My talk at Columbia University: “Computational Complexity and Explanations in Physics”
Last week, I gave the Patrick Suppes Lecture in the Columbia University Philosophy Department. Patrick Suppes was a distinguished philosopher at Stanford who (among many other things) pioneered remote gifted education through the EPGY program, and who I was privileged to spend some time with back in 2007, when he was in his eighties.
My talk at Columbia was entitled “Computational Complexity and Explanations in Physics.” Here are the PowerPoint slides, and here’s the abstract:
The fact, or conjecture, of certain computational problems being intractable (that is, needing astronomical amounts of time to solve) clearly affects our ability to learn about physics. But could computational intractability also play a direct role in physical explanations themselves? I’ll consider this question by examining three possibilities:
(1) If quantum computers really take exponential time to simulate using classical computers, does that militate toward the many-worlds interpretation of quantum mechanics, as David Deutsch famously proposed?
(2) Are certain speculative physical ideas (e.g., time travel to the past or nonlinearities in quantum mechanics) disfavored, over and above any other reasons to disfavor them, because they would lead to “absurd computational superpowers”?
(3) Do certain effective descriptions in physics work only because of the computational intractability of violating those descriptions — as for example with Harlow and Hayden’s resolution of the “firewall paradox” in black hole thermodynamics, or perhaps even the Second Law of Thermodynamics itself?
I’m grateful to David Albert and Lydia Goehr of Columbia’s Philosophy Department, who invited me and organized the talk, as well as string theorist Brian Greene, who came and contributed to the discussion afterward. I also spent a day in Columbia’s CS department, gave a talk about my recent results on quantum oracles, and saw many new friends and old there, including my and my wife’s amazing former student Henry Yuen. Thanks to everyone.
This was my first visit to Columbia University for more than a decade, and certainly my first since the upheavals following the October 7 massacre. Of course I was eager to see the situation for myself, having written about it on this blog. Basically, if you’re a visitor like me, you now need both a QR code and an ID to get into the campus, which is undeniably annoying. On the other hand, once you’re in, everything is pleasant and beautiful. Just from wandering around, I’d have no idea that this campus had recently been Ground Zero for the pro-intifada protests, and then for the reactions against those protests (indeed, the use of the protests as a pretext to try to destroy academia entirely) that rocked the entire country, filling my world and my social media feed.
When I asked friends and colleagues about the situation, I heard a range of perspectives: some were clearly exasperated with the security measures; others, while sharing in the annoyance, suggested the measures seem to be needed, since every time the university has tried to relax them, the “intifada” has returned, with non-university agitators once again disrupting research and teaching. Of course we can all pray that the current ceasefire will hold, for many reasons, the least of which is that perhaps then the obsession of the world’s young and virtuous to destroy the world’s only Jewish state will cool down a bit, and they’ll find another target for their rage. That would also help life at Columbia and other universities return to how it was before.
Before anyone asks: no, Columbia’s Peter Woit never showed up to disrupt my talk with rotten vegetables or a bullhorn—indeed, I didn’t see him at all on his trip, nor did I seek him out. Given that Peter chose to use his platform, one of the world’s best-known science blogs, to call me a mentally ill genocidal fascist week after week, it meant an enormous amount to me to see how many friends and supporters I have right in his own backyard.
All in all, I had a wonderful time at Columbia, and based on what I saw, I won’t hesitate to come back, nor will I hesitate to recommend Jewish or Israeli or pro-Zionist students to study there.
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Comment #1 October 16th, 2025 at 7:35 pm
The Second Law project sounds really interesting! Is it close to a preprint?
Comment #2 October 16th, 2025 at 7:58 pm
Daniel #1: Thanks! Might be a few more months until we have a preprint.
Comment #3 October 16th, 2025 at 9:46 pm
I was wondering if there is a recording or a transcript of your lecture available? If not, do you have any plans to give a similar talk in the near future that might be recorded?
Comment #4 October 16th, 2025 at 10:03 pm
John Gates #3: Sorry, they didn’t record it. Maybe I’ll give it again someplace where it’s recorded. In the meantime there are the slides!
Comment #5 October 17th, 2025 at 5:22 am
Hi Scott. What do you think of Quantum Darwinism compared to Everett’s picture? I gather from Zurek’s 2022 review paper that you and he have had some stimulating discussions.
Comment #6 October 17th, 2025 at 6:08 am
This is very interesting! I’m looking forward to learning more about your work on the Second Law.
I notice that you did not discuss work related to uncomputability in physical systems, usually involving embedding a Turing machine in the mathematical representation of the system (see https://arxiv.org/pdf/2410.16532).
Comment #7 October 17th, 2025 at 11:12 am
Peter Woit just wrote the following:
About the idea that “the measures seem to be needed, since every time the university has tried to relax them, the “intifada” has returned, with non-university agitators once again disrupting research and teaching”, this is delusional nonsense with no basis in reality.
Care to comment / elaborate?
Comment #8 October 17th, 2025 at 11:42 am
MK #7: Alright then. My comment is simply that I was directly reporting what several of my Columbia colleagues told me when I asked them, since I wasn’t there to see it firsthand.
And yes, I know many people would reply that it’s right to disrupt research and teaching over this, since Israel is unique in its bloodthirsty, baby-killing evil, and that consideration overrides everything else. But at that point, they’ve moved the discussion from the Columbia campus to the Middle East, and I’d then like them at least to contend with my and many others’ perspective, namely that Israel just fought (and won, for now) a war for its continued existence on earth, against an actually explicitly genocidal enemy — and that, while this war was much smaller in scale, its moral issues were not so different from those of the brutal war that the Allies fought and won against Hamas’s direct ideological predecessors, the Nazis. Peter’s stance on this perspective, of course, is that he’s aggressively unwilling even to consider it. Which, very well: if someone won’t discuss the merits of the case, then let them go back to discussing the free speech protections, the time, place, and manner restrictions, the civil rights protections, etc that are needed to run a research university. If you read this blog, you’ll see that I’ve never treated these issues as obvious, even while I have treated it as obvious that the Trump administration shouldn’t use them as a pretext to destroy academic science.
Comment #9 October 17th, 2025 at 12:22 pm
Please keep us posted about the second law paper, so we can learn! It is exciting to see such connections between physics and computational complexity.
Comment #10 October 17th, 2025 at 2:31 pm
“based on what I saw, I won’t hesitate to come back, nor will I hesitate to recommend Jewish or Israeli or pro-Zionist students to study there”
I don’t understand the logic behind that statement. Columbia already turned on a dime from being OK before the war to being unlivable for most of the last 2 years (according to its own antisemitism report that you blogged about). What would prevent the university from dismantling the security measures and turning back into a center for antisemitism in the near future?
