Hey You Wonderful Person! I Just Started Studying Bio And Was Wondering If You Had Any Advice On Thinking

Hey you wonderful person! I just started studying bio and was wondering if you had any advice on thinking like a biologist?

hey you wonderful person as well and budding biologist!

Thinking like a biologist.. hmmm! never been asked something like this before, so this is great for me to think about it too! here are 7 “rules of biology” if you may, that i personally find truth in. it’s definitely not complete, and maybe not all 100% correct, since i am just one person. but it’s what i believe:

nothing in biology is absolute. this field is about as lawless as lawlessnes gets. for example: “smoking causes lung cancer”–yes, in some cases, but not everyone who smokes gets lung cancer, and not everyone who gets lung cancer smokes. because individuality exists in biology, it makes things complicated. that’s not to say there’s no rhyme or reason; it’s just that nothing happens in a vacuum/by itself so the answer to a lot things is: “well, it depends.” that’s why you’ll see a lot of words like “may”, “can”, “sometimes”, and “suggests” in biology.

science is a tool created by humans to understand nature. thus, science can never be 100% free from human bias and error. we try to be as unbiased and close to the truth as we can by using things like experimental controls and large sample sizes, but at the end of the day, sometimes science can still be flawed. and that’s ok! but we need to be able to edit past discoveries to what we know now. (and going off of that, I really don’t like that popular quote by neil degrasse tyson: “science is true whether you believe it or not”. that’s not accurate. what’s accurate is “NATURE is true” because humans doing science can be very very flawed)

going off of that, question everything. don’t accept something is true until the evidence is sound (ie. good study design, no false interpretation of data, reputable sources, etc). even if someone well respected in the field says something, doesn’t always mean it’s true. be your own advocate in finding out the facts.

sometimes the “outlier” can teach us the most. take cancer, for example. it’s definitely a non-normal state of health and being, but from it we learned so much about normal cellular and organ function. or how we’ve been able to discover some drug metabolism gene variations in certain populations because they didn’t respond well to a treatment during a clinical trial. a lot of knowledge in biology can come from studying what goes wrong or contrary to what we expected.

your personal ethics may be challenged at times. this is particularly applicable for things like: science vs religion, research on animal models, who and what gets funding priority (eg. a cancer drug with the potential for pharma companies to make billions vs a tropical disease that primarily affects poor communities?), the high cost of pharmaceuticals/health-care in general, open-access knowledge vs getting scooped, is it right to sequence every individual’s genome, etc. you will truly need to know yourself, especially your beliefs and your limits, to navigate these situations.

everything is connected, sometimes extending beyond the realm of biology. this is related to what can happen in a given situation is always “it depends”. everything affects everything; we–every living unit from microorganisms to cities–are all connected in some way. for example, recent research has shown certain populations of bacteria in our guts can alter our mental health, and it’s easy to see how that can change our day-to-day-life, which in turn can affect society in general.

never cease to be fascinated. the biology of nature is amazing, everything from the smallest virus to the largest ecosystem. no matter how jaded you may become later in your career, never let go of that childlike curiosity that first brought you to the field.

good luck and have fun on your adventure as a biologist :) and i’m always here if you need anything!

Tags

biology tips

Python as a first language: a roadmap to getting started.

I personally prefer Java as a first language. Put non-technically, it is a lot less convenient, so you get a more realistic idea of how computers work. Nonetheless, Python is an amazing language (with convenience as one of it’s values) so it makes sense as a gentle introduction. It’s also a popular language for data science and machine learning, so it’s great to have experience with.

The 3 ingredients you need to get started:

The Python Language Interpreter: when you write some code in a text file and save it as a .py file, the Python interpreter is what turns that code into commands that your computer can then actually preform. This is necessary.

An Integrated Development Environment (IDE): An IDE is like a helpful text editor for programming. Some basic features include auto-complete, typo and mistake catching, and automatic text coloring to make some parts of your code easier to find. This is optional but highly recommended.

Some learning resources: We’re going to need something about programming basics, problem solving in computer science, using an API, learning how to use google and stackexchange, data types, control structures, and then maybe an object-oriented programming intro, and eventually all the neat advanced features of the python language. Then we need to learn how to use Numpy (for scientific computing), Pandas (for easy data storage), and Tensorflow (machine learning!). Add some handy cheat-sheets for python, numpy, pandas, and Tensorflow, and we’re good to go.

