Elementary Particles

[studiot]

The original atomic theory introduced the idea that the 'stuff of the universe' is made up from different arrangements of a small number of 'indivisible particles' .

Each different such aprticle was identified with a particular element, from whence we obtain the modern term 'elementary particles' , which we still regard as indivisible.

 

The original particles were subsequently found to be actually divisible into a smaller number of sub atomic particles which carried or mediated their observable properties and could be arranged diferently to form the original atoms of the theory.

 

 

More recently (some of) these sub atomic particles have again been divided into particles which carry observable properties. this time a greater number of particles emerged. We now call these 'elementary particles'.

 

However we have not atributed certain properties on a one to one basis to these elementary particles so some are properties are possessed by several.

 

For instance charge is possessed by electrons and some quarks.

 

So why do we believe that these are indivisible.

 

Why are we not searching for an elementary indivisible particle that carries only charge?

[Severian]

People do look for this. In fact, there are a few models about that speculate that the current "fundamental" particles are indeed composite particles, composed of more fundamental things. However, all these theories make predictions that can be tested (as all good theories should) and so far all of them have failed the tests.

[imatfaal]

People do look for this. In fact, there are a few models about that speculate that the current "fundamental" particles are indeed composite particles, composed of more fundamental things. However, all these theories make predictions that can be tested (as all good theories should) and so far all of them have failed the tests.

 

But surely any theorist who posits a "yet-undetectable" sub-particle, whether they be preons or others, must acknowledge that their undetectable sub-particle perforce could be made up of sub-sub-particles; and thus any postulation that isn't firmly seated in observations is open to repetition ad absurdum. And there is no (little) evidence at present to lead us to the view that quarks should be further subdivided.

[studiot]

So how do you account for the fact that some elementary particles have charge and some don't?

 

In other words why is there not an elementary charge carrier?

[RichIsnang]

Is it theoretically possible for there to be infinite smaller particles?

i personally think that it will stop relatively soon, like maybe we may find a couple more layers of 'sub-currently elementary' particles, then we will have the correct ones,

but it is possible for it to go on forever, particles getting smaller and smaller?

Does Planck length/mass come into it, does it state that there is a theoretical limit that particles cant be smaller than?

or are there any other concept that come into it?

[Severian]

But surely any theorist who posits a "yet-undetectable" sub-particle, whether they be preons or others, must acknowledge that their undetectable sub-particle perforce could be made up of sub-sub-particles; and thus any postulation that isn't firmly seated in observations is open to repetition ad absurdum. And there is no (little) evidence at present to lead us to the view that quarks should be further subdivided.

 

Of course. The only criterion for suggesting something new is the better explanation of data. So if a preon theory for example could explain the masses of the quarks, or the flavour interaction structure, it would have value as a theory to replace the SM. But as I said, none of them so far work convincingly.

 

So how do you account for the fact that some elementary particles have charge and some don't?

 

In other words why is there not an elementary charge carrier?

 

That is fairly easy to explain with GUT theories (though the explanation I can give has no direct evidence in support of it yet). You could have an SU(5) symmetry at very high energies which is broken by a high energy analogue of the Higgs mechanism. Then the SU(5) breaks fairly neatly into SU(3)xSU(2)xU(1), the gauge group of the Standard Model. The nice thing here is that the representations of SU(5) tell you automatically what the U(1) charges should be after breaking, and consequently the value of the electric charge for each particle. Miraculously, it all falls out beautifully. SO(10) and E6 both work nicely too.

[Pymander]

The original atomic theory introduced the idea that the 'stuff of the universe' is made up from different arrangements of a small number of 'indivisible particles' .

Each different such aprticle was identified with a particular element, from whence we obtain the modern term 'elementary particles' , which we still regard as indivisible.

 

The original particles were subsequently found to be actually divisible into a smaller number of sub atomic particles which carried or mediated their observable properties and could be arranged diferently to form the original atoms of the theory.

 

 

More recently (some of) these sub atomic particles have again been divided into particles which carry observable properties. this time a greater number of particles emerged. We now call these 'elementary particles'.

 

However we have not atributed certain properties on a one to one basis to these elementary particles so some are properties are possessed by several.

 

For instance charge is possessed by electrons and some quarks.

 

So why do we believe that these are indivisible.

 

Why are we not searching for an elementary indivisible particle that carries only charge?

 

Here's a thought. In chemistry, two hydrogen atoms may each fill their first electron shell to maximum 2, and a covalent bond exists. The protons are rather attracted to the electron charge between them, and so, do not repel each other. Energy is released as photons (and perhaps neutrinos as well, how would we know?).

 

In like manner, an electron with sufficient energy and thus shorter wavelength may hold two protons together at orders of magnitude shorter distances and release orders of magnitude more energetic photons, to become deuterium. A electron sandwiched between protons in plasma or in a nova could overcome the initial repulsion of the protons as the electronic charge concentrates with increasing frequency, so that repulsion is overcome and reverts to attraction instead, finally releasing more energy than is initially absorbed.