Comment #11 October 17th, 2025 at 3:14 pm
AF #10: Well, nothing is necessarily permanent! But I met a fair number of Jews and Israelis during my short visit to Columbia who seemed like they were thriving there, despite the overwhelming impression one gets from news and social media. And certainly no one can complain any longer about the federal government having failed to send a message to Columbia that it’s going to treat a hostile environment for pro-Israel Jews as a civil rights violation, or about the Columbia administration having failed to receive that message. I just wish that a way had been found to do this without cancer research and quantum computing research and all the rest getting strafed in the crossfire.
Comment #12 October 17th, 2025 at 3:36 pm
“This was my first visit to Columbia University for more than a decade, and certainly my first since the upheavals following the October 7 massacre. Of course I was eager to see the situation for myself, having written about it on this blog”
” But I met a fair number of Jews and Israelis during my short visit to Columbia who seemed like they were thriving there, despite the overwhelming impression one gets from news and social media.”
maybe you have been manipulated ?
Comment #13 October 17th, 2025 at 3:50 pm
zzz #12: I doubt it, because my reasons for being invited there had nothing to do with my blogging about this subject, and some of the people I met were ones who I’ve known for years and wouldn’t lie to me about such things.
Comment #14 October 17th, 2025 at 4:18 pm
Scott, as I understand it, part II of your talk can be roughly summarized as exploring the proposition that “If some hypothetical efficient physical process could solve a very computationally hard problem, then it probably can’t happen in the real world.” (I realize that you are not staking a firm claim to the truth of this proposition, but are merely positing that it is worthy of serious consideration.)
Do you think that the contrapositive proposition – “If some efficient physical process can happen in the real world, then it probably isn’t solving a very hard computational problem” – could plausibly give circumstantial evidence for any questions in computational complexity theory? For example, if we both (a) empirically observe some physical process occuring in the real world, and (b) argue that that process could be used to solve some concrete, well-defined, purely computational problem, then do you think that those two facts would give circumstantial evidence that that computational problem lies within BQP (or some other “reasonably tractable” complexity class), even if we can’t figure out any specific quantum or classical algorithm that solves the problem efficiently? Do you think it’s conceivable that this might actually happen in real life for a real computational problem?
I acknowledge that this is a rather fanciful proposal. But it’s funny to imagine that, just like in physics, new conjectures in computational complexity theory could be motivated from experiment. By “experiment”, I don’t mean numerical experimentation – which is of course a totally routine tool in computational complexity research – but actual, physical experimentation!
Comment #15 October 17th, 2025 at 4:49 pm
What a fascinating talk! The connection you drew between computational complexity and fundamental physics really pushes the boundaries of how we think about explanations in science. I’m especially intrigued by the idea that intractability could influence which physical theories are plausible. It must have been inspiring to discuss these topics with such a brilliant group at Columbia, including Brian Greene. Your exploration of time travel, many-worlds, and the firewall paradox offers so much food for thought—truly a thought-provoking lecture.
Comment #16 October 17th, 2025 at 5:47 pm
scott #13.
thats what i am saying.
before you launched a crusade against Columbia maybe you should
have checked with those people
Comment #17 October 17th, 2025 at 6:10 pm
zzz #16: I never “launched a crusade against Columbia”; what alternate reality are you writing from?! Even as I expressed 100% justified concern about the contents of the antisemitism task force report written by Columbia faculty members, I always did so from an obvious position of warm feelings for the university and for my many friends and colleagues there. And I always did check with those I knew there, who (as I faithfully reported) had varied perspectives on what was going on.
Comment #18 October 18th, 2025 at 7:45 am
Hi Scott, I have to ask.
The Columbia staff who silently allowed or even supported antisemitism and the persecution of Jewish students haven’t really changed since October 7th. Do you think what you saw on campus reflected a real change, or is antisemitism just going underground for a few years, maybe because of Trump?
I’m not sure what I’d do if I get invited there, so no judgement from my side.
Comment #19 October 18th, 2025 at 8:15 am
I’m against Trump now as you know, but the way I see it, cutting off funding to Columbia was one of the things he did right. Why should the American taxpayer pay for a place which is a den of extremist anti-Zionism, leftism, wokeism etc? Why should they pay to brainwash kids into hating America and Israel? Do you understand the populist backlash to universities—after seeing all these high-profile incidents of anti-Zionist and anti-American extremism at the universities, Middle America is sick of footing the bill. Note that I’m against defunding the NIH and NSF in general. The question though is whether the American taxpayer should pay for woke / anti-Israel brainwashing centers.
Comment #20 October 18th, 2025 at 9:09 am
In the recent Aaronson talk, one of the slides referenced Kurt Goedel’s 1956 letter to John von Neumann (available at anilada.com).
https://www.anilada.com/notes/godel-letter.pdf
If the constant “k”: mentioned by Goedel were equal to googolplex, it is far from obvious that what Goedel claims would be true.
Comment #21 October 18th, 2025 at 12:24 pm
Y #18: I think antisemitism was always negligible within the hard sciences there. Even in the social sciences and humanities, I don’t think most people are antisemites. I think there seems to have been way too much tolerance of antisemitism in social science and humanities departments at Columbia, but students in those departments aren’t the ones who I’d be advising anyway. In any case, I’m someone who’s always strongly believed in responding to events on the ground. Imagine what the anti-Zionists would’ve said if I’d said I still wouldn’t recommend Jewish students go to Columbia, even after everything the administration has now done — “you see?!? since none of it makes any difference anyway, we might as well indulge all our impulses to globalize the intifada and chase away the evil Zionist enemy!”
Comment #22 October 18th, 2025 at 12:38 pm
What did you work on with Pat on back in 2007? I was at EPGY (and have continued on with Stanford OHS) since 1995. Was working with Pat on one or two papers around that time. Did you ever come by Ventura Hall? Wish I would have had the chance to meet you back then.
Comment #23 October 18th, 2025 at 1:12 pm
Gary Oas #22: I never worked with Suppes. I spent a very enjoyable hour talking with him when I was being recruited to be faculty at Stanford (I came within a hair of accepting but ultimately chose MIT).
Comment #24 October 18th, 2025 at 1:34 pm
Scott #23: Ah, would have been nice to have you at Stanford, could have leaned on you when I created a quantum computing course at Stanford Online High School a number of years ago. I remember when Chris Fuchs was in consideration and Pat had him over for dinner and they had an excellent debate about Bayesianism -got Chris to concede a few points. I imagine you and Pat had (and would have had) several similar views.
Comment #25 October 18th, 2025 at 1:54 pm
I also find the lecture—and the various themes discussed in it—fascinating, as well as the broader connection between computational complexity (and theoretical computer science) and philosophy.
Let me offer a few comments on one of the items in Scott’s lecture: “Complexity as Armor for Effective Theories.”
Scott asks: Should we penalize physical hypotheses not only for high descriptive complexity, but also for computational complexity?
His view is:
Actually, my general view is quite similar. Regarding skepticism about quantum computing, I am aware of four computational complexity insights that have been offered to rule out scalable quantum computation (or certain fragments of it):
1) Efficient factoring is such science fiction that the rational conclusion is that quantum computation cannot work.
