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Even Physicists Don’t Understand Quantum Mechanics

156 points by projectileboy 7y ago

speeder 7y ago
What I don't exactly understood is why the hostility toward theories that could lead to quantum gravity and whatnot? What are the historical reasons for it?
- TheOtherHobbes 7y ago
  It's complicated, and it's going to take a long time for historians - and multiple books - to untangle the failure. But so far as I can tell it started because Bohr was a bit of a tyrant and didn't like having the Copenhagen Interpretation questioned. So that set the tone for the first few decades. And QM was still developing, so it was more important to solve specific problems than worry about generalities. After that, progress was still being made on the Standard Model, so there was academic selection pressure pushing graduates towards PhD specifics and away from more philosophical speculations about Quantum Origins. And after that the String Theory people were much better at aggressive self-promotion than any of the competing QG theories. So something related happened again. Now there's no data to allow further fundamental progress on the Standard Model. SM alternatives continue being ruled out. And String Theory has run into very serious problems, So there's more interest in Quantum Origins and alternative QG theories. The odds of a big breakthrough are very low, they're higher than they used to be. And also it's really kind of annoying not to understand what's happening.
  - whatshisface 7y ago
    >And after that the String Theory people were much better at aggressive self-promotion than any of the competing QG theories. I'm not sure if that's a fair interpretation of history. At the time string theory still looked like the best option, and some say that even today it is the closest thing we have to a consistent theory.
    - tim333 7y ago
      Was there ever a sting theory that looked plausible to explain gravity say? As far as I can tell it started off as a simple model of how the nucleus held together - to stop the protons flying apart lets model stings holding them together. And then after that it's been let's play with the maths and the aggressive self-promotion thing mostly.
- abledon 7y ago
  In this Lex Freidman interview, Eric Weinstein (a bit kooky) explains his view on the trenches of advanced mathematics/physics: https://www.youtube.com/watch?v=2wq9x2QcZN0 https://www.youtube.com/watch?v=2wq9x2QcZN0 He goes into depths about the problems right now in academia
- tim333 7y ago
  I think a problem is the current theoretical attempts to get to quantum gravity are not very good leading to a certain amount of waffling about probably irrelevant stuff.
- pts_ 7y ago
  Vote bank politics version of academia.
solinent 7y ago
I think quantum mechanics is well-understood, the mathematics behind it provide us with excellent predictions. I think because at its core it is a probabilistic (or perhaps there are many worlds, but the implications are identical) theory--there is some inherent uncertainty in the predictions. This uncertainty builds up over time if left unmeasured, due to the chaotic nature of the system. We won't be able to result this uncertainty until we have more precise and accurate measurement devices. I was thinking, the only real way for us to progress was to get the results out of CERN we were expecting--either smaller particles or some detection method which allows us to peer even deeper into the atom. I think certain physicists are tired of the search for a unifying theory since it probably won't help us make better predictions. We need to get out there and get new empircal data.
- tempguy9999 7y ago
  I've no idea about nuffink, but > We need to get out there and get new empircal data. To do this it's necessary to formulate the right questions first, as gathered data (which are in effect, answers) provide no information alone. Edit: "provide no information alone" is a bit too strong. What I'm trying to say is more precise questions tend to produce more precise answers in normal discourse, I'm generalising that.
- jdc 7y ago
  Would higher precision of measurements help here?
  - analog31 7y ago
    Certainly. Effects can show up as qualitatively new things such as a new kind of particle, but also as tiny discrepancies between theory and experiment. There might be interesting new physics in every digit that gets added to the fundamental constants, for instance.
- chr1 7y ago
  Quantum computers working (or not working) would be another important test for quantum mechanics. Because quantum computer with n qubits to work requires amplitudes to behave the way quantum mechanical equations predict to the precision of 1/2^n which for 256 bits is much larger than the precision amplitudes can be measured in principle (e.g. for a spin ~1/planck length)
whatshisface 7y ago
The idea that someone with equal ability to do calculations with both could understand Newtonian mechanics better than they understand quantum mechanics belies an extremely naive view of how easy it is to perceive the true metaphysics of classical mechanics. In fact, the metaphysics of classical mechanics remains unsettled even today, the only reason it seems like there isn't a lot of philosophical debates left to have is that it has fallen out of fashion. A brief conversation with any philosopher will reveal that nobody "understands" the basic essence of being or whatever you want to call it. In fact, if "understand" means "have direct sensation of the true nature of reality," or even "have some grasp of the true metaphysics," then nobody understands anything. To give a specific example, let's say you have a classical system with only three particles in the entire universe, and further let's say they are interacting via a conservative force. So, how many things are there in the universe? Is each particle communicating with the others to organize their movements? Then, there would be three things in the universe. Is there a potential field permeating all of space, into which the particles project their influence? That would be four things. Is there a "strand of force" connecting each particle to every other particle? Then, there would be six things. The debates in the paragraph above were alive and well in Newton's time. However they were philosophical debates, not physical debates, because the three suggestions I proposed (along with the other possibilities I didn't mention) are all mathematically equivalent and would lead to the same motion.