 

Thus our nova, for example, first collapses, and then explodes, leaving a neutron star, but in our present sun, the deuterium soon becomes helium as in the hydrogen (deuterium and tritium) bomb. And like in chemistry, some molecules are stable and others are not. But the 'neutron' ejected from an atom is an ion of sorts, and likewise unstable, only that it is neutral. We now have an explanation for complex nuclei without requiring further particles, even the neutron being a transient composite. Let's face it, all further particles beyond the photon, the proton, and the electron rapidly dissociate into these.

 

The 100% symmetric antiparticles, defined as such relative, again, to the observer, seems inescapable. That this is not so is only a cover for an apparently mostly matter universe - one more hypothesis. Do neutrinos and photons manifest in pairs also and how would we know? All further particles require more energy to compile, and live shorter lives, perhaps to a limit which may well be the Higg's Boson. Are they really necessary to explain the bonds of forces? This seems sufficient, other than quantum states defining finite numbers of possible entities. Even the universe is finite, though unbounded, the three dimensional surface of a four dimensional hyper sphere, at least for matter!

 

Do we really need to compound hypotheses, cook up scrambled mathematics, and disengage the right hemisphere for science? Special relativity: The velocity of light is constant irrespective of the relative velocity of the source. General relativity: The force of gravity is indistinguishable from the inertial force of acceleration. Unified Field Theory: There exists One Force only - perhaps? The antiphoton (initially called a negatron) was discovered the year Einstein departed this life.

 

Our universe may only have required these three particles and their antiparticles for its existence, with sufficient 'properties' to make all of manifestation, the 'firmament', possible. If you like, only the photon (and perhaps the neutrino is a necessary antiparticle in gravity or inertia, analogous to positive and negative charges participating through relatively in electric and magnetic fields) brought initially into manifestation, invested with energy and properties, has brought the universe into existence. We can learn these properties but we cannot explain them! Not so incidentally, ancient traditions relate that light (ether) and then darkness (vibration into light and dark energies) were the first creation, not Bigbangium. The Higg's Boson may well be the Lawrencium of the subatomic world, and as per tradition perhaps going a little farther back than we know, or from (verifiable) psychic sources, God is light.

 

Ridicule this for raining on the parade, especially at the cost. Ridicule it for suggesting to 'science' that God (by any name) may invest creation with purpose, and our concepts need to progress to such an understanding. I may deserve it and I may also be right. Only time brings in all the evidence blind men need, first to argue, and finally, to recognize an elephant. They still won't know its colour. I'll just say, eat your vegies too.

[studiot]

Hello severin and thank you for taking an interest.

 

But you are not really answering the question.

 

The electric charge on quarks is +2/3 or -1/3 and on leptons is -1.

 

This implies (to me at any rate) there is 'something' with a charge of 1/3 or -1/3 that I should be able to isolate and perhaps isolate three of them from a lepton.

[robheus]

As I understand it (at least that is what susskind tells in online lectures of stanford university) there is no such thing as a "fundamental particle" in the traditional (classical) sense as something that can not be divided up into smaller parts. What in modern physics is considered to be an elementary or fundamental particle is the aspect that if you add a minimal quantum of energy, it's exciting state becomes clearly visible. Therefore a macroscopic object like a football isn't a fundamental particle, because adding a quantum of energy gives it such a relative small amount of energy that it forms a near continuum, while for a proton you can clearly see a different energy level from the ground state.

 

So wether something is a fundamental particle has to do with the particle spectrum of excitation states.

 

EDIT: and in so far this explenation is correct, the fundamentall-ness of a particle isn't realy a boolean value (it is either or it is not) but is some continuüm, some phsyical objects are more fundamental or elementary then others, and there is a range of them which show a very distinct spectrum for the first excitation state in the spectrum that one can consider them fundamental.

And of course, if string theory is correct, the fundamental objects are not the particles, but strings and branes.

Edited July 7, 2012 by robheus

[Severian]

Hello severin and thank you for taking an interest.

 

But you are not really answering the question.

 

The electric charge on quarks is +2/3 or -1/3 and on leptons is -1.

 

This implies (to me at any rate) there is 'something' with a charge of 1/3 or -1/3 that I should be able to isolate and perhaps isolate three of them from a lepton.

 

I think something you are missing is that electric charge isn't fundamental. It is a mixture of hypercharge and weak isospin according to [math]Q=I_3+\frac{1}{2}Y[/math] left over after the symmetry breaking.

 

So your charge +2/3 up quark has this value because it has [math]I_3=\frac{1}{2}[/math] and hypercharge [math]Y=\frac{1}{3}[/math].

Similarly the down quark has charge -1/3 because it has [math]I_3=-\frac{1}{2}[/math] and hypercharge [math]Y=\frac{1}{3}[/math].

In contrast the left handed electron has [math]I_3=-\frac{1}{2}[/math] but hypercharge [math]Y=-1[/math], giving charge -1.

