A Century of Quantum Mechanics(home.cern)
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A Century of Quantum Mechanics
https://home.cern/news/news/physics/century-quantum-mechanics
98 comments
There is no new foundational physics. The standard model of particle physics is from the 1970s, and the lambda-cmd model of cosmology is from late 1990s.
Of course there is lots of new speculative ideas being produced, but it's really difficult to get anything confirmed.
Of course there is lots of new speculative ideas being produced, but it's really difficult to get anything confirmed.
Quantum mechanics is not the standard model. Quantum mechanics is the stuff developed in the 20’s and 30’s. It is really useful for solving real world problems, and for that reason is what is taught to undergraduates in a “modern physics” class. It is not a correct or complete description of reality, however, and is about 50ish years out of date.
The standard model is 100% quantum mechanics. It's just QM as applied to fields. While undergrads start with single or few particle quantum mechanics.
There is a lot of hard math and fundamental physical ideas that pop out when we apply quantum mechanics to fields, but it's still QM.
The work of Heisenberg, Schrodinger, Dirac, Pauli from 1925-28 or so is absolutely not our date.
There is a lot of hard math and fundamental physical ideas that pop out when we apply quantum mechanics to fields, but it's still QM.
The work of Heisenberg, Schrodinger, Dirac, Pauli from 1925-28 or so is absolutely not our date.
We are getting into definitions and common usage debates, which is the most uninteresting debate to have. I will simply state that “quantum mechanics” unqualified typically refers to the description of reality developed on Copenhagen in the 1920’s. When people are referring to quantum field theory, they are usually explicit in doing so.
What do you mean? It's not "out of date", as Kepler's laws or the ideal gas law or whatever is not out of date. It's just incomplete.
Also, "modern physics" is a term of art, vs "classical physics".
Also, "modern physics" is a term of art, vs "classical physics".
Every physical description of reality is correct to within some error bars. Quantum mechanics is still useful and correct, there are just more precise theories that provide refinement. And in that sense are the "current" theories if they are the most precise ones currently known.
Not true at all. Blackbody radiation goes to infinity with Wien's distribution; error bars aren't going to get you there.
Likewise, our 1/r^2 understanding of forces goes to infinity as distance goes to zero, but we currently can't resolve that problem with error bars for the nucleus of an atom, where Heisenberg tells us any two protons can sometimes appear closer to each other than the "radius" of the nucleus.
You can't make Schottky diodes using Maxwell and error bars.
That is the entire problem: the classical models weren't merely inaccurate; they predicted completely absurd (and provably wrong) results at extreme scales.
Likewise, our 1/r^2 understanding of forces goes to infinity as distance goes to zero, but we currently can't resolve that problem with error bars for the nucleus of an atom, where Heisenberg tells us any two protons can sometimes appear closer to each other than the "radius" of the nucleus.
You can't make Schottky diodes using Maxwell and error bars.
That is the entire problem: the classical models weren't merely inaccurate; they predicted completely absurd (and provably wrong) results at extreme scales.
Infinite error bars.
What? What are the more precise theories that aren't fundamentally QM?
Quantum field theory and string theory. Fundamentally they are QM, but not formally.
I didn't know string theory makes any verified more precise predictions.
Quantum gravity is difficult to verify, because it's exotic, so it remains a theoretical exercise.
I think "new foundational [science]" is a bit of an oxymoron: theories need time to become established as foundational. There may well be ideas (currently hypotheses) that will someday be considered foundational, but we lack the hindsight and experimental validation to claim that status now.
And if you try to present your theory as foundational from the outset — like S. Wolfram does — you’ll be laughed at, much like he is.
And if you try to present your theory as foundational from the outset — like S. Wolfram does — you’ll be laughed at, much like he is.
Hmm, I don't think so. General relativity and quantum mechanics were acknowledged as fundamental (relative to previous theories) more or less immediately, because they provided a coherent theoretical scheme that accounted for the observations which were problems for previous theories, and they also made many new predictions which were experimentally confirmed within a few years.
The problem for theoretical physics now is that all experiments from the LHC and so on are consistent with the standard model. So there are no recalcitrant observations that can guide new theory formation. The regime where we might get new physics, where gravity and QM are both significant, is so far experimentally inaccessible, though see here for a nice talk by Carlo Rovelli on one such experiment that might be plausible in the coming years: https://www.youtube.com/watch?v=tgieRctZ4dE
The problem with Wolfram/Gorrard's model is that it doesn't relate to any experiments. As far as I know the most that can be said for it is that Gorrard showed that in some limit the model is able to replicate some features of GR and QM, so that by definition doesn't go beyond the predictions of GR nor QM.