Other posts will adress download, installation, and resources.

A curriculum:

Like I said up above, we need to know how to do the following. Save this and make it a checklist.

Learn to use google to answer questions about installing or using python, any packages, or computer science.

This also includes getting to know how to search Stackexchange, the website for coding questions n’ stuff.

How to install python 3 and get set up

How to install an IDE like Eclipse (with PyDev), IDLE, or Notebook++.

Programming basics: how does python work? What does the language look like? How does tabbing work?

Understand basic logic, including AND, OR, XOR, NOR, NAND, XNOR, Implies, and If…Else statements.

Variables: what are they, how do I set one and change it?

Basic math in Python.

Data types: what kinds of variables can I have? How does my computer store data? How do I use those types of data? What are the key commands and operations I know how to do?

Control structures: if, else, elif, for loops, while loops, break, continue

Methods! What are they, how do I make one, what can I do with it?

The open() command, the all() command, other neat built-in methods

<function name>= lambda <your variables>: <single line method>

Problem solving in computer science: now do fizbuzz.

What’s a package?

Importing packages, installing packages you don’t have with PIP

Using an API: how do I find one and how do I read it?

object-oriented programming in Python: what’s a class, how do I make one, how do I reference and instantiate one, methods, class vars, etc

Error handling: how to do exceptions

All the neat advanced features of the python language: iterators, generators, list comprehensions, enumerate, range, assert, with…as, etc.

Read through the Numpy API (for scientific computing), data types, matrices, stats, methods, etc. A short detour through scikit would be helpful.

Read through Matplotlib.pyplot API, plotting, plotting options, histograms, scatterplots, etc.

Pandas (for easy data storage), data frames, series, built-in operations on columns and rows, loading from a CSV, saving as a csv, apply, etc

Tensorflow (machine learning!) For basic stuff, shoot for knowing how to use the estimator package, which is discussed elsewhere on this blog. Also get to know the nitty gritty, including tensors, layers, tensorboard, etc.

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learning cs

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swirlspill-study

2 years ago

How to Study Like a Harvard Student

Taken from Sophia Chua-Rubenfeld, daughter of the Tiger Mother

Preliminary Steps 1. Choose classes that interest you. That way studying doesn’t feel like slave labor. If you don’t want to learn, then I can’t help you. 2. Make some friends. See steps 12, 13, 23, 24. General Principles 3. Study less, but study better. 4. Avoid Autopilot Brain at all costs. 5. Vague is bad. Vague is a waste of your time. 6. Write it down. 7. Suck it up, buckle down, get it done. Plan of Attack Phase I: Class 8. Show up. Everything will make a lot more sense that way, and you will save yourself a lot of time in the long run. 9. Take notes by hand. I don’t know the science behind it, but doing anything by hand is a way of carving it into your memory. Also, if you get bored you will doodle, which is still a thousand times better than ending up on stumbleupon or something. Phase II: Study Time 10. Get out of the library. The sheer fact of being in a library doesn’t fill you with knowledge. Eight hours of Facebooking in the library is still eight hours of Facebooking. Also, people who bring food and blankets to the library and just stay there during finals week start to smell weird. Go home and bathe. You can quiz yourself while you wash your hair. 11. Do a little every day, but don’t let it be your whole day. “This afternoon, I will read a chapter of something and do half a problem set. Then, I will watch an episode of South Park and go to the gym” ALWAYS BEATS “Starting right now, I am going to read as much as I possibly can…oh wow, now it’s midnight, I’m on page five, and my room reeks of ramen and dysfunction.” 12. Give yourself incentive. There’s nothing worse than a gaping abyss of study time. If you know you’re going out in six hours, you’re more likely to get something done. 13. Allow friends to confiscate your phone when they catch you playing Angry Birds. Oh and if you think you need a break, you probably don’t. Phase III: Assignments 14. Stop highlighting. Underlining is supposed to keep you focused, but it’s actually a one-way ticket to Autopilot Brain. You zone out, look down, and suddenly you have five pages of neon green that you don’t remember reading. Write notes in the margins instead. 15. Do all your own work. You get nothing out of copying a problem set. It’s also shady. 16. Read as much as you can. No way around it. Stop trying to cheat with Sparknotes. 17. Be a smart reader, not a robot (lol). Ask yourself: What is the author trying to prove? What is the logical progression of the argument? You can usually answer these questions by reading the introduction and conclusion of every chapter. Then, pick any two examples/anecdotes and commit them to memory (write them down). They will help you reconstruct the author’s argument later on. 18. Don’t read everything, but understand everything that you read. Better to have a deep understanding of a limited amount of material, than to have a vague understanding of an entire course. Once again: Vague is bad. Vague is a waste of your time. 19. Bullet points. For essays, summarizing, everything. Phase IV: Reading Period (Review Week) 20. Once again: do not move into the library. Eat, sleep, and bathe. 21. If you don’t understand it, it will definitely be on the exam. Solution: textbooks; the internet. 22. Do all the practice problems. This one is totally tiger mom. 23. People are often contemptuous of rote learning. Newsflash: even at great intellectual bastions like Harvard, you will be required to memorize formulas, names and dates. To memorize effectively: stop reading your list over and over again. It doesn’t work. Say it out loud, write it down. Remember how you made friends? Have them quiz you, then return the favor. 24. Again with the friends: ask them to listen while you explain a difficult concept to them. This forces you to articulate your understanding. Remember, vague is bad. 25. Go for the big picture. Try to figure out where a specific concept fits into the course as a whole. This will help you tap into Big Themes – every class has Big Themes – which will streamline what you need to know. You can learn a million facts, but until you understand how they fit together, you’re missing the point. Phase V: Exam Day 26. Crush exam. Get A.

