Online reading assignment: QED, strong, weak interactions

Physics 205B, spring semester 2019
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

"The Feynman family poses by the famous camper"
Ralph Leighton
symmetrymagazine.org/article/may-2014/saving-the-feynman-van

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"In a Feynman diagram matter particles and force particles interact with each other."

"Quantum electrodynamics can be explained simply with the feynmans diagrams. Electrons that are going toward eachother will emit a photon which causes the repel of one another. The positron and electron can annihilate into photons which is detectable."

"Feynman diagrams contain one line going in, one coming out, and one squiggly (or else invalid). Positrons annihilate electrons."

"How to draw a Feynman and for the most part what I means with the particles and the photons. I am starting to understand how to read the diagrams for example what kind of interaction is happening."

"A system can borrow some energy for a long time or a lot of energy for a short time. This meaning that if a system creates a highly energetic virtual particle, then that particle is shorter-lived."

"About as much as I did after the last lesson. I'm starting to get what we covered last lecture in class but I'm still really fuzzy on a lot."

"I understand nothing."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"A lot of this material from the reading was really hard for me to understand. I struggled the most with figuring out the charges on photons, pions, etc."

"I'm having a hard time understanding the section in general. I kind of get how to read the Feynman Diagrams, but other than that I don't get the conceptual meaning behind it all."

"ALL OF THE THINGS."

"Pretty much everything."

The above (valid) Feynman diagram depicts an electron exerting a (repulsive) electric force on another electron. The charge of the "virtual" photon (γ) exchanged between them is:

negative.	**** [4]
zero.	************** [14]
positive.	*** [3]
(Unsure/guessing/lost/help!)	***** [5]

The above (valid) Feynman diagram depicts two nucleons exerting (attractive) forces on each other. The charge of the pion (π) exchanged between them is:

negative.	**** [4]
zero.	** [2]
positive.	************ [12]
(Unsure/guessing/lost/help!)	******** [8]

The above (valid) Feynman diagram depicts weak force interaction between a proton and a electron. The charge of the "intermediate vector boson" (W) exchanged between them is:

negative.	*** [3]
zero.	**** [4]
positive.	********* [9]
(Unsure/guessing/lost/help!)	********** [10]

The (valid) Feynman diagram in the previous question above depicts a(n) __________ decay process.

α.	* [1]
β+.	***** [6]
β–.	* [1]
electron capture.	****** [6]
γ.	** [2]
(Unsure/guessing/lost/help!)	********** [10]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I'd like to know what is these symbols in the diagram and be able to read them."

"Can you go over the diagrams again and how to read what the letters mean? I'm having trouble understanding."

"I think I will be fine after having a lecture on this material. I am just wondering how much of this we are going to need to know since we have one week left of class."

"For future classes, would there be any way to break up the QED readings into a more digestible form? Or break up the readings into smaller chunks? I think that might help to keep people from being overwhelmed by the amount of confusing information in the readings. I know that makes a lot more work for you, but I think it could help. Even if you didn't do anything with it, I think it could be helpful if you warned people to take it in small chunks over multiple days (I'm a chronic procrastinator, so I definitely didn't do that, but a heads up might help future classes) :) Keep up the hard work! The semester is almost over :)"

Online reading assignment: Feynman diagram vertices

Physics 205B, spring semester 2019
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

The Big Bang Theory (Pilot)
Warner Bros. Television (2007)
bigbangtheory.wikia.com/wiki/User_blog:Sheldon_Cooper_PhD/Pilot

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Feynman diagrams show the interaction of matter particles and force particles. Their interaction is at the vertex of lines where there must be an arrow pointing into the vertex and an arrow pointing out of the vertex. A squiggly line represents a photon, it is placed at the intersection of these lines representing electrons and positrons. Electrons and positrons form photons when they interact."

"e+ is a positron, e- is an electron and the gamma is a photon. Positron has a left facing arrow, electron has a right facing arrow and photon is the squiggle line."

"Positrons annihilate electrons."

"In Feynman diagrams there are two kinds of lines: one straight with an arrow and one wiggly. There can only be connected pieces with on arrow going into the vertex and one coming out."

"We read the diagrams left to right. They represent particles like positrons, electrons and photons."

"I am feeling lost."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"The orientation of the diagrams is confusing. I do not understand the significance of these particles and forces moving in a certain direction over time."

"The more complicated Feynman diagrams were hard to understand. The rules are hard to keep up with, might need more examples in class."

"I think utilizing the diagrams in a useful way is challenging to me."

"What internal/virtual particles actually are."