- haecceity 7y ago
  Do people understand causality?
  - bsder 7y ago
    Causality is probably okay. Continuity? Not so much. The fact that we assume that the rules yesterday are the same as the rules today is one of those axioms that we simply have to accept in order to make progress.
  - internet_user 7y ago
    Not sure why this is being downvoted?
nitwit005 7y ago
> Physicists don’t understand their own theory any better than a typical smartphone user understands what’s going on inside the device. This article seems to take a confused definition of "understand". Not admitting to a full and complete understanding is rather different from knowing nothing at all. And to give your typical smartphone user some credit, most of them probably have some idea of the concepts of radio waves and computers, even if they don't grasp the details.
- titanomachy 7y ago
  I think it's a somewhat legitimate comparison. The average person can use a smartphone but couldn't tell you much about why it works the way it does. They can accomplish all sorts of things with it but they have little insight of its internal structure. It's the same with Schroedinger's equation: I can use it just fine, and it's clearly a useful way of looking at the world, but I don't understand why reality is like that.
taneq 7y ago
"If you think you understand quantum mechanics, you don't understand quantum mechanics." - Richard P. Feynman
- analog31 7y ago
  A related comment from one of my physics profs: "You don't understand quantum mechanics, you just get used to it."
  - jeffwass 7y ago
    Never heard that one before, but I love it.
    - platz 7y ago
      The original version is from Von Neumann John Von Neumann once said to Felix Smith, "Young man, in mathematics you don't understand things. You just get used to them."
mellosouls 7y ago
Despite the forthright title, it is worth noting that this is an Opinion piece in the NYT and there are other physicists who would be uncomfortable with the popularising tendency to woo-ify our most successful scientific theory.
- platz 7y ago
  This opinion piece is written by a well-known research professor at CalTech and sits behind Feynman's old desk. He's been extolling this exact message for years. I think he would say he's trying to de-woo QM by asking folks to think critically about it's principles He is not saying that the predictions that QM gives is wrong. He's a hard materialist and rejects the Copenhagen interpretation of QM (as many do who think intently about it) and prefers Many World's Interpretation, but admits there's more work to be done. He's saying in the article that folks should work on it. https://en.m.wikipedia.org/wiki/Sean_M._Carroll https://en.m.wikipedia.org/wiki/Sean_M._Carroll
  - mellosouls 7y ago
    I'm well aware of the author's credentials, writings and views - and would have thought that being in a position of popular renown would have made him more cautious of playing to the crowd with titles that indicate mysticism is the acknowledged heart of the scientific project.
    - deleted 7y ago
      [deleted]
    - tim333 7y ago
      I'm not sure how you get from a title like "Even Physicists Don’t Understand Quantum Mechanics" to the "mysticism is the acknowledged heart of the scientific project" thing. The heart of science has been trying to figure out things we don't understand which is not the same as mysticism.
      - mellosouls 7y ago
russellbeattie 7y ago
I think the author (Sean Carroll - whose other books I've read and pre-prdered the one this article comes from) is trying to point out that we're at a stage where maybe we should regroup a bit and find better analogies for what's happening in the quantum world, which may lead to better understanding in the future. The mish-mash of crazy phenomena could be laid out a bit more logically than "wow, check out this insanity!" We need to kill Shrodinger's cat, stop yammering about entanglement, and stop talking about wave functions as if they're real things. There has to be better ways to describe this stuff. Personally, I think they should start with the nomenclature. It may have been amusing at first to call things strange and up and down and colored, etc. but at this point it's a mess, especially when it's now clear that many particles are just the same thing with varying energy levels. Also, while I'm on a rant, the double slit experiment is crap. It never shows the particle grouping pattern, just the interference pattern. They talk about measuring the photon at the slit, collapsing the wave function and creating a grouping as if by little ping-pong balls, but it's never demonstrated!
- AstralStorm 7y ago
  Stop BSing and run it with protons, electrons or neutrons. Measure charge distribution in the sensor, track paths in a bubble chamber, call it a day. De Broglie called from afterlife to check if people still run simple experiments.
- tim333 7y ago
  > They talk about measuring the photon at the slit, collapsing the wave function... but it's never demonstrated! I believe they have done real experiments, Feynman mentions doing it with electrons going through the slit and a light source to make a flash by the slit when the electron passes. If you use short enough wavelength light to tell which slit then the interference goes. But true it was done in a lab sometime, not as a popular demonstration.