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studying tips

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swirlspill-study

4 years ago

I think a lot about what it is to be a woman in science, but I have the inherent privilege that comes with being a white woman to shield me from the worst of it. I had an absolutely eye opening conversation with classmate of mine last year, and I’d like to share it with y’all.

This other lab member of mine became a great friend of mine around the time I decided to switch labs. She had a different PI and was a year ahead of me, so I was comfortable bringing my concerns to her. Her support was instrumental in my decision and my current happiness in my new lab. She presented in a lab meeting the day I went to the director of our grad school and requested a change in PIs, so I missed it. I knew she had been nervous (it was meant to prepare her for for her preliminary exam) so I asked her the next day how it had gone.

Now. To put this in context, I need to explain my old PI. He was an almost eighty year old white man, and if it wasn’t his opinion, it was wrong. He was very, very bad at being a PI. He was also probably worse at being a co-worker. I recall at least three lab meetings that devolved into him yelling with another PI, and several student presentations that he was terribly mean and unnecessarily fixated on insignificant details. So it comes as no shock that he went after my friend.

My old PI (who was not involved in bacteria research AT ALL) had taken some issue with the strain of bacteria she was using, one that was selected based on clinical relevancy. This had resulted in a dissolving of my friends presentation into him interrogating her about this strain, interrupting her explanations and generally getting louder and louder and louder until her PI stepped in. Upon hearing all of this, I apologized profusely for his behavior and asked how she was doing now. She expressed to me how she had struggled to remain calm, and how she was ultimately grateful to her PI for de-escalating the situation.

Now here’s the part that hit me hard: my friend explained to me that she was grateful mostly because she wasn’t sure how much longer she would have been able to withstand his nonsense without raising her voice, to which I responded, “he would have deserved it. You were right and he was wrong, and it’s beyond time he was put in his place. He’s not your PI, and he’s not on your committee, so I think you would have been wholly justified in standing up for yourself.”

“If I’d had raised my voice at him, even a little, I would have been labeled an angry black woman, and everyone in that room would have written me off as a stereotype of my race.”

Oh. Ohhhhh. OH that hit me in the heart and the brain and the soul and I’m shocked I didn’t get a bruise. My sweet, strong, smart friend, who was a mom and a wife and a brilliant student and a kind soul, had to weigh every word out of her mouth with a gravity I couldn’t understand, and had never considered until that moment. And it probably says a lot about my white privilege and my bubble I’ve grown up in that I was 24 years old before this came across to me. But this conversation has lived in my head ever since, and my perspective of the world shifted because of it. I think what made this particular incidence so eye opening to me was that being interrogated by this man over stupid details was something that happened to me regularly, and had just pushed me over the edge. Realizing some level of privilege had protected me all along from it being worse was enlightening.

