This is an entry in my series where I read physics articles in Scientific American, and provide my weary perspective as a former physicist.
Today I’ll be discussing the article “Quantum Steampunk”, by Nicole Yunger Halpern, in the May issue of SciAm. This one is paywalled, but you can still check out the opening paragraph, in which the author appears to excerpt a paragraph from her latest novel.
It’s a bit indulgent, but hey, whatever works as a hook.
From my perspective, the hook does not really match the content of the article. The rest of the article is a review of the field of quantum thermodynamics research. Quantum thermodynamics was a I thing I studied at university, albeit not at the cutting edge level, and it’s not something I would really think to associate with the steampunk genre. Quantum thermodynamics is literally everywhere, not just in retro-futuristic technology but also in ordinary non-technological materials. You could say my own research on superconductors was also quantum thermodynamics.
But then, I’m not sure I could think of any way to properly introduce this topic, nor explain its content. It’s just a really broad topic. Like, what if I wrote an article that reviewed all of particle physics? Maybe I’d be at such a loss for a proper introduction that I’d decide to include excerpts from my upcoming werewolf fic.
But enough making fun. I really do think the article suffers, not from an indulgent hook, but from an overly broad scope. A lot of time is spent pointing to a bunch of ongoing research projects, without really dedicating the space required to make it understandable to typical readers.
To give an example, the article contains the following paragraph, the only paragraph where fluctuation relations are discussed:
A third area of focus in our quest to update thermodynamics is to derive equations called fluctuation relations. These equations are extensions of the second law of thermodynamics, which dictates that the entropy in a closed, isolated system cannot decrease. Fluctuation relations govern small systems subjected to strong forces and tell us about the work those forces perform
Dear reader, do you know what a fluctuation relation is now? Because I don’t. I think I’ve heard theoretical physicists talk about it before, but it’s at the edge of my physics knowledge, and I’ve never really understood what they meant. I did not learn what it was from a quick google either. I’m sure the author could explain it given more time, but the whole article is such a whirlwind tour that it’s not possible.
The one subject that the author discusses at greater length (presumably because she was one of the major participants) is a quantum engine. It’s like a steam engine, but minus the steam, and plus lasers.
Steam engines are a subject I studied in first year of undergrad, and then never returned to. I guess physicists tend to leave those details to the engineers. But the basic idea is to extract work from a a temperature difference between two bodies. All other things being equal, cold gas is easier to compress than hot gas. So you use the cool body to cool down the gas, compress it, use the warm body to heat it up, decompress, and repeat. This process is called an engine cycle.
The quantum engine also has an engine cycle, although when you cool down the system it transitions into a “many body localization” state (MBL). The important thing about the MBL phase is that individual particles are separated from each other and transfer relatively little heat, so you could say that the different particles aren’t necessarily the same temperature as each other.
Details aside, the concept is fundamentally the same as a steam engine. I think what’s impressive about it is not the theoretical concept, but the fact that these are working physical objects in someone’s lab.
The May issue still doesn’t have anything about COVID-19, except a mention in the letter from the editor. He says that he wrote it on March 15, so that explains it. The one funny thing about this letter is its quaint way of putting “social distancing” in quotes.
I gave this month’s article a hard time didn’t I? I mean, it’s fine, really. In retrospect, among the articles I’ve reviewed in this series so far, I would only say the first one failed in a major way, by failing to point out that its central theory didn’t require quantum mechanics at all.
But the way I see it, one purpose of this series is to show how a scientist (or former scientist) reads a science article. Criticism and griping are a very important–and frequent!–part of that. When you first start reading scientific papers, it can be hard to be judgmental, because you don’t really have the background knowledge and expectations. But if you work hard enough, you too can be one of those grouchy peer reviewers that everyone is polite to but secretly hates.