity with the other forces.

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