The Quantum Physics of Covid Testing

Do I, or do I not, have Covid?

This is a question that occupies millions of us every day with varying degrees of urgency. The answer may determine whether we go to work, whether our children go to school, whether we get to see our friends or relatives for dinner this weekend or for a long-anticipated reunion, whether those European vacation plans get executed or put on hold, again. And that’s if we’re lucky, if we’re able, because of vaccines and boosters and sound immune systems, to view Covid, at least in its latest Omicron variant form, not as a life-threatening disease but as a nuisance illness like a cold or flu.

But even if we are that lucky, getting Covid means, if we’re the least bit conscientious and civic-minded, that we’re going to have to follow a lot of testing and quarantining protocols that are at best disruptive to daily life, and at worst a total pain in the ass.

My fully-vaxxed daughter and her husband and two young boys all came down with Covid recently — which is to say, they all tested positive with a combination of PCR and antigen tests. My daughter was flat in bed, feeling miserable, for the better part of a week, while the males in the family all got off with nothing more than the symptoms of a mild head cold. We all know stories like these; it’s the now-common experience of Covid roulette. But regardless of how sick each of them was, they were all stuck at home for days, the boys back to remote schooling, the adults Zooming to work when they weren’t popping Tylenol, obsessively monitoring their symptoms, and napping.

So whether or not we have Covid, even in its mildest form, means a great deal to a great many of us. And fortunately, the means to answer that question with a reasonable degree of accuracy, at least for a moment or a day, have become broadly available, either in the form of lab-run PCR tests, or by means of self-administered antigen tests, which the federal government just began offering online and for free.

I didn’t wait that long. In my usual paranoid prepper fashion, I bought several antigen self-tests a couple of months ago, in that brief ebb tide between the Delta and Omicron waves, when self-test kits were languishing on drugstore shelves. Later, I learned from a doctor friend about a more accurate, if pricey, PCR-like molecular self-test that you can order online, and bought a few of those. All hoarded against the day when that scratchy throat or dry cough might make my wife and I look up at each other and say, “Covid?”

As it happened, we never had the sore throat or the cough, or even the newly-popular congested nose. But someone else did. An old business friend flew across the country from Seattle to Fort Myers, which must be about the longest nonstop in the continental United States, to visit us and some other local friends. I told him before he came that I’d never make such a trip right now, just as I’d told him countless other things during our long working life together that he also ignored. So he came and hobnobbed among us for a weekend and went home — and promptly tested positive for Covid on a PCR test.

Once we got over our annoyance, we consulted our doctors and were told to wait a few days to see if we developed symptoms and, at that point, to test ourselves regardless. And when the few days had passed, with both of us still symptomless, I pulled out the fancy molecular self-tests and set them up for my wife and me, ran the swabs around her and my noses, stuck the swabs in the vials of purple liquid, and went off to play the piano and wait the 30 minutes it would take for the little lights to blink “Positive” or “Negative.”

As I waited, I thought of Schrödinger’s cat.

Erwin Schrödinger was an Austrian physicist who, in the 1930s, along with Niels Bohr and Werner Heisenberg, developed the mathematical postulates behind what we call quantum physics. Chief among those postulates is that — bear with me — quantum systems, like atoms and maybe people and universes, remain in multiple potential states of energy and location corresponding to different outcomes, until the system interacts with or is observed by another external system, whereupon the potentialities “collapse” into a new, resolved state. (If this makes no sense to you, be assured that no one else understands it either.) The classic laboratory example of this phenomenon is when a beam of photons is seen to change its path when another, parallel photon beam is interrupted or even observed, meaning that two separate states of potentiality are “entangled,” happily co-existing independently unless and until the measurement is taken.*

Schrödinger sought to illustrate the potential absurdity of this situation with a thought experiment in which a cat is placed inside a steel box containing a device that would measure whether radioactive material decayed within a certain period of time, with the likelihood of such an event being an even 50-50. If the material decayed, a canister inside the cat’s box would release a poison, killing the cat; if not, the cat would be unharmed.

Taken to its logical conclusion, quantum theory states that, before the box is opened and the result is observed, the cat must be both alive and dead, in a state of suspended potentiality, or what the physicists call superimposition. Schrödinger’s thought experiment forces the strange logic of quantum physics into the macro world, where it becomes not just strange, but paradoxical. Albert Einstein congratulated Schrödinger for having exposed the limitations of quantum theory. Nonetheless, a conceptual offspring of Schrödinger’s cat experiment is the “many worlds” hypothesis of quantum mechanics, beloved by sci-fi fans everywhere, whereby our choices are continually proliferating alternative branches of reality. (There’s even an app for that.)

The Covid pandemic has dropped us all down a rabbit hole and into Schrödinger’s cat box. If you’re mildly or not at all symptomatic, until you actually have the results in hand, you might have Covid, or you might not. I was all too happy to delay testing a few more days when our doctor suggested it, as that meant I could continue to not know if I had Covid, and could go about my life as if I didn’t. Another friend who’d also been exposed to our Covid-positive visitor delayed testing herself until after a speaking appearance she had to make (asymptomatic, masked and distanced, to be sure, but still), as though she wouldn’t have Covid until she was told she had it, and could act accordingly, just as Schrödinger’s cat is neither alive nor dead until we look inside its box.

So do I have Covid, or don’t I? Is Schrödinger’s cat alive or dead? Obviously, even before I see the result of my test, I either have Covid or I don’t. And yet part of me wants to believe the causal fallacy that it is the test that will decide whether or not I have Covid, rather than whether or not I have Covid determining the result of the test. My wife and I actively discussed (but dismissed) not looking at the results of our self-tests until after we went out to dinner that night, as though then we wouldn’t “have Covid” until it was more convenient. And of course, there are those who won’t even get vaccinated, let alone tested, because to do so would acknowledge an alternate reality they want nothing to do with.

Back in the little quantum state we call home, when our own particular wave functions collapsed, my wife and I were both negative. We cheered quietly, went out to our dinner, toasted our good fortune, went home, and later crept, cat-like, off to bed.


*For a sprightly history of the development of quantum physics, see Carlo Rovelli, Helgoland: Making Sense of the Quantum Revolution (Riverhead Books, 2021).

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