On tardigrades, superdeterminism, and the struggle for sanity
(Hopefully no one has taken taken that title yet!)
I waste a large fraction of my existence just reading about what’s happening in the world, or discussion and analysis thereof, in an unending scroll of paralysis and depression. On the first anniversary of the January 6 attack, I read the recent revelations about just how close the seditionists actually came to overturning the election outcome (e.g., by pressuring just one Republican state legislature to “decertify” its electors, after which the others would likely follow in a domino effect), and how hard it now is to see a path by which democracy in the United States will survive beyond 2024. Or I read about Joe Manchin, who’s already entered the annals of history as the man who could’ve halted the slide to the abyss and decided not to. Of course, I also read about the wokeists, who correctly see the swing of civilization getting pushed terrifyingly far out of equilibrium to the right, so their solution is to push the swing terrifyingly far out of equilibrium to the left, and then they act shocked when their own action, having added all this potential energy to the swing, causes it to swing back even further to the right, as swings tend to do. And I see all this and I am powerless to stop it.
In such a dark time, it’s easy to forget that I’m a theoretical computer scientist, mainly focused on quantum computing. It’s easy to forget that people come to this blog because they want to read about quantum computing. It’s like, who gives a crap about that anymore? What doth it profit a man, if he gaineth a few thousand fault-tolerant qubits with which to calculateth chemical reaction rates or discrete logarithms, and he loseth civilization?
Nevertheless, in the rest of this post I’m going to share some quantum-related debunking updates—not because that’s what’s at the top of my mind, but in an attempt to find my way back to sanity. Picture that: quantum mechanics (and specifically, the refutation of outlandish claims related to quantum mechanics) as the part of one’s life that’s comforting, normal, and sane.
There’s been lots of online debate about the claim to have entangled a tardigrade (i.e., water bear) with a superconducting qubit; see also this paper by Vlatko Vedral, this from CNET, this from Ben Brubaker on Twitter. So, do we now have Schrödinger’s Tardigrade: a living, “macroscopic” organism maintained coherently in a quantum superposition of two states? How could such a thing be possible with the technology of the early 21st century? Hasn’t it been a huge challenge to demonstrate even Schrödinger’s Virus or Schrödinger’s Bacterium? So then how did this experiment leapfrog (or leaptardigrade) over those vastly easier goals?
Short answer: it didn’t. The experimenters couldn’t directly measure the degree of freedom in the tardigrade that’s claimed to be entangled with the qubit. But it’s consistent with everything they report that whatever entanglement is there, it’s between the superconducting qubit and a microscopic part of the tardigrade. It’s also consistent with everything they report that there’s no entanglement at all between the qubit and any part of the tardigrade, just boring classical correlation. (Or rather that, if there’s “entanglement,” then it’s the Everett kind, involving not merely the qubit and the tardigrade but the whole environment—the same as we’d get by just measuring the qubit!) Further work would be needed to distinguish these possibilities. In any case, it’s of course cool that they were able to cool a tardigrade to near absolute zero and then revive it afterwards.
I thank the authors of the tardigrade paper, who clarified a few of these points in correspondence with me. Obviously the comments section is open for whatever I’ve misunderstood.
People also asked me to respond to Sabine Hossenfelder’s recent video about superdeterminism, a theory that holds that quantum entanglement doesn’t actually exist, but the universe’s initial conditions were fine-tuned to stop us from choosing to measure qubits in ways that would make its nonexistence apparent: even when we think we’re applying the right measurements, we’re not, because the initial conditions messed with our brains or our computers’ random number generators. (See, I tried to be as non-prejudicial as possible in that summary, and it still came out sounding like a parody. Sorry!)
Sabine sets up the usual dichotomy that people argue against superdeterminism only because they’re attached to a belief in free will. She rejects Bell’s statistical independence assumption, which she sees as a mere dogma rather than a prerequisite for doing science. Toward the end of the video, Sabine mentions the objection that, without statistical independence, a demon could destroy any randomized controlled trial, by tampering with the random number generator that decides who’s in the control group and who isn’t. But she then reassures the viewer that it’s no problem: superdeterministic conspiracies will only appear when quantum mechanics would’ve predicted a Bell inequality violation or the like. Crucially, she never explains the mechanism by which superdeterminism, once allowed into the universe (including into macroscopic devices like computers and random number generators), will stay confined to reproducing the specific predictions that quantum mechanics already told us were true, rather than enabling ESP or telepathy or other mischief. This is stipulated, never explained or derived.
To say I’m not a fan of superdeterminism would be a super-understatement. And yet, nothing I’ve written previously on this blog—about superdeterminism’s gobsmacking lack of explanatory power, or about how trivial it would be to cook up a superdeterministic “mechanism” for, e.g., faster-than-light signaling—none of it seems to have made a dent. It’s all come across as obvious to the majority of physicists and computer scientists who think as I do, and it’s all fallen on deaf ears to superdeterminism’s fans.
So in desperation, let me now try another tack: going meta. It strikes me that no one who saw quantum mechanics as a profound clue about the nature of reality could ever, in a trillion years, think that superdeterminism looked like a promising route forward given our current knowledge. The only way you could think that, it seems to me, is if you saw quantum mechanics as an anti-clue: a red herring, actively misleading us about how the world really is. To be a superdeterminist is to say:
OK, fine, there’s the Bell experiment, which looks like Nature screaming the reality of ‘genuine indeterminism, as predicted by QM,’ louder than you might’ve thought it even logically possible for that to be screamed. But don’t listen to Nature, listen to us! If you just drop what you thought were foundational assumptions of science, we can explain this away! Not explain it, of course, but explain it away. What more could you ask from us?
Here’s my challenge to the superdeterminists: when, in 400 years from Galileo to the present, has such a gambit ever worked? Maxwell’s equations were a clue to special relativity. The Hamiltonian and Lagrangian formulations of classical mechanics were clues to quantum mechanics. When has a great theory in physics ever been grudgingly accommodated by its successor theory in a horrifyingly ad-hoc way, rather than gloriously explained and derived?
Update: Oh right, and the QIP’2022 list of accepted talks is out! And I was on the program committee! And they’re still planning to hold QIP in person, in March at Caltech, will you fancy that!