Sure would be handy if we had some third kind of matter that could interact with both matter and anti-matter without the instant massive total annihilation problem.
Does any physics model predict the possible existence of such a substance? Most of our other bi-polar systems in particle physics seem to have “neutral” particles. Why no “neutral” particle when it comes to matter / anti-matter?
sorry, meant to post this in general questions if a mod can move it…
Well … while you’re stille here we could discuss whether that neutral particle should be allowed to marry another neutral particle, or whether it should be allowed to carry a gun, or whether it is somehow all a fault of the Obama administration.
Anyone?
Anti-particles, should be allowed to marry particles, who care’s if they would instantly annihilate? check your matter-ist privelige ableist cis-scum! 
Gotcha covered.
What of the children, man, have you given any thought to that?
Photons?
A photon is its own anti-particle, and interacts with both anti-matter and matter equally. Want to build a containment or handling system? Something that uses photons to mediate force between things made of matter and anti-matter? Its called a magnet. Its both that simple, and about all we have.
Ok yes I am aware there are various ways of keeping particles and anti-particles apart using electro magnetic forces eg the Penning Trap
But is there any theoretical possibility of a solid substance which could serve as a physical barrier between matter/anti-matter? if not, then why not?
Well, the only “solid substances” we know of are made of protons, neutrons and electrons, or conversely, their antiparticles. There are particles that don’t interact with either matter or antimatter, or interact only very weakly (eg. neutrinos), but they don’t interact with each other either, so they can’t form solids. Anyway, even if they could, the very fact that they don’t interact with matter/antimatter means such hypothetical solids couldn’t “contain” normal matter. A bottle of water stops the water from passing through only because the bottle molecules interact with the water molecules via electromagnetism.
–Mark
Right, so I guess what I’m asking, is why as well as protons and anti-protons, there are no “neutral protons” and same for the electrons and neutrons. Most other particles seems to have positive - negative and neutral variants, but for matter-anti matter that’s not the case.
The photon is not the neutral variant of a proton etc, since it’s massless. So I guess another way of asking my question is why is there no particles with mass which are their own anti-particle?
I think there’s some confusion there. There are particles come in positive and negative varieties, but not positive/negative/neutral. For example, we have electrons and positrons (anti-electrons), but there is no neutral variety of the electron. There are up quarks and anti-up quarks with the opposite charge, but no neutral up quark. What examples were you thinking of?
–Mark
Do neutrinos not form solids because of an inherently low cross section with each other? Or because their temperature is so high (and no way to cool down)? After all, most baryonic matter is not solid, either.
A “neutral proton” is a contradiction in terms; a proton (a baryons, one of the class of fermions that follow Dirac statistics) is comprised of two up quarks and one down quark and naturally has a charge of +1⋅e. It’s complementary antiparticle has two up antiquarks and one down antiquark with a charge of -1⋅e. The ‘basic’ neutral baryon is the neutron with one up and two down quarks, and its antimatter complement has one up and two down antiquarks. The same is true for other complex neutral lambda, sigma, xi, and omega baryons. There are hypothetical fermions called Majorana particles (which follow Majorana statistics) which are their own antiparticle, but no one has ever definitively observed one, and they can only emerge in very specific conditions that don’t exist in “normal” space.
Your notion of a “solid material” that could contain antimatter without the application of magnetic fields belies a misapprehension that the field is somehow separate from the particles that generate it. In fact, for a charged particle the electromagnetic fields are a fundamental and inseparable property of how the particle interact with other charged particles, and the photons (virtual in the case of magnetic fields and many other specific interactions) are just a quantized expression of the field. Without that field there would be no interaction; hence why neutrinos, which have no charge and do not interact using the electromagnet field at all, are capable of going through large amounts of solid baryonic material (i.e. planets) with only a tiny number of interactions when they happen to be close enough to a nucleus to interact via the W[SUP]±[/SUP] and Z[SUP]0[/SUP] bosons. Baryons, on the other hand, only interact by electromagnetic forces which make matter appear to be solid, but it isn’t as if at any time particles are actually “touching”, or indeed that it even makes sense to think in those terms at the atomic level. The only physical barriers are fields, and the only fields that repulse antimatter are electromagnetic fields that are generated by charged particles.
Stranger
Neutrinos, regardless of temperature, react with each other (or anything else) only weakly (in both senses of the word). I suppose that theoretically, if they were cold enough, even those weak interactions might be enough to hold them together, but it would have to be a damned cold temperature, and even then, they might just form something like a liquid instead of a solid.
It’s also important to note that there is no clear distinction between matter and antimatter. By convention, we call positive protons and negative electrons “matter” (because they appear to be common in our universe), and negative protons and positive electrons “antimatter” (because they appear to be rare). And it’s simple enough to extend this definition to other baryons and leptons. But what about, say, the mesons? A pi+ and a pi- are clearly antiparticles of each other, but which one is the matter and which one is the antimatter? There’s no way to say.
Neutrinos cannot form solid structures or flows (e.g. those that can be described by continuum mechanics) because like photons they have no electric charge which allows for the covalent, ionics, and metallic bonds that we identify as being a continuous solid or liquid. Their main interactions with each other are via gravity (and the weak force, but only over very short ranges which the particles usually have too much momentum to remain in long enough for a significant volume of interactions to occur), hence any identifiable structural patterns will only occur over very long ranges (e.g. the size of galaxies or larger).
The interesting thing is that a slight tweak of fundamental contents would render no ability to create solid or liquid matter, giving a physical makeup and chemistry to the universe that is literally incomprehensible. It may seem that we are very fortunate to live in a universe where the physics makes it possible for us to exist, but then again, if it didn’t we wouldn’t, so there is no extrinsic conclusion to be drawn from this fact.
Stranger
I think you meant “fundamental constants” rather than “fundamental contents”? Although both phrases make sense, actually.
I’ve seen hypothetical descriptions of alternate universes with fundamental constants just a bit different from what we have, in which universes you can have nothing but a universe full of vibrating complex fields (or whatever you call them) that can never coalesce into anything more substantial than quark-like particles, if even that.
Seems like such a waste of a whole universe.
Then there’s dark matter . . . whatever that is . . .
Is it not abstractly possible to make a kind of matter out of only one kind of quark, so that it would only react with antimatter made of the same antiquark?
You’d have – I dunno – “Strange” fluid, which is inert to everything except “anti-Strange” fluid. But mix them, and whango.
There do exist particles made out of a single kind of quark, like the Delta++ (made out of three ups). But they’re all quite short-lived, and decay in various ways (often actually producing antimatter in the process).
During the short period they exist, do they interact/annihilate other forms of matter or antimatter? Would such a Delta++ go boom if introduced to a proton…or an antiproton? Or are they so short-lived nobody knows?