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Link to thread of next article. Basic Feynman diagram of QED vs QCD Date: 1996/02/01
I have read in this newsgroup that one is not to make more of Feynman diagrams then one is right to, but here goes.
The basic Feynman diagrams for QED and QCD look the same, two straight lines and one curvy line are joined at a point.
But consider the basic Feynman diagram of QCD in "Quarks and Leptons" by F. Halzen and A. Martin, page 9. Here the basic Feynman diagram of QCD is shown in two similar representations, one as described above, and one by only two bent lines which don't join. This is hard to describe )=, but looks like: or Can we take this way of thinking with the basic vertex of QED? but now do it like Halzen does it for QCD or? So a virtual photon in the Feynman diagram might be thought of as an electron making a turn and thereby creating an electron-positron pair with the positron heading off with the initial electron as a virtual photon and the created electron heading off into the sunset?
Question, how would one transfer this idea to the same basic QED and QCD vertex when one thinks of particles not as points but as strings which sweep out a tube in spacetime?
Homework, an up electron at rest and in a moving frame? Date: 1996/03/25
The Dirac wavefunction of an electron at rest is?
Now this is the cool part, the above wavefunction is the only one we need. From it, transformations can be applied to the above wavefunction to get the wavefunction of an electron (or positron ?) with any spin and any momentum?
Consider the following transformations we we can apply to this wavefunction:
Homework:
1) discuss the effect of each of the transformations applied to the above wavefunction once. Contrast and compare how the transformations effect the spacetime part of the wavefunction [ exp(-iwt) ] and the spinor part of the wavefunction,
2) discuss the effect of any two of the above transformations applied one after the other, consider all 144 possibilities. Please be brief.
The wavefunction for a spin up electron at rest is
but in a moving frame the above wavefunction transforms to?
where
Homework, extra credit.
3) copy the above wavefunction and the above transformations, and pin it on your wall. get mystical with this pin-up for no more then one hour, write down your comments.
4) what is the connection between the Dirac wavefunctions and the quantum field theory view of the electron.
5) when an electron leaves a track in a bubble chamber (high energy physics kind of thing) how is one to think of such an event using the above wavefunctions and in the quantum field theory approach to the electron.
6) come up with your own questions and write them down, try to answer them.
Homework due on sci.physics by 29/3.
You may work together but everyone should understand the answers he hands in.
Re: Speed of Gravity is c? Date: 1996/04/12
In article <4ki3gr$1d1o@news-s01.ny.us.ibm.net> darac@ibm.net writes:
> How about proposing an experiment which will set bounds on the speed of gravity? > > Bob Chapman
Do the following two experiments.
1 measure the force between two masses
2 measure the rate that a gyroscope (which is in a polar orbit around some spinning mass, say the earth) axis changes its orientation
Now one can use this information to determine the speed of gravitational radiation ?
Link to thread of next article. When GR weds QM, what are likely offspring? Date: 1996/04/19
When SR was wed to QM by Professor Dirac we got spin and anti-matter. Do we have any clues what we might get if and when GR weds QM?
Link to thread of next article. Re: What is equivalent of K.E. in EM wave? Date: 1996/01/08
In article <19960107.161224.357@vnet.ibm.com> jonathan_scott@vnet.ibm.com (Jonathan Scott) writes:
> If a continuous transverse sine wave propagates through a material > medium, each element of the material oscillates to and fro with > approximately constant extra energy, having kinetic energy at the middle > of the oscillation and mechanical potential energy at either end. > > In an electromagnetic wave propagating at c, the energy density averaged > over complete cycles is consistent with the assumption that the > instantaneous energy density is given by epsilon_0 (E^2 + (cB)^2)/2, but > it seems that this quantity only corresponds to the potential energy in > a mechanical wave, being zero at nodes in the wave (along with E x B, > Poynting's vector, which represents energy flow in this case). > > Clearly, from Maxwell's equations, there is plenty going on with the > derivatives at the nodes of an E/M wave. Is there a quantity in there > which can be matched up with the kinetic energy in the mechanical wave? > Or does the energy in an E/M wave really come in blobs, one half-cycle > at a time? > If there is something (a medium :) then the distortion of the medium could correspond to the electric field and the relative motion (and the kinetic energy?) of the medium would correspond to the magnetic field. So in a plane E&M wave at a point where the electric field is maximum this could correspond to a maximum distortion of the medium :) and a quarter cycle later the medium would then have maximum velocity corresponding to maximum magnetic field. But we all know that with a plane wave the magnetic and electric fields max out together :( . Hey, so I'm off by 90 degrees :)
If a charge causes the medium to distort (or is the distortion) with an amount proportional to 1/r^2, then when the charge moves the medium will readjust itself and this flow of the medium could be the magnetic field.
