FRIHOST FORUMS SEARCH FAQ TOS BLOGS COMPETITIONS
You are invited to Log in or Register a free Frihost Account!


Bosons and the Standard Theory





Dennise
Can someone please answer a couple pretty basic physics questions?

1. Does the "Standard Theory" explain why an atomic nucleus doesn't fly apart from the mutual repulsion of all those protons with +charges on them over the tiny atomic distances?

2. Similarly, does the "Standard Theory" explain why an atom's - charged electrons, attracted by its mother nucleus, doesn't just spin into the nucleus itself?

3. If the Standard Theory does NOT explain the above, can an explanation be expected from the Higgs Boson discovery?

Just wondering .........
Bikerman
a) Quantum theory does that. Electrons can only occupy fixed (quantised) positions.
The nucleus is bound by gluons which exert a force which cannot be overcome - it is greater than the colomb force (the 'charge' repulsion) at distances over 1 and a bit femotometres I think. It turns repulsive at very close proximity methinks.
kelseymh
Dennise wrote:
1. Does the "Standard Theory" explain why an atomic nucleus doesn't fly apart from the mutual repulsion of all those protons with +charges on them over the tiny atomic distances?


Yes. The protons and neutrons in a nucleus are bound together by the "strong nuclear force." This involves the exchange of massive particles (pions and other mesons), which means that it is only effective over the very short distances within a single nucleus. The electromagnetic repulsion of protons is effective over those distances as well, which is why (a) the diproton is not a stable bound state, and (b) as nuclei get larger, they have more and more neutrons compared to protons.

Quote:
2. Similarly, does the "Standard Theory" explain why an atom's - charged electrons, attracted by its mother nucleus, doesn't just spin into the nucleus itself?


Yes. You can work this out yourself using the Schrodinger equation for the 1/r nuclear potential. The minimum energy state for the electron is that with exactly one unit of orbital angular momentum (the "1S" state).

Quote:
3. If the Standard Theory does NOT explain the above, can an explanation be expected from the Higgs Boson discovery?


Both of the questions above are aspects of the existing Standard Model, or of basic quantum mechanics, and don't require spontaneous symmetry breaking (the Higgs mechanism) for an explanation.
Bikerman
I'm glad you tidied that up for me...I was struggling to remember details and thought I might screw it up...Actually I didn't do too bad from memory - 1.7 fm is quoted by wiki as the range and I got 1 and a bit Smile
kelseymh
Bikerman wrote:
I'm glad you tidied that up for me...I was struggling to remember details and thought I might screw it up...Actually I didn't do too bad from memory - 1.7 fm is quoted by wiki as the range and I got 1 and a bit Smile


You notice that I was carefully noncomittal about the "actual" range of the pion Yukawa coupling Smile Since it is an "effective" force, not a fundamental one, parameters like the range are somewhat data driven.

The intranuclear potential is one of my current areas of responsibility. I maintain and develop some simulation software for the interaction of particles with matter, and my focus is on "intranuclear cascade" models: a particle enters a nucleus, collides with one of the nucleons to produce secondary particles, which go on and collide with other nucleons, and so forth. The nuclear potential determines both the density of nucleons through the nuclear region, as well as how the secondary particles' trajectories are affected as they propagate.
Bikerman
Wow..... So you model this on a powerful computer I imagine ?
I seem to remember that the strong force doesn't follow inverse square but does drop-off exponentially - even faster - with distance...is my memory working OK ? Smile
_AVG_
Let me add some interesting details about the strong nuclear force and quantized shells.

1) As Bikerman said, the force-carriers are called Gluons. Like particles with an electric charge repel/attract each other by "exchanging" photons, particles with a "color charge" do so by exchanging gluons. Such particles are quarks. Actually quarks make up neutrons and protons (and the mutual attraction of their color charges actually holds the neutrons and protons together). Each nucleon actually consists of 3 quarks (hence these are hadrons). Notably, the mesons mentioned earlier contain 2 quarks. Now, the reason why nucleons are attracted to each other by the strong nuclear force is that the attraction of quarks "spills out" of each nucleon just far enough that the closest other nucleons (actually the quarks in these nucleons) are attracted. This is what keeps the nucleus together. But I am unsure as to what keeps the quarks together as far as their electric charges are concerned. Anyway, if you want more accurate information I suggest looking up QED (Quantum Electrodynamics) and QCD (Quantum Chromodynamics).

2) This probably requires a higher understanding of math (and the concept of eigenvalues and eigenfunctions). When solving a partial differential equation subject to certain boundary conditions, sometimes there are infinitely many solutions that vary based on an unimportant parameter (usually this can take any integer value). This happens while solving the Schrodinger Wave Equation in 3 dimensions and hence there are 3 parameters that can be varied. These are usually called n, l and m and are called Quantum Numbers. There is one more Quantum Number added (the spin) but this is intrinsic to the electron (the other 3 are derived from the interaction between the electron and the nucleus). In any case, choosing possible integer values for n, l and m give the different quantized states or energy levels of the electron. Hence the electron cannot just exist anywhere around the nucleus but must have discrete "regions" of existence.

