Another good resource for general phyisics is 'Motion Mountain' - not as dry as Feynman's lectures with lots of little puzzles and interesting side stuff to keep one entertained.
Feynman diagrams for dummies (like me)!
1. The diagrams are made up of arrowed lines which represent matter particles, and wiggly lines which represent force exchange particles.
2. The point where the lines join, the vertex, represents an interaction.
3. Matter particles are indicated by arrows which point from left to right and antimatter particles are indicated by arrows which point from right to left.
Above, the right pointing arrow is an electron and the left pointing arrow is a positron. The wiggly line is the force exchange particle - a gamma ray photon.
4. Feynman diagrams are read from left to right.
In the first diagram an electron and positron annihilate each other, producing a photon which then produces another electron-positron pair. In the second diagram, an electron interacts with a passing positron via an exchange photon, without ever touching the positron.
All this, and much more, is to be found here: Quantum Diaries
1. The diagrams are made up of arrowed lines which represent matter particles, and wiggly lines which represent force exchange particles.
2. The point where the lines join, the vertex, represents an interaction.
3. Matter particles are indicated by arrows which point from left to right and antimatter particles are indicated by arrows which point from right to left.
Above, the right pointing arrow is an electron and the left pointing arrow is a positron. The wiggly line is the force exchange particle - a gamma ray photon.
4. Feynman diagrams are read from left to right.
In the first diagram an electron and positron annihilate each other, producing a photon which then produces another electron-positron pair. In the second diagram, an electron interacts with a passing positron via an exchange photon, without ever touching the positron.
All this, and much more, is to be found here: Quantum Diaries
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I've always struggled with Feynman diagrams, but my understanding is it is a virtual particle on the central wiggly line, not a real photon. More research needed:
Motion Mountain - The Captivating Free Physics Pdf Book
Rather good books IMO. I have already learned that Spin 3/2 particles exist. They are 3 component nuclei, certain atoms, and maybe excited states of Baryons like protons.
240 degree symmetry. 2/3 turn. How weird is that? Maybe this 1/3 and 2/3 charge business might make sense? 😕
Motion Mountain - The Captivating Free Physics Pdf Book
Rather good books IMO. I have already learned that Spin 3/2 particles exist. They are 3 component nuclei, certain atoms, and maybe excited states of Baryons like protons.
240 degree symmetry. 2/3 turn. How weird is that? Maybe this 1/3 and 2/3 charge business might make sense? 😕
That is correct.
The external arrowed lines correspond to incoming or outgoing particles. The internal wiggly lines represent virtual particles that can never be directly observed.
The virtual photon, in each case, mediates the interaction between the electron and the positron.
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Thanks go to you for that information, and to Steve for the link: Motion Mountain - The Captivating Free Physics Pdf Book
I've downloaded the files on 'Relativity and Cosmology' and 'The Quantum of Change'. 😎
In the light of Steve's comment, I see my explanation of Feynman diagrams is in need of slight revision. I hope I'm not labouring the point! 🙂
Feynman diagrams represent the interactions beween elementary particles.
1. The diagrams are made up of arrowed lines which represent matter particles, and wiggly lines which represent virtual particles (force exchange particles).
2. The point where the lines join, the vertex, represents an interaction between particles.
3. Matter particles are indicated by arrows which point from left to right and antimatter particles are indicated by arrows which point from right to left.
Above, the right pointing arrow is an electron and the left pointing arrow is a positron. The wiggly line (the gamma) is a virtual photon - a force exchange particle.
4. Feynman diagrams are read from left to right.
In the first diagram an incoming electron and positron annihilate each other, producing a virtual photon which then produces an outgoing electron-positron pair. In the second diagram, an incoming electron interacts with an incoming positron via a virtual photon, without ever touching the positron.
Feynman diagrams represent the interactions beween elementary particles.
1. The diagrams are made up of arrowed lines which represent matter particles, and wiggly lines which represent virtual particles (force exchange particles).
2. The point where the lines join, the vertex, represents an interaction between particles.
3. Matter particles are indicated by arrows which point from left to right and antimatter particles are indicated by arrows which point from right to left.
Above, the right pointing arrow is an electron and the left pointing arrow is a positron. The wiggly line (the gamma) is a virtual photon - a force exchange particle.
4. Feynman diagrams are read from left to right.
In the first diagram an incoming electron and positron annihilate each other, producing a virtual photon which then produces an outgoing electron-positron pair. In the second diagram, an incoming electron interacts with an incoming positron via a virtual photon, without ever touching the positron.
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I think I might be getting the idea here. Read a Feynman diagram from left to right. Though the more likely outcome is an Electron and a Positron collide with the release of two or three real Gammas depending on spin orientation.