(Levin, Goldreich, and others since the mid-1990s.)
A common response is that factoring is not such a big deal—it is low in the complexity hierarchy, and some even believe it lies in P.
2) Precise sampling according to the values of permanents—a task beyond the polynomial hierarchy—is such science fiction that, even if one accepts efficient factoring (classically or quantumly), the rational conclusion remains that quantum computation cannot work.
(This idea appeared around 2010.)
3) NISQ computers are such primitive classical computational devices that they cannot be used for achieving “quantum supremacy.”
(Kalai–Kindler, 2014; and subsequent works by me.)
This relies on standard noise modeling with constant noise levels. Even under a broad range of subconstant noise levels, the resulting samples consist of inherently noise-sensitive components plus computationally trivial ones. Guy and I described a complexity class LDP that captures the sampling power of NISQ devices in a wide range of noise rates.
4) NISQ computers (and the complexity class LDP) are also too primitive to produce high-quality quantum error-correcting codes, thereby breaking the chain reaction needed for quantum fault tolerance. (Kalai, following item 3.)
I think that all four arguments are fairly strong—though surely not ironclad. The advantage of the last two (closely related) points is that (if correct) they exclude not only far-future possibilities but also some near-term experimental hopes and even certain current experimental claims.
I fully agree that we should not be too dogmatic, and that these matters will ultimately be clarified by experiments, as well as by further theoretical developments. It is also worth noting that tensions between computational complexity and physics—or even between different insights within physics—often lead to fascinating mathematical questions.
In my view, it would be very fruitful if other items from Scott’s lecture also sparked discussion—for example, the Harrow–Hayden proposed solution to the firewall paradox, the connections between thermodynamics and complexity, or the relationship between the Many-Worlds Interpretation and Shor’s algorithm, among others. Several of these topics relate to the possible reality of a “world devoid of quantum computation,” which I have explored over the years.
Finally, it goes without saying that I share the relief brought by the ceasefire in Gaza, the release of the living Israeli hostages, and the hope that this ceasefire will hold.
Comment #26 October 18th, 2025 at 3:23 pm
https://elderofziyon.blogspot.com/2025/09/weve-all-been-fighting-antisemitism.html
Comment #27 October 18th, 2025 at 4:06 pm
Ty #26: He’s right about all of it of course, but it’s far from obvious whether following his advice will help—haven’t many people already been trying these things?
Comment #28 October 18th, 2025 at 4:53 pm
Scott:
I’m curious whether you think the left-wing campus variety of anti-Zionism is
1.Primarily animated by a hatred of Jews, or
2.Primarily animated by a hatred of Western civilization
I think there are good arguments for both.
Comment #29 October 18th, 2025 at 5:25 pm
Julian #28: I think it’s much more 2 than 1, as the left-wing antizionists — in contrast to their right-wing counterparts — are only too happy to trumpet the thousands of Jews (“AsAJews”) who are on their side, the ones who want to join them in tearing down Western civilization, starting of course with Israel (I mean, where else would you start??), in order to usher in the universal peace and brotherhood that would surely follow such an act, just like the peace and brotherhood that followed the earlier glorious revolutions of Lenin and Mao and Khomeini. But it’s also complicated and not either-or.
Comment #30 October 18th, 2025 at 5:29 pm
David Brown #20: Yes, obviously. I explained that caveat when I delivered the talk, as I do every time I give talks introducing P vs NP to people who might not have seen it.
Comment #31 October 18th, 2025 at 5:34 pm
Ted #14: Yes. Indeed I’ve often engaged in exactly that sort of reasoning, as for example with protein folding, which long before AlphaFold, I and others argued was “presumably in P or at least BQP in the sense that’s practically relevant, notwithstanding any worst-case results to the contrary, because Nature solves it.”
Comment #32 October 18th, 2025 at 5:52 pm
David Deutsch first asked his “Where does the calculation occur?” question even back in his 1985 paper, where he ponders how a quantum computer could sometimes be used to more efficiently predict the stock market. His later 1997 question posed in *The Fabric of Reality* changed the game from the rather cute Deutch’s algorithm to the much, much more dramatic Shor’s algorithm.
It’s interesting to observe this development. His 1985 posting seems like an earnest and humble rhetorical question, that is, as an invitation to debate. His later, post-Shor ’94 question seems more assertive and dispositive in shifting the burden to those that challenge MWI.
But even still, is not the answer to the question of “where was the work done”, in Deutsch’s and Shor’s algorithm, “in Hilbert space!”?
Comment #33 October 18th, 2025 at 6:07 pm
Only an amateur speculation, but has anyone applied statistical methods to everettian multiverses?
Its often stated that “observation = entanglement + splitting”, which brings up the puzzle of why the number of worlds is so fantastically large. For example we write that (a|0> + b|1>)|Cat> decoheres to (a|0>|Cat-Alive> + b|1>|Cat-Dead>), but |Cat> is really a gigantically large number of atoms the associated photons and air molecules etc. The transition involves a gigantic number of interactions, and per-many worlds at every single interaction we have a many possibilities. The result is an extraordinary number of worlds in the everettian picture.
However we cannot actually distinguish these worlds! The outcomes group in to just 2 thermodynamically distinguishable states:|Cat-Alive> and |Cat-Dead>. The vast numbers of worlds has “collapsed” in to 2, which is not that far fetched. Now in classical Stat Mech we dont consider the micro-states to be actually indistinguishable in the QM sense so our need for statistics is explained away as ignorance. But perhaps what we are observing is an everettian multi-verse or atoms of photons, where many of the vast number of branches are in fact actually indistinguishable from each other and should be counted as one.
To make this relevant to Scott’s presentation: perhaps we should only count as branches those which we can distinguish by a reasonably computation. Perhaps we will find that there are much fewer than we thought.
Comment #34 October 18th, 2025 at 6:32 pm
Mark Spinelli #32: I mean, I certainly like the answer that “the computation was done in Hilbert space, that’s where.” Deutsch, as you know, would then raise the further question of how you could possibly deny the existence of the Everettian multiverse, once you’ve accepted the ontological reality of an exponentially large Hilbert space. For my own tentative answers to that question, you can refer back to my slides! 🙂
Comment #35 October 18th, 2025 at 6:48 pm
https://www.timesofisrael.com/ny-anti-israel-activists-hold-vigil-for-oct-7-hamas-chief-sinwar-on-anniversary-of-his-killing/
Anti-Israel activists in New York City on Thursday set up a display with images of several terror chiefs to mark the first anniversary of Hamas leader Yahya Sinwar’s death.
….
An announcement for the event was shared by other anti-Israel activist groups in the city, including the anti-Israel campus coalition at Columbia University.
“His embrace of death was not nihilistic but rooted in the conviction that martyrdom sustains the struggle,” Columbia University Apartheid Divest said in a Thursday statement hailing Sinwar.