The problem for theoretical physics now is that all experiments from the LHC and so on are consistent with the standard model. So there are no recalcitrant observations that can guide new theory formation. The regime where we might get new physics, where gravity and QM are both significant, is so far experimentally inaccessible, though see here for a nice talk by Carlo Rovelli on one such experiment that might be plausible in the coming years: https://www.youtube.com/watch?v=tgieRctZ4dE
The problem with Wolfram/Gorrard's model is that it doesn't relate to any experiments. As far as I know the most that can be said for it is that Gorrard showed that in some limit the model is able to replicate some features of GR and QM, so that by definition doesn't go beyond the predictions of GR nor QM.
>The problem with Wolfram/Gorrard's model is that it doesn't relate to any experiments
That's because quantum gravity regime is so far experimentally inaccessible?
That's because quantum gravity regime is so far experimentally inaccessible?
No, I don't think it's to do with quantum gravity. Their model makes no experimental predictions at all.
Fair point. Thanks for the link!
Quibble: "Gorard".
[deleted]
Is standard model confirmed? Then what is dark matter?
In physics, there is never confirmation. At best there is "measurement agrees with the model as exactly as it is currently possible to measure". The standard model is confirmed in that sense.
Dark matter is a problem from cosmology and astronomy, that maybe has a solution in an extension to the standard model. Maybe it hasn't and that solution will come from elsewhere, maybe there is a totally cosmological explanation after all. In all cases, the dark matter problem is not a contradiction to the standard model in our current experiments. If there were a particle-physics explanation to dark matter, it would be a sufficiently small alteration to the standard model that our current experiments couldn't tell the difference, to within experimental error. That's how confirmation and new models in physics work.
Dark matter is a problem from cosmology and astronomy, that maybe has a solution in an extension to the standard model. Maybe it hasn't and that solution will come from elsewhere, maybe there is a totally cosmological explanation after all. In all cases, the dark matter problem is not a contradiction to the standard model in our current experiments. If there were a particle-physics explanation to dark matter, it would be a sufficiently small alteration to the standard model that our current experiments couldn't tell the difference, to within experimental error. That's how confirmation and new models in physics work.
One of the major problems with dark matter and dark energy is, that the standard model has been experimentally confirmed to such high precision. All possible extensions proposed so far which tried to explain dark matter /dark energy have been basically falsified by the experiments.
The standard model is so descriptive and accurate, there is just no room for extensions which predict new physics but are still consistent with existing data.
The standard model is so descriptive and accurate, there is just no room for extensions which predict new physics but are still consistent with existing data.
I don't believe all possible extensions have been ruled out: e.g. right-handed neutrinos are still a viable dark matter candidate as far as I know, and these are in fact motivated by the standard model, because every other fermion has both right and left chiral forms.
https://en.wikipedia.org/wiki/Sterile_neutrino
https://en.wikipedia.org/wiki/Sterile_neutrino
So likely dark matter is a different flavor of something already in the model. Dr. Mills' Hydrino theory presents hydrogen with the electron in a lower orbit that does not radiate as a candidate for dark matter. These states are stable like the ground state. Transition into or between hydrino states emit light in the UV or soft X-ray wavelengths that is not seen in optical telescopes.
https://brilliantlightpower.com/atomic-theory/
https://brilliantlightpower.com/atomic-theory/
Why isn't this mysterious state of hydrogen detectable in tests?
The page you link to is essentially a big list of links. Useless.
I am immediately suspicious of anyone who generates buzzwords to describe their theory. Heck, he even registered "hydrino" as a trademarked term.
I'm not saying he's wrong. I'm saying he walks like a duck, sounds like a duck, wears feathers and swims all day in a lake.
The page you link to is essentially a big list of links. Useless.
I am immediately suspicious of anyone who generates buzzwords to describe their theory. Heck, he even registered "hydrino" as a trademarked term.
I'm not saying he's wrong. I'm saying he walks like a duck, sounds like a duck, wears feathers and swims all day in a lake.
There are many ways Mills claims to have experimentally verified the existence of hydrinos but the most obvious one is the faster than hydrogen transit through a gas chromatograph.
