"This rather fanciful interpretation of Quantum Physics has now become accepted by many theoretical physicists as being more satisfactory than the Copenhagen interpretation, despite the fact that the mechanism which causes the splitting of the Universe is not explained in any more detail than wavefunction collapse. As you can probably tell, I am in the minority of physicists who finds the Many Worlds interpretation dificult to accept, and not particularly illuminating."
I think these lectures are a good intro to QM. This statement feels very emotional though. Many-worlds just states there is no such thing as wave function collapse. The many worlds are a logical conclusion following. Copenhagen simply refuses to elaborate to when wave-function collapse happens, which to me is not a complete theory.
You could have some critique of many-worlds in relation to statistics, although I think many people have given quite satisfactory explanations.
Many worlds is just bare bones QM.. If any other theory is proposed, it should be falsifiable (like pilot wave theory for example). Doesn't mean it won't be difficult to measure.
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.
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Given we havenât bridged quantum with gravity yet, my bet is the function collapses right at the boundary when gravity starts to play a meaningful role.
Thatâs a more physically plausible interpretation than ever âtickâ 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 doesnât seem plausible.
How would you define exactly âwhen gravity starts playing a roleâ. It always plays a role, from photons to planets.
And on the âevery tick creates more universesâ: we are completely fine with superposition in nanoscopic systems. Itâs just uneasy to follow that conclusion to the logical end. Just my two cents. I think just because the conclusion seems hard to grasp, the reasoning to get there is completely sound..
âStarts to play a roleâ means when the effect of gravity becomes significant to the quantum equations which currently donât have any placeholder for gravity.
Just like Newtonâs equations are accurate to describe gravity and motion but only because the full equations Einstein worked simplify to them at small speeds.
So similarly it would make more sense that quantum equations and relativity are two sides of the same coin and thereâs some missing mathematical bridge where at small particle sizes it simplifies to quantum and at large particle scales gravity matters and we get Newton and then further relativity.
Using Occamâs razor thatâs at least my prior vs some undefined mechanism of action where all possible interactions of every particle actually creates an infinite superposition of universes where that did happen and you get an infinite number of such superpositions ad infinitum. Much easier to believe the huge gaping hole between two very accurate theories explains how quantum mechanics turns into classical mechanics, especially since we know gravity exists, what it is, and quantum mechanics canât explain gravity.
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?
Yes. Many worlds is just the Schrödinger equation without the wave function collapse. It makes less assumptions. Falsify the Schrödinger equation, and you have falsified many worlds. However, is the wave function collapse falsifiable? It's one postulate which many worlds doesn't make, and it cannot be confirmed or falsified by experiment.
This is not what falsifiability means in the Popperian sense. You are confusing falsifiability of a theoryâs predictions with falsifiability of an additional claim of what those theories mean. We might as well say that the simulation hypothesis is falsifiable because the laws of physics govern our simulated universe, so if you can falsify those laws you can falsify the simulation hypothesis. That being said, the concept of falsifiability is not without its weaknesses.
> Many worlds is just the Schrödinger equation without the wave function collapse.
It is not, it is the Schrödinger equation plus an extra rule that says that classical observers are only certain kinds of quantum states. There's no explanation in the MWI for why a device never reads out that a particle is 1/sqrt(2) |here> + 1/sqrt(2)|there>, even though that is exactly as probable a state as being |here>. And it turns out that this is exactly equivalent to positing wave function collapse / the Born rule.
And no, decoherence has nothing to do with this. Decoherence explains why there is no observable interference at the classical level between these states, not why you can only observe some states.
This is known as the preferred basis problem, for anyone who wants to read more about it.
Exactly.
Any good scientific theory must create falsifiable hypotheses.
Otherwise itâs just a nice story.
>Any good scientific theory must create falsifiable hypotheses.
For any behavior inside the world, this is good.
But for the world itself and what harbor's it, asking for falsifiability is like measuring the expansion of space using a ruler that inhabits the same space.
Even science, that works in terms of cause and affect, which implies space and time, cannot be used to describe space and time itself.
Vanilla "scientists" have been trying to do that, but that is a dead end.
Sharing in case useful for someone. Started getting into this subject in 2015, and full disclosure: I'm no physicist by any means. Without the formal background, the math and concepts were really hard to conjure and comprehend purely from the page, so I built an interactive self-study guide to "feel" the equations from Newton to holography. https://apples-to-entanglement.jasonrys.com/
Of possible interest
Basic Concepts Of Quantum Mechanics by L. V. Tarasov
https://archive.org/details/tarasov-basic-concepts-of-quantu...