—-
Comment #36 October 18th, 2025 at 6:49 pm
Ty #26: I don’t think it will work once you account for the fact that the antisemites vastly outnumber the Jews and Israelis and Zionists. Repeating the truth might, at best, only persuade a few antisemites at a time to let go of their false and hateful beliefs. To quote Scott’s zombie planet post: “[persuasion] can boot a few of the zombies’ brains back up. But even then, I fear that these reboots will be isolated successes. For every one who comes back online, a thousand will still shamble along in lockstep, chanting ‘brainsssssss! genocide! intifada!'”
A better solution would involve some combination of 1. building more safe spaces for Jews and pro-Israel people, and 2. appealing to allies who abhor the various ideologies that have eaten the antisemites’ brains (leftism, Islamism, etc.).
The biggest example of strategy 1 is the Zionist movement, whose founders in 1880s central and eastern Europe despaired of “fighting antisemitism” in the persuasion sense, and sought protection in the form of a Jewish state. On campuses in the diaspora, this strategy might look like funding more campus Hillels and Israel engagement centers. It might also mean hiring more security guards to protect Jewish spaces.
For strategy 2., allies can join the fight either for their own ideological reasons (rightism, counter-jihad, anti-wokeness, pro-Enlightenment centrism, etc.) or because they are apolitical and do not like it when deranged lunatics block traffic and scream slogans in their faces. There are still many downsides even if allies do come to support us, for instance as Scott #11 mentioned, Trump cut funding for science and medical research as part of the fight with antisemitism-enabling university admins.
Of course, the pro-Israel community should still continue to tell the truth. The truth needs to be told again and again for its own sake, even if no one is listening.
Comment #37 October 18th, 2025 at 9:35 pm
Scott #27:
“…haven’t many people already been trying these things?”
I’m not so sure they have. One would think critical thinking should be the backbone of liberal arts courses, but it seems to me schools/colleges/universities must teach very little in the way of it. Otherwise, how is it so many students blindly believe social media post on their feed without a questioning mind, seeking evidence or considering different perspectives?
Are our schools/colleges/universities failing young people by not giving them a thorough grounding in critical thinking? You are closer to the teaching world than me, so maybe you have a different take on things.
I also think there is something to the same blogger’s post linked below.
https://elderofziyon.blogspot.com/2025/10/free-speech-isnt-enough-universities.html
Comment #38 October 18th, 2025 at 9:39 pm
everytime I hear parallel world being taken seriously I cringe.
parallel worlds is just pure bs, nothing useful has ever come out of it.
people who like it tend to have particular attitudes towards life itself, so to my eye it is more like they are looking for something that is aligned with their attitude towards life than real hypnosis that they try to find evidence to rule out or support. it is for people who cannot handle random processes, so they have to assume that if you have a random process and an observation of the outcome, to achieve symmetry you need a parallel world in which the other possible outcomes occur. it is a confusion of possibility with actuality.
the issues with quantum physics that parallel world interpretation is trying to answer, point out actually to witnesses in the foundations of quantum physics, and point towards not talking quantum physics too seriously and physicists did with Newtonian physics for centuries.
a lot of physics theories are built upon unrealistic simplifications, assumptions that are needed because otherwise doing physics becomes too hard for our human brains computationally. we need to assume that we have isolated systems but in reality there is no small isolated system. etc. etc.
like many sciences, physics is built on top of some practical lies, and that is ok, but if we forget that and take the theories too seriously that is a problem.
who knows, many in 100 years we will learn that quantum physics breaks under particular conditions and the nice simplified theoretical foundation needs to be made much more complex to reflect better how reality works.
the idea that all the time infinite number of parallel universe get created out of no where is such a bizarre belief, it is completely against the Occam’s razor to believe in existence of such things.
Comment #39 October 18th, 2025 at 10:13 pm
anon #38: Since you’re so confident about these matters, surely you’ll be able to enlighten all of us novices. What is true about the world, such that we should describe it using the quantum formalism? What decides when unitary evolution is suspended and the wavefunction collapses instead? If not many-worlds, do you advocate Bohmian mechanics? A dynamical collapse mechanism? Perhaps some new view of your own invention? Don’t hold back!
Comment #40 October 18th, 2025 at 10:50 pm
who says that to rule out a wrong answer to a question you need to present what is the right answer?
confusing computation and model with reality is a mistake.
quantum physics can calculate some things but when it comes to interpreting things, it is big mess.
I define some mathematical entity, and I take a path integral to compute some entity, and I provide experimental evidence that the mathematically computed entity matches to some precision under some assumptions the experimentally measured one. Then I caim that because this is how I mathematically defined it or computed it, that process of computing it should reflect the reality.
no, it does not!
it is well know how often physics abuses mathematics as it pleases and then some try to make some philosophical claims based on that mathematics, that is just ridiculous.
parallel worlds is a useless baseless game of words.
you rule out that the God of Judaism does interferes in every experiment to determine the outcome of every random process and I will rule out for you that parallel worlds interpretation is bs.
of course, like us mathematicians don’t like the dirty laundry about the foundations of math being exposed to general public cause it might shake their belief in math on general, like the fact that both assuming and rejecting axiom of choice leads to unexpected strange consequences and there is no way to prove which one is really correct, the physicist don’t like the dirty laundry about their pragmatic assumptions being out exposed to general public.
there is zero evidence for parallel worlds interpretation, and there is no way to refuse it cause it does not make any observable and refutable predictions.
you have a foundations problem in quantum physics theory, you make up some stories to get around that, I can make a many others, including some of the basic instated unstated assumptions being incorrect, until you make predictions that can be verified and refuted, it is just a story. and as a story it is pretty incoherent one if one starts to take it seriously from philosophical perspective.
apply your own favorite Occam’s Razor: why should one assume existence of such things with no experimental evidence and no serious argument for their existence?
the parallel worlds interpretation is as satisfactory explanation for what we cannot explain as assuming the God of Judaism as the explanation for what we cannot explain, i.e. not satisfactory at all.
Comment #41 October 19th, 2025 at 3:11 am
Your blog motto says: “quantum computers won’t solve hard problems instantly by just trying all solutions in parallel.”
Okay, but quantum computers do not solve problems by tapping into parallel universes either. That is an even more erroneous explanation. So why do you promote that as a good way to conceptualize quantum computers?
Both explanations have some intuitive value for some people. But neither is needed for Shor’s algorithm. Many-worlds is especially BS, for all the reasons given by anon#38. I suggest you augment your motto with “… or by using parallel worlds.”
Comment #42 October 19th, 2025 at 10:43 am
I like how these two out-of-context snippets seem to answer each other, as if by coincidence:
#39>What is true about the world, such that we should describe it using the quantum formalism?