Obligatory
https://xkcd.com/2035/
https://xkcd.com/2035/
Intuitively speaking, if dark matter interacts only with gravitational field, then it's not affected by most standard model symmetries. A field bubble, so to say. Tachyons are somehow thought of as possible, meaning standard model doesn't say much about them?
IIRC there has been no confirmation yet that dark matter actually exists - it might as well be true that our model of cosmology is wrong.
Dark matter is the worst model, except for all those other models that have been tried from time to time.
>what is dark matter?
I suspect in the end it will turn out to neither be exotic new particles nor modifications to gravity, but rather that there is something fundamental about large scale structure formation in the universe that we just do not understand at the present.
I suspect in the end it will turn out to neither be exotic new particles nor modifications to gravity, but rather that there is something fundamental about large scale structure formation in the universe that we just do not understand at the present.
How can insights into large scale structure formation help explaining galaxy ration curves, lensing observations or barionic acoustic oscillations?
the late 1990s is actually fairly recent
haha. the same year the moving assembly line was invented.
[stub for offtopicness]
If this is the definition of offtopic then 90% of HN comments are offtopic. https://en.wikipedia.org/wiki/Sturgeon%27s_law at work!
Hard to respond to this unless you say specifically why! Which comment do you think should not have been treated as offtopic?
In the context of a submission about “A century of QM” that says things like
“To celebrate 100 years of quantum mechanics, the CERN Courier looks back at the impact of this theory and examines how it keeps delivering new puzzles, experimental ideas and technologies.”
the following comment may be completely misguided but I didn’t find it offtopic (maybe offreality):
“This is probably the slowest branch of the sciences, not able to get out of labs even after a century.”
But now I see that the author says that he meant quantum computing so the comment makes even less sense and is indeed slightly offtopic.
“To celebrate 100 years of quantum mechanics, the CERN Courier looks back at the impact of this theory and examines how it keeps delivering new puzzles, experimental ideas and technologies.”
the following comment may be completely misguided but I didn’t find it offtopic (maybe offreality):
“This is probably the slowest branch of the sciences, not able to get out of labs even after a century.”
But now I see that the author says that he meant quantum computing so the comment makes even less sense and is indeed slightly offtopic.
There are degrees of offtopicness, of course. In this case I moved the subthread because it was a generic tangent that had little to do with the specific article.
Good on-topic subthreads usually show some sign of contact with the body of the article—not just the title, and certainly not the most generic phrase (in this case "quantum mechanics") that can be abstracted from the title.
But one can always argue particular cases either way and I agree that the counter-argument was stronger for that one.
Good on-topic subthreads usually show some sign of contact with the body of the article—not just the title, and certainly not the most generic phrase (in this case "quantum mechanics") that can be abstracted from the title.
But one can always argue particular cases either way and I agree that the counter-argument was stronger for that one.
dave333(2)
This is probably the slowest branch of the sciences, not able to get out of labs even after a century. The fundamental problem appears to be that we are trying to control probabilistic nature using concrete real world things. I suspect this is not allowed, at least at an industrial scale. At some point humanity might need to stick what they need instead of what they can.
What do you mean? We have been profiting massively from the fruits of QM for the last five decades easily. Transistors, LEDs, Lasers, MRT imaging, solar panels, CCD cameras, etc. have arguably changed the world and would not have been possible without QM. It came out of the lab a long time ago.
Not to mention the entire science of chemistry and everything made from it.
Quantum mechanics started with the description of electron orbitals around an atom; how they work is the foundation of chemistry.
Quantum mechanics started with the description of electron orbitals around an atom; how they work is the foundation of chemistry.
That’s engineering not science
>not able to get out of labs even after a century
It got out of labs in a quite spectacular way in the summer of 1945, eighty years ago.
It got out of labs in a quite spectacular way in the summer of 1945, eighty years ago.
Thought experiment: did we really need quantum mechanics to build an atom bomb? Couldn't we have built one with a model of the atom based on classical particles (with protons leading to a chain reaction)? Is either the quantized or the uncertainty aspect of QM necessary for this?
Most of the science going into the Manhattan Project was experimental measurements and phenomenological models, not fundamental physics at the QM level. There were no usable quantum-mechanical models of nuclear physics at that point.
No; they didn't really need it.
No; they didn't really need it.
It’s just a coincidence that they employed so many experts in quantum mechanics to do those nothing-to-do-with-quantum-mechanics experimental measurements.
Coincidence. If you wanted to do something with elementary particles, you couldn't possibly ignore quantum physics.
