PhD Bubble Diagrams: An Illustration of Different Types of PhDs

I recently had a conversation about the now-classic “PhD Bubble Diagram” with UW Allen School Security Lab member Miranda Wei. I like certain aspects of the diagram and dislike others. When asked to explain what I disliked about the diagram, I ended up drawing my own:

“An Illustration of Different Types of PhDs” by Tadayoshi Kohno. A small blue bump connected to a large red bubble represents the addition of new knowledge to an existing, extensive research area. A small blue bubble floating by itself represents the advancement of new knowledge in a new area. A blue tube connecting two different red bubbles represents the advancement of new knowledge connecting two previously separate research areas.

The size of a bubble represents the amount of knowledge in a research space. The research done as part of a PhD is in blue; prior knowledge is in red.

There are multiple blue regions. I highlight a few:

  • A small blue bump connected to a large red bubble. This represents the addition of new knowledge to an existing, extensive research area.

I found and read one article about the conventional “PhD Bubble Diagram”: https://matt.might.net/articles/phd-school-in-pictures/. I don’t know if this article is the origin of the now-classic diagram, or if there were prior diagrams like this.

I do not disagree with what that author says; in fact, the author says a lot of things I agree with! I had previously only seen the final diagram and had not read the corresponding discussion. From the diagram itself, and without the context of the article, I worry that someone might interpret a PhD as having to advance depth in a single, existing area of knowledge (the first bullet above), versus the diversity of options available as part of a PhD. Hence, the diagram that I drew.

The bubbles in the earlier figure and my figure represent different things. In the classic figure, the bubble represents all of human knowledge. In my figure, each bubble represents knowledge in a given research area. Thus, as noted above, the earlier figure is not wrong. Rather, our figures provide complementary perspectives and visualizations.

There is still a risk of misinterpreting the diagram that I provide. In my diagram, as well as the original diagram, there is a significant focus on the research results. My philosophy is that the addition of new knowledge is a byproduct of the PhD process. To me, the most important part of a PhD is experiencing the PhD process — learning how to: (1) identify potential research projects, (2) select which problems to work on, (3) approach working on those problems, (4) publish and otherwise share the results, and (5) deal with setbacks along the way.

Of course, I learned a lot about the PhD process from my own advisor, Mihir Bellare, who wrote “The Ph.D. Experience” years ago. I am always continually revising and updating my own approach and philosophy as I advise my own PhD students and learn from the insights of others. Thank you to Miranda Wei for a great conversation about these diagrams and for helpful feedback on this post.

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Tadayoshi Kohno (Yoshi Kohno)

Tadayoshi (Yoshi) Kohno is a professor in the UW Paul G. Allen School of Computer Science & Engineering. His homepage: https://homes.cs.washington.edu/~yoshi/.