#38>The fact that both assuming and rejecting axiom of choice leads to unexpected strange consequences and there is no way to prove which one is really correct
But I’d opt for a more succinct version of #40:
>What decides when unitary evolution is suspended and the wavefunction collapses instead?
The way you model it.
>If not many-worlds, do you advocate Bohmian mechanics? A dynamical collapse mechanism? Perhaps some new view of your own invention?
Yes—all of them. These are models. Use them when they serve a purpose. Invent new ones when the old ones fall short.
Comment #43 October 19th, 2025 at 11:28 am
While I completely disagree with anon and Roger Schlafly’s views on MWI for other reasons, I also struggle with the idea that quantum complexity theory sheds light on the question.
In particular, I wonder how Deutsch’s “notorious 1997 challenge” (Scott’s slide 15) is different to saying something like “to those who cling to the single-universe view of classical physics, explain how the AKS primality testing algorithm works. In particular, where were the (exponentially many) potential prime factors being checked, if not in an exponentially large array of parallel classical worlds?”
You could also make a similar challenge about classical probabilistic algorithms, whose state space (of probability vectors) dimension is exponentially large. Where is the computation happening if the exponentially large state space isn’t real?
If quantum computers could solve an *unstructured* search problem over an exponentially large space in a polynomial time, I think Deutsch’s argument would seem a lot more convincing. As things stand, I agree with Scott’s view on p17.
A second point about MWI is that, while overall I think there are excellent physics reasons for accepting this interpretation or at least taking it very seriously, overall I haven’t found the intuition from MWI useful in understanding QC.
Partly this is because in practice it seems quite important to cleanly separate quantum and classical operations (with decoherence prevention and quantum error correction being necessary for just the former) and partly if you’re not careful it will lead you to believe quantum computers are far more powerful than they are (e.g. that an unstructured search in poly time really is possible).
There are a couple of exceptions I can think of:
(a) the deferred measurement principle,
(b) the no signalling theorem.
To me, the fact MWI exists (and the experiments involved can be understood in MW terms) makes these results almost obvious, and in particular gives an intuition towards their proofs (which are then valid in other interpretations too).
Still, the fact MWI led Deutsch to invent QC obviously trumps my probably-faulty intuitions about what seems useful. OTOH my guess is that many comparably important QC breakthroughs have been made over the years by those indifferent or even hostile to MWI, though I don’t have data on that.
Comment #44 October 19th, 2025 at 11:36 am
Anon #38, anon #40, Roger Schlafly #41:
Your arguments against many worlds are built off of the argument from incredulity (https://yourlogicalfallacyis.com/personal-incredulity) and not from any actually rational or empirical disproof of many worlds.
Also, you are misusing Occam’s Razor. Most of the argument was already made here: https://www.lesswrong.com/rationality/decoherence-is-simple. Tl;dr: Occam’s Razor counts the complexity of the theory, and not the complexity of the world that emerges from the theory. Many worlds uses the math of QM without add-ons like collapse or particles guided by pilot waves. So yes, there is plenty of evidence for many worlds: it is the same as the evidence for QM itself. The evidence also fits the other interpretations, but the other interpretations add complications that many worlds does not add.
Also, the worlds do not become parallel without decoherence, and most of the effort on the engineering side of QC is about preventing decoherence from happening during the calculation. So, yes, it would make sense to say that Shor’s algorithm is implemented in many worlds. Those worlds are interfering with one another, and it is that very interference that, if choreographed correctly, leads to a high chance of getting the right answer once the quantum computer is allowed to decohere and interact with the environment. So you are only right to augment the motto with “or by using parallel worlds” because of the word “parallel”.
Comment #45 October 19th, 2025 at 11:45 am
Peter Woit fan here.
I believe you are being unfair.
Peter did not call you a a mentally ill fascist. He said that you were inadvertently collaborating with an authoritarian regime (Trump) by amplifying their lies about Columbia, and that your theoretical Trolley arguments were lending moral support to an ongoing genocide. To be honest, I don’t understand what’s going on in Israel and Palestine, and I don’t want to present myself as some kind of expert on American politics either. I don’t know who’s wrong or right here, but I do know, from the perspective of an outside observer, that you are misrepresenting what Peter said.
Comment #46 October 19th, 2025 at 12:37 pm
Josh #45: The genocide accusation alone should be sufficient reason to discredit Woit. Also, Scott did not lie about Columbia. He repeated what Columbia’s own investigators put in their antisemitism report.
Comment #47 October 19th, 2025 at 12:58 pm
Josh #45: When I pointed out that, week after week, Peter chose to use his blog to call me a mentally ill, genocidal fascist, Peter’s only correction to that was indeed “fascist collaborator.” I … uhh, accept the correction.
Meanwhile, if you want to talk about unfairness, Peter has aggressively, gleefully refused even to entertain my best understanding of reality — namely that Israel, a flawed democracy surrounded by actual genocidal maniacs, just fought and won yet another war for its continued survival on earth, and it’s hardly surprising that much of the world strongly opposed its doing so, because much of the world has strongly opposed Jewish existence altogether for more than 2000 years. Peter insisted on rewriting my words into something horrible that I never said and never would say, that Israel should kill Gazan civilians because they might kill Jews in the future. No, of course not, any more than the Allies should’ve killed German children because they might grow up to be Nazis. The goal, in both cases, is simply to win the war, while killing as few civilians as feasible, which unfortunately will never be zero when facing an enemy who places civilians in harm’s way. This is such a simple concept that I have difficulty seeing how anyone could fail to understand it, except if
(1) they’re wildly misinformed, or
(2) they’re actually on the side of the Nazis (then) or Hamas (now), and wish for that side to win.
With many of the Columbia protesters who Peter defends, we know that the right answer is (2), because they’ve told us so (“honor Yahya Sinwar and all our martyrs!,” as they recently chanted). Peter pretended for a long time not to have any position on the conflict, before finally revealing himself to be on the intifada side. I’ll give you the benefit of the doubt that you really don’t know what’s at stake here; happy to give reading recommendations if you want.
Comment #48 October 19th, 2025 at 1:24 pm
Hi Scott,
Thanks for your response.
Unfortunately, though, it leaves me even more confused!
Peter, like me, is a traditional pro-Israel Zionist—meaning not that he supports every military campaign of the IDF including the horrific recent ones in Gaza, but just that he believes that Israel should exist as a secular democratic but culturally Jewish state in the Middle East.
What he’s opposed to is not the existence of the state of Israel, but the exploitation of October 7th as a pretext to destroy Gazan society and realize the territorial “irredentism” of the Israeli far-right (as embodied by Smotrich and Ben-Gvir)—i.e., the creation of a “greater Israel.”
The weird thing is, I used to think you agreed with him about this—that the Israeli far-right had this “greater Israel” project, and that pursuing it was anti-humanitarian and idiotic.
But after October 7, though, you seem to have lost all sense. You seem to have lost recognition of the obviois reality that the Israeli far-right would seize on the horrors of October 7 as a pretext for implementing the “final solution to the Palestinian question”—the destruction of Gaza, the displacement of its inhabitants elsewhere, and its absorption into “Greater Israel.”