The dialogues of the author engages with various personas and the reader that are interspersed as Prelude and Interludes are really enlightening.
For example:
Classical Physicist: Can one seriously speak about an object without having an idea of what it looks like? Isnât it strange that we study, for example, the behaviour of an electron in a crystal while we donâ t even know what an electron actually is?
Author: I donât agree that we donât even know what an electron is. I have just indicated a number of precisely determined characteristics and properties of an electron. More detailed properties of microparticles in general and electrons in particular were considered in the preceding sections of the book (and will be considered in the following sections). In fact, we know quite a lot about the electron and know, in particular, about its behaviour in a crystal. This is evidenced by the large number of semiconducting devices fabricated and used by us in practice. As you will see, the absence of a âphysically intuitiveâ model of the electron has in no way turned out to be a serious obstacle. We may even go a step further and state that an understanding of natural phenomena in which Planckâs constant plays an important role is possible only through a significant rejection of a graphic description. By the way, this idea was given by Heisenberg, in whose works much attention was given to questions of the use of physically intuitive methods.
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.
Somewhat related: a book that really helped me is Picturing Quantum Processes by Bob Coecke. It's a visual representation of quantum processes, which really helped me understand the concept
Funny, both books scream default LaTeX
This looks quite interesting; thanks for sharing.
Saying I don't understand Quantum Mechanics is like saying, "I don't understand how attention/transformers explain the human brain."
It doesn't. It's model. All models are wrong (including quantum mechanics and attention) but some are useful. You understand the domain of the model, the problems it can solve, the math behind the models and use the model to make predictions. If you are competent at linear algebra and functional analysis, you can do quantum mechanics.
If you make the error of believing that quantum mechanics is ontological god's honest truth of nature, you will end up with blunders like using it to explain consciousness like Prof Penrose. His math was impeccable, but he was making a category error.
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.
The trick to a top HN comment is to basically reflexively react to the title with no regard for the substance of the relevant article. Amusingly, pointing out this self-evident truth is itself frowned upon and more offensive than the described trick, according to the sacred text.
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.
Are you implying that on a basic level or for simple arrangements transformers do explain what happens in the brain? If so, I would be curious to hear how.
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".
As someone with a degree in physics and math, I find the line you're trying to draw rather blurry.
> Quantum physics is a theory, as in "as far as we can tell, this is an exact mathematical description of the world".
Is it?
If by "mathematical exactness" you merely mean we have somehow been able to produce some numbers that later on we measured in experiments, then yes. (Though we haven't been able to produce such numbers in all cases, see e.g. [0].)
I my book, though, mathematical exactness means your model is mathematically consistent and is applied with the necessary mathematical rigor.
Quantum mechanics and quantum field theory, as they are commonly taught in universities, are everything but. They are a bunch of concepts and recipes that, albeit successful, are held together loosely with duct tape and lots of hand waving to make you ignore the logical gaps & jumps and the fact that many of the "mathematical" objects physicists refer to don't even exist[1]!
[0]: https://www.scientificamerican.com/article/this-simple-exper...
[1]: Haag's Theorem, AizenmanâFröhlich Triviality Theorem, etc.
Iâm not sure most physicists would make that specific distinction between "theory" and "model". We know QM is wrong or at the very least incomplete as long as thereâs no theory of quantum gravity. Every theory, like every model, has a domain of applicability and gives wrong or even nonsensical answers when applied outside its domain.
What a theory is, is more like a model (or maybe meta-model) with a particularly broad scope or high explanatory value, often a mathematical framework that gives a common foundation and theoretical justification for multiple experimentally-derived models.
This is really a misunderstanding of what quantum mechanics is. It's not a particular theory. It's a category of theories that fit into a certain framework.
Quantum electrodynamics is a quantum theory. Quantum chromodynamics is a quantum theory. String theory is a quantum theory. I'm sure there is a correct quantum theory of gravity - we just don't know what it is yet.