"How to draw them and how to interpret them. The diagrams just look like particles bouncing off each other creating photons."

"I found the interpretation of the diagrams to be a bit confusing at first but it got better with more practice. The only issue is when there are multiple interactions trying to see the big picture of what is being told."

"Pretty much all of it. I was understanding it at the very beginning, but then towards the middle/end I got completely lost and my brain couldn't handle any new information."

"It is all very daunting but with some practice it seems possible to understand. For right now how to draw one is clear but everything else that goes with understanding this type of diagram is beyond me."

"I'm struggling. Please help."

"The Feynman diagrams are a bit confusing. Some review on them would be really helpful."

"The reading was straightforward."

When reading Feynman diagrams, time runs from:

bottom to top.	* [1]
top to bottom.	*** [3]
left to right.	******************** [20]
right to left.	* [1]
(Unsure/guessing/lost/help!)	******* [7]

Describe how the path of an electron and the path of a positron are drawn differently on a Feynman diagram. (Note that both paths have the same "e" labels.)

"The electron moves from left to right and the positron moves from right to left."

"Electrons have arrows pointing left to right, positrons right to left."

"I'm not sure."

"I'm struggling. Please help."

"I will be getting back to this after Wednesday. "

Describe what will happen if an electron meets a positron.

"Explosion."

"They annihilate each other."

"They destroy themselves mutually."

"A photon is formed."

"Annihilation occurs and a photon is emitted, which could later creates a new electron and positron."

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	** [2]
emitting a photon.	*********************** [23]
annihilated by a positron.	* [1]
(Unsure/guessing/lost/help!)	****** [6]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	**** [4]
emitting a photon.	***** [5]
annihilated by a positron.	******************* [19]
(Unsure/guessing/lost/help!)	**** [4]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	********************* [21]
emitting a photon.	****** [6]
annihilated by a positron.	[0]
(Unsure/guessing/lost/help!)	***** [5]

Explain why the above Feynman diagram is invalid.

"Must have one arrow going into the vertex and one arrow coming out of the vertex."

"The particles cannot go on the same direction where they meet the vertex. One must be going away from the vertex."

"Two electrons cannot form a photon."

"Both arrows are going in when it needs to be going in and then out."

"It violates rule 2 for Feynman diagrams, which follows a theory of quantum electrodynamics. It is an incomplete diagram of annihilation, matter and antimatter colliding."

"The electrons are both annihilated which is inaccurate?"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I was confused on what exactly a photon is. Like is it just energy?" (Yes, in particular a form of energy that also carries momentum with it, and travels at the speed of light.)

"Feynman diagrams are confusing, yet interesting."

"The images really confused me, I think going over these GIFs would be helpful too!"

"I like these diagrams so far! I like how it is pretty easy to tell a story."

"Hi P-dog, I am sorry I have a chemistry midterm on Tuesday before our physics midterm and I have spent all of my time studying for that :/."

"I found this video from PBS to be very helpful in understanding Feynman diagrams, if you would like to share it." (This is great, just be aware that they are using the convention where time runs from bottom-to-top rather than from left-to-right.)

Online reading assignment: QED, strong, weak interactions

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

"The Feynman family poses by the famous camper"
Ralph Leighton
symmetrymagazine.org/article/may-2014/saving-the-feynman-van

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"We use lines and intersections to draw diagrams that represent particle interactions."

"I am beginning to better understand Feynman diagrams. I understand how time goes and what line is what."

"The decay processes are specific to what each electron is doing. They can all interact with each other in different ways with each process."

"A positively charged proton exchanges photons with a negatively charged electron, producing the Coulomb force of electrostatic attraction. The strong force holds the nucleus together."

"Feynman diagrams are drawings that depict the interactions of electrically charged particles and the virtual proton or photon particles that can be generated. In addition, all of these diagrams must have a particle moving in, a particle being moved out, and a photon being generated or else the electrical particle interaction is not possible."

"If energy is borrow a little amount will last a long time, but a large amount will last a short period of time. As well as the concept of photons, particles, and anti particles."

"In quantum mechanics, forces are attracted by exchanging virtual particles. Virtual means they are measurable by momentum, not mass. The force carriers for nuclear forces are pions. Protons and neutrons are baryons, a type of hadron. Pions are bosons with zero spin."

"I spent most of today reading my chemistry book for a quiz that thankfully is covering the different decay types and electron capture."

"I am really understanding Feynman diagrams. They are quite interesting now."

"The drawing of Feynman diagrams is making more sense now."