Peter’s perspective is not that the horrors of October 7 were justified or right, bur rather that the Israeli response was not what is needed to keep Israel safe, but rather aimed at the total destruction of Gazan society, with October 7 as a mere pretext. Just look at the statistics: most Gazan buildings, residential and commercial, destroyed, most Gazan farmland destroyed, all Gazan schools and universities destroyed, most Gazan hospitals destroyed, 100,000+ Gazan civilians killed. This is not what “destroy the nerve centers of Hamas, even if they’re under civilian centers” looks like. This is what “destroy an entire society and force them to leave” looks like. Why can’t you see this?
Comment #49 October 19th, 2025 at 1:45 pm
Scott, re the description of Copenhagen on slide 14 as “learn to stop asking the question”, I was wondering if you had thoughts about the modern updates of this interpretation? While QBism and other “epistemic” approaches have received a lot of attention in recent years, I’m thinking more of Griffiths et al’s Consistent Histories approach from the 1980s, since this seems very much in the spirit of Bohr’s complementarity principle, but without the obscurity or verbiage.
Comment #50 October 19th, 2025 at 2:15 pm
Also, have you thought even once about talking to Peter Woit in person to clear this up? Or do you just want to insult him from the distance of your internet connection?
Comment #51 October 19th, 2025 at 4:37 pm
Josh #48: Yes, there is a far right in Israel that would love to annex Gaza and the West Bank, and yes, I’ve consistently opposed them.
And no, this has basically nothing to do with the “genocide” blood-libel against Israel, which Peter decided to join.
As I see it, it’s impossible to be any sort of Zionist while also believing that Israel is guilty of genocide. For if Israel were actually guilty, then it would deserve to be obliterated as a political and military entity, just like Nazi Germany and Imperial Japan were. And, consistently with that, pretty much all the activist groups around the world who’ve accused Israel of “genocide” also oppose any two-state solution, in favor of the Arab countries’ original “Israel gets annihilated” solution (as shown by their chanting about “the river to the sea”).
But of course, the claim that Israel committed “genocide” has as much going for it as the previous claims that the Jews poisoned wells and baked the blood of Christian children into their Passover matzo, and is being spread for the same purpose.
In a real genocide (like the one that destroyed most of my extended family), the population being annihilated doesn’t increase in number over the course of the “genocide.” In a real genocide, the perpetrator doesn’t agree to a ceasefire as soon as it achieves some (not even all) of its military objectives, especially the return of its innocent hostages. When you or Peter or Greta Thunberg say “genocide,” the word that you’re looking for is “war.”
What happened, again, is that Israel fought and won yet another war for its continued survival, against a force (Hamas) that sought a genocide of the Jews. And say whatever you want about Netanyahu (let alone Smotrich and Ben-Gvir)—my condemnations of them could fill pages—a left-wing Israeli government would almost certainly have fought roughly this same war, with roughly the same number of Palestinian casualties, because no one ever suggested any better way to defeat Hamas, a goal that became self-evidently necessary after October 7.
In short, when people accuse Israel of “genocide,” whatever their protestations, they’re recklessly spreading a libel whose whole point is to justify an actual genocide: Hamas’s genocide of the Jews, the generations-old dream that they believe to be the will of Allah, and worth sacrificing an unlimited number of their own people for.
I wouldn’t have believed such impulses could motivate Peter Woit, who I was cordial with for 20 years. But, together with his contemptuous dismissal of hundreds of Jewish students’ reports of the antisemitism they experienced at Columbia, an all-too-consistent picture emerged, so I went where the evidence led.
Comment #52 October 19th, 2025 at 4:44 pm
flergalwit #49: Actually I always thought of consistent histories as much more similar to many-worlds than Copenhagen—indeed, as basically an elaboration of many-worlds. But it’s true that there’s a sort of continuum with “Copenhagen-like” views on one end and “many-worlds-like” views on the other, with the slider controlling just how explicit you want to be about the ontological reality of the “other” branches (the ones we don’t experience), versus leaving them buried in the Schrödinger equation with the whole question left politely unasked.
Comment #53 October 19th, 2025 at 5:01 pm
Josh #50:
Also, have you thought even once about talking to Peter Woit in person to clear this up? Or do you just want to insult him from the distance of your internet connection?
Why did it never even occur to you to ask the same question of Peter? I mean, he’s the one who defected first, calling me a “fanatic” who “needs therapy,” a “fascist collaborator,” etc. etc. while I was trying hard to staying focused on the issues!
More broadly: do you understand how painful it’s been, since October 7, to suffer total ruptures not just with Peter, but with at least a half-dozen other people who I thought were my friends? Do you understand how I don’t take such a step lightly?
The good news is that there are hundreds of others of all backgrounds with whom I’ve maintained or even strengthened my relationships—without having to agree with them about everything. None of those people have indulged in blood libels, or dismissed well-documented antisemitism as fake, both of which are sort of red lines for me.
Comment #54 October 19th, 2025 at 5:08 pm
Josh #48: “100,000+ Gazan civilians killed” – where did you get the numbers for this? Going by this source I found in a Google search (https://www.pbs.org/newshour/world/palestinian-death-toll-in-gaza-passes-64000-officials-say-after-ceasefire-talks-break-down), the Gaza Health Ministry says that the total death toll in Gaza for the war is 64,231. Since the Gaza Health Ministry is controlled by Hamas, they have every incentive to exaggerate, so we should take this number as an upper limit. I think that at least half of that figure is terrorist casualties, so the actual civilian death toll in Gaza is probably 30,000. I don’t know where you got the 100,000+ figure from, but it seems like you are trying to pull something here by stating such a ridiculously large number.
Comment #55 October 19th, 2025 at 5:31 pm
You are wrong about the definition of genocide. Here’s Wikipedia:
Genocide is violence that targets individuals because of their membership of a group and aims at the destruction of a people.[a][1] Raphael Lemkin, who coined the term, defined genocide as “the destruction of a nation or of an ethnic group” by means such as “the disintegration of [its] political and social institutions, of [its] culture, language, national feelings, religion, and [its] economic existence”.
and
It is a common misconception that genocide necessarily involves mass killing; indeed, it may occur without a single person being killed.
One way to destroy a people is by killing them. Another way is through forced displacement. Another way is by by separating children from parents and indoctrinating children (e.g., the forced “education” of American Indians at boarding schools).
I don’t know where you got the figure that the Gazan population increased since 2023. Share it? I didn’t know they could do a census now, in the bombed-out hellscape that is Gaza today. What I have seen are quality surveys (e.g. from the Lancet) showing deaths multiple times higher than recorded, so potentially in the hundreds of thousands.
The destruction of more than half the residential and commercial buildings, 60% of the farmland, all the schools and universities, most of the hospitals etc. certainly looks like an attempt to destroy a culture.
