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# Particle Physics watch

1. Now let's take an example of the attraction between protons and electrons. There is an electrostatic force between them. But I would like to know what causes this force? How are they attracted to each other. What's there developing this connection between them. Are there fundamental particles involved maybe?
2. (Original post by Daniel Atieh)
Now let's take an example of the attraction between protons and electrons. There is an electrostatic force between them. But I would like to know what causes this force? How are they attracted to each other. What's there developing this connection between them. Are there fundamental particles involved maybe?
Do you wonder why the electrons are not attracted by the protons and don't get into the nucleus? as far as I know its the circular motion of the electrons themselves. This circular motion causes a centrifugal force which is contrary to the attraction of the protons in the nucleus.

Without this motion, there is no centrifugal force, so electrons will be attracted by protons because of the different charges between them.
3. The "nature" of the forces is up to open discussion as far as I know. I remember reading somewhere that at some point, you've got to take something as a postulate in physics and go from there e.g. F=ma. I don't think Physicists quite know why there are four forces, like, why not 5, why not six etc, but its also great your asking these questions. Maybe you should be a theoretical physicist.

PS: I don't do Physics so I might be off the mark.
4. (Original post by Daniel Atieh)
Now let's take an example of the attraction between protons and electrons. There is an electrostatic force between them. But I would like to know what causes this force? How are they attracted to each other. What's there developing this connection between them. Are there fundamental particles involved maybe?
If you find an answer for this, be sure to tell me!

(Original post by Kallisto)
as far as I know its the circular motion of the electrons themselves. This circular motion causes a centrifugal force which is contrary to the attraction of the protons in the nucleus.

Without this motion, there is no centrifugal force, so electrons will be attracted by protons because of the different charges between them.
Ewww no. God heavens don't bring 'centrifugal force' into this. Even Bohr's model is wrong.

Can be explained in a horribly brief and uncertain way by the Heisenberg's Uncertainty Principle.
5. (Original post by Phichi)
(...)
Ewww no. God heavens don't bring 'centrifugal force' into this. Even Bohr's model is wrong.(...)
Yeah, there is an extension by Sommerfeld where the pathways are not seen as circular ones only, but also as ellipses, see here:

Is that what you meant?
6. (Original post by Kallisto)
Yeah, there is an extension by Sommerfeld where the pathways are not seen as circular ones only, but also as ellipses, see here:

Is that what you meant?
I don't like the whole defined orbit idea, whether it's circular or elliptical. Classical modelling with some quantum mechanical 'bodge job'.
7. (Original post by Phichi)
I don't like the whole defined orbit idea, whether it's circular or elliptical. Classical modelling with some quantum mechanical 'bodge job'.
I see. But when the classical modelling is a contradiction to the quantum mechanical, what is the right one? are there new theories far away from classical anyway?
8. The simple answer to your question is photons are the particles that cause the attraction or repulsion, in the standard model.

Have a look at feynman diagrams, or even better read QED by feynman.

http://voyager.egglescliffe.org.uk/p...ts/parts1.html
9. (Original post by 2^1/2)
The simple answer to your question is photons are the particles that cause the attraction or repulsion, in the standard model.

Have a look at feynman diagrams, or even better read QED by feynman.

http://voyager.egglescliffe.org.uk/p...ts/parts1.html
You've identified the force carrier, but that really gets you no where into answering the question.
10. (Original post by Phichi)
You've identified the force carrier, but that really gets you no where into answering the question.
Isn't this always go into infinite regress? I remember a Horrible Histories book advising readers to ask 'why' to their teachers until said teachers broke down in tears and gave up.

What would be nice to know is if charge represents the probability of emitting/absorbing a photon, how do oppositely charged particles know to do this when brought close? Or do they constantly emit photons but then reabsorb them? (Also, don't the photons have to carry oppositely signed momenta for attraction than for repulsion? Who decides the sign?)
11. As someone said further up the page, the nature of the four fundamental forces (strong, weak, electromagnetic and gravity) are up for discussion. There are several models which attempt to combine the forces, such as the "electroweak" which suggests these two forces are the same force acting at different distances.