"I understand how to draw the diagrams but knowing exactly what they mean is still a little confusing."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"The reading was pretty heavy material. I anticipate lecture informing us on what we need to know."

"More time spent will clear up a lot of things I think, but right now I am very confused about all the different types of interactions and am looking forward to hearing about them in lecture."

"I'm not sure why we have to use Feynman diagrams to describe these sub-atomic reactions, why not write them out as a chemical reaction like the nuclear decay processes?"

"How to tell if something is positively or negatively charged on a Feynman diagram."

"I think I'm alright for now."

"Still confused with the Feynman diagrams, some of the Greek letters confuse me."

"Just need a general overview in class, this material is a lot and a bit dense for sure."

"I am confused when I try to interpret the diagrams. I understand the ABC (always balance charges) and CBA (cancellation by annihilation) rules along with the validity of each (1 line in/out, 1 squiggly). I do not understand how to interpret the diagram themselves. I do also understand that time moves left-to-right. Everything, so sorry."

The above (valid) Feynman diagram depicts an electron exerting a (repulsive) electric force on another electron. The charge of the "virtual" photon (γ) exchanged between them is:

negative.	**** [4]
zero.	********* [9]
positive.	******** [8]
(Unsure/guessing/lost/help!)	*** [3]

The above (valid) Feynman diagram depicts two nucleons exerting (attractive) forces on each other. The charge of the pion (π) exchanged between them is:

negative.	******** [8]
zero.	*** [3]
positive.	********** [10]
(Unsure/guessing/lost/help!)	*** [3]

The above (valid) Feynman diagram depicts weak force interaction between a proton and a electron. The charge of the "intermediate vector boson" (W) exchanged between them is:

negative.	** [2]
zero.	********** [10]
positive.	******* [7]
(Unsure/guessing/lost/help!)	***** [5]

The (valid) Feynman diagram in the previous question above depicts a(n) __________ decay process.

α.	* [1]
β+.	********* [9]
β–.	***** [5]
electron capture.	**** [4]
γ.	* [1]
(Unsure/guessing/lost/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"For antimatter, do paths always travel reversed (right-to-left) with respect to time?" (Yes, that's the convention we're using with these Feynman diagrams, although antimatter doesn't literally go backwards in time.)

"I really want to understand every single lessons that we did (even though I do okay in general) before learning new contents... It really bothers me to be so slow to understand the concepts."

"Please go over examples above."

Online reading assignment: Feynman diagram vertices

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

The Big Bang Theory (Pilot)
Warner Bros. Television (2007)
bigbangtheory.wikia.com/wiki/User_blog:Sheldon_Cooper_PhD/Pilot

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Feynman diagrams are used to describe the interactions between electrons and positrons. The interactions of electrons and positrons can resulting in absorbing a photon, emitting a photon, or a electron being annihilated by a positron."

"Lines in these diagrams represent particles. Every particle has to meet at an intersection that is called an interaction. You can't have a vertex with only squiggly lines (photons) with no particle lines flowing into or out from it."

"Feynman diagrams are how we can visualize particle physics, specifically the interactions of electrons, positrons, and photons. We read the diagrams left-to-right, as they are a representation of what happens over a certain amount of time."

"The Feynman diagrams are meant to indicate the path that the particles take through space. We interpret the x-axis as the direction of time and the y-axis as the space direction."

"A left-to-right arrow is an electron, the opposite is a positron and a wiggly line is a photon. the rest is very vague and I need more explanations on various cases and what they mean."

"Positrons point to the left, electrons point to the right. Gamma (squiggly line) are photons. A Feynman diagram should only contain connected pieces, and any diagram with arrows going into a gamma needs arrows coming out or else it isn't an accurate diagram."

"Honestly, there wasn't much I understood."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"Everything. I don't get Feynman diagrams."

"Why do we use Feynman diagrams? They just seem like squiggles a 3 year-old could draw, why is there not another way to represent these forces interacting?"

"Is an electron moving in the opposite direction a positron? What actually is a positron?"

"All good so far."

"Specifically how the diagrams are to be used."

"I don't think I would really be able to interpret them on my own. It would be helpful to do this in class."

"This is all pretty trippy. I want to learn more about what diagrams are possible and which are not."

When reading Feynman diagrams, time runs from:

bottom to top.	[0]
top to bottom.	** [2]
left to right.	******************* [19]
right to left.	* [1]
(Unsure/guessing/lost/help!)	**** [4]

Describe how the path of an electron and the path of a positron are drawn differently on a Feynman diagram. (Note that both paths have the same "e" labels.)