Please, because I’m not as wise about war as you, could you enlighten me why the IDF needed to destroy more than half the buildings, 60% of the farmland, all the schools and universities, and most of the hospitals? Were there Hamas bases beneath every one? It’s truly amazing how many secret bases Hamas has, it must be in the thousands by now—more than any military on Earth!
Comment #56 October 19th, 2025 at 5:47 pm
#44
no, they are not based on that. I understand pretty well what is being said and I find it bs.
no, you don’t understand Occam’s Razor. You cannot assume existence of such things to explain something like your issues with conceptual problems that have existed with the quantum physics from the beginning.
the rest of what you wrote does not advance your position for the parallel world being a reasonable story.
a story making you feel better or feeling it helps you does not make it true, there is no experimental evidence for it, there are no refutable predictions, there are no reasoning, …. it is just a story and it is a pretty lousy and incoherent magical story
it really cringes me when I see people making statements like these, who don’t actually understand deeply what they are talking about (like when people try to make philosophical claims based on Godel’s incompleteness theorem but don’t actually understand its assumptions).
if it was up to me, I would add a required course of methodology of science to every science degree.
you have your mathematical definitions and theories and models, you have your mathematical tools, you see that your theory can make useful predictions about what we can observe and measure **to some precision** and **under some assumptions**. that makes the theory useful. it does not make the theory a description of reality.
you have problems with explaining why your mathematical theory works and how to interpret some things you do in your mathematical theory and relating them to reality. guess what? not everything in your theory needs to have a corresponding thing in the reality, your mathematical theory is NOT a description of reality.
when you have issues conceptually or when your theory starts to fail, you start thinking about fixing the theory, and you make a better one that makes better predictions and is more useful.
a pseudo-science theory however will tell stories to cover up the problems with the theory. it will make arbitrary things to make the theory look better without telling us anything new about the world as we interact with it.
does parallel worlds interpretation tell us anything interesting or useful about the world? no, it does not!
physics these days is getting more extreme in trying to cover up problems they have with relating how observations and theory based computations are related. your integral doesn’t predict the reality? introduce massive number of particles coming into existence and disappearing from existence randomly to make the theoretical computation match the reality.
it is such a lousy way of doing science, assume whatever it pleases you about the reality, modify it as you please without any experimental evidence or serious argument, just to make your calculations match measurements with the theory. one might say it is really becoming as bad as ancient Greek gods.
you cannot even explain what you call a measurement and then you are asking why when we measure the wave finding collapses.
the output of Shor’s algorithm is not the aggregate across the branches, you have to run out many times and record the output and then compute the statistics, you don’t get the answer by observing the outcome of one run! You have to run it many times to find the answer. And then someone is acting as if the outcome of one run of Shor’s algorithm is encompassing the information over all possible branches, I cringe. That is NOT how a probabilistic algorithm works and what is NOT how a BQP algorithms work!
To be able to actually use these algorithms you need a source of randomness! if you don’t have that, then it does NOT work! if you cannot accept that there is randomness, and for all possible branches much correspond to some reality you have much bigger problems. for each branch I can just assume superdeterminism from the perspective of an observer in that branch. and I will run into more and more problems like what happens to the observer of a quantum state collapse? ….
if someone really takes parallel worlds seriously they will quickly see it is completely incoherent mess. all this for what? so that can we can feel a bit better about what we call “measurement” and “collapse of wave funding”?
Comment #57 October 19th, 2025 at 5:50 pm
As a physics grad student, I was pretty good at differential equations, and thus doing the problems in QM books. Partly due to being uneasy about my lack of knowing what was really going on in QM, I switched to math, where I knew what was going on. Now, a half century later I have been reading up on QM foundations, and have a couple remarks.
1. Most interpretations of QM seem like obvious or at least reasonable approaches to figuring out what happens when a measurement is made. But MWI is different.
2. While logically simple, MWI seems crazy AF. Next time you look at a deep space image of zillions of galaxies, ponder how many splittings happen each second, and where do all these branches live? Yikes! Given that we have no idea what is really going on, maybe this works, but I doubt it. I realize that a lot of smart and seemingly sane experts, e.g., Sean Carroll, like MWI, so there is that. I hope to live another couple hundred years so I can see how this plays out.
3. Apparently no one has any idea why Everett proposed MWI. It might have been to put QM on a solid foundation, or a prank or joke, or to show off how sharp he was, or who knows what. In any case he put in the work to flesh it out, and then left academia. It would have been great if he had stayed with physics and maybe specialized in foundations of QM. Incidentally, Everett’s son (a very original and very famous musician (eelstheband.com)) has an autobiography emphasizing his unusual childhood.
Comment #58 October 19th, 2025 at 5:50 pm
AF:
I got my numbers from Wikipedia:
77,659+ reported killed, including:
68,159 killed[17][18]
9,500 missing and presumed dead[19][g]
Your numbers missed the 9,500, which are corpses buried under the rubble of collapsed buildings and never counted.
According to this same wikipedia article, internal Israeli sources say about 83% of deaths are civilians, so that’s about 66,000 civilian deaths.
The GHM numbers are widely regarded as highly accurate by experts. Every body is identified and accounted for. In fact, this count is almost certainly an undercount because of all the poor people including babies buried under the rubble of buildings never to be seen again—the 9,500 is almost certainly an undercount. They can’t count all the deaths because most of the Gaza Health Ministry is dead.
According to a study published in the Lancet, the GHM underreported deaths by about 40% until June 2024–the official figure was 37,000 and they estimated 64,000 traumatic injury deaths. Extrapolating that same underreporting factor to today, you would expect 66,000 /0.6 =110,000.
https://www.cnn.com/2025/01/09/middleeast/gaza-death-toll-underreported-study-intl
Comment #59 October 19th, 2025 at 6:03 pm
Josh #48:
It’s certainly didn’t take you long to go from (Josh #45):
“To be honest, I don’t understand what’s going on in Israel and Palestine…”
to confidently asserting (“the obvious reality”), or agreeing with others who you claim assert, the existence of ulterior motives for Israel’s actions in Gaza (“Greater Israel”), comparing contemporary Israeli policy to that of the Nazis (“final solution to the Palestinian question”), and Genocide being the goal from the beginning (“aimed at the total destruction of Gazan society, with October 7 as a mere pretext”).
With such a quick transition, it’s not surprising nuance does not feature heavily in your thought process. Given you didn’t “understand what’s going on in Israel and Palestine” a day ago, can you provide links to the evidence (including alternate views you rejected) that helped you achieve clarity so quickly?
Comment #60 October 19th, 2025 at 6:25 pm
>The goal, in both cases, is simply to win the war, while killing as few civilians as feasible
Your need to believe that is palpable. But please ask yourself: what number of *unfortunate casualties* would finally compel you to question that belief? Would it take the same number of civilian deaths as those abjectly murdered by Hamas? The same proportion of the population? More? How much more?
