Interpreting Physics Research

Recently I was reading a very interesting paper that discusses information and complexity in physical measurement processes. This is Inferring Statistical Complexity by James P. Crutchfield and Karl Young. There was just one problem, I didn’t understand a thing. While trying to get a foothold in the material, I found myself using several strategies for building my comprehension of the material.

Science publications have their own unique quirks and languages. I will share some tips that helped me understanding complex academic material. While my own specialization is physics, this can apply to many different academic fields.

Break it down

Don’t try to understand the entire paper all in one go. Tackle one section at a time. If the paper isn’t already organized into sections, skim the paper and try to break it down yourself.  Identify sections that contain what you need to know. Usually all the preceding sections are needed to understand that material, but sometimes you can get away with skimming sections when you have a specific purpose (Example: skimming the experimental apparatus when studying the theoretical implications). Always make sure you understand the introductory section before moving into the body of the paper.

Know the Language

Most papers have an introduction that provides some higher-level discussion of the foundational physics. Usually this includes more general topics that most readers will have some experience in. As the paper goes on, the language becomes more and more specific to whatever topic or sub-field this paper discusses. As you read this section, jot down any concepts you don’t understand, and jot down a few that you do understand. It is important to understand at least the base definitions of terms used in this sub-field. Watch out! Some terms that you know in a general sense might have a very particular meaning in a sub-field.

Read the Cited articles

If you aren’t already actively performing research in a sub-field, you probably aren’t up-to-date with all the existing research and techniques. Most papers don’t spend the time to fully describe all the foundations approaches and techniques. Naturally there is only so much space for detailing mathematically derivations or previously derived conclusions. Regardless, these are important pieces for understanding research. So as you read the paper, find areas that you don’t understand and dig up the articles that are cited for that area.

For example, when reading that paper on statistical complexity, I discovered that one of the citations was an extremely long and detailed thesis on the material that one of the authors had written . Reading the thesis not only familiarized me with the models they were using, but also the underlying assumptions of the research.

Draw Your Own Picture

Sometimes you need to draw your own picture of what is happening. As much as the authors of the paper try to make things clear, they are usually targeting their writing at researchers and academics. What they might consider to be a clear picture might be completely incomprehensible to anyone without a masters in the field. Instead of relying on their own presentation of the material, draw your own. As you read through the paper, built a visual map of interrelated concepts and factors in the research. Even if details aren’t explicitly stated, you can work out the gaps by looking at what is missing in your visual picture.

Learning is a skill, and you can develop your learning abilities to learn new concepts and skills more efficiently and effectively. While these methods work for me, they might not all be the approach that everyone takes.  As you read and learn, you’ll develop your own techniques as well to suit your learning style and way of thinking.

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Defects Work Like Waves

A very interested approach. Worth checking out as a different perspective on both dislocation defects and waves.

Physics News Blog

In crystals one of the more common defects is that of the dislocation. This is where there is an irregularity in the crystal structure such as the two demonstrated here.

A screw dislocation (thank you to Wikityke on Wikipedia for this image)

An edge dislocation (also by Wikityke)

Both of these would be defined as line defects as as whole rows of atoms have been put out of place in these structures. The line of dislocation, more clearly existing and drawn in blue for the edge dislocation is where the displacement is most severe. These defects can act to either strenghen or weaken the crystal in which they exist.

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Quick Intro: Group Theory

A group is an abstract description of how a system can transform.

Now and again in higher-level Physics you might run into terms like this: SO(3), Lie Group, U(2), etc… These sound like strange and disconnected terms but they are all part of how we categorize systems into groups.

What is a group you might ask? A group is an abstract description of how that system can transform. Specifically, a group consists of a set of elements that create our group space. With this group there is an operator that allows us to combine any two elements into a third element. The operator is usually represented by a plus + symbol so that if A, B and C are group elements, a statement like A + B = C makes sense. You might notice that this looks a lot like simple algebra, and groups do form their own algebra in a sense, but they aren’t limited to the math operators that we learned in primary school.

Since a group is completely abstract, it can have different ‘representations’ that express the group. A cyclic group can be represented by the way we rotate an object, so that if you add two rotations, you might end up rotating the object 360 degrees and returning to the original position. Another example of a group representation would be how we can combine simple twists of string to form complex braids (the group in this case is called the braid group).

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One example of a group is the ways that we can flip a mattress. This helpful article explores group theory in that scenario: https://opinionator.blogs.nytimes.com/2010/05/02/group-think/

While there are infinite representations of groups, we try to reduce each group to it’s simplest form, known as the irreducible representation. This allows us to compare different systems in terms of their groups.

Breaking systems down into their fundamental groups allows us to predict transitions that appear in the group before we can even observe them. Group theory can also be used to understand symmetry, this perspective can not only be applied to the physical sciences, but the study of art.

As far as physics goes, here are a few common groups that come up a lot:

SO(3): The special orthogonal group in three dimensions. This group consists of simple rotations in 3 dimension space around a fixed point.

U(2): The unitary group of degree 2. This group consists of all 2×2 matrices that are unitary.

SU(2): The special unitary group of degree 2. Like the unitary group, but the determinant of each matrix is equal to 1.

There are a few ways of discussing different types of groups. Many groups are characterized by some kind of symmetry, which is defined by a parameter of the system that doesn’t change during a transformation. For example matrices in the special unitary group always have a determinant equal to 1, or the special orthogonal group doesn’t change the length of a given radius as it rotates.

A Lie group is any group that is defined by a continuous transformation. A particle might have discrete transformation between one energy state of another, but rotations can be made continuously.

There are so many different ways of looking at groups. Even if it doesn’t become your field of study, it can make for a very interesting way of looking at different systems. Here are a few sources where you can learn a little bit more about groups:

PDF/BOOK: Introduction to Group Theory for Physicists – Marina von Steinkirch
This book breaks gives us the mathematical formulation of group theory and looks at a number of groups that have special significance for Physics.
http://www.astro.sunysb.edu/steinkirch/books/group.pdf

VIDEO: Group Theory – Robert de Mello Koch
The first in a series of lectures that cover the study of group theory and representations. A great place to start if you have some experience with Quantum Mechanics.
https://www.youtube.com/watch?v=3wNPrSwbtQ8

Learning through Blogging

I welcome you to join me in this expedition into the the world of physics blogging. I have created this blog in the hopes of sharing some of the interesting ideas that I discover in my physics studies.

For students of physics, this might bring some perspective on concepts that you may study in your courses. For the untrained physicist, I might provide a looking glass into some of the difficult topics of theoretical physics. For myself, I hope to cultivate a deeper understanding that can only be gained by teaching these concepts to others. Teaching and learning are two sides of the same coin, and if I cannot explain these ideas to others, how can I claim to have really understood them?

Along the way, I will share the resources and learning strategies that I use to understand these topics. Even if I do not explore these topics further, I want anyone to have a launching point to pursue it themselves.

So again, I welcome you to this experiment. Feel free to send me a message and ask any questions. My inbox is always open.