I was yakking with my old Bedford College, London Science mate Physiologist Doctor Cliff tonight on the phone. How we used to laugh at some of the nonsense the College used to perpetuate. "The Pig on the Roof"! "The Brains of the Physiology Department"! The midnight burning of dead bodies from dubious animal experiments. He still has our ruthless magazine expose of this stuff. 😱
I thought this library washroom graffiti was goodish:
"Heisenberg probably rules OK." 🙂
Cliff told me that Heisenberg's old House has been adorned with a supplemental plaque:
"Heisenberg probably lived here." 😀
I was yakking with my old Bedford College, London Science mate Physiologist Doctor Cliff tonight on the phone. How we used to laugh at some of the nonsense the College used to perpetuate. "The Pig on the Roof"! "The Brains of the Physiology Department"! The midnight burning of dead bodies from dubious animal experiments. He still has our ruthless magazine expose of this stuff. 😱
I thought this library washroom graffiti was goodish:
"Heisenberg probably rules OK." 🙂
Cliff told me that Heisenberg's old House has been adorned with a supplemental plaque:
"Heisenberg probably lived here." 😀
Yes, all the particles are moving from left to right.
Confusion can arise because of the arrows on the particle lines, which do not indicate the direction in which the particles are moving, but merely denote whether the particles are matter or antimatter.
I recall there were not just one, but two PBS Nova episodes dedicated to Feynman, one before and one after his death. In one of them he told a story about being out camping in some national park somewhere, and a stranger coming up to talk: "He said 'excuse me sir, why do you have Feynman diagrams painted on the side of your van?' I told him, well, I'm Richard Feynman."
The Feynman diagram for electron-positron annihilation, where the final state is two gamma photons, is shown below.
The diagrams of electron-positron interaction shown in my simplified tutorial are illustrated here: Bhabha scattering - Wikipedia
They're a starter for ten, but quantum electrodynamics quickly goes over my head!
I'll give Feynman diagrams a rest before I get well out of my depth. 😱
As Feynman himself said in 1967, "I think that I can safely say that nobody understands quantum mechanics".
I'll give Feynman diagrams a rest before I get well out of my depth. 😱
As Feynman himself said in 1967, "I think that I can safely say that nobody understands quantum mechanics".
On an earlier theme:
Mark Hanhardt explains why he does fundamental research and discusses its benefits.
Why Do Fundamental Research? | Interactions
Mark Hanhardt explains why he does fundamental research and discusses its benefits.
Why Do Fundamental Research? | Interactions
There was a bio on him a while ago on MSN with that letter. Bummer.
I'm getting a lot of science/quantum physics articles on my browser lately.
I'm getting a lot of science/quantum physics articles on my browser lately.
I always thought Quantum Mechanics was rubbish. 😱
Until I watched Sidney Coleman.
Sidney Coleman, Quantum Mechanics in Your Face [1994] - YouTube
He and Dick Feynman and Lenny Susskind attended a Dinner Party together. Friends.
Leonard Susskind: My friend Richard Feynman - YouTube
Just my opinion. But three great Physicists. As Lenny said, we can only attend to our own sandwiches. As a tribute to Dick, cut out the Baloney. 😀
Until I watched Sidney Coleman.
Sidney Coleman, Quantum Mechanics in Your Face [1994] - YouTube
He and Dick Feynman and Lenny Susskind attended a Dinner Party together. Friends.
Leonard Susskind: My friend Richard Feynman - YouTube
Just my opinion. But three great Physicists. As Lenny said, we can only attend to our own sandwiches. As a tribute to Dick, cut out the Baloney. 😀
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The problem with quantum physics is that it not only contradicts our everyday experience, but it goes against our very concept of reality.
The idea that an electron which has a high chance of being found on the screen of my old computer monitor actually has some chance of being found on the far side of the Moon, or in my pint of Feynman's beer, goes beyond my understanding!
Yet, quantum theory has never failed a test. And it's been tested more than any other theory in science.
Fortunately, the probability that massive objects will arrive at the destination predicted by Newtonian mechanics is very nearly one. Hence large objects move just as predicted by Newton.
What I learned from watching Sidney Coleman is that Quantum Mechanics is right. 😀
Not a comfortable experience. 🙄
Thanks to M'Learned friend Bonsai, we know have in excess of 3000 pages to get through before drawing any conclusions.
Online Reading of Motion Mountain - The Physics Textbook
This might take some time. I have downloaded all 5 volumes. 😕
Not a comfortable experience. 🙄
Thanks to M'Learned friend Bonsai, we know have in excess of 3000 pages to get through before drawing any conclusions.
Online Reading of Motion Mountain - The Physics Textbook
This might take some time. I have downloaded all 5 volumes. 😕
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