Comment #61 October 19th, 2025 at 6:40 pm
Josh #55: For someone who just yesterday was pretending not to know anything about this conflict, you’re suddenly bursting with facts! But of course, not all the facts.
Were you unaware that the very definition of “genocide” was recently changed, specifically so that Israel could be accused of it?
Were you unaware that the parts of Wikipedia dealing with Israel/Palestine were recently ideologically captured, rewritten, and then locked down by an organized group called “Tech for Palestine”—a development that’s been extensively covered in the press and condemned by Wikipedia cofounder Larry Sanger, and that (alas) has called the entire future of the Wikipedia project into question?
Were you unaware that Hamas spent billions of dollars in aid money over the past two decades transforming Gaza into a giant base from which to attack Israel, with entrances to its tunnel system from thousands of meticulously booby-trapped schools, hospitals, and residences, and that this is why the IDF needed to level so much? (The alternative would’ve been to bomb essentially everything, indiscriminately, as for example the Allies did in Tokyo, and of course Hiroshima and Nagasaki, in WWII. That would’ve saved hundreds of Israeli soldiers’ lives, but was ruled out on humanitarian grounds.)
You, sadly, have now revealed yourself to be what I described in a previous post as one of the millions of ideologically-captured zombies who now roam the earth. There’s nothing new about that! For as long as there have been Jews, people have been creating whole theoretical frameworks to justify the Jews’ annihilation, always using whatever concepts are in vogue at the time (right now it’s “genocide,” “colonialism,” “apartheid,” etc). But time has shown me the futility of arguing with such zombies on my blog. You are banned from this comment section for life. That doesn’t come close to expressing the full extent of my contempt for you, but it will have to do.
Comment #62 October 19th, 2025 at 6:56 pm
anon #56: After defending myself against people who would justify my family members’ annihilation from the earth, it feels almost relaxing to argue with someone who “merely” thinks I’m an idiot about quantum mechanics, which I’ve spent the majority of my life on! 😀
Look, you don’t need to be a fan of many-worlds. I’m not a hardcore many-worlder myself, and often argue against many-worlders when I meet them.
But Sean Carroll, David Deutsch, Stephen Hawking, Don Page, Wojciech Zurek, and Lev Vaidman all are (or were) hardcore many-worlders. From that alone, we deduce that there can’t be anything trivial about quantum mechanics (or math and physics more generally) that the many-worlders simply fail to understand.
Indeed, given certain axioms about what a scientific theory is supposed to do for you, what we mean by the “simplicity” of a theory, etc., you’re led inevitably to many-worlds, as an almost “conservative” picture of whatever reality the Schrödinger equation is describing. And given those same axioms, your retort that “it’s just math, there doesn’t have to be any picture of reality behind it” sounds just as dumb as when the Church said the same to Galileo about heliocentrism.
To be sure, given other axioms about what a scientific theory is supposed to do for you and what we mean by the “simplicity” of theories, you’re led inevitably to something like Copenhagen (where you seem to be), or to something like Bohmian mechanics, or to the rejection of quantum mechanics itself and the hope for its amendment by some future dynamical collapse mechanism. That’s the reason why this has been a whole debate for a century!
Comment #63 October 19th, 2025 at 7:06 pm
Anon#42 #60: During the Holocaust, the Nazis easily killed 2/3 of all European Jews (while the Palestinian leadership of the time cheered, offered its assistance, and campaigned for the Final Solution to be brought to the Jews of Mandate Palestine—Hamas is the direct descendant of that leadership).
It would’ve been even easier today for Israel to kill 2/3 of all Palestinians, had it wanted to. The moment I saw any movement toward such a goal (rather than hundreds of IDF soldiers falling in battle so that Israel could win this war while killing “only” 2-3% of Gazans), I’d admit that my whole picture of reality was wrong. But of course I haven’t seen that, and am not wrong.
Comment #64 October 19th, 2025 at 7:06 pm
Everyone: I’ll close this thread later tonight, since (perhaps inevitably) the zombies are now out in force.
Comment #65 October 19th, 2025 at 7:19 pm
https://elderofziyon.blogspot.com/2025/08/why-idf-must-flatten-buildings-in-gaza.html
Comment #66 October 19th, 2025 at 8:22 pm
Roger Schlafly #41:
Your blog motto says: “quantum computers won’t solve hard problems instantly by just trying all solutions in parallel.”
Okay, but quantum computers do not solve problems by tapping into parallel universes either. That is an even more erroneous explanation. So why do you promote that as a good way to conceptualize quantum computers?
Both explanations have some intuitive value for some people. But neither is needed for Shor’s algorithm.
I agree that many-worlds isn’t necessary to explain quantum computing — and unlike Deutsch, I’ve never claimed that it is.
On the other hand, in two decades of actual on-the-ground experience teaching quantum computing to undergrads, I’ve seen again and again how confused they get by the fact that a CNOT from |ψ⟩ to an ancilla qubit, has exactly the same local effect on |ψ⟩ as if someone had measured it, mapping a pure state to a mixed state. And again and again I’ve found myself saying: “look, imagine if you like that the one qubit measures the other qubit! what did you think measurement was in the first place, if not the measured state getting entangled with the measuring apparatus and the larger environment?” And I’ve seen how much this Everettian way of thinking helps pedagogically, even if the student doesn’t want to swallow the full Everettian metaphysics, as I’m not sure that I do. So these ideas do pay rent, even if they aren’t logically indispensable.
Comment #67 October 19th, 2025 at 8:23 pm
I definitely don’t think you are an idiot, I like your work overall.
that doesn’t mean what you say is always high quality. as a fellow mathematician and computer scientist who also has studied philosophy quite a bit, take this from me that when you cross to make philosophical claims, you walk on very thin ice often. people might like it and you might enjoy philosophical thoughts but you are not a careful thinker on these areas in my experience of reading your writings and listening to your interviews and lectures, which I generally enjoy.
I strongly disagree with appeal to famous physicists as authority on matters of philosophy or methodology of science. the same way most mathematicians are not authority on matters of foundations of math, most physicists, even very famous ones, are no authority on such matters.
and no, parallel worlds interpretation is not simple when taken seriously. it might look simple as it looks simple to a religious person to explain everything using God as the explanation, but it is not simple.
we want to explain conceptual problems with measurement and collapse of wave function and to do that we assume existence of infinite number of worlds, actually uncountable number of worlds, created all the time by measurement and observation, which itself is one of the conceptual problems. it is a total mess that looks simple initially.
Comment #68 October 19th, 2025 at 8:28 pm
anon #67: OK, but there are also serious philosophers of science, like Saunders and Wallace, who are MWI proponents. Appeal to authority doesn’t work to tell you which opinion is right, but it sort of does work to tell you which opinions can’t be wrong for completely stupid or obvious reasons … at least if you pick the right authorities! 🙂