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Is Quantum Theory About Reality or What We Know?
- fiatjaf 9y ago"Physicists know how to use quantum theory—your phone and computer give plenty of evidence of that." What?
- lumost 9y agoIntegrated Circuits and associated lithography based manufacturing techniques rely heavily on quantum mechanics. The transistors and gates wouldn't work if quantum mechanics did not provide an accurate depiction of the physics involved.
- ekianjo 9y ago> lithography based manufacturing techniques rely heavily on quantum mechanics. Are you sure ? > The field of quantum lithography is in its infancy, and although experimental proofs of principal have been carried out using the Hong–Ou–Mandel effect,[3] it is still a long way from commercial application. From https://en.wikipedia.org/wiki/Quantum_lithography https://en.wikipedia.org/wiki/Quantum_lithography
- kirrent 9y agoConventional lithography also requires an understanding of quantum effects at the scales it's being used at. Not to mention modelling light/mask layer interactions.
- lumost 9y agoThe most direct requirement on Quantum Mechanics in existing lithography systems is the lasers used as light sources https://en.wikipedia.org/wiki/Laser#Foundations https://en.wikipedia.org/wiki/Laser#Foundations https://en.wikipedia.org/wiki/Photolithography#Light_sources https://en.wikipedia.org/wiki/Photolithography#Light_sources
- dreamcompiler 9y agoSemiconductors couldn't work without quantum mechanics [0]. Heck, the sun couldn't work without quantum mechanics [1]. [0] https://physics.stackexchange.com/questions/112615/why-is-it-said-that-without-quantum-mechanics-we-would-not-have-modern-computers https://physics.stackexchange.com/questions/112615/why-is-it... [1] https://www.forbes.com/sites/ethansiegel/2015/06/22/its-the-power-of-quantum-mechanics-that-allow-the-sun-to-shine/#2014a30143f7 https://www.forbes.com/sites/ethansiegel/2015/06/22/its-the-...
- dreamcompiler 9y ago(This does not make your phone a quantum computer. Your phone is an ordinary computer that happens to be enabled by quantum mechanics.)
- zobzu 9y agoThis sounds like saying our phone shows a demonstration of E=MC2. Not a great intro / not giving a lot of confidence to the reader when it starts like that. In fact, it'd make Einstein laugh. His late life was devoted to unify the theories and asking quantum physicists to demonstrate the quantum theory in the real world or through though experiments. He'd probably still be upset today. I, for one, am still waiting for the 'unified relative quantum theory' as well.
- erikpukinskis 9y agoSeems like it changes reality. The presence of a measurement changes the interference pattern for all observers, no? If the waveform collapse only happened in my reality then if I observed a field, I would expect others to see an interference pattern, even if I only saw a clear field. If other people can observe an interference pattern while I observe a clear field, then that's a multiverse. That means you need a whole new universe for every observation. Seems like poor compression. Although I guess if it's an append-only store then it works out ok.
- gumby 9y agoThe article describes an alternative interpretation.
- badosu 9y agoI hope Pilot Wave Theory [0][1] gets more recognition and future work is able to extend it to account for relativity, there's hope that we actually can find a deterministic approach to Quantum Mechanics. Here's a amusing video of an analogous macroscopic experiment, droplets oscillating and interacting with each other at stable states: https://www.youtube.com/watch?v=JUI_DtzXdw4 https://www.youtube.com/watch?v=JUI_DtzXdw4 [0]: https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory [1]: https://en.wikipedia.org/wiki/Pilot_wave https://en.wikipedia.org/wiki/Pilot_wave
- DiThi 9y agoVeritasium video about the topic https://www.youtube.com/watch?v=WIyTZDHuarQ https://www.youtube.com/watch?v=WIyTZDHuarQ
- rtpg 9y agoI've been fairly interested in pilot wave thoery, and the more I delve into it, the less I feel it's useful. My understanding is that the statistical equivalent of the pilot wave theory is "when you flip a coin, there is not a 50/50 chance, but a 100% chance of getting the result, because you got the result". Hyper-determinism. The programming equivalent is "all functions are built with lookup tables, with precomputed values". Great, but I still want to predict the values of the lookup tables to describe the function. From the wiki description of the "guiding function" (basically, the universe's step function): >The main fact to notice is that this velocity field depends on the actual positions of all of the N particles in the universe. This feels totally infalsifiable! "in the exact state of the universe you get the result you get". None of the results end up being usable because there's always the "out" of "the universe has changed". You end up going into hyper-determinism, which is almost all about negating free will. Even if the pilot wave theory is the "real thing", the other model of quantum mechanics ends up being more useful because at least you can make some predictions on the state of the universe. (Would love to have someone explain to me how we can apply Pilot Wave Theory in a "local-ish" fashion, people worked hard on this stuff so I imagine there's some use)
- SomeStupidPoint 9y ago
- slackerjack 9y agoI really enjoyed the article. Every time I read about Quantum Theory it reminds me about a story I read online some time ago. I can't fully remember it: I think it was about a guy who made a Quantum Computer to answer any question in the universe by asking it to different dimension of himself. I think he uses it to win the lottery but in the end he mistrusts himself to answer the question "how to live a happy life" and ends up living an unhappy life. I really want to re-read it. Does anyone know where I can find this story? I spend weeks now to find it ... with no luck.