I’ve benefitted my whole life from white privilege (a thing my family doesn’t think exists). I’m nowhere near perfect as an ally or a friend or a person, but I want to be better at standing up for and alongside those who need the protection my privilege offers. I share this now in case it resonates with someone else the way it did with me.

Black lives matter. Black people matter. Your hearts matter and your ideas matter and your feelings and your dignity and hurt and anger and fear. It shouldn’t require stating but it does, and I am so so sorry for your pain, for every situation I wouldn’t think twice in that you have to navigate carefully. I’m sorry, and I stand with you.

Tags

blm stories racism

780 notes View Post

swirlspill-study

2 years ago

I’m going to uni this autumn, and I feel like most of studyblr’s incoming freshmen are just as clueless as I am. Here’s a bunch of tips from the more experienced among us, and I hope it’s just as useful to you as it is to me!

this took forever to make so i’m really hoping it’s good

Money Matters

Textbooks

Sites where you can get free textbooks by @thearialligraphyproject

Get textbooks online

Tips for textbooks by @theorganizedcoyote

Websites to get cheap textbooks by @theorganisedstudent

Ultimate guide to buying college textbooks

Safe ways to get free textbooks

Saving Money

A girl called jack: eating under the line

Qriket

Scholarship masterpost by @wallcalendar

Save money while shopping online

College scholarships 2016-17 by @wonderstudying

Tips for finding & getting scholarships

How to budget

Where to find student discounts by @collegerefs

Searching for scholarships by @collegesmarts

Creative ways to save money in college

Places that offer discounts with student id

Ways to save/earn money

Paying for college by @collegerefs

Student Life

Dorm & Living

PSA for college freshmen

Dorm tips from @humanitaes

Ultimate school locker (uni bag) kit by @girl-studying

Resolving issues with roommates

Tips for living like an adult

How to eat healthy in dining halls

DIY dorm decor by @notquitenightingale

Everything I actually used in my freshman dorm room

Guide to living alone by @piratestudy

Living with a roommate by @collegerefs

Packing Lists

Thing I forgot to bring to college by @myberkeleyadventure

Sam’s ultimate failproof guide to packing by @staticsandstationery

Ultimate college packing list for freshmen

College packing list by @kimberlystudies

What to bring to college

Checklist for dorms & campus living

Packing up: preparing for college in @theacademiczine

College dorm packing list by @produitivity

Recipes

One-pot chicken fajita pasta

100 dirt cheap recipes for students

57 go-to recipes for college students

Cheap & healthy recipes

Over 400 fast & healthy recipes

Classes

Studying & Taking Notes

Organizing notes with Google Docs by @academla

How to write a lecture summary efficiently by @collegerefs

Symbols & abbreviations for note-taking

How to take lecture notes by @hstrystdyblr

How to take notes in college by @determinationandcaffeine

Getting the most out of lecture by @strive-for-da-best

How to get your best grades in college by @saralearnswell

If you have a bad college professor

Essays

Transition words for essays by @soniastudyblr

How to analyze historical sources by @rewritign

How to write a university level essay by @healthyeyes

Analyzing a written text

Essay writing: university vs. high school

How to write a history paper by @thehistorygrad

How I plan and write literature papers by @notaperfectstudent

Exams

A quick guide to finals by @emmastudies

10 revision tips for final & first year exams

High school exams vs. college exams

Crucial study tips for finals week in college

3 day study plan by @getstudyblr

Low stress college study strategy by @plannerdy

+ More

Masterposts

A college student’s masterpost by @eruditekid

Random college tips by @determinationandcaffeine

College advice by @studenting

Giant college masterpost by @heyiwantyoutostay

Advice

Advice for college by @collegerefs

10 tips for starting uni by @studycubs

Advice from a college senior

Great tips from @fuckstudy

10 more excellent tips

Things nobody tells you about university by @polcry

Miscellaneous

8 things successful students do by @frankfurter-studies

Email tips by @haileymostudies

@collegerefs‘ entire blog– so much good stuff that’s incredibly useful

my grace.uni tag– all the posts I’ve saved for university

Staying in contact with high school friends

How to make friends in college

Tags

reference Advice

13K notes View Post

swirlspill-study

6 years ago

hey everyone! so, after creating a studyblr, i have found so many essay writing resources and since writing (whether or not it’s for academic purposes) is something i and several others struggle with on a daily basis, i decided to put together a bunch of excellent resources in this little masterpost. hope you enjoy (bc writing can be very fun when you feel like you actually know what you’re doing) and hope this helps!

