Are we really sure that the universe is mostly matter?
I mean, do we really know that some super cluster millions of light years away is not antimatter? How?
Rav
We don’t know. But if there were a region of anti-matter, we would expect there to be a boundry between the matter region(s) and the anti-matter region(s). At the boundry there would be collisions converting the mass to energy. There is no evidence of boundries in the visible universe. This does not mean they don’t exist, but it does make it unlikely.
Virtually yours,
J Matrix
They’ll live for 8 whole hours? That’s amazing–I was thinking something on the order of “minutes”. Thanks!
I’m too full of questions, maybe, but just how “exotic” can these particles get when you smash generation after generation into each other? Is there a point beyond which the sequence begins repeating previous levels of organization? Or do they just keep getting more exotic (and, I assume, smaller)?
Hope this isn’t “thread hijacking”,
David
SoulFrost wrote:
“just how “exotic” can these particles get when you smash generation after generation into each other? Is there a point beyond which the sequence begins repeating previous levels of organization? Or do they just keep getting more exotic (and, I assume, smaller)?”
Actually, the particles that people study (quarks and leptons) all have zero dimension as far as anyone can tell – they are all “point” particles. The idea is not to get smaller particles, but to get HEAVIER particles (the more kinetic energy you have in your smash-up, the more can be converted to mass.) So with increasing energy you get heavier particles. These are all acompanied by the less exotic particles, which makes it harder to sift the wheat from the chaff. Particles currently being studied: b quarks (5 times the mass of the proton), tau leptons (2 times the mass of the proton), top quarks (170 times the mass of the proton), Z and W bosons (80-90 times the mass of the proton.)
-k-
Karen Lingel, Physicist and Penguinist
Ahhhh! Thanks so much, Karen–that explains a LOT!
Much appreciated
David
WHOA! You’re the same Karen that wrote the Mailbag article?
I have to tell you–that was one of the drop-dead BEST pieces of writing that I’ve seen here. And considering which board we’re on, that’s quite an accomplishment!
Many kudos, and I hope to see more of your work soon…
David
Karen, you got a fan club arready?
This isn’t Karen’s first Mailbag posting, however:
-How are up and down defined?
-How many dimensions are there?
[Note: This message has been edited by CKDextHavn]
Wait a second, isn’t a proton made from two up quarks and one down quark? Just the added weight of the two up quarks would be 340 times that off the proton they constitute. Is it a question of mass-energy conversion?
Only humans commit inhuman acts.
The three quarks mass does add up to more than the mass of the proton they make up. The extra mass is converted to the binding energy. The is the amount of energy you would need to “free” the quarks. The mass-energy is not lost it is just converted.
Virtually yours,
J Matrix
Also, Karen said “top” quark, not “up” quark.
My own question concerns the “zero dimension” reference you tried to sneak past us…a “dimensionless” point with mass is different from a singularity exactly how (besides, of course, the AMOUNT of mass - at least for ex-star singularities - and the size of the event horizon)? (For that matter, is there a more-current term for a Black Hole than “singularity?”)
The up and down quarks are very, very light. The exact masses of the quarks are somewhat unknown, since you never “see” a quark by itself, so you have to do some estimates of binding energy and so forth, but here is a handy guide to quark masses:
up quark: 0.2%-0.5% mass of proton
down quark: 0.3%-1% mass of proton
strange quark: 6%-18% mass of proton
charm quark: a little heavier than a proton
b quark (also called bottom or beauty quark): 4.5 times the mass of the proton
top quark: 185 times mass of the proton
The reason the point-masses are not singularities is that they can be “renormalized”. This is a theoretical trick where you bundle the divergences together in such a way that they no longer diverge. It’s a little like that old conundrum: to get somewhere, you first have to go halfway, then half the remaining distance, then half, then half, etc, and you never “get there”. Well, if you do the integral correctly, e.g., to go half the distance it only takes half the time, such that your velocity is constant, then you do in fact, “get there”. Renormalization is like that, except with quantum mechanics thrown in. It’s the kind of thing they make you calculate once in graduate school, then you just trust the theorists when they say they’ve renormalized something. (Of course, if you ARE a theorist, you have to remember how to renormalize things. I myself couldn’t do it again to save my life. Sorry.)
The up and down quarks are very, very light. The exact masses of the quarks are somewhat unknown, since you never “see” a quark by itself, so you have to do some estimates of binding energy and so forth, but here is a handy guide to quark masses:
up quark: 0.2%-0.5% mass of proton
down quark: 0.3%-1% mass of proton
strange quark: 6%-18% mass of proton
charm quark: a little heavier than a proton
b quark (also called bottom or beauty quark): 4.5 times the mass of the proton
top quark: 185 times mass of the proton
The reason the point-masses are not singularities is that they can be “renormalized”. This is a theoretical trick where you bundle the divergences together in such a way that they no longer diverge. It’s a little like that old conundrum: to get somewhere, you first have to go halfway, then half the remaining distance, then half, then half, etc, and you never “get there”. Well, if you do the integral correctly, e.g., to go half the distance it only takes half the time, such that your velocity is constant, then you do in fact, “get there”. Renormalization is like that, except with quantum mechanics thrown in. It’s the kind of thing they make you calculate once in graduate school, then you just trust the theorists when they say they’ve renormalized something. (Of course, if you ARE a theorist, you have to remember how to renormalize things. I myself couldn’t do it again to save my life. Sorry.)
I seem to recall from QFT and GR that renormalization is a fudge, because there is no physical justification for the cutoff distance required. I also thought this rendered every standard relativistic field theory not asymptotically free, hence fundamentally suspect, and that this cannot be fixed until gravity has been properly dealt with at the Planck length.
Hence I thought the question of why a point particle is not a gravitational singularity was actually far from satisfactorily solved.
But I am only an egg.
Karen,
One thing I’ve never gotten a straight answer about is whether matter-antimatter annihilation only occurs between particles and their respective antiparticles or between any form of matter and antimatter. I seem to remember that dissimilar collisions were being used in a German accelerator to search for the “leptoquark” (another topic on its own).
Thanks, Steve
To have pure and true annihilation, you need a particle and its twin antiparticle. Particles are defined by their collection of quantum numbers, and for annihilation, the additive quantum numbers have to all add to zero. Here are some of the quantum numbers for electrons, positrons, and up quarks:
e- e+ u
charge -1 +1 +2/3
lepton # +1 -1 0
baryon # 0 0 +1/3
up-ness 0 0 +1
etc etc etc etc
So if you add the electron’s quantum numbers to the positron’s quantum numbers, they all add to 0 everywhere, and ta da, annihilation. If you add the positron and the up quark, you get… well, you get a big mess, but it isn’t zero, so no annihilation.
However, there are other ways that particles interact, for instance a “fusion” type interaction. At the German Electron Synchrotron (DESY) they smash positrons and protons (which are full of u and d quarks). They hope that the positron and quark will fuse into some other particle that would have BOTH lepton-type quantum numbers AND quark-type quantum numbers: voila, a leptoquark.
And if anti-matter is scarce in your neck of the woods, you can smash accelerated matter into a stationary matter target and hope for photon-gluon fusion, or gluon-gluon fusion. We used to produce charm particles at Fermilab this way.
-k-
Karen Lingel, Physicist and Penguinist