The neutrino has [math]I_3=\frac{1}{2}[/math] but hypercharge [math]Y=-1[/math], giving charge 0.

 

So hypercharge is more fundamental, and there is a particle that carries only hypercharge: the right handed electron.

 

As I said before, if you are willing to accept an SU(5) GUT model, these hypercharge assignments fall out of the group algebra.

 

I suspect what you want to do though is consider a quark as a bound state of an object carrying only colour and an object carrying only hypercharge. Is this correct? I am afraid this cannot be done since they need to have at least some quantum number in common in order to interact. Otherwise there would be no force that could act on both.

[juanrga]

The original atomic theory introduced the idea that the 'stuff of the universe' is made up from different arrangements of a small number of 'indivisible particles' .

Each different such aprticle was identified with a particular element, from whence we obtain the modern term 'elementary particles' , which we still regard as indivisible.

 

The original particles were subsequently found to be actually divisible into a smaller number of sub atomic particles which carried or mediated their observable properties and could be arranged diferently to form the original atoms of the theory.

 

 

More recently (some of) these sub atomic particles have again been divided into particles which carry observable properties. this time a greater number of particles emerged. We now call these 'elementary particles'.

 

However we have not atributed certain properties on a one to one basis to these elementary particles so some are properties are possessed by several.

 

For instance charge is possessed by electrons and some quarks.

 

So why do we believe that these are indivisible.

 

Why are we not searching for an elementary indivisible particle that carries only charge?

 

We still regard elementary particles as "indivisible" because all experiments made up to now confirm that elementary particles are not composite. Predictions made by some speculative models (as some models of preons) were experimentally ruled out.

[studiot]

Juanrga, thank you for your interest.

 

Dalton could equally have claimed all experiments to date show atoms to be indivisible, as could Rutherford and Chadwick claim about nuclear particles.

 

My desire to have a one to one correspondence between a property and a carrier particle has not been assuaged, although I am looking into severin's details.

 

 

[juanrga]

Juanrga, thank you for your interest.

 

Dalton could equally have claimed all experiments to date show atoms to be indivisible, as could Rutherford and Chadwick claim about nuclear particles.

 

And all them would be right then when available data supported them.

 

At the time of writing this, elementary particles are indivisible and fundamental. No known experiment contradicts this. Maybe tomorrow new observations/experiments will suggest otherwise, but not today.

Edited July 7, 2012 by juanrga

[studiot]

At the time of writing this, elementary particles are indivisible and fundamental. No known experiment contradicts this. Maybe tomorrow new observations/experiments will suggest otherwise, but not today.

 

I don't disagree - But it is not a question of known experiment.

 

We have not succeeded in dividing these particles.

 

But that does not answer the question is there a single particle that carries sharge or spin or colour or mass or whatever any more than saying we have never observed a magnetic monopole proves they do not exist.

Edited July 7, 2012 by studiot

[swansont]

I don't disagree - But it is not a question of known experiment.

 

We have not succeeded in dividing these particles.

 

But that does not answer the question is there a single particle that carries sharge or spin or colour or mass or whatever any more than saying we have never observed a magnetic monopole proves they do not exist.

 

But it is a question of known experiment. We can't say absolutely that they don't exist. We can't say they do. There's no evidence to which one might point, either way. So as far as I can tell your question cannot be answered as you have framed it. What we can say is that fundamental particles are fundamental at the energies we can probe and we see no indication that they have any structure, and all that that implies.

 

All that's left after that is conjecture, which is outside the realm of known experiment.

[michel123456]

The search for elementary particles involves a presupposition: that size is an absolute feature.

If suddenly one admits that size may be a relative feature, then the search for fundamental blocks will vanish.

Quoting J.Barbour

In a fully relational theory, not only time and position should be relative but also size – if all distances in the universe were suddenly doubled, nothing observable would change.

from Scale-invariant gravity: particle dynamics. Classical and Quantum Gravity 20 1543 (2003). (arXiv:gr-qc/0211021)

 

Note: quoting again J.Barbour from the same link

Attractive as this idea is, it appears to be in strong conflict with the evidence from cosmology. For me, this is a great mystery and a stimulus to further research.

Edited July 7, 2012 by michel123456

[MigL]

Severian, the SU(5) symmetry model is the simplest such model, and has the strong force 'breaking away' at 10^15 GeV, and the electrowek 'break-up' at 250 GeV, leaving symmetry groups which you've already mentioned.

However, the SU(5) model also predicts proton decay after 10^32 yrs. All current experiments have failed to find a single result of proton decay, and have estabilished a lower limit on a proton's half-life which is several orders of magnitude higher than 10^32 ( don't recall exact min. half-life, you'll have to look it up ).

 

I don't have much exposure to group theory, so unfortunately the SU(5) model is the only one which I can hope to make some sense of. Maybe some of the others can elaborate on other GUT models.

Edited July 13, 2012 by MigL