I. ESSAY WRITING

+ where do i start?

how to: brainstorming

how to write an outline

essay checklist

writing an essay, in a nutshell

write a university-level essay

how to write a great essay

how to write a great essay pt. ii

a great ppt by a true lifesaver

+ how do i connect my ideas?

writing transitions

masterpost of transition words

transition words for different purposes

+ different types of essays

narrative essay

expository essay

descriptive essay

literary analysis essay

college application essay

descriptive narrative essay

argumentative/discursive essay

+ tips and advice

general advice

avoiding cliches

for: history essays

for: literature essays

writing ur best college essay

+ even more college essay tips

II. OTHER ACADEMIC WRITING

formatting ur papers

general academic writing tips

planning + writing literature papers

III. RESUME WRITING

+ where do i start?

resume template

guide to writing a good resume

writing a resume when u have 0 xp

+ tips and advice

44 tips

25 tips

IV. WRITING ESSENTIALS

+ tips and advice [for writing in general]

funny little guide to writing well

improve ur writing habits asap

create mind maps to organize ur ideas

+ resources for research

refdesk

webMD

wolfram alpha

google scholar

state health facts

u.s. census bureau

internet public library

the library of congress

the old farmer’s almanac

finding data on the internet

+ grammar/vocab/spelling essentials

the owl [grammar resources from the purdue uni]

tip of my tongue [find a word u can’t remember properly]

hypergrammar

grammar girl

+ revising and editing

hemingway [checks the readability of ur essay]

paperrater [rates ur essays and papers]

autocrit [checks grammatical errors + more]

editing checklist [by grammar girl]

+ citations

citation guide

create a bibliography

citation machine

google cite!!!

+ fun stuff

freerice [donate rice while testing ur vocabulary]

rainymood [listen to the rain]

coffitivity [listen to coffee shop sounds]

rainycafe [combination of rainymood + coffitivity]

find out which author u write like

+ my other masterposts

a complete guide to studying (well)

note-taking

more to come soon!

this entire list includes some of the best writing resources (imo) but feel free to message me in case 1) any of the links are broken, 2) u want me to add on to something, 3) u have a suggestion for a masterpost [i would love that so go ahead and ask if u do] or if u just wanna talk! also, feel free to reblog and add ur own comments/resources. hope this helped someone!!!

Tags

writing resources essays notes

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swirlspill-study

7 years ago

11 . 06 . 2016 // more photosynthesis notes!

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Inspiration sciences

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swirlspill-study

6 years ago

Medical School Resources! (and other human biology,physiology,biochemistry-related resources)

Hi Everyone!

Update: I am now officially done with my second year! I know i’ve been MIA on here for a while now - but that’s only because I was drowning in textbooks and assignments! I will be writing a whole other post on what my second year in medical school was like - so watch out for that :)

I, for one, can not just rely on one method of learning. Meaning, I’ll jump from videos, to textbooks, to flashcards. In this post I’m going to list some of my holy grail youtube channels that have helped saved me.

1) Handwritten Tutorials

https://www.youtube.com/user/harpinmartin

Every video in this channel is short, but not so much that you feel like you’re missing out on information. Definitely one to save as a favourite!

2) Armando Hasudungan

https://www.youtube.com/user/armandohasudungan

The best thing about this channel is the fact that there are over 300 videos, covering a wide range of core topics in endocrinology, neurology, physiology and pharmacology. Another pro is the presentation of topics (otherwise considered snooze-worthy) in an artistic manner!

3) Speed Pharmacology

https://www.youtube.com/channel/UC-i2EBYXH6-GAglvuDIaufQ

Raise your hand if you’ve ever fallen asleep trying to read about the mechanism of action of opioids, their side effects and contraindications. I know I have. Fret not, for this youtube channel will introduce you to a world where pharmacology is actually interesting.

4) Wendy Riggs

https://www.youtube.com/user/wendogg1

Wendy Riggs is a very down-to-earth professor in Northern California, and she covers a wide range of topics in Anatomy, Physiology and General Biology.

5) Anatomy Zone

https://www.youtube.com/user/TheAnatomyZone

A better way to learn anatomy is to supplement your textbook information with videos from this channel. The explanations and visuals provided are absolute gold.