"Electrons point right and positrons point to the left."

"A position is indicated as e+ therefore, the electron will always be drawn traveling from right to left. Meanwhile, an electron is indicated by an e- and will always be drawn traveling left to right. This way, when they are being read, we can see that the arrows are point in the direction of the flow of electron charge."

"Positrons (antimatter) point to the left, electrons point to the right."

Describe what will happen if an electron meets a positron.

"Annihilation will happen."

"They will cancel each other out and create pure energy."

"They make a big bang!"

"It becomes something else (the other symbol thing)?"

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	*** [3]
emitting a photon.	******************* [19]
annihilated by a positron.	* [1]
(Unsure/guessing/lost/help!)	*** [3]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	*** [3]
emitting a photon.	***** [5]
annihilated by a positron.	************** [14]
(Unsure/guessing/lost/help!)	**** [4]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	***************** [17]
emitting a photon.	* [1]
annihilated by a positron.	**** [4]
(Unsure/guessing/lost/help!)	**** [4]

Explain why the above Feynman diagram is invalid.

"Two arrows are going into the vertex. One needs to be going out."

"The two electrons cannot intersect at the same point how this one is depicted."

"The two electrons cannot crash like that."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"What are all these squiggles and arrows about?"

"A very basic lecture on what every symbol is called and what happens when they mix would be of great benefit."

"My mind is blown.:

Online reading assignment: QED, strong, weak interactions

Physics 205B, spring semester 2017
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

"The Feynman family poses by the famous camper"
Ralph Leighton
symmetrymagazine.org/article/may-2014/saving-the-feynman-van

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Quantum electrodynamics describes how light and matter interact. It is the first theory where full agreement between quantum mechanics and special relativity is achieved."

"Interactions of charged particles can create imaginary particles and violate energy conservation, as long as it is within the energy-time uncertainty principle. Sometimes imaginary particles will 'become real' if real particles leave the electron."

"Repulsive force between electron pairs and positron pairs occur because of a virtual photon being emitted, which exist as momentum. Virtual particles can phase in and out of existence spontaneously according to the energy-time uncertainty principle. There are four fundamental forces in the universe: electromagnetic, strong, weak, and gravity. Nuclear force, the force mediating proton-neutron interactions, also originates from emission of virtual particles."

"How to draw a single Feynman diagram and that there is an electron than can absorb or emit a photon into a positron and it can go the other way. There are also incorrect ways to draw Feynman diagrams and I know that time has to travel from left to right."

"You absolutely have to read the diagram from left to right, and I can tell you what's happening in the simpler diagrams."

"I have a strong grasp of Feynman diagrams from the online presentation as well as the introduction during our lecture of the previous week. These diagrams are visual and conceptual which makes easier to get a grasp of."

"Honestly, not much."

"Not a single thing."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I still have a hard time understanding how to draw a Feynman diagram. I still don't understand how to tell what is a virtual electron or photon."

"I'm not really sure how you tell the charge of the photon."

"I am a bit confused on how to determine the charge of some of the intermediate particles such as bosons."

"I find it confusing when the exchange particle is not drawn straight up and down, it makes me think it happens over time and is not an instant exchange."

"Everything."

"All of it! No really, I definitely do not get this."

The above (valid) Feynman diagram depicts an electron exerting a (repulsive) electric force on another electron. The charge of the "virtual" photon (γ) exchanged between them is:

negative.	*** [3]
zero.	************* [13]
positive.	**** [4]
(Unsure/guessing/lost/help!)	** [2]

The above (valid) Feynman diagram depicts two nucleons exerting (attractive) forces on each other. The charge of the pion (π) exchanged between them is:

negative.	** [2]
zero.	***** [5]
positive.	********** [10]
(Unsure/guessing/lost/help!)	***** [5]

The above (valid) Feynman diagram depicts weak force interaction between a proton and a electron. The charge of the "intermediate vector boson" (W) exchanged between them is:

negative.	**** [4]
zero.	*** [3]
positive.	******** [8]
(Unsure/guessing/lost/help!)	******* [7]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"One more week!"

"I <3 you P-dog. This year of physics has been great. Thank you so much."

"More explanation of gluons please!"

"Is it possible for me to ask this question from multiple parallel universes?"

"I am so so lost in this subject... lost as in like a dark post-apocalyptic place... so not a good lost."

"How do we know the virtual particles are there if we can't see them?"

"Please go over the more obscure particles, i.e. quarks, pions, etc."

"Interesting to see how this relates to the physical world!"

