It is said that the force between two quarks increases as they are pulled apart which is ultimately resisted by the strong nuclear force.  Correct me if I'm wrong,  but my physics teacher once said that if I put enough energy to seperate two quarks, I end up creating a new pair of quarks. Why is that?
27056
I simply know that a single free quark does not exist. What is the reason that we can not get a free quark?  If we can't get a free quark then what is single-top-quark?
102256
I have found from this link  that: Nuclei are made up of protons and neutron, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. The difference is a measure of the nuclear binding energy which holds the nucleus together. This binding energy can be calculated from the Einstein relationship: Nuclear binding energy $= Δmc^2$. Now from the above it seems that the nuclear binding energy should be positive to compensate the energy difference between between the mass of the protons and neutron and the mass of a nucleus. But my question is how the binding energy can be positive if this binds the nucleons by attractive force? I have also gone through this  , but didn't get my question resolved.
55219
We know that like charges repel each other. But my professor claimed that two electrons can attract each other as well. What he said was that due to screening an electron travelling at some speed won't repel another electron, but that they will, in some cases, attract each other due to weak phonon exchange. What does that mean? What is phonon exchange? Do two electrons really attract each other?
53198
It is known that there are no diproton or dineutron nuclei.  Does this mean that two protons or neutrons are not actually attracted to each other? Even if the attraction was weak, wouldn't it cause bound states anyway?  Related:
9684
Is it possible to create matter? In a recent discussion I had, it was suggested that with enough energy in the future, "particles" could be created.   It seems like this shouldn't be possible due to conservation but perhaps I could be wrong. Would any of you Physics masters care to elaborate?  (Note... I will understand the basics, I am by no means an expert.)
45609
I was wondering this: suppose you have two oxygen atoms. They will both have 8 protons and 8 neutrons in the nucleus (at least if they are the most common isotope). Now, will all those particles be arranged in the same way in both atoms? If they are, why would that be, and if not, does that affect the element's properties in any way?  But then I also thought that maybe the uncertainty principle doesn't let us even ask this question. Maybe you can't tell the particles' positions so accurately, so all you can say is that you have 8 protons and 8 neutrons all together in a small space.  So, which one is it? Can we even tell where all the particles are, and if we can, does it matter exactly how they are arranged?
61170
As we know that matter-antimatter asymmetry is one of unsolved problems in physics. One possible solution to this problem is given as baryogenesis which produce asymmetry in rate of creation between matter and antimatter particles. But doesn't alternate solution like "different regions of space with different type of particles " holds more ground..  Means in one region matter particle dominates (the region we live ) and another region anti matter particle will dominate. When particle-antiparticle pair created from energy (at that energy is so much high that particle- antiparticle pair could be created from energy according to $E=mc^2$) before they meet and annihilate with each other they also has equal chance of meeting with same type of particle in neighborhood, because after some time of big bang the four force were united and gravity was as powerful as remaining three forces. So now in 50% of all pairs destroyed by annihilation and other 50% clumps together with same type of particle means matter with matter and antimatter with antimatter and then inflationary epoch throw these clumps from each other at very large distance so that they can not meet each other and have chance of annihilation. And we now can not see these regions because of accelerated expansion of universe because of dark energy.   Doesn't this hypothesis is more or at least equally valid with baryogeneis hypothesis.
93230
There is a recent paper in , also on the  that claims the discovery of a fifth force, mediated by a 17 MeV boson, which explains an anomaly in nuclear decays.  Is this a real effect? Could the claimed particle be some sort of composite particle such as a pion?
58558
Why do quarks tend to bond in groups of three?   I understand why they might in bond in groups of three to create a net charge of zero (i.e. neutrons), but I don't understand why they form protons and not, for example, commonly form in groups of four. I have done background research on this question, and did not find any information. The wikipedia article on baryons () was not helpful either.  To summarize, why are mesons and baryons more common than other hadrons?
