The physics of jigsaw puzzles

Wholesome jigsaw puzzle youtuber Karen Kavett recently did a challenge where she assembled a 1000 piece puzzle by selecting 100 pieces at random at a time. For a while, this just looked like a bunch of scattered pieces with only a few connections. But once she had 700 or 800 pieces, the whole puzzle started to come together, despite the gaps.

I found this fascinating, because it is a live demonstration of a concept in physics/math: the percolative transition. This is something I often think about when assembling puzzles.

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The speed of light in different directions

As a reminder, I’m open to requests to discuss any popular physics articles or videos, to append to my “I read popular physics” series. This video was not requested, but was shared by a friend of a friend a while back, and I have things to say about it.

Recently, the YouTube Channel Veritasium posted a video “Why the Speed of Light* Can’t be Measured”. The video argues that all measurements of the speed of light involve sending light in one direction, and waiting for it to come back. However, the light could theoretically be traveling faster in one direction than the other. It seems we are not directly measuring the speed of light, but rather the average speed of light in both directions. The constant speed of light in all directions is a matter of theoretical convention rather than empirical fact.

In the Facebook thread where I first saw the video shared, many people were incredulous. As for myself, I immediately understood the argument from the title, and immediately agreed that it was correct. However, I feel the video is misleading, as it does not explain why there is a theoretical convention that the speed of light is constant. And by doing so, I feel it misses the point of relativity theory.

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A year of reading popular physics

At the beginning of 2020, I received a one-year subscription to Scientific American. I embarked on a blogging series in which I read articles about physics, and offer my commentary as a person with a PhD in physics. I may continue this series in 2021, but instead of reading articles in Scientific American, I’ll take reader requests. Just send me any articles or videos that you’d like me to discuss or explain. Requests must obey the following restrictions:

  • It must be intended for popular audiences, as opposed to scholarly audiences.
  • It must be about physics or adjacent to physics. I will also consider requests for math-related articles.
  • I must have access to the article or video. Note, I still have a Scientific American subscription, so those are fair game.

New or old articles are welcome, and videos too.  I will exercise my own discretion among qualifying requests, taking into consideration how much time it would take me to process, and how interesting I think it would be to write about.  To make a request, leave a comment or e-mail me at

Below the fold, I have my review of the articles I’ve written about so far.

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I read popular physics: Explosions at the edge

This is part of my series where I read physics articles in Scientific American, and rant about barely related tangents in order to provide “context”.

After the November issue, which didn’t really have any physics articles at all, the December issue has two major articles! One is astronomy, the other one is about the fusion reactor, ITER. But, after complaining about how all the physics articles are about astronomy, it looks like I’m still choosing the astronomy article. The ITER article is just a bunch of photos of the engineering, and I don’t have much to say about that.

So, the astronomy article is “Explosions at the Edge” (or that’s how it’s titled in print). It’s about the surprisingly diverse ways that massive stars can go supernova. For example, rather than simply exploding, a star may first shed a layer of gas, and then the subsequent explosion will collide with that gas, producing a prodigious burst of light.

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I read popular physics: Orbital Aggression

This is part of my series where I read physics articles in Scientific American, and publicly ponder what choices in life brought me to this point. This month’s “physics” article is not really about physics at all, but that’s the bed I made.

The article is titled “Orbital Aggression” (paywalled), and it’s about the possibility of space war. Space war refers not to war rained down from space, but rather war that targets satellites. Especially in the US, satellites play an important role in communication and imaging, such as transmitting credit card transactions or monitoring weather. They’re also used by the military, again especially the US military, which occupies every corner of the globe.

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I read popular physics: Interstellar Interlopers

This is an entry in my series where I read physics articles in Scientific American, and get annoyed that the only good ones are about astronomy.

I skipped a month, because the September issue was a special 175-year anniversary edition. I actually liked that one, but the physics article was a review of how cosmology had changed in the past 175 years, and I don’t have much to say about that. I learned that Scientific American basically predates the scientific establishment as we know it, and it started out as a thing for like, inventors and hobbyists.

The October issue has a presidential endorsement, the first endorsement that the magazine has ever made in its long history. No points for guessing who they endorsed.

Anyway, the physics article for this month is “Interstellar Interlopers” (no paywall this time), about the first two interstellar objects ever observed in the Solar System. I had never heard of these before, but I guess they made news a while back, as reporters breathlessly speculated about aliens.

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I read popular physics: Quantum Leap

This is an entry in my series where I read physics articles in Scientific American, under the theory that having a physics PhD will save me.

This month’s article is “Quantum Leap” about the theory behind the quantum hall effect. Out of all the articles in this series so far, this is the closest to my actual field of study (I was a condensed matter experimentalist who studied superconductors). But I positively groaned when I saw it. It’s bad.

But before I get to the main attraction, I have some general commentary on the August issue. After two months of putting the coronavirus on the cover, SciAm’s cover has finally moved on, now featuring a story about oak trees. The columnists are all still talking about the virus, one about racial health disparities, one about masks, one about science denial. I think these articles are written 1-2 months in advance, so they’re a bit of a time capsule. Wait, aren’t we still talking about all the same things?

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