I hope you all find these channels as helpful as I did!

Tags

reference

7K notes View Post

swirlspill-study

6 years ago

This makes me sound stupid but what does a feynman diagram mean?

You don’t sound stupid! They can be pretty confusing at first, and I’m sure you’re not they only one that doesn’t fully understand them (myself included) so let’s learn how to draw Feynman diagrams!

You do not need to know any fancy-schmancy math or physics to do this!

I know a lot of people are intimidated by physics: don’t be! Today there will be no equations, just non-threatening squiggly lines. Even school children can learn how to draw Feynman diagrams. Particle physics: fun for the whole family.

For now, think of this as a game. You’ll need a piece of paper and a pen/pencil. The rules are as follows (read these carefully):

1. You can draw two kinds of lines, a straight line with an arrow or a wiggly line:

You can draw these pointing in any direction.

2. You may only connect these lines if you have two lines with arrows meeting a single wiggly line.

Note that the orientation of the arrows is important! You must have exactly one arrow going into the vertex and exactly one arrow coming out.

3. Your diagram should only contain connected pieces. That is every line must connect to at least one vertex. There shouldn’t be any disconnected part of the diagram.

In the image above, the diagram on the left is allowed while the one on the right is not since the top and bottom parts don’t connect.

4. 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!)

That’s it! Those are the rules of the game. Any diagram you can draw that passes these rules is a valid Feynman diagram. We will call this game QED. Take some time now to draw a few diagrams. Beware of a few common pitfalls of diagrams that do not work (can you see why?):

After a while, you might notice a few patterns emerging. For example, you could count the number of external lines (one free end) versus the number of internal lines (both ends attached to a vertex).

How are the number of external lines related to the number of internal lines and vertices?

If I tell you the number of external lines with arrows point inward, can you tell me the number of external lines with arrows pointing outward? Does a similar relation hole for the number of external wiggly lines?

If you keep following the arrowed lines, is it possible to end on some internal vertex?

Did you consider diagrams that contain closed loops? If not, do your answers to the above two questions change?

I won’t answer these questions for you, at least not in this post. Take some time to really play with these diagrams. There’s a lot of intuition you can develop with this “QED” game. After a while, you’ll have a pleasantly silly-looking piece of paper and you’ll be ready to move on to the next discussion:

What does it all mean?

Now we get to some physics. Each line in rule (1) is called a particle. (Aha!) The vertex in rule (2) is called an interaction. The rules above are an outline for a theory of particles and their interactions. We called it QED, which is short for quantum electrodynamics. The lines with arrows are matter particles (“fermions”). The wiggly line is a force particle (“boson”) which, in this case, mediates electromagnetic interactions: it is the photon.

The diagrams tell a story about how a set of particles interact. We read the diagrams from left to right, so if you have up-and-down lines you should shift them a little so they slant in either direction. This left-to-right reading is important since it determines our interpretation of the diagrams. Matter particles with arrows pointing from left to right are electrons. Matter particles with arrows pointing in the other direction are positrons (antimatter!). In fact, you can think about the arrow as pointing in the direction of the flow of electric charge. As a summary, we our particle content is:

(e+ is a positron, e- is an electron, and the gamma is a photon… think of a gamma ray.)

From this we can make a few important remarks:

The interaction with a photon shown above secretly includes information about the conservation of electric charge: for every arrow coming in, there must be an arrow coming out.

But wait: we can also rotate the interaction so that it tells a different story. Here are a few examples of the different ways one can interpret the single interaction (reading from left to right):

These are to be interpreted as: (1) an electron emits a photon and keeps going, (2) a positron absorbs a photon and keeps going, (3) an electron and positron annihilate into a photon, (4) a photon spontaneously “pair produces” an electron and positron.

On the left side of a diagram we have “incoming particles,” these are the particles that are about to crash into each other to do something interesting. For example, at the LHC these ‘incoming particles’ are the quarks and gluons that live inside the accelerated protons. On the right side of a diagram we have “outgoing particles,” these are the things which are detected after an interesting interaction.

For the theory above, we can imagine an electron/positron collider like the the old LEP and SLAC facilities. In these experiments an electron and positron collide and the resulting outgoing particles are detected. In our simple QED theory, what kinds of “experimental signatures” (outgoing particle configurations) could they measure? (e.g. is it possible to have a signature of a single electron with two positrons? Are there constraints on how many photons come out?)

