terminology - Question about physical principles

How are principles created i.e. how is it decided that something qualifies as principle?

What is the difference between a principle, a law and a theory?

Were there any principles that were proved to be wrong or are principles always right? For example, the reason why Einstein proposed that the speed of light is constant is because the Principle of Relativity would be violated otherwise.

Are physical principles comparable to mathematical axioms?

Is there a list of physical principles? I couldn't find any on google.

How can helicity be conserved but chirality not?

I read in a book that for $\beta$-decay the electrons have always been found to have an expectation value for their helicity of $h=-v/c$.

Then ist is said in the book, that it follows from this fact that such electrons are in a left-handed chiral state which is characteristic for the weak interaction.

In another article I read that the chiral state of an electron is not conserved in time. The electron will soon evolve a component with a right-handed chiral state and it will be a mixture of right- and lef-handed chiral states.

Suppose after the decay one electron moves like a free particle.
When it evolves a right-handed chiral component in addition to the left-handed component it starts off with, how can its helicity be conserved?

quantum chromodynamics - Do gluons have properties other than color charge that distinguish them from each other?

Gluons in quantum chromodynamics (QCD) come in eight color charge varieties. But, it has never been clear to me if they differ from each other in other respects the way that, for example, photons do. Obviously, they also have a direction and location associated with them (subject to the uncertainty principle) and presumably, as massless bosons, always travel as the speed of light.

Do they have different frequencies or differing amounts of energy? Do they have different helicity? Do they have polarizations or chirality that is distinct from color charge? Are there other possible properties that I've overlooked?

Answer

Gluons are essentially a more complicated version of photons; their colours are just a multidimensional analogue of electric charge (which photons don't even have, because electromagnetism isn't self-interacting). In particular, gluons are massless spin-$1$ bosons. This gives the same polarisation, chirality and helicity details as photons, and an arbitrary four-momentum (satisfying $k_\mu k^\mu=0$ if the gluon is real).

electricity - Why is there no current flow when I connect two opposite terminals of two separate batteries?

I don't understand this..maybe there is something wrong with my understanding of battery or electricity.

I am learning about electricity more deeply this time. So please bear with me.

So lets begin with what I know:

• follow of current occurs when there is voltage drop.


• voltage drop happens when there is imbalance in charge.


• a battery is basically two separated chemicals. One side with electrons to spare and other side that needs electron to balance itself. which is imbalance in charge.


• When both sides are connected + side snatches electrons from - side. (And if there is a medium, conductor, then first electrons are taken from conductor that in turn snatches from - side, which not being able to keep electrons lose them and give up those electrons, we label it as excessive.)

The analogy i was taught with used marbles in pipe... When one side has excessive marbles And this pipe is connected to other side that has no marbles the marbles will instantaneously start falling out so even though marbles from container with excessive marbles haven't traveled there yet, they still start falling because filled side marbles are pushing marbles in pipe and which in turn push the last marbles in pipe out.

1st, Aren't electrons pulled by atoms that can use more electrons, and not move because one side is overfilled with electrons so they can't wait to push some out.

Questions:

1. if I connect a conductor to positive side of a battery, shouldn't it make all electrons/marbles fall into empty container as empty container will pull marbles as atoms need electrons?


2. if I connect two batteries' only opposite sides to each other shouldn't they drain (balance the each other out, cancelling all - & + charges)?

Answer

There exists a similar question here.

This description of a voltaic battery solves the conundrum which the question raises:

If one connects the + and - of the same battery with no resistance, one shorts and discharges it anomalously. There should always be a resistance ( the lamp in the drawing) on the same battery.It is clear in the diagram that a chemical path exists, a current of ions that closes the circuit and current flows.

A chemical circuit has to be closed for current to flow. Two different batteries have two different chemical flows . Electrons that might leave the anode to go to the cathode of the other battery cannot close the chemical circuit of the parent cell because the ions have no reason to move as no charge has gone to the copper cathode of the original cell. At the same time the second cell is at the same fix , as no chemical circuit is closed there too, no charge has left the zinc anode, no motion of ions possible.

quantum field theory - Vacuum Expectation Value and the Minima of the Potential

Often times in quantum field theory, you will hear people using the term "vacuum expectation value" when referring to the minimum of the potential $V(\phi )$ in the Lagrangian (I'm pretty sure every source I've seen that explains the Higgs mechanism uses this terminology).

However, a priori, it would seem that the term "vacuum expectation value" (of a field $\phi$) should refer to $\langle 0|\phi |0\rangle$, where $|0\rangle$ is the physical vacuum of the theory (whatever that means; see my other question).

What is the proof that these two coincide?

newtonian mechanics - Can torque relations actually be *derived* from Newton's Laws, or is it something extra?

For a long time I have wondered if there is a way to show that the rotational analogs of Newton's Laws are a direct consequence of just those laws, or are we adding more to them?

I understand mathematically that we take Newton's second law and do "r cross both sides," but that has always struck me as using more than just the 2nd law.

Here it matters where forces on the body are applied, but I don't see where Newton's Laws talk about points where forces are applied to a body. For translational motion it doesn't matter. So are we adding a sort of "extra law" when we do this for rotation?

The only thing I can think of would be to "disassemble" an extended body into differential point masses and work with internal constraint forces that make the body rigid. If every mass is just a point mass it would get around the issue I'm having. I've never seen any discussion along those lines, though.

electrostatics - Can a conductor run out of electrons to cancel external electric fields?

We have studied so far that electric field inside a conductor if no charge is placed inside is zero. But we know that every conductor has only a limited number of electrons. What happens when ALL the electrons have aligned to cancel the field inside conductor under application of external field and then we increase the field a little bit more certainly there are no more electrons to cancel the field and this additional field must be present inside the conductor now.

I know that practically under electric fields of magnitude that can drag out all electrons from the conductor's body to surface field emission and/or electrical breakdown would be taking place, But is this phenomenon theoretically possible ?