do the particles ever collide in QED

[Farsight]

ok, so what does " that is, it cannot be superposed onto it. " have to do with " Do you know also where does the negativity of the anti-proton
come from? " ?

Look at the two trefoils at the top of http://www.math.ist.utl.pt/~rpicken/tqft/ . They aren't the same. They can't be superposed. They have opposite chiralities. Think of the one on the left as the proton and the one on the right as the antiproton.

are you seriously saying that, the anti-proton is negative because of no symmetry ?
if you are referring to parity inversion, then i suggest looking into this with weak interactions.
becuase it is hard to find/ identify/define in stronger reactions.
i'm also suggesting looking into point reflection

Huh? We talk about positive and negative charge purely by convention. The antiproton has the opposite charge to the proton like an anticyclone is the opposite of a cyclone.

 

[krash661]

funny, (shakes head) i'm keen to your pretending and lack of comprehension.

 

[QuarkHead]

Look at the two trefoils at the top of http://www.math.ist.utl.pt/~rpicken/tqft/ . They aren't the same. They can't be superposed. .

Actually you mean superimposed, a graphical concept

Superposition refers to the fact that a quantum system in a state S can be said to be simultaneously in states A and B such that S = A + B, where the state S is quite different from either A or B

Interestingly, if the measurement of the state A gives the value a, and the measurement of the state B gives the value b, then the measurement of the state S at different times is either exactly a or exactly b (usually weighted by some statistic)

 

[PhysBang]

No, but she'd understand my explanation. See this thread where I likened electrons and positrons to cyclones and anticyclones.

Yes, see the thread in which Farsight refused to produce the necessary justification to establish that his ideas can do as well as the physics that he insults.

That thread is a great example of how Farsight simply cannot do physics: he refuses over and over again to produce evidence.

 

[Arlich Vomalites]

The positron is anti-matter. Not the electron.

Positron emission is a particular type of radioactive decay and a subtype of beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron.
http://en.wikipedia.org/wiki/Positron_emission

So there are anti-matter particles, positrons, inside nuclei of ordinary matter atoms.

Therefore it is also possible that there are ordinary matter particles, electrons, inside nuclei of anti-matter atoms.

Now, what's wrong with this picture?
View attachment 275

It is too easy to see what is wrong with that picture, why do you ask? Matter particles are electron and proton.
Anti-matter particles are positron and anti-proton.

 

[Fednis48]

I'm sorry, but I just have to ask. Farsight, what do you think a neutron is?

 

[Farsight]

Actually you mean superimposed, a graphical concept

Not specially. I stuck with krash's word because superposition also refers to "the overlapping of waves" and proton diffraction, demonstrates the wave nature of matter. There is no state S that's simultaneously in states A and B where A is a proton and B is an antiproton.

 

[Farsight]

I'm sorry, but I just have to ask. Farsight, what do you think a neutron is?

A "topological quantum field structure" that's only stable when braced by other structures. Think in terms of a slip knot which doesn't slip if you keep up the tension.

I played around with paper strips to try to visualize it. The picture below depicts Beta decay. The Weyl spinor symbol represent the antineutrino, the trefoil represents the proton, the Moebius represents the electron:

If you make everything on the right out of paper strips, then undo the ends and tape them all together, what you get is the thing on the left.

 

[Beer w/Straw]

Did you do the above with paper?

 

[PhysBang]

Did you do the above with paper?

I think he plagiarized that picture, or at least the idea, from a website.

 

[Beer w/Straw]

That would be pretty low.

 

[PhysBang]

That would be pretty low.

I'll try to find the original. I'm pretty sure it was in a link he posted somewhere.

 

[James R]

QuarkHead:

Just to put a cat among the pigeons........

$$F_{\mu \nu}$$ is not actually a tensor, it refers to the scalar components of a tensor when expanded on a tensorial basis, which can be represented in matrix form as
$$F_{\mu \nu} =\begin{pmatrix}0&-E_x &-E_y& -E_z\\E_x&0& B_x & -B_y\\E_y & -B_z & 0 &B_x\\E_z & B_y & B_x &0 \end{pmatrix}$$ where $$E_x \equiv \frac{\partial \mathbf{E}}{\partial x}$$ etc And assuming (as I did there) that $$\mu$$ references the rows and $$\nu$$ the columns, it is easy to see that the matrix elements may be separately or severally zero - i.e of a magnetic or electric nature only - but still allowing the notation $$ F_{\mu \nu}$$ for the components of this tensor

Yes. A tensor is certainly not the same as its components in a particular basis. I suppose I should have said something like $$F$$ is the tensor, and $$F_{\mu \nu}$$ are its components.

Note also that we are here talking about a tensor field (Jackson's comment makes no sense otherwise). It is common for physicists to say "a vector" or "a tensor" when in reality they are talking about fields. They are BAD BOYS.

I plead guilty as charged, your Honour. Physicists are often a bit cavalier with precise mathematical terminology, at least when the meaning is clear (they think...). Thus, it is not uncommon to see things like "The electric field is a vector", when we should write "The electric field at a point is a vector" or "The electric field is a vector field".

