Many-worlds is an interpretation and not a theory. It makes no additional predictions beyond what QM does. Believing in any interpretation (or shutting up and calculating) is purely emotional; it has no scientific content.

The quantum world involves states that are a complex linear superposition of all possible states. It isn't just that the world bifurcates into one where the cat is |alive> or |dead>, but also all c1 |alive> + c2 |dead>, where c1^2+c2^2 = 1 and c1 and c2 are complex. The MWI has no explanation for how this other infinity of possible states disappears into just two states. You still wind up with the collapse of the wave function--involving a lot of hand-waving or appealing to some nebulous property of consciousness.

Given we haven’t bridged quantum with gravity yet, my bet is the function collapses right at the boundary when gravity starts to play a meaningful role.

That’s a more physically plausible interpretation than ever “tick” of the universe actually creates infinitely more universes because every fundamental particle is quantum and each one is constantly interacting under the wave function every plank second. And the infinite number of possible events that a single particle would experience is multiplied by the joint combination of all particles in the entire universe. It doesn’t seem plausible.

When the future has multiple instances of you, it becomes problematic to define what the Born rule means.

For example, "Many Worlds, the Born Rule, and Self-Locating Uncertainty" notices that the rule doesn't mean anything, but it is rational to behave like it does. It's not a very satisfying position, I'd say.

Is many worlds falsifiable?

"Many-worlds just states there is no such thing as wave function collapse" is the emotional statement. The contempt for many-worlds is both principled and rational.

Don't take the title too literally. It's an article aimed at lay people, using a typical lay person's expression as the title.

I disagree. The human brain is difficult to understand due to the extreme complexity. Quantum mechanics is weird even for simple arrangements of a few building blocks such as the double-slit experiment or Bell tests.

Quantum physics is a theory, as in "as far as we can tell, this is an exact mathematical description of the world".

Models are simplifications/approximations made on purpose, as in "I know this is wrong on some level, but it's close enough for my use case", or "this makes the maths solvable".

One problem with your analogy is that transformers do not even attempt to model the human brain, while Quantum Mechanics does attempt to model real physics.

> All models are wrong

That famous quote could use attribution: https://en.wikipedia.org/wiki/All_models_are_wrong

> If you make the error of believing that quantum mechanics is ontological god’s honest truth of nature

This is why science & experiment exists. The author holds no such belief, and the paper makes that very clear. That is what he actually meant by “I Don’t Understand Quantum Physics”. Jump to the very last section, “Is Quantum Theory Correct and Complete?” He’s pointing out the confusing and contradictory nature of the model so far, and saying that Quantum is incomplete and needs work. He is not making any category error.

I think the vast majority of physicists have been perfectly able to avoid Penrose's error. I would also think the lesson would be simply to strive to avoid making errors or the kind he did, not necessarily to sacrifice realism about physical objects just to avoid the possibility of someone's mistake. Plenty of people, in fact I would say many more people abuse the observer effect in QM to make crackpot claims about consciousness. But it doesn't mean the observer effect is wrong.

I also think you can be a realist without having to make the jump to ontological irreducibility. You can say that our latest theory is a better approximation than the previous one and the previous one was an approximation as well.

What a strange statement. Quantum mechanics is a physical model of the world. Attention and transformers are not. They can be construed into one in principle, but they are not models of the world themselves.

Yes, but even with a model, you should aim for some serious intuition as to how and why it works.

Penrose has fallen into the same logical fallacy that many older, retired theoretical physicists have (notable einstein?).

> It doesn't. It's model. All models are wrong (including quantum mechanics and attention) but some are useful.

Sure, but what if you don’t understand the model?

Somehow hacker news makes the top comment about some weird unrelated ai take. So unrelated. The take mostly doesn't make sense either.

There are only a few things that I think are exactly correct in physics, and quantum mechanics is one of them, alongside Relativity.

Quantum mechanics is a framework for how theories are built, not a specific theory, and it's really all or nothing. There's not much between the quantum and classical ways of viewing the world.

Full PDF https://www.cs.ox.ac.uk/people/aleks.kissinger/PQP.pdf

This looks quite interesting; thanks for sharing.

Classical physicists had conceptual difficulty when something stopped behaving as "body" even macroscopically. For example when they tried to determine coefficient of friction of pure coper, throughly cleaned, in vacuum to prevent any oxidation, the surfaces cold-welded together. The copper did not get the memo that it is supposed to be two physical bodies.

Second this book, but you need a source before this to study QP successfully. This requires a lot of UG maths and physics knowledge that I think most would not have.

See also, Atomic Physics for Everyone: An Introduction to Atomic Physics, Quantum Mechanics, and Precision Spectroscopy with No College-Level Prerequisites. - https://news.ycombinator.com/item?id=46961595

I see 502 bad gateway

To be precise, Bell's inequality rules out a local hidden variable theory. Pilot wave theories/Bohmian mechanics is an attempt to describe a nonlocal hidden variable theory of quantum mechanics.