However, we do have some good ideas of how the forces could work.

Strong force: The field on the mechanics of the strong force is called "Quantum chromodynamics" and is based on the idea that quarks have a property which scientists decided to call colour. The colour of a quark can take one of 3 values, usually red, green or blue. Quarks are said to be continuously exchanging gluons, a fundamental particle which carries the colour of one quark and takes it to another. So these quarks are continuously swapping colours, but the colours always add up to 0 (this is where the colour analogy works, the colours summing to 0 is a bit like the primary colours mixing to produce white). The energy of the gluon field is so huge, that when one quark is pulled away from the others, a quark anti-quark pair will spontaneously form, resulting in a meson and a hadron, although the meson will usually decay almost instantly.

The other forces don't have quite such interesting theories behind them: the weak force is the exchange of W and Z bosons, which can allow quarks to change flavour, gravity is a complex one, Einstein had to change it to fit with his theories of relativity - you can view gravity as the universe as a sheet stretched over a frame, and masses are weights on that sheet which cause small wells to form - if you're a ball on that sheet you're going to roll into a nearby well, from which it's very difficult to escape!

Your example of the electromagnetic force between protons and electrons, yes you're right it involves fundamental particles. The idea is that photons carry the electromagnetic force between quarks in the proton and the electron (which is a fundamental particle by itself). You might ask - how do they know where other charged particles are to exchange with? Well there's a theory which says charged particles are constantly emitting "virtual photons" ie. photons which aren't really there until they interact with another charged particle.

That's about the extent of my knowledge I'm afraid, sorry I can't explain exactly how these exchanges result in a force, but as far as I'm aware no-one really knows!

Hope this helps!
12. Why does the fact that quarks have colour charge mean that they can only exist inside of other particles?

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13. This is a very deep question that you are asking and unfortunately does not have a simple answer. It also does not have an answer that is generally agreed in the physics community. However, it appears that the previous posters have also not got far enough into physics courses in order to understand much of this question.

The best hope of answering this question lie in different problems related to unification/quantum gravity. Depending on your approach, your interpretation of different forces can be modified. But, talking generally, most physicists agree that the laws of nature manifest from some geometrical property. Nowhere is this more appropriate than General Relativity. I am assuming that no one here has studied gauge theory or advanced differential geometry, and thus it would be pointless of me to present the detailed mathematics. However, as an example, an early attempt of unification of EM and GR is that of Kaluza-Klein compactification. In this model, the electromagnetic field was an internal symmetry group of each point in space-time. This is an example of how different forces can be interpreted as an underlying geometry.

So, although I cannot definitively answer your question, my gut feeling (along with most physicists) is that forces are simply an illusion of some underlying geometry we are not seeing. Maybe space-time is defined with much higher ranked tensor fields for example. For now, it is a mystery.
14. The question is slightly the wrong way around here.

We have two types of particles that contain quarks, namely Baryons and Mesons. Now, all quarks obey fermionic statistics, and thus are bound by Pauli's exclusion principle. It is this that necessitates the existence of a colour charge, for if not, the quarks would violate the Pauli exclusion principle.

The existence of colour has no bearing on the fact that they have to exists in "particles". The fact that quarks make up "particles" necessitates the existence of colour.

(Original post by Edminzodo)
Why does the fact that quarks have colour charge mean that they can only exist inside of other particles?

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15. (Original post by Kallisto)
(Original post by djpailo)
(Original post by Phichi)
(Original post by 2^1/2)
(Original post by james153)
(Original post by WishingChaff)

I highly appreciate your participation in this question. Many utterly interesting responses. I'm genuinely thankful to all of you.

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Updated: January 22, 2015
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