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Quantum mechanics is the operating system other physical theories run on (2007)
- WoahNoun 3y ago[2006]
- sampo 3y agoMore like, quantum mechanics is the OS for 3 out of 4 fundamental forces in physics. After 100 years of trying, nobody has managed to express gravity in the language of quantum mechanics.
- queuebert 3y agoAaronson does quantum computing. He might be slightly biased.
- Tomte 3y agoHe says that explicitly in the text.
- lokimedes 3y agoWhat AS/400 is to Banking, nonrenormalizable.
- elcritch 3y agoI miss doing “random” renormalizations in physics problems. Though probably best we can’t renormalize the universes QM OS itself. ;)
- TZubiri 3y agoMore like the assembly of Physics then? Gravity would be like Deep Learning Models, no one is able to explain them at the fundamental level.
- nathan_compton 3y agoIn this banal set of metaphors it would have to be something else. There may arguably be some mysteries with respect to how deep learning is effective, but its precise mechanistic explanation as a series of operations on a processor is not mysterious. There is not presently a quantum theory of gravity (in fact, I'd argue that despite the practical successes of QFT there isn't really a theory of quantum mechanics _either_ in the sense that algebraic quantum field theories of non-trivial character are so far elusive and no one knows what quantum field theory at large actually is or why it works, but I digress). In the current account of the world there is literally know way for us to understand how gravity arises from the rules we presently believe must be true based on our successes with the other theories.
- umvi 3y agoMaybe because gravity isn't a force at all but a consequence of the curvature of spacetime?
- jerf 3y agoGravity is a "consequence of the curvature of spacetime" in a particular theory that we know can't be the foundational description of reality, because all it has is mass and spacetime in it. Since it's a known-incorrect or known-incomplete theory (pick which one you like), we are not in a position to declare that gravity is absolutely, positively "curvature in spacetime" and nothing else. Moreover, quantum mechanics comprehensively lacks gravity. It isn't just "oh, well, maybe this system is also accelerating due to gravity but we can ignore it". It's, if atoms are in a superposition of "over there" and "over here", what is the gravity of the resulting system? We know we can produce such superpositions in the real world, and when those systems exist, there must be some answer to that question, even though we don't know what it is. What impact does very, very high gravity have on the non-superposition-related aspects of the standard model? How do energies of all the various bits of the proton change in such a field? And so on. It doesn't help at all to simply reiterate the theory of relativity. The conflict between relativity and QM is deep, real, and very very challenging.
- SJC_Hacker 3y ago> the foundational description of reality How can we ever really know that? Isn't the best we can do is just models?
- deleted 3y ago[deleted]
- wdh505 3y agoI think that the same way that energy is shed when a particle steps from high energy to low energy is the way that "gravity aka possibility energy" is shed when quantum superposition collapses into position. I have daydreamed of becoming a physicist just to try testing this. To directly answer your question, by experimental results.
- mellosouls 3y agoFrom the article: quantum mechanics is the operating system that other physical theories run on [...] with the exception of general relativity [...]
- datavirtue 3y agoBecause of emergence. Unintuitive properties that arise from the aggregate interactions of discrete entities. Temperature is an emergent property arising from the movement of all atoms within a space. There are no hot and cold atoms. The graviton doesn't exist. Gravity emerges from the interaction of matter (energy?) with spacetime. They are literally inseparable in our version of the universe. For those still looking for the graviton, the reasoning has led to the realization that you would create a black hole if you made the device that could detect it (as I understand it).
- skirmish 3y agoCarlo Rovelli argues in "The Order of Time" that time itself emerges solely from thermodynamics since there is no arrow of time otherwise in physics. Given that, spacetime itself is not at all foundational but a result of limited human perception.
- Tomte 3y agoReal title: PHYS771 Lecture 9: Quantum
- cl3misch 3y agoVery true, but I thought this lecture is mainly known/interesting for the "OS for physics" quote.
- bluish29 3y agoUnless you are working on numerical relativity or cosmology.
- nyrikki 3y agoThen it's just an implementation detail. ;)
- api 3y agoIs a black hole like the TPM on your CPU then?
- vindex10 3y agoWith its performance quantized by the fTPM stuttering xD [1] [1] https://www.phoronix.com/news/Torvalds-fTPM-RNG-Woes https://www.phoronix.com/news/Torvalds-fTPM-RNG-Woes
- jskherman 3y agoComplex numbers! I didn't expect complex numbers to have a deeper relation to quantum mechanics. It feels like negative probabilities is just the "sqrt(-1) doesn't make sense" topic all over again. Yeah, why is it Quantum Mechanics taught on how it was historically sequentially discovered instead of reorganizing it in a clear manner for future students? This may be long overdue and might even yield new perspectives on quantum mechanics from future researchers.