That said, consider this. Suppose a n-manifold (don't get excited - $$R^n$$ for any strictly positive integer n is a manifold) and that X, Y, Z,..... are tensor fields. Then let me write $$\mathfrak{X}$$ for the set of all such fields on my manifold. Since $$\alpha X + \beta Y \in \mathfrak{X}$$ for arbitrary scalars $$\alpha,\,\,\beta$$, it follows that $$\mathfrak{X}$$ is a vector space (this is just the definition of a vector space), so that, since elements of a vector space are vectors (obviously) then a tensor field is a vector.

Heh. Yes.

It's this kind of thing that makes mathematics such a joy for the unitiated, isn't it?

 

[exchemist]

QuarkHead:


Yes. A tensor is certainly not the same as its components in a particular basis. I suppose I should have said something like $$F$$ is the tensor, and $$F_{\mu \nu}$$ are its components.


I plead guilty as charged, your Honour. Physicists are often a bit cavalier with precise mathematical terminology, at least when the meaning is clear (they think...). Thus, it is not uncommon to see things like "The electric field is a vector", when we should write "The electric field at a point is a vector" or "The electric field is a vector field".


Heh. Yes.

It's this kind of thing that makes mathematics such a joy for the unitiated, isn't it?

Actually James, speaking as a non-specialist in this area, I find "The electric field is a vector" is a fairly incomprehensible statement, whereas "The electric field at a point is a vector" makes everything crystal clear. So it's more than mathematical pedantry, I think.

 

[Farsight]

...whereas "The electric field at a point is a vector" makes everything crystal clear...

Oh, so it's crystal clear is it? So which way is this vector pointing? Inward for an electron and outward for a positron? If so, when I've set down two particles that move linearly apart, why can't you tell whether they're electrons or two positrons? And when I set down an electron and a positron which move linearly together, why can't you tell which is which?

 

[Arlich Vomalites]

Remember this: hydrogen atoms don't twinkle, magnets don't shine.

Do the photons radiate?

Explain why they don't.

 

[Farsight]

According to the very-precise theory called quantum electrodynamics, electromagnetic force is said to be mediated by virtual photons. People think that these are real photons that pop in and out of existence like magic, but they aren't. They're "field quanta". It's like you take an electromagnetic field and divide it into arbitrary abstract chunks for the purposes of calculation. And this calculation works because when an electron and a proton move towards one another to make a hydrogen atom, they "exchange field" such that the hydrogen atom has very little field remaining. But they aren't throwing photons at one another. Virtual photons aren't real photons. They're field quanta.

 

[tashja]

I have the following question: do the particles ever collide into each others in QED?

Or do the particles only act on each others from distance? The thing that that Einstein rejected as spooky
action at distance.

Look at the following picture where two ice skaters act on each others from distance by throwing an invisible
ball back and forth between them:

https://www.hep.ucl.ac.uk/undergrad-projects/3rdyear/photons-at-HERA/guage.htm

There seems to be a spooky action at distance that the two ice skaters have on each others.

Prof. Don Lincoln:

In the Standard Model, electrons don’t physically collide. They have (effectively) zero size and the interactions are from exchanged photons. It is possible (in my opinion likely, but this is only my opinion) that electrons are themselves composite objects. If this is true, there will be a point at which a different physical theory beyond QED must be invoked.

However, to the level of precision available to modern experiments, this conjecture is not true. Two point-like electrons can be shot arbitrarily close to one another and they never interact except by exchanging photons.

Hope this helps.

D

 

[QuarkHead]

Oh, so it's crystal clear is it? So which way is this vector pointing?

Ya know Farsight, the concept of a "vector pointing" is something you should grown out of many years ago. Clinging to this childish notion is what leads you to your....er childish analogies.

I doubt you will bother reading the following, but others may (or may not) be interested.

A vector space $$V$$is defined as

1} a set of mathematical objects that is closed under arithmetic addition - $$u+v=w \in V$$.....

2) ......together with a scalar field $$\mathbb{F}$$ (usually but not always the Real or Complex numbers) such that $$\alpha v \in V$$.

No mention of "pointing" or "direction". It follows that any object with these properties is a vector. Of possible relevance here, consider the Schrodinger wave function $$\psi$$ in QM. Since these functions describe the state of a quantum system, and since they have all the properties above, they are called "state vectors". P.A.M Dirac introduced the notation $$|\psi\rangle$$ for these state vectors and called them "kets"

The very notion of a state vector "pointing" is ludicrous, as I am sure you will agree.

BTW James - for miscreants who use the term "a vector/tensor" when they are referring to fields, the Math Police tend to allow them off with a caution, since their algebras are identical, at least for all practical purposes

 

[exchemist]

Oh, so it's crystal clear is it? So which way is this vector pointing? Inward for an electron and outward for a positron? If so, when I've set down two particles that move linearly apart, why can't you tell whether they're electrons or two positrons? And when I set down an electron and a positron which move linearly together, why can't you tell which is which?

Yes. It is crystal clear. To me, at least.