I've got a feeling that our intuitive ick around spooky action at a distance is due to out intuitive view on locality and the nature of space, maybe time too, being wrong. IOW remote is really not remote.

Perhaps we've got it backwards and quantum entanglement is what defines "locality" rather than mysteriously existing in the face of it.

If you saw that in section 15, the very next paragraph covers Bell.

it doesn't if you assume superdeterminism

Also see https://news.ycombinator.com/item?id=50220891

A useful analogy might be understanding quantum mechanics versus understanding a computer. In the early days of computing, an engineer might plausibly have known every component in a computer, understood how these components worked, and understood why each one was there. As computers got more complicated, no longer could anyone understand the entire system on that level. But still, as an individual engineer, you can understand the system at a high-level, and for each lower-level component, you can have an approximate idea of why it's there, what it does, and how to learn it in more detail if you ever have to. Any "why" question that you might have about it has a straightforward answer that can be stated in a few sentences.

With quantum mechanics, there's a lot that you have to accept when you learn the subject without understanding why. Why complex numbers? Why infinite-dimensional Hilbert spaces? Why non-commutative algebra? You can kind-of, with great effort, make arguments that all of these are at least reasonable. But nobody really understands "why" at a level beyond "because the theory works".

That’s not the meaning of “understand” that was being used. This article points out that nobody understands QM well enough, not even the experts. (Do note the author is an expert!) By “I Don’t Understand”, what he actually means is that QM is incomplete in the same way that Newtonian Mechanics is incomplete; it doesn’t explain physics well enough to understand or explain what’s really there. This is, of course, why there’s an ongoing debate among the experts about what QM even means and how to interpret it.

You can imagine waterfall of sand - the fluidity here comes from all those small sand particles moving simultaneously.

>>>Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math.

That sounds a lot like gate keeping and has no actual backing - to understand QM you still need to understand Physics, as mechanics of both of them are explaining each other - the scale is the only difference.

Why can AI generate pictures of waterfalls if it has never lived on Earth?

Whether this was even true in Feynman's time, it's much less true now.

I also like "If you think you understand quantum mechanics, you don't understand quantum mechanics" which is supposedly also from Feynman.

It's completely counterintuitive, but that's how it works experimentally. For example:

Measure the spin of electrons in direction X (that's done with a weirdly shaped magnet). You'll get either +1 or -1 in a conveniently chosen unit system. That's already weird, you'll never measure +0.5 for example. Keep only the +1 electrons. You can measure them again and again, you'll always get +1 in the X direction.

Now measure those electrons in the Y direction, you'll also get either +1 or -1.

But now, if you measure in the X direction again, you'll get +1 or -1 with 50% probability; although before measuring in the Y direction, these electrons always had spin +1 in the X direction.

It has been shown that you can keep determinism (Bohm etc), but what follows is not necessary something you'll find more intuitive or cleaner or more logical.

There's a section at the start that talks about what "understand" actually means.

It cannot be usefully analogized to things you can experience (or even to other things you might already understand).

Yes this is a particular interest of mine, the various interpretations of QM. Most physicists subscribe to the Copenhagen interpretation, but I still find it has philosophical quandaries. He mentioned many-worlds. Bohmian mechanics has been shown to be inadequate.

Blokhinstev's ensemble interpretation, which I like, is unattractive to many.

Situation: There are 12 major interpretations of quantum mechanics.

Quantum Bayesianism (QBism): We need to eliminate the interpretational conundrums that have beset quantum theory. A quantum state should not be thought to offer a description or representation of physical reality – instead it represents the degrees of belief an agent has about the possible outcomes of measurements.

Situation: There are 13 major interpretations of quantum mechanics.

https://xkcd.com/927/

>can the unknown that's being collapsed not be a pre-determined value that therefore is not traveling faster than the speed of light?

This is known as a "hidden variable theory". People will tell you that a local (things can only affect their immediate surroundings) version of the theory is impossible because it would be a violation of Bell's inequality, but there is a loophole that requires accepting the idea of "superdeterminism". This is the idea that where what measurement a scientist chooses to measure is predetermined and correlated with what the particle being measured is going to do.

So if a particle lands on a screen according to distribution p when going through a double slit, but with distribution p' when one of the slits is measured at, conventional QM says that the measurement "collapses the wave function". But a superdeterministic local hidden variable theory would imply that the choice of whether to measure at the slit or not was already set in stone at the same time that the particle "decided" which path to take to land on the screen, more or less.