> Jonathan Scott > jonathan_scott@vnet.ibm.com or jscott@winvmc.vnet.ibm.com
Re: megaphones with English in and Spanish out with only a small time delay? Date: 1996/01/16 ale2 (ale2@psu.edu) wrote:
> Do they have Walkman sized things with the name Sony on it, that you > speak in one language and then when you play it back, what you said > comes out in another language? They have just about solved voice > recognition haven't they? > > Or do they have World Internet? Where if i look at a Russian net > article that is originally written in Russian it is automatically > translated into English or any other language I might choose?
Is this April fools day, or are you really asking this?
People who hold the opinion "there's no such thing as a stupid question" obviously haven't seen too many of your questions. -- Ben Bullock @ KEK (national lab. for high energy physics, Tsukuba, Japan) e-mail: ben@theory.kek.jp www: http://theory.kek.jp:80/~ben/ 1-1 Oho, Tsukuba, Ibaraki 305, Japan. tel: 0298 64 5403, fax: 0298 64 7831
Link to thread of next article. Re: Back to the Ether? Date: 1996/01/15
We conceive for ourselves symbols or images of external objects, and the form that we give them is such that the necessary consequences of the images in thought are always the images of the necessary consequences in nature of the things pictured.
-------------------Heinrich Hertz(1894)
Link to thread of next article. Is physics physical? (was: Re: Neutrinos do not have mass...) Date: 1996/01/15
In article <billa-1301960047150001@user10.znet.net> billa@znet.com (Bill Arnett) writes:
> In article <4d5ibg$edk@marina.cinenet.net>, vergon@cinenet.net (Vertner > Vergon) wrote: > > >... Physics is *physical* and the physical can be visualized (at least > approximately) ... > > There seems to be a lot of drivel on this thread, but let me take it to a > more interesting turn: is the above statement really true?
If you think you have some theory that is right, I don't =(
> Obviously, SR > and QM are pretty hard to visualize.
Yep, or we would of heard about it.
> Does that make them "incorrect"? > Obviously not, in the conventional sense of "correct" i.e. that it matches > the data. But does it mean that there MUST BE some grander theory of > which SR and QM are subsets that both matches the data
I think so.
> AND is easily > visualized?
Not a chance.
> Clearly, we would all like that to be so. But our > preferences do not influence nature. I applaud anyone who tries to make > such a theory SO LONG AS it still matches the data
Only fair.
> (at least most of it).
Ok, 95% of it.
> But in the absence of a successful theory of that sort what are we to do?
Do what you got to do.
> Must we accept that the world is bizarre or that our minds are just not > capable of intuitively grasping the subtleties of nature? > I guess the question comes down to "is the real world such that an > accurate visualizable model of it can be constructed in a human mind?"
Mathematicians come up with some pretty wild stuff, ask them for advice, or come up with your own ideas, we do have a lot of clues.
> or > "is there some sort of isomorphism between our minds and the real world?" > It seems to me that our minds were evolved so as to be able to generate > models of the ordinary everyday world. Nothing in our evolutionary > history had anything to do with the world at the microscopic level or at > very high speeds or high gravitational potentials. If the ordinary world > is really as different from the world of QM and SR as it seems to be from > the data we have, then it may very well be the case that our minds just > can't grasp it intuitively. I see nothing a priori wrong with this > notion, depressing though it may be.
Don't find it depressing(well not today) because today I think it can be grasped. > > -- > Bill Arnett "Science is a way of trying > billa@znet.com not to fool yourself." -- Feynman > <URL:http://www.seds.org/billa/arnett.html>
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