So we see that the external lines correspond to incoming or outgoing particles. What about the internal lines? These represent virtual particles that are never directly observed. They are created quantum mechanically and disappear quantum mechanically, serving only the purpose of allowing a given set of interactions to occur to allow the incoming particles to turn into the outgoing particles. We’ll have a lot to say about these guys in future posts. Here’s an example where we have a virtual photon mediating the interaction between an electron and a positron.

In the first diagram the electron and positron annihilate into a photon which then produces another electron-positron pair. In the second diagram an electron tosses a photon to a nearby positron (without ever touching the positron). This all meshes with the idea that force particles are just weird quantum objects which mediate forces. However, our theory treats force and matter particles on equal footing. We could draw diagrams where there are photons in the external state and electrons are virtual:

This is a process where light (the photon) and an electron bounce off each other and is called Compton scattering. Note, by the way, that I didn’t bother to slant the vertical virtual particle in the second diagram. This is because it doesn’t matter whether we interpret it as a virtual electron or a virtual positron: we can either say (1) that the electron emits a photon and then scatters off of the incoming photon, or (2) we can say that the incoming photon pair produced with the resulting positron annihilating with the electron to form an outgoing photon:

Anyway, this is the basic idea of Feynman diagrams. They allow us to write down what interactions are possible. However, you will eventually discover that there is a much more mathematical interpretation of these diagrams that produces the mathematical expressions that predict the probability of these interactions to occur, and so there is actually some rather complicated mathematics “under the hood.” But just like a work of art, it’s perfectly acceptable to appreciate these diagrams at face value as diagrams of particle interactions. Let me close with a quick “frequently asked questions”:

What is the significance of the x and y axes?These are really spacetime diagrams that outline the “trajectory” of particles. By reading these diagrams from left to right, we interpret the x axis as time. You can think of each vertical slice as a moment in time. The y axis is roughly the space direction.

So are you telling me that the particles travel in straight lines?No, but it’s easy to mistakenly believe this if you take the diagrams too seriously. The path that particles take through actual space is determined not only by the interactions (which are captured by Feynman diagrams), but the kinematics (which is not). For example, one would still have to impose things like momentum and energy conservation. The point of the Feynman diagram is to understand the interactions along a particle’s path, not the actual trajectory of the particle in space.

Does this mean that positrons are just electrons moving backwards in time?In the early days of quantum electrodynamics this seemed to be an idea that people liked to say once in a while because it sounds neat. Diagrammatically (and in some sense mathematically) one can take this interpretation, but it doesn’t really buy you anything. Among other more technical reasons, this viewpoint is rather counterproductive because the mathematical framework of quantum field theory is built upon the idea of causality.

What does it mean that a set of incoming particles and outgoing particles can have multiple diagrams?In the examples above of two-to-two scattering I showed two different diagrams that take the in-state and produce the required out-state. In fact, there are an infinite set of such diagrams. (Can you draw a few more?) Quantum mechanically, one has to sum over all the different ways to get from the in state to the out state. This should sound familiar: it’s just the usual sum over paths in the double slit experiment that we discussed before. We’ll have plenty more to say about this, but the idea is that one has to add the mathematical expressions associated with each diagram just like we had to sum numbers associated with each path in the double slit experiment.

What is the significance of rules 3 and 4?Rule 3 says that we’re only going to care about one particular chain of interactions. We don’t care about additional particles which don’t interact or additional independent chains of interactions. Rule 4 just makes the diagrams easier to read. Occasionally we’ll have to draw curvy lines or even lines that “slide under” other lines.

Where do the rules come from?The rules that we gave above (called Feynman rules) are essentially the definition of a theory of particle physics. More completely, the rules should also include a few numbers associated with the parameters of the theory (e.g. the masses of the particles, how strongly they couple), but we won’t worry about these. Graduate students in particle physics spent much of their first year learning how to carefully extract the diagrammatic rules from mathematical expressions (and then how to use the diagrams to do more math), but the physical content of the theory is most intuitively understood by looking at the diagrams directly and ignoring the math. If you’re really curious, the expression from which one obtains the rules looks something like this (from TD Gutierrez), though that’s a deliberately “scary-looking” formulation.

You’ll develop more intuition about these diagrams and eventually get to some LHC physics, but hopefully this will get the ball rolling for you.

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