Nucleon orbitals rely a little on Pauli exclusion principle, which you need to add as an ad hoc hypothesis every time in classical physics.
>did we really need quantum mechanics to build an atom bomb?
Yes. Nuclear reactions require understanding and modeling of the strong force, you can't understand or even see what protons and neutrons are without understanding the strong force. The mixture of positively charged and neutral particles being stuck together with enormous force which essentially does not exist at all outside of the nucleus of an atom. (there is more than three pounds of force between every pair of protons inside every nucleus with the strong force counteracting the electrostatic force)
You couldn't design a bomb without being able to model the strong force and you couldn't get to that point of investigating the atom without coming up with QM.
You couldn't get the idea of isotopes and enriching U-235 to U-238 or transmuting uranium to plutonium without understanding QM.
Or the circumstances that would lead someone to blindly creating a controlled nuclear reaction without coming up with QM in the process would be pretty absurd.
The idea for the bomb came from the understanding of the strong force. Step one: notice that there's a crazy powerful force keeping positively charged particles stuck together in the nucleus. Step two: the eureka moment of realizing you can "release" that force by causing a chain reaction of fission in heavy elements.
Yes. Nuclear reactions require understanding and modeling of the strong force, you can't understand or even see what protons and neutrons are without understanding the strong force. The mixture of positively charged and neutral particles being stuck together with enormous force which essentially does not exist at all outside of the nucleus of an atom. (there is more than three pounds of force between every pair of protons inside every nucleus with the strong force counteracting the electrostatic force)
You couldn't design a bomb without being able to model the strong force and you couldn't get to that point of investigating the atom without coming up with QM.
You couldn't get the idea of isotopes and enriching U-235 to U-238 or transmuting uranium to plutonium without understanding QM.
Or the circumstances that would lead someone to blindly creating a controlled nuclear reaction without coming up with QM in the process would be pretty absurd.
The idea for the bomb came from the understanding of the strong force. Step one: notice that there's a crazy powerful force keeping positively charged particles stuck together in the nucleus. Step two: the eureka moment of realizing you can "release" that force by causing a chain reaction of fission in heavy elements.
The very idea of matter and energy being quantized into particles and photons is the starting point of “quantum” mechanics.
>Planck discovers the quantum nature of energy in
1900
https://www.pbs.org/wgbh/aso/databank/entries/dp00qu.html
https://www.pbs.org/wgbh/aso/databank/entries/dp00qu.html
It wasn’t developed into a mechanics until the 1920’s.
Nature is probabilistic. And we know how to calculate those probabilities, that is one of the core ideas of quantum mechanics. Why is it "not allowed"? By whom? Since you are commenting on HN, you are already are using the very mature applications of QM out of laboratory. The proverbial cat (is it Schröedinger's?) is out of the bag!
Theory is probabilistic, nature isn't.
I don't know dog, that is a pretty bold statement given everything we can presently firmly say about the universe.
Like we can imagine some kind of purely deterministic thing going on but when the rubber meets the road the best ways of working stuff out seem to very strongly imply some fundamental indeterminism. No one likes it, but thats the way it is.
Like we can imagine some kind of purely deterministic thing going on but when the rubber meets the road the best ways of working stuff out seem to very strongly imply some fundamental indeterminism. No one likes it, but thats the way it is.
When the rubber meets the road the best ways of working stuff out is to shut up and calculate, you don't figure out anything by assuming unobservable fundamental indeterminism.
No one assume it.
ok, postulate
No one does that either. The nondeterminism in QM is basically just an experimental fact which sort of inveigles itself into the structure of the mathematical framework which makes it hard to ignore when one tries to understand what the theory may mean philosophically.
I've been to phil. physics conferences and I've never encountered anyone who has any kind of strong attachment to nondeterminism. In fact, in general, I think almost every physicist who learns QM has a prejudice against it which never entirely goes away unless they get deep into foundations which forces a more detached perspective.
I've been to phil. physics conferences and I've never encountered anyone who has any kind of strong attachment to nondeterminism. In fact, in general, I think almost every physicist who learns QM has a prejudice against it which never entirely goes away unless they get deep into foundations which forces a more detached perspective.
Not really, "it just is" isn't how facts work. Preferably it should be a quantity.
But it's the opposite, all people with shallow understanding of QM believe in indeterminism, because it's the first thing they learn from the start, and then this belief ossifies. Oh and Heisenberg uncertainty principle tells you that reality is unreal. Conversely foundations are deeply mathematical with basically nothing uncertain or random is sight. In fact it's foundations that have bias for mathematics and determinism. How do you interpret the evolution operator as random?