I apologize if any of the information given above is inaccurate. Look up the relevant concepts on Wikipedia or something for a better understanding.
Bikerman
Don't worry - you have a real expert, not just amateur bikerman, looking over your shoulder. This is Mike's world Smile
kelseymh
Bikerman wrote:
Wow..... So you model this on a powerful computer I imagine ?


Sometimes. I run the simulation code (GEANT4) on my MacBook when i'm doing development work. For a few GeV pi- incident on an iron/scintillator calorimeter (a stack of alternating iron plates and plastic) it takes a couple of hours to run 5,000 events.

Quote:
I seem to remember that the strong force doesn't follow inverse square but does drop-off exponentially - even faster - with distance...is my memory working OK ? Smile


Correct, the potential is "super" exponential: (1/r)exp(-kmr), where m is the mass of the exchanged meson. See http://en.wikipedia.org/wiki/Yukawa_potential
kelseymh
_AVG_ wrote:
[...]But I am unsure as to what keeps the quarks together as far as their electric charges are concerned.[...]


The strong force is stronger than electromagnetism by about two orders of magnitude. At a fixed distance (say, 0.5 fm), the QCD force holding two quarks together is of order 1, while the EM force pushing them apart is ~1/137. Hence, the electromagnetic repulsion is a very small effect compared to the strong attraction.
Bikerman
kelseymh wrote:
Bikerman wrote:
Wow..... So you model this on a powerful computer I imagine ?


Sometimes. I run the simulation code (GEANT4) on my MacBook when i'm doing development work. For a few GeV pi- incident on an iron/scintillator calorimeter (a stack of alternating iron plates and plastic) it takes a couple of hours to run 5,000 events.
That's still quite a lot of crunching but less than I thought.....Do you work improving the models that the software is based on by feeding-back experimental results? Or is it the other way around - using the system to design experiments? (Or neither of course - I'm speaking from a profound ignorance Smile
kelseymh
Bikerman wrote:
kelseymh wrote:
Bikerman wrote:
Wow..... So you model this on a powerful computer I imagine ?


Sometimes. I run the simulation code (GEANT4) on my MacBook when i'm doing development work. For a few GeV pi- incident on an iron/scintillator calorimeter (a stack of alternating iron plates and plastic) it takes a couple of hours to run 5,000 events.
That's still quite a lot of crunching but less than I thought.....Do you work improving the models that the software is based on by feeding-back experimental results? Or is it the other way around - using the system to design experiments? (Or neither of course - I'm speaking from a profound ignorance Smile


Both! The models used in the simulation are all validated against experimental data, both recent and going back to the late 1960's. That is part of my job as a member of the GEANT4 collaboration.

But the purpose of the software, for the user community, is in designing and running experiments. I'm also a member of the CDMS (dark matter) experiment, and we use GEANT4 as our simulation toolkit. I'm working with it now as part of designing the shielding system for our 100+ kg expansion, SuperCDMS.

GEANT4 is used in high-energy physics, nuclear physics, space applications, medical physics (both proton and carbon beams and brachytherapy), "homeland security" (detection of nuclear materials), and so on.
Bikerman
It sounds interesting. From the brief look I had I'm thinking that GEANT4 is actually a library of standard routines, and you 'pick and mix' the required routines to write an overall model?
Do you use/need programming skills or do you work at a higher level and have code-monkeys who do the actual coding?

PS - by 'higher' I only mean as in the computer sense, not the status sense Smile ie higher level -> closer to native language
PPS - code-monkeys is what we (network/systems managers) semi-affectionately call programmers
kelseymh
Bikerman wrote:
It sounds interesting. From the brief look I had I'm thinking that GEANT4 is actually a library of standard routines, and you 'pick and mix' the required routines to write an overall model?


Yes, indeed! We call it a "toolkit." It is up to the end user to write a main(), and register their subclassed versions of the required driver functions (including what we call the "physics list" of which kinds of processes are to be simulated), and then the simulation takes over.

Quote:
Do you use/need programming skills or do you work at a higher level and have code-monkeys who do the actual coding?


GEANT4 is written in C++, and it is expected that the end user is conversant in C++. There is a Python interface to GEANT4, but having never used it myself, I don't know how useful it is to a non-C++ person.

We provide a large number of examples which can be used as a basis for developing your own application. We also have active discussion fora ("Hypernews") where the user community and the developers can address issues that come up.
Dennise
Thanks guys .... I get it. Er ... I think I do Very Happy
Related topics
What is Truth
What is Philosophy to you?
Time-Travelling Experiment
Gravity and Acceleration
Elusive Higgs within reach
Theory of Relativity - Part 1
Temperature in empty space
What is the universe expanding into?
Newton Institute Lecture - String Theory
Intelligent Design - Science or Religion?
What's the difference between matter and antimatter?
God exists - and here's the proof
string theory
Gravity waves? Big Bang?
Reply to topic    Frihost Forum Index -> Science -> The Universe

FRIHOST HOME | FAQ | TOS | ABOUT US | CONTACT US | SITE MAP
© 2005-2011 Frihost, forums powered by phpBB.