60376
Firstly I think shades of this question have appeared elsewhere (like , or ).  Hopefully mine is a slightly different take on it.  If I'm just being thick please correct me.  We always hear about the force of gravity being the odd-one-out of the four forces.  And this argument, whenever it's presented in popular science at least, always hinges on the relative strength of the forces.  Or for a more in depth picture .  But, having had a single, brief semester studying general relativity, I'm struggling to see how it is viewed as a force at all.  A force, as I understand it, involves the interaction of matter particles with each other via a field.  An energy quantisation of the field is the force carrying particle of the field.  In the case of gravity though, particles don't interact with one another in this way.  General relativity describes how space-time is distorted by energy.  So what looked to everyone before Einstein like two orbiting celestial bodies, bound by some long distance force was actually two lumps of energy distorting space-time enough to make their paths through 3D space elliptical.   Yet theorists are still very concerned with "uniting the 4 forces".  Even though that pesky 4th force has been well described by distortions in space time.  Is there a reason for this that is understandable to a recent physics graduate like myself?     My main points of confusion:   Why is gravity still viewed as a force? Is the interaction of particles with space time the force-like interaction? Is space-time the force field? If particles not experiencing EM/weak/strong forces merely follow straight lines in higher-dimensional space (what I understand geodesics to be) then how can there be a 4th force acting on them?     Thanks to anyone who can help shed some light on this for me!
120829
I came across this relation while reading on the Bohr atomic model. Are there any other forces for which these relations hold good?
8239
I have came across this recent development in the LHC: Breakthrough at the Large Hadron Collider:  Leptoquarks and leptons - quarks unification:   Leptoquarks (LQs) are hypothetical particles that would interact with quarks and leptons. Leptoquarks are color-triplet bosons that carry both lepton and baryon numbers. Their other quantum numbers, like spin, (fractional) electric charge and weak isospin vary among theories.  Does this mean that we are heading for a strong-EM forces unification? Is the Electron after all coupled to the individual quarks in the nucleus via these new boson? And therefore new unifying force discovered?
58105
I couldn't find a straight and clear answer to this question on the internet: Why is the weak interaction (charged), the only interaction which can change the flavours of the quarks?
109929
We know that the protons in a nucleus are positively charged, whereas the neutrons do not possess a charge; we also know that unlike charges attract. So why does the nucleus stay intact, even though there isn't supposed to be any electrostatic force of attraction within it? Instead, why isn't there any repulsion between the protons which are like-charged?
112981
Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force.  I've been told that unifying these with the strong force is likely to be far easier than unifying them with gravity, albeit still very hard.   Apparently this is because of the fact that electromagnetic, weak nuclear and weak nuclear force equations are relatively similar, whereas the equations for gravity differ greatly.  What are the fundamental differences between these equations? (If you could write some that would be great, and then explain the technical differences, if necessary.)  What is it about these differences that make them much harder to unify?
49990
Say you have a conductor, filled with free electrons. The nuclei have a weak pull on the valence electrons so they are moving around in the conductor.  But the electrons don't leave the solid. If you bring a positively charged object near the conductor, the electrons might move to the other side of the object, but won't leave it, almost as if there's a "wall" blocking it.   Why do surfaces act like barriers/walls for free electrons?  I have gotten the following explanations:  1) They are attracted by the nuclei so they are pulled back.  My problem with this: Conductors have a weak attraction force on the electrons, so why does it take an extremely large force to counteract the pull by the nuclei? And also what makes the boundary so special?  If the electron can move within the solid freely, what makes it so much harder to move outside the solid, since the force by the nuclei is the same?  2) Think of the electrons as being held by the nuclei by a string. If you pull on it, you might be able to move the electron away but you would need a stronger force to break the "string" of the nuclei.  My problem with this: This analogy doesn't work. Elastic strings follow Hooke's Law:  $$F = kr$$ where $k$ is a constant and $r$ is the distance. As the distance increases, the force pulling back increases.  Electromagnetic forces however follow Coloumb's Law:  $$F = \frac{kq_1q_2}{r^2}$$  As the distance increases, force pulling back decreases.  I am not looking for a mathematical proof. I am looking for an intuitive explanation. Something like an analogy would help a lot, but any other explanation you feel would be more helpful is welcome.  Also note that I know that you can get electrons to leave a conductor, but this requires a high voltage.  Related:
46608
This question may sound stupid but why do we visualize nuclei as composed of a bunch of neutrons and protons? Wouldn't the nucleons be too close together to be viewed as different particles? Isn't the whole nucleus just a complicated low energy state of QCD?