- mensetmanusman 7y ago
  The double slit experiment has been repeated many times in single-particle (photon, etc.) mode. https://www.researchgate.net/figure/Esperimento-della-doppia-fenditura-effettuato-con-elettroni-Le-immagini-sono-prese-dopo_fig47_262251891 https://www.researchgate.net/figure/Esperimento-della-doppia... Here is data showing particle grouping patterns. This forms the basis of the many-particle interference pattern. If you put a detector near the slits to try to measure what passes through, then this pattern does not arise.
Jerry2 7y ago
Sean Carroll, the author, is a huge proponent and believer [1][1.1] in Many-Worlds Interpretation (MWI) interpretation of QM. MWI's basic idea is that the wavefunction is real and that there is no wavefunction collapse. Each time there's a decoherence, there's a universe split. Some physicists think this is pseudoscience or 'crackpottery' at best [2] since it can never be proven. A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value (if you assume it to be true, there's nothing that this belief 'buys' you). So when Carroll talks about 'physicists not understanding QM', he's just unhappy that most physicists don't share his view about QM and he's been known for trying to shame physicists for not sharing his view too. [3][3.1] [1] http://www.preposterousuniverse.com/blog/2014/06/30/why-the-many-worlds-formulation-of-quantum-mechanics-is-probably-correct/ http://www.preposterousuniverse.com/blog/2014/06/30/why-the-... [1.1] https://www.youtube.com/watch?v=HxgGYJ3OjM8 https://www.youtube.com/watch?v=HxgGYJ3OjM8 [2] https://motls.blogspot.com/2014/07/many-worlds-pseudoscience-again.html https://motls.blogspot.com/2014/07/many-worlds-pseudoscience... [3] http://www.preposterousuniverse.com/blog/2013/01/17/the-most-embarrassing-graph-in-modern-physics/ http://www.preposterousuniverse.com/blog/2013/01/17/the-most... [3.1] https://www.youtube.com/watch?v=ZacggH9wB7Y https://www.youtube.com/watch?v=ZacggH9wB7Y
- acqq 7y ago
  In the article, there is a statement: "Empirically minded physicists have realized that the phenomenon of measurement can be directly probed by sufficiently subtle experiments." Then please write about these probes, and not just the rant that "nobody understands." The public doesn't have to worry (and we don't have to read) about the "interpretations" until there is a specific proposition of how to do such probe an the experiment can be constructed and performed. He writes "students who demonstrate an interest in the topic are gently but firmly — maybe not so gently — steered away, sometimes with an admonishment to “Shut up and calculate!”." My answer to this article would be, to theoretical physicists: "shut up and construct an experiment that can be performed." As long as there's no practical difference (in the sense that any experiment that can be imagined can demonstrate it) there's just no physics there. So yes... "shut up and calculate."
  - 7y ago
deleted 7y ago
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scotty79 7y ago
I think the problem is that people have trouble shedding the illusion that particles are small balls on 3d billiard table. If they accepted that the wave function with all it's weirdness is the particle they colud get a better feel for quantum mechanics. Funny thing is that Schrodinger equation that describes how wave function evolves simplifies to classical movement equation if you consider "pointlike" wave function. https://en.m.wikipedia.org/wiki/Ehrenfest_theorem https://en.m.wikipedia.org/wiki/Ehrenfest_theorem There's no need for thinking that there's a collapse of the wave function and then some little ball pops up that's governed by different equation. The equation is the same. Just a lot od terms can be simplified if wave fuction is small and sharp. Just like there is no collapse when you slow down from relativistic speed even though you can now skip relativistic terms in equations and still get mostly correct result.
- millstone 7y ago
  How did you conclude that there's no need for thinking that there's a collapse of the wavefunction? How does wavefunction collapse arise from the Schrodinger equation?
  - scotty79 7y ago
    https://en.m.wikipedia.org/wiki/Ehrenfest_theorem https://en.m.wikipedia.org/wiki/Ehrenfest_theorem Basically classical mechanics is just Schrodinger equation for sharp, small wave functions. So you don't need to think that due to measurement classical particle pops up out of fuzzy thing that the wave function is. Instead you can think instead that due to measurement wavefunction itself reshapes to be really narrow and sharp but it still obeys same shrodinger equation. Just now thanks to sharpness you can simplify the equation a lot so it becomes classical motion equations.
    - username90 7y ago
      An integral part of quantum mechanics is the actual discrete states, ie the eigen values which it probabilistically chooses during a wave function collapse. Hence it doesn't behave like a wave, also it doesn't behave like a particle, it behaves like a mix of both. That is quantum mechanics and we don't fully understand the maths of it yet, ie when do these waves behave like particles and when do they behave like waves ie when do the wave function collapse?
keypusher 7y ago
> If you think you understand quantum mechanics then you don't understand quantum mechanics. Richard Feynman
- mayankkaizen 7y ago
  This is the third time I'm reading this quote here.