Online reading assignment: Feynman diagram vertices

Physics 205B, spring semester 2017
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

The Big Bang Theory (Pilot)
Warner Bros. Television (2007)
bigbangtheory.wikia.com/wiki/User_blog:Sheldon_Cooper_PhD/Pilot

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Feynman diagrams give us an easier way to understand the interactions of subatomic particles. Time is represented as going upwards and space is represented as going from left to right. These diagrams tell us what is happening between the interaction of two electrons."

"I was able to follow the drawing of Feynman diagrams, and I understand that if the arrow points from left-to-right, then it is an electron, but if the arrow is from right-to-left, then it is a positron. The wiggle line is a photon. Other than that it was kind of a lot of information to take in."

"Arrowed lines are electrons. Positrons while the wiggly lines are photons."

"You can only draw lines that touch if their arrows are not pointing in the same direction. One has to be going in while the other is moving out."

"The basic concepts and rules of Feynman diagrams, and basic examples."

"In theoretical physics, the Feynman diagrams is used as a representations of the mathematical expressions describing the behavior of subatomic particles using images."

"What’s really important are the endpoints of each line, so we can get rid of excess curves. You should treat each line as a shoelace and pull each line taut to make them nice and neat. They should be as straight as possible. (But the wiggly line stays wiggly!)"

"Not a single thing."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I'm still confused as to how orientation of the diagram relates to what is going on."

"Still a little unsure on how to read Feynman diagrams."

"I could use some more examples of the double-action diagrams because it's pretty hard just figuring out a one-vertex diagram."

"The diagrams and what the paths represent. I am having a difficult time to determine what path will be valid or invalid for the diagram."

"I need more clarification about the second part of the reading that talks about momentum conservation, loop diagrams, and attractive and repulsive forces. I want to be able to understand how it all fits with the diagrams that we learned to draw in the first section of the reading."

"I didn't find to much confusing. Although reading these diagrams can be challenging."

"Almost everything haha..."

When reading Feynman diagrams, time runs from:

bottom to top.	* [1]
top to bottom.	** [2]
left to right.	******************* [19]
right to left.	[0]
(Unsure/guessing/lost/help!)	*** [3]

Describe how the path of an electron and the path of a positron are drawn differently on a Feynman diagram. (Note that both paths have the same "e" labels.)

"Electrons move left to right, positrons move right to left."

"e^– are electrons and their arrows point from left to right and e⁺ are positrons (antimatter) and their arrows point in the other direction."

"The antiparticles are denoted by solid lines, but the arrow is reversed. The virtual particles, such as protons, can be seen as wavy or broken lines. Electrons are denoted by a solid lines with an arrow pointing in the direction of the travel"

"Drawn in opposite ways."

Describe what will happen if an electron meets a positron.

"An annihilation event occurs and gamma rays are produced."

"They will cancel each other out."

"From what I understand a photon will be produced."

"Boom!"

"Will turn into an Autobot or Decepticon?"

"They cancel each other out to make an 'anti-tron?'"

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	* [1]
emitting a photon.	****************** [18]
annihilated by a positron.	** [2]
(Unsure/guessing/lost/help!)	**** [4]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	***** [5]
emitting a photon.	**** [4]
annihilated by a positron.	************* [13]
(Unsure/guessing/lost/help!)	*** [3]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	*************** [15]
emitting a photon.	** [2]
annihilated by a positron.	**** [4]
(Unsure/guessing/lost/help!)	**** [4]

Explain why the above Feynman diagram is invalid.

"One of the straight lines needs to point to the left to denote that it is a positron."

"The arrows are pointing towards the vertex."

"The lines are pointing in the same direction. One should point inwards and the other outwards."

"There must be one arrow going into the vertex and one arrow coming out."

"Electrons can not crash into each other?"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Help reading the diagrams and giving correct interpretations...like in this homework assignment."

"So can we create positrons?" (Well, you just need to find unstable isotopes that undergo beta-plus decay.)

"How do they detect antimatter when electrons collide with positrons?" (An electron-positron annihilating each other will emit gamma rays, which have energies exactly equal to the mass that "disappears" (E = m·c²). This is how a PET scan (positron emission tomography) works, you are injected with a sugar solution that has unstable fluorine isotopes, which undergoes beta-plus decay (emitting positrons), and when this happens in certain places in your body that metabolizes this sugar, those positrons combine with nearby electrons to annihilate, and emit gamma rays from that location that are triangulated by a surrounding detector.)

"Is a squiggly line always a gamma ray?" (Yes, or more generally, any type of photon (light).)

"Can we hard core review this in class?"