But it's the opposite, all people with shallow understanding of QM believe in indeterminism, because it's the first thing they learn from the start, and then this belief ossifies. Oh and Heisenberg uncertainty principle tells you that reality is unreal. Conversely foundations are deeply mathematical with basically nothing uncertain or random is sight. In fact it's foundations that have bias for mathematics and determinism. How do you interpret the evolution operator as random?
I don't really get your point - the time evolution operator is deterministic, but it describes the wave function, which itself gives a probability distribution for the outcome of measurements. Typically exegeses of QM are roughly given in two parts: deterministic time evolution of the wave function and random selection of the outcome of measurements. So it really is just right there in the formalism: some stuff is random.
From the point of view of foundations of physics there really is no easy way out of this apparently fundamental randomness. We can be wave-function substantivalists and then we must explain why and how we don't see wave functions but concrete outcomes. We can adopt t'Hooft's cellular automata interpretation but that framework cannot easily support even something as simple as basic interactions in QFT (last I checked). We may list any number of ways of interpreting QM but all of them that I know of only at most banish randomness to the initial conditions, but not totally eliminate it from the ontology.
I'm not saying that reality is fundamentally non-deterministic. But I am saying that most of the ways one squares basic quantum mechanical predictions with basic physical measurements suggest a type of uncertainty that is at least very close to being "fundamental."
From the point of view of foundations of physics there really is no easy way out of this apparently fundamental randomness. We can be wave-function substantivalists and then we must explain why and how we don't see wave functions but concrete outcomes. We can adopt t'Hooft's cellular automata interpretation but that framework cannot easily support even something as simple as basic interactions in QFT (last I checked). We may list any number of ways of interpreting QM but all of them that I know of only at most banish randomness to the initial conditions, but not totally eliminate it from the ontology.
I'm not saying that reality is fundamentally non-deterministic. But I am saying that most of the ways one squares basic quantum mechanical predictions with basic physical measurements suggest a type of uncertainty that is at least very close to being "fundamental."
Evolution operator shows that state evolves deterministically and doesn't hide randomness anywhere. You use probabilities when you want to explain human experience, because you can't practically compute human's state. But you don't strictly need fundamental randomness for this optimization, Bayesian probabilities work in the same way, whether randomness is fundamental or not is difficult to observe. That said, computational difficulties start in the measurement device, that's where you should do collapse if you don't want exponentially complex calculations.
Outcomes of observation are explained by linearity of evolution operator and decoherence, but then you get human factor: different people have different problems with this explanation, I think it's because unitary motion is unintuitive, Aristotle knew explanation of heliocentrism, but it didn't work, because geocentrism was more intuitive for him. Some apparently suggest that to explain human experience you need to calculate mind from physics, which needs to solve the hard problem of consciousness, which is impossible.
Outcomes of observation are explained by linearity of evolution operator and decoherence, but then you get human factor: different people have different problems with this explanation, I think it's because unitary motion is unintuitive, Aristotle knew explanation of heliocentrism, but it didn't work, because geocentrism was more intuitive for him. Some apparently suggest that to explain human experience you need to calculate mind from physics, which needs to solve the hard problem of consciousness, which is impossible.
Nature doesn't obey your opinions.
That's an argument against solipsism at best, not much else.
Of course it is. What you are suggesting is classical determinism.
Slapping the "classical" label on it isn't quite correct. If it's not classical physics, then it's nonclassical determinism.
What has physics ever done for us? Apart from computers, satellites, planes, communications, sensors, and health... What has physics ever done for us?
The roads?
Well obviously the roads go without saying!
The roads?
Well obviously the roads go without saying!
What a take. All of modern technology, materials, solid state, semiconductors, transistors... And uhhh did you forget chemistry itself?
Just came back from work to see all the battering and downvoting. Clam down. I meant Quantum computing using qubits. Apologies for not being specific. Quantum computing itself is also a century old (almost)? Where are we with this?
Jeez - HN is brutal. Even a bot could have understood the context I meant.
Jeez - HN is brutal. Even a bot could have understood the context I meant.
Quantum computing is very much not a century old
In the library there were some old physics books, looked at one that was like 70 years old and it was covering the stuff we learned that quarter... Guess I have a LONG way to go until I learn "new" things xD