If you split up an entangled pair of particles and measure them in a the same 50/50 basis simultaneously (sort of like a coin flip) at distantly removed places, the results will be individually random but perfectly correlated when compared with each other. It seems natural to assume that something here was pre-determined. i.e. There's was some kind of hidden information that we haven't found a way to measure yet. The way in which the coin-tosses were going to pan out was determined when the pair of particles were entangled.

Quantum physics makes predictions that suggest this isn't so. You can design experiments (e.g. A Bell inequality test) in which quantum physics predicts correlations that go beyond what would be possible with some hidden local information attached to the entangled particles that we just don't know about. Experiments don't prove theories to be correct. That's not how science works. However, experimental tests of Bell inequalities have pretty conclusively shown that local hidden variable theories are inadequate to explain what's going on.

Yes, it appears what Einstein called "spooky action at a distance" seems to propagate close to instantly. It's important to appreciate that you can't transmit information this way though. We can only make sense of the quantum correlations after communicating other information at classical speeds. Sometimes you see quantum entanglement devices allowing FTL communication in sci-fi, but that's pure horse hockey.

That all being said, I don't understand quantum physics either.

One of the "coping mechanisms" is to say that information cannot travel faster than light, even if entanglement is propagated instantaneously and measurement acts faster than light. If Alice and Bob share an entangled pair of spins and Alice measures it, Bob has gained no information until Alice communicates (sublight speed) her result. No new information is shared at measurement time. This is known as the no-communication theorem.

https://en.wikipedia.org/wiki/Hidden-variable_theory

>It sounds all superior and mysterious to quote Feynman here,

It isn't about being superior, mysterious, or clever. The following "nobody understands" type of quips and thought experiments are different ways of saying our intuitions don't help us understand it :

- "God does not play dice with the universe.", Albert Einstein

- "Shut up and calculate", N. David Mermin

- "Schrödinger's cat" being both alive and dead

- various interpretations/analogies explaining quantum physics leading to absurdities or contradictions

Yes, humanity has harnessed quantum mechanics with mathematic frameworks and repeatable experiments to make useful things... but that's a different layer of "understanding" than the deeper levels in the above quotes.

"Nobody understands what gravity is." ... Wait, if nobody "understands" gravity, how did we send people to the moon?!?

Because those are different usages of the word "understand".

I think the disconnect here is the use of the word "understand". What Feynman presumably meant was really "interpret" not "understand", and theories are not made to be interpreted - they are made to make experimental predictions.

Many people of course, Feynman obviously included, understand the theory in the sense of knowing how to correctly apply it to make predictions.

If one does understand quantum mechanics well enough to use it, then one also understands that there are aspects of it we do not fully understand.

Can’t we say the same about LLMs? Yet interpretability of them is rough.

We can build black boxes and exploit the behavior of what we see.

But we can’t always go to deeper and deeper layers of understanding.

QM is not a black boxes we built but one could perhaps say it’s a black box that we see.

Listen, people were able to make calendars by observing skies and assuming that Sun was orbiting Earth. It is not exactly the same, but very much how people understand QM - they do not need to known mechanics, but observing end results is enough to "understand" how it functions.

Also billions of people understand how to operate mobile phones, but "understanding how they operate" would be rather stretch and even the biggest specialists of QM have understanding only on how to interpret end results in QM - at best and that is basically it.

Quite frankly, I'm confused about these bold statements. I assume there seems to be some knowledge background of what you are saying - it very much reminds me what stupid strawman arguments I had in high school with my schoolmates then as a part of learning process, but rather far from actual wisdom.

Forgive my ignorance but which machines depend almost entirely on quantum principles?

does building those machines require us to fully understand quantum mechanics?

Or we understand just enough to make things and instruments that only work on (and up to) the layer that we understand.

Ancient humans could build boats 5000 years ago and expand throughout the planet, but they didn't know about water being made up of hydrogen+oxygen, or the tides being caused by the moon, etc.

Their calculations served them on the layer they operated on.

We understand part of it but not how it works.

> 2. Academia basically forces you to believe the doctrine or you fail the class.

Yes, but if you can make a reliable experiment that disagree with the doctrine, it will change, even if everyone hates the idea. In particular https://en.wikipedia.org/wiki/Wu_experiment

I disagree. Science is what we do to find out what is the case, i.e. real. The fact that it also has useful applications is directly tied to the extent to which the findings are real. It works because it describes something real.

And in case it wasn't already obvious, that URL indicates Doug was at the University for a long time. The University stopped letting even its staff pick a username years ago, maybe even decades ago and the default assigned usernames are... a bit dull.

Addendum:

The author also wrote a sequel; I DO Understand Relativity - https://news.ycombinator.com/item?id=50220891

Sorkin is great. I think causal sets make some things simpler but other more mysterious. I also found t’ Hooft’s automata and Spekkens toy illuminating in different ways.

So, not gravity or radio waves?