- layer8 3y agoQuantum states are represented as vectors of length 1 (unit vectors), or corresponding complex numbers, so really just positions on a circle or n-dimensional sphere. To me that makes more sense than talking about roots of negative numbers or negative probabilities, and complex numbers are just a mathematically convenient representation.
- elashri 3y agoYes, it is a very convenient representation, and it is possible to formulate quantum mechanics without using complex numbers at the fundamental level of the mathematical representation. In standard quantum mechanics, the state of a quantum system is represented by a complex-valued wave function or a vector in a complex Hilbert space. Observables are represented by self-adjoint operators acting on this complex Hilbert space. The complex nature of the wave function gives rise to the phenomenon of quantum interference and the probabilistic interpretation of quantum mechanics. However, in this real quantum mechanics, the complex Hilbert space is now replaced by a real Hilbert space, and the complex wave function is replaced by a real-valued wave function or a vector in this real Hilbert space. The observables are represented by self-adjoint operators acting on the real Hilbert space. One way to achieve this is by using real algebra or real matrix representations. Now we let the complex numbers represented by 2x2 real matrices of the form: a + ib = [a -b] [b a] now a and b are real and the imaginary unit i is represented by the matrix: i = [0 -1] [1 0] One also can use quaternions, but now it will be more complicated without much to gain.
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- jimbokun 3y agoI couldn't really follow all the math in the article, but "the mathematics of quantum mechanics is based on probabilities but with negative values" just blew my mind. Never heard that before.
- Jun8 3y agoFor a more lighthearted approach to the topics in this lecture you might want to check out the comic Aaranson created with Zach Weinersmith: http://www.smbc-comics.com/comic/the-talk-3 http://www.smbc-comics.com/comic/the-talk-3.
- SJC_Hacker 3y agoEverything is science is just models. QM/QFT is a particular model that has wide explanatory power in a certain realm. However, once you start getting further and further away from this realm, the model becomes increasingly less helpful, even though it might be "true"/correct in a sense. Example: QFT should explain all chemical behavior, yet the wave equation only has "nice" solutions for a simple case: hydrogen. After that, the PDE is non-linear and non-separable, so. you have to resort to numeric methods. But the computational demands are very heavy, and even with todays machines you can only get up to ~10 valence electrons or so last I checked. So modelling the behavior of say, a complex organic compound, such as a drug, first-principle QFT is of little aid. Which is why chemists have their own models which are loosely based on QM/QFT, and are simplifications (e.g the idea of electron "jumping" from one molecule to the other). Yes you have Pauli exclusion principle, Hund's rule, based on QFT, but there are exceptions, and I never got a good explanation it doesn't apply to the entire compound (or the entire object, or the entire universe)
- random3 3y agoI assume this is because most models are linear models and implicitely approximate a non-trivial amount which can become problematic from a stability perspective in many of the real-world settings?
- rmah 3y agoNo, that's not why. It's because models are not reality, they are a (mathematical) description of reality. And descriptions rarely perfectly match reality.
- elcritch 3y ago> After that, the PDE is non-linear and non-separable, so. you have to resort to numeric methods. But the computational demands are very heavy, and even with today’s machines you can only get up to ~10 valence electrons Well as you mention, many of the models can be simplified at levels. For example regular QM and solid state physics like semiconductor assume nuclei’s are essentially stable compared to electrons. Applying this and other simplifications allowed us to build amazing semiconductors tech for example. DFT lets us estimate far more chemical interactions than pure QM, much less full QFT. However fundamentally knowing the core rules doesn’t help us predict complex scenarios. Personally I don’t see it as too different to the halting problem in CS. It doesn’t prevent us from creating and understanding amazing things. Actually I’m quite excited the rise of AI in quantum chemistry. These AI models can learn complex rules to simplify calculations like physicists figured out by hand, but can scale it out absurdly. > Yes you have Pauli exclusion principle, Hund's rule, based on QFT, but there are exceptions, and I never got a good explanation it doesn't apply to the entire compound (or the entire object, or the entire universe) It’s not clear to me exactly what you meant, but usually quantum tunneling and other effects are limited by decoherence. Yes an electron in your body can tunnel to say the moon. It’s just absurdly unlikely as the number of other electrons it would possibly interact with first is staggeringly large. Even in a single molecule evolved for tunneling like chlorophyll, the probabilities of tunneling outside a few key paths quickly become too small to represent with 64bit floating point numbers. I did the computations in my physics days, and it was challenging to compute.