- masterleep 9y agoTry https://www.reddit.com/r/tipofmytongue/ https://www.reddit.com/r/tipofmytongue/
- paviva 9y agohttps://physicsnapkins.wordpress.com/2013/05/20/all-paths-to-happiness/ https://physicsnapkins.wordpress.com/2013/05/20/all-paths-to...
- slackerjack 9y agoYES, That is it! Thank you!
- yters 9y agoDoesn't Bell's inequality address this question?
- millstone 9y agoIt addresses a related but slightly different question. You flip a coin: there is a 50/50 chance of heads or tails. These probabilities are due to our incomplete knowledge: the coin knows which face is up, and it's only because we don't know that we assign probabilities. Now if we have a particle that is 50/50 spin up or spin down, we may think that it is like a coin: the spin is already determined, we just don't know which it is. This is where Bell's Inequality comes in and shuts that idea down. Until the particle is observed, it simply does not have a spin, in the same way that a coin has an up face. So if a pre-observed particle does not have a spin, what does it actually have? This is the core of the dispute in the article. There's two possible answers: 1. A wavefunction (psi), aka a quantum state. This is the psi-ontic view which argues the wavefunction is a real and physical thing that evolves in time regardless of any observations. MWI and Bohm are both psi-ontic theories. 2. Nothing. This is the psi-epistemic view which holds that it makes no sense to talk about a particle's reality in-between observations. In this view, only measurements and their results are real; the wavefunction is a state of knowledge. Copenhagen, Consistent Histories, and the minimalist ensemble interpretations are psi-epistemic.
- TheOtherHobbes 9y agoThe argument about what "a real and physical wavefunction" means boils down to this question: "Is there a science of the wavefunction beyond QM?" Can you ask more questions about it, break it down into constituent processes, maybe re-engineer it? Or is it opaque and closed and there is no possible way to do further science on it? My money is on option 1, because it's hard to imagine an organising principle you can't possibly do any science on. Wavefunction science may be weird and like nothing ever seen before - especially given non-locality and possibly non-realism. But it's a good rule of thumb in science that when nature becomes counterintuitive you're on the right track. If the answer was obvious and familiar you wouldn't need original and creative thinking to find it. Option 2 seems like an admission of total defeat. It would be the first time in science where we hit a wall and didn't even try to understand what it was made of. That doesn't mean it can't be correct. But it does mean we shouldn't give up without trying for quite a while longer. And if we do give up, it should only be after discovering some kind of meta-Bell theorem which proves there's no way to go further.
- catpolice 9y agoOh Hey, I know the author of this! In fact, I think I introduced him to that Spekkens paper. Small world.
- roycoding 9y agoThis is closely related to QBism (quantum Bayesianism) https://en.wikipedia.org/wiki/Quantum_Bayesianism https://en.wikipedia.org/wiki/Quantum_Bayesianism https://www.quantamagazine.org/20150604-quantum-bayesianism-qbism/ https://www.quantamagazine.org/20150604-quantum-bayesianism-...
- tzakrajs 9y agoAs a laymen, it seems to me that quantum theory is similar to the expanding universe theory in that scientists substitute complexity (cause of expansion, quantum states) with a token (dark matter/energy, indeterminacy) until you better understand the underlying systems. Can anyone tell me why I am incorrect?