This is an important distinction. Quantum mechanics as a framework is the correct description of reality as far as we can measure (excluding some loopholes like superdeterminism). This is as close to the foundation or "god" or whatever you want to call it as it gets. If you look at specific quantum model descriptions (like the Schrödinger equation), we know they are not complete. Even relativistically correct Dirac equation is still not the full picture, because we don't fully understand how gravity fits into this on short length scales. But the current principles like Bell's theorem exist independently with all their implications on our reality and they will not go away, no matter what else we discover at the bottom.
>>>Quantum physics is a theory, as in "as far as we can tell, this is an exact mathematical description of the world".
... which "we think" is functioning that way not to mention that theory itself might be wrong and be replaced as most of the supporters of quantum theory doesn't seem to look on it as something that explain mechanics of it, but rather how magic of "unexplainable" quantum mechanics works.
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 godâs 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 âI Donât Understand Quantum Physicsâ. Jump to the very last section, âIs Quantum Theory Correct and Complete?â Heâs 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.
>That famous quote could use attribution
It could, but doesn't need it.
That models are not direct truth is just logical. If there were such a thing that were indistinguishable from the direct truth, it would be the direct truth, not some other thing called a model.
This is why I've never understood the "revalatory" nature of Godel's incompleteness. Of course any axiomatic system must not contain all truths. Axiomatic systems are models and models can't contain all truth. If an axiomatic system contained all truth it would just be all truth rather than some other thing called an axiomatic system.
The only case in which Godel's argument surprises is the case in which one has a fundamental misunderstanding of what a model can and cannot be, which I suppose must have been more common in his time, but I was really confused when my highschool teacher went to great lengths to explain that a model cannot contain the whole truth because...of course it can't?
> of course it canât?
If obvious, can you prove it without reading Gödelâs proof or anyone elseâs?
The important (2nd) part of Gödelâs proof is not that a model canât contain all truth, itâs that a model cannot prove itself true, which is a far stronger statement than the intuition you describe. Of course, belief that your own intuition is independent of history is also highly questionable; you were raised and educated in an environment in which people were already aware of Gödel. Itâs like saying the number zero is obvious (which it is now) despite the fact that it took thousands of years before it was used formally as a number. There was a time when it wasnât obvious to the smartest people alive.
Note that formal axiomatic systems arenât physical systems; what Gödel was talking about and what George Box was talking about are related but somewhat different concepts. It is obvious in physics that a parabolic ballistic trajectory model doesnât account for air turbulence. Itâs not at all obvious that all of math itself is guaranteed to produce contradictions and cannot prove itself, especially if youâre allowed to change math or use any system you want.
If I present a novel, unique axiomatic system, with no intent that it refers to anything in the world, what is it a model of?
Unfortunately, this work perpetuates the misunderstanding of Bell's theorem and its implications with respect to hidden variable theories. See the Scholarpedia article on Bell's theorem for an in-depth discussion, including quotes from Bell himself, deeply frustrated at the misunderstanding.
I see 502 bad gateway
It seems to be intermittent right now. Internet Archive can help.
https://web.archive.org/web/*/https://scholarpedia.org/artic...
This piece looks great, adding to my ever-growing "to read" collection on Zotero.
If anyone is interested in self-studying quantum physics, QFT for the Gifted Amateur [1] is very well regarded.
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.
I like QM for engineers.
It is much more shut up and calculate.
But I do believe that is atleast in part Feynmans point. The way we have explored QM for the past... 120 years (? Wow is it really that old!?) is you don't need to understand it, here are the rules and tools to carry out extraordinary calculation.
I believe the likes of Sean Caroll are trying to bring understanding back to physics and meet philosophy.
It really depends on your goal. If you wish to use it day to day then you do need to understand it but yes you can use the handy Dirac notation to let you calculate lots without ever going too deep.
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
That pre-determined value idea is exactly local hidden variables, and Bell's inequality rules it out, Aspect's 1982 CHSH experiment measured the violation.
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.
To be even more precise, it rules out hidden variable theories that satisfy Bell locality, i.e. the assumptions that the theorem makes.
Superdeterminism and retrocausality both allow for local hidden variables - itâs just that they donât satisfy Bellâs assumptions.
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
I don't understand the superdeterminism idea. Wasnât that already the classical/Newtonian view - that everything was predetermined, a universe of billiard balls following their destiny exactly?
Newtonian is just plain determinism. One thing causes another, but does not imply things are fixed in any particular way.
Superdeterminism implies that things are fixed in advance in such a way that the things we "choose" to measure always looks as if there are no local hidden variables (e.g. Bell's inequality) even though there are.
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