Freebase: Discussion about Web Ontologies

Electron: Particle type?

2009-12-06T18:40:32.0008Z

Jeff: composition is already non-unique. Ideally, what I'd like to end up with is something like the structure pictured here, but none of the "xxx" nodes make sense to be topics themselves.

Electron: Particle type?

2009-12-05T11:00:08.0020Z

I've deleted particle statistical family and group - the particle type is looking nice and clean now.

For π⁰, I guess we could have a formula (i.e. text) similar to a chemical compound formula, but then we lose the linkage to the quarks it makes up. Otherwise I think we'll have to leave composition of π⁰ etc and self antiparticles as open questions for now.

Another question: why doesn't the Browse view for an Electron display its particle properties?

Electron: Particle type?

2009-12-04T18:37:21.0013Z

Composition of π⁰: Could composition be non-unique, and defined as "possible compositions"?

Electron: Particle type?

2009-12-04T12:05:57.0011Z

I've added particle family to the particle type so I think we can now drop particle statistical family and group. I've also engaged in some property reciprocation.

Self antiparticles: ugh. The double links solution is pretty horrible. The only other solution I can think of would be to have a "self antiparticle" boolean, but that's probably even worse.

Composition of π⁰: in slight handwaving terms, the π⁰ can be thought of as alternating between being composed of (an up quark and an up antiquark) and (a down quark and a down antiquark), but never (an up quark and a down antiquark) or any of the other combinations. The only ways I can see to model this either end up with CVTs inside CVTs or creating a topic for something like "composition of the π⁰".

Spin: yeah, I screwed up the pion spins. Good catch. Now fixed, I think.

Electron: Particle type?

2009-12-04T00:49:03.0013Z

I like the hadron type!

I've changed spin to float and updated the spins that were already entered in (note: Wikipedia says pions have zero spin? also, should spins be negative?). I'll start moving types from my base to the new base soon.

Electron: Particle type?

2009-12-03T18:48:31.0031Z

Self antiparticles: There isn't a way to set a particle to be its own antiparticle using a sibling-relationship CVT -- the CVT has only one property to hold both particles, and you cannot enter the same topic as a value for a property more than one time. The only work-around would be to use something that resembled a phylogeny pattern, with two linked properties "antiparticle" and "antiparticle of". This is kind of ugly, but would handle the π⁰ case. The problem with this pattern is that you have to enter all the relationships in twice for all particles that aren't antiparticles of themselves -- once in the "antiparticle" property, and once in "antiparticle of".

Composition of π⁰: I'm not sure what "linear combination of (up-antiup) and (down-antidown)" means, but I can see in Wikipedia's list of mesons that there are several mesons with similarly complex compositions.

Uncertainties: we can do this -- see how we handled it for atomic masses.

Spin: Agreed -- let's make it just be a float for the particles. We can refactor the Particle Spin type separately.

Electron: Particle type?

2009-12-03T13:07:45.0013Z

More from me... it doesn't at the moment to seem possible to set a particle to be its own antiparticle (try it with the π⁰). Any thoughts on a way round this one?

Also, we need to find a way to model the composition of the π⁰, which is a linear combination of (up-antiup) and (down-antidown).

I'll shut up for a bit now and let other people get a word in edgeways :-)

Electron: Particle type?

2009-12-03T10:14:50.0012Z

Two more thoughts from the way to work: do we want to include uncertainties on properties like mass, etc? Also, I created a hadron type to model the composition of baryons and mesons.

Electron: Particle type?

2009-12-03T08:38:34.0006Z

Yes, it would allow people to enter the class as "fermion". If we really wanted to avoid that possibility, we could have "particle family" type (quark, gauge boson, meson, etc) which link to a "particle class" type (fermion, boson, hadron), but that seems to me to be to getting towards creating types for the sake of it.

Spin: just a floating point number, yes. The particle spin used in chemistry is the same concept, but it's typically expressed in a different way.

In other news, I've created the particle [physics bas](http://particlephysics.freebase.com/)e and added the particle family type. Luke, you're an admin so you can move your types over there if you want.

Electron: Particle type?

2009-12-03T01:01:54.0010Z

I've deleted "composition" - you're right, it's redundant. (I only had it in because Wikipedia included it :/ )

I'm not sure how "particle family" can be an enumerated type and have sub-classes. If we do this, won't that allow people to fill in "fermion" as the "group" of a particle? (Which could be valid, but we'd prefer a more precise classification.)

So how about for "spin", we just have a floating-point number? (The "particle spin" for isotopes is a separate topic if I understand correctly.)