- aroberge 9y agoThe two examples you give are very different. I would argue that you are, indeed, very incorrect. The purpose of scientific theories is to be able to make predictions about physical systems. Fundamental theories are based on some postulates (assumptions; in mathematics, we would have axioms). Quantum mechanics is based on a few postulates (which are expressed in very mathematical terms, like "Physical observables are represented by Hermitian matrices on a Hilbert Space H"). If the theory makes incorrect predictions, it is deemed to be wrong. If it makes predictions that cannot be explained using "common sense", then non-specialist come out of the wood work stating that it is obviously incorrect, that specialists simply do not understand. For the expanding universe ... we have a theory (Einstein's Theory of General Relativity) which has been extremely well tested in all kinds of scenarios, and has always been found to make correct predictions. Your phone's GPS would not work if it would use predictions from Newton's theory rather than Einstein's. The Theory of General Relativity can be thought as a set of 16 equations of the form: (aspect of geometry of space time) = (stress-energy-momentum content of the universe) In simplified terms, the left-hand side of these equations relates to the observed expansion of the universe. The right-hand side of these equations is what type of "energy/matter" we observe. We find that simply including baryonic (i.e. "normal") matter that we can see by looking (using telescopes) at the sky leads to inconsistencies with the observed expansion. If we include different type of energy/matter that we cannot see (i.e. dark), each obeying precise equations of state, we can have predictions that are consistent with what we observe. Thus, we use General Relativity + observations about the expansion of the universe to make predictions about what is the energy/matter content of the universe. What you see as a failure, I see as a success of G.R. as it makes predictions about what is found in the universe which we did not know before, and had no way to know simply using the tools we had. "Fun fact": many years before modern neutrino experiments nailed down the number of "normal" light neutrino species to 3, using General Relativity and known nuclear physics, one could use the observations of the ratio of light elements (He/H, Li/H, etc.) produced in the early universe to make the prediction that the number of light neutrino species had to be equal to 3.
- danesparza 9y agoIf you're interested in the subject matter, I highly recommend Richard Feynman's 'Six Easy Pieces' series (available on Youtube here: https://www.youtube.com/playlist?list=PLBxHpsmcxyNghmwd6MJByuhwMr-WkfoB8 https://www.youtube.com/playlist?list=PLBxHpsmcxyNghmwd6MJBy... ). Feynman was a key member of the Manhattan project (Wikipedia link here: https://en.wikipedia.org/wiki/Manhattan_Project https://en.wikipedia.org/wiki/Manhattan_Project ). I trust him to know what he's talking about. :-)
- eli_gottlieb 9y agoI think that "reality vs knowledge" is a false dichotomy. After all, our knowledge is a classical-level feature of reality, not a core element of nature's physical ontology. What does nature's physical ontology require, such that once it all builds up to the classical level, we can know things? Information as an element of physics is what I'd guess.
- whack 9y ago"Measuring a system will generally change its state from one in which each possible outcome has some non-zero probability to one in which only one outcome occurs. That’s a lot like what happens when, in the die game, you learn that the die does, in fact, show a six. It seems strange to think that the world would change simply because you measured something. But if it is just your knowledge that changes, things don’t seem so strange." This is the only interpretation of quantum theory that makes sense to me. The idea that an objective reality of the world has changed, through our act of observation, leads to absurd conclusions such as Schrodinger's cat being simultaneously alive and dead at the same time. I believe this is the same point that Schrodinger tried to make with his thought experiment as well.
- wu-ikkyu 9y agoSo the most logical interpretation of quantum physics is that reality is subjective, correct?
- philipov 9y agoNo, the most logical interpretation of quantum mechanics is that you can't measure things without using particle interactions, and particle interactions change what they interact with.
- danharaj 9y agoI don't think that's enough. Particle interactions are unitary, but measurement looks non-unitary from the point of view of the observer. Reality is intersubjective, but not subjectivist.
- philipov 9y agoI think confusion arises when people hear 'measurement' and jump to thinking "wait, what's so special about measurement? Would the world not exist if we weren't there to measure it?" This is due to an imprecise understanding of measurement, and should be corrected by pointing out all particle interactions are measurements. Our classical world exists without superposition because there are enough particles interacting with each other that everything is constantly being measured.
- singham 9y agoAnyone who thinks that QM is making stuff up, please watch this video. Here Rubidium atoms (mind you atoms and not electrons or photos) are made to interfere with each other. https://www.youtube.com/watch?v=a_w6AGe_fIo https://www.youtube.com/watch?v=a_w6AGe_fIo Quantum mechanics is a foundation of physics, chemistry and materials science. Still, there is an ongoing debate about the emergence of the classical, macroscopic world from the well-understood microscopic world of quantum mechanics. We contribute to this discourse by demonstrating quantum superposition of massive particles at the distance (0.5 m) and time scales (2 s) of everyday life, thereby advancing the state-of-the-art of atom de Broglie wave interferometry by nearly two orders of magnitude [1]. In addition to testing a central tenet of quantum mechanics, we pave the way for new precision tests of gravity, including the possible observation of gravitational waves and tests of the equivalence principle. In related experimental work, we demonstrate that entangled clusters of approximately 1000 atoms can be used to achieve 10-fold improvement in the sensitivity of quantum sensors based on atomic transitions; the levels of performance achieved could not have been realized with any competing (non-entangled) method [2].