- ziofill 3y agoI think of physics as the APIs that Nature gave us. Human laws are very limited wrappers around those APIs.
- dekhn 3y agoScott's work is really just a small part of a particular subset of quantum mechanics, but he seems set on expanding its domain to cover all of it.
- klyrs 3y agoThis is a grad-level physics lecture dating back to 2007. Pretty ordinary stuff for a physics prof to have on their webpage.
- dekhn 3y agobut he's a computer scientist/mathematician, not a physics prof.
- klyrs 3y agoMy mistake. His specialty, as a computer scientist, is quantum computing. I maintain that this is a baseline skill, to be expected of anybody claiming his credentials. I get that he's got a lay-fanbase, but it's a little cringe when folks are impressed by the mundane. It's honestly a little insulting.
- prof-dr-ir 3y agoAh, I see that it is time to raise my objection again. As I wrote before [0], I think that what Aaronson's calls "the theory" is a somewhat bastardized version of quantum mechanics that might suffice for quantum computing but, in my opinion, not for physics. I discussed the difference here: https://news.ycombinator.com/item?id=38255476 https://news.ycombinator.com/item?id=38255476 [0] https://news.ycombinator.com/item?id=39627618 https://news.ycombinator.com/item?id=39627618
- nextaccountic 3y agoOkay, but what's the implication of that? You can't get the whole quantum mechanics by just doing the generalization of probability thing?
- Koshkin 3y agoNo, because physics is not mathematics.
- notfed 3y agoUhhh...says who?
- Koshkin 3y agoSays the fact that their objects of study are different.
- dekhn 3y agoMost people. Physics uses math to model the world, but is independent (math is not a science). At least we don't have any further evidence to say otherwise. There's a lot of interesting ideas around this in https://www.maths.ed.ac.uk/~v1ranick/papers/wigner.pdf https://www.maths.ed.ac.uk/~v1ranick/papers/wigner.pdf and many of us believe that the universe itself is effectively an embedding of a large mathematical structure in a 3D-space 1D-time. But that would be effectively impossible to prove in any convincing way.
- akomtu 3y agoQM and GR look like two equally fundamental views on reality: GR is a spatial representation of energy distribution, while QM is a sort of frequency representation of the same energy. QM feels like the Fourier transform of GR. I suspect that another mental roadblock that prevents further progress is how we see time: a straight arrow slightly bended by local gravity. It's quite possible that a proton naturally exists in 3-dimensional time that on average appears 1-dimensional to us.
- deleted 3y ago[deleted]
- glyphy177 3y ago[dead]
- dang 3y agoRelated: PHYS771 Lecture 9: Quantum - https://news.ycombinator.com/item?id=37198673 https://news.ycombinator.com/item?id=37198673 - Aug 2023 (31 comments) PHYS771 Lecture 9: Quantum (2007) - https://news.ycombinator.com/item?id=33188276 https://news.ycombinator.com/item?id=33188276 - Oct 2022 (52 comments) Quantum mechanics as a generalization of probability (2007) - https://news.ycombinator.com/item?id=8377680 https://news.ycombinator.com/item?id=8377680 - Sept 2014 (79 comments) New straighforward approach to teaching quantum mechanics - https://news.ycombinator.com/item?id=4319276 https://news.ycombinator.com/item?id=4319276 - July 2012 (55 comments - top one just added to https://news.ycombinator.com/highlights https://news.ycombinator.com/highlights) Quantum mechanics for mathematicians - https://news.ycombinator.com/item?id=83594 https://news.ycombinator.com/item?id=83594 - Nov 2007 (12 comments)
- agnosticmantis 3y agoIf I didn't know this was from 2007 I'd have said it shows that he's been hanging out with OpenAI kids. (He worked there working on watermarking and stuff.) (Altman having said they're working on an AI OS or something.)
- rbanffy 3y agoQM is kind of the "Principles of Operation" document IBM has for mainframes, detailing everything the software sees (and some more). It's not the OS, but spells out the rules of the universe.
- quantum_state 3y agoFascinating ... but not sure about the relevancy to our endeavor in exploring nature ...
- notfed 3y agoThe relevancy is that at its heart, quantum mechanics really only has a few key different phenomena from classical, and you can understand those phenomena more easily using qubits than esoteric particle canon experiments.
- nitwit005 3y agoYou know how students raise their hands and ask when they will ever use some math? This is essentially suggesting you don't tell them, and entirely skip the history of why it's relevant. I'd personally just walk out of class and cancel the course.