GistNoesis 7y ago
Time to grab your tinfoil hat. Of course physicists don't understand Quantum Mechanics, it has been classified in 1964. Before that time we didn't really have the computational resources to use the alternate model efficiently. You've got to remember we are talking about the technology which make nukes. What if the physics world was as simple as the one we teach in high school, a simple classical world with a twist. In the 1950s there were even science kits for kids with Uranium. We were on the track towards a world with clean infinite energy. Clean, yes, because the first fusion bomb had just been tested, and fusion technology was just around the corner. Then the cold war paranoia made everything change. The Vietnam War brought what ifs ? What if the know how was so simple that any Vietcong could build a nuke ? What if one of those damn pacifists decided to make one at home ? They gathered a few people from Los Alamos to seek council. The tale has it that it was Von Neumann that put the final nail in the coffin of the green world utopia. With machines using its architecture, it would, before a few decades, be simple for everyone to simulate everything from chemistry to atom bombs. It was simply not acceptable. They devised a plan to make sure that was not going to happen. The beauty of science is that once you accept a false result, you can easily disprove the true theories. Then it's just a question of smoke and mirrors (should I say vapor chambers, and single particle detectors ?). Control the experiment results by making sure the experimenters know the theory it needs to prove. That's how in 1964, a crackpot physicist made the world non-local. It was such a success to attract young new people to the field, that those who knew better played along. Of course since then smart people saw through the veil and are thankful for the elders' wisdom to not free the dragon.
- Bombthecat 7y ago
  I can't follow, what do you recht to say? That quantum physics doesn't exist?
- beders 7y ago
  " it has been classified in 1964" oh, and math too? All over the world? Seriously...
  - GistNoesis 7y ago
droptablemain 7y ago
"If you think you understand quantum mechanics, you don't understand quantum mechanics." - Richard Feynman
wozer 7y ago
You can read about the newer theory mentioned (but not explained) in the article here: https://en.m.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory https://en.m.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%8...
jvanderbot 7y ago
Isn't this a tautology? It's the same with all probanalistic descriptions of a phenomenon, isnt it? You can use probability to model all kinds of things that you cannot (yet) directly model, cannot observe, and do not understand. It seems natural that it's a way to describe a system not well understood. Isn't many worlds what you get when you interpret the Randomized Model as Truth?

156 points by projectileboy 7y ago

What I don't exactly understood is why the hostility toward theories that could lead to quantum gravity and whatnot? What are the historical reasons for it?

TheOtherHobbes 7y ago
It's complicated, and it's going to take a long time for historians - and multiple books - to untangle the failure. But so far as I can tell it started because Bohr was a bit of a tyrant and didn't like having the Copenhagen Interpretation questioned. So that set the tone for the first few decades. And QM was still developing, so it was more important to solve specific problems than worry about generalities. After that, progress was still being made on the Standard Model, so there was academic selection pressure pushing graduates towards PhD specifics and away from more philosophical speculations about Quantum Origins. And after that the String Theory people were much better at aggressive self-promotion than any of the competing QG theories. So something related happened again. Now there's no data to allow further fundamental progress on the Standard Model. SM alternatives continue being ruled out. And String Theory has run into very serious problems, So there's more interest in Quantum Origins and alternative QG theories. The odds of a big breakthrough are very low, they're higher than they used to be. And also it's really kind of annoying not to understand what's happening.
- whatshisface 7y ago
  >And after that the String Theory people were much better at aggressive self-promotion than any of the competing QG theories. I'm not sure if that's a fair interpretation of history. At the time string theory still looked like the best option, and some say that even today it is the closest thing we have to a consistent theory.
  - tim333 7y ago
    Was there ever a sting theory that looked plausible to explain gravity say? As far as I can tell it started off as a simple model of how the nucleus held together - to stop the protons flying apart lets model stings holding them together. And then after that it's been let's play with the maths and the aggressive self-promotion thing mostly.
abledon 7y ago
In this Lex Freidman interview, Eric Weinstein (a bit kooky) explains his view on the trenches of advanced mathematics/physics: https://www.youtube.com/watch?v=2wq9x2QcZN0 https://www.youtube.com/watch?v=2wq9x2QcZN0 He goes into depths about the problems right now in academia
tim333 7y ago
I think a problem is the current theoretical attempts to get to quantum gravity are not very good leading to a certain amount of waffling about probably irrelevant stuff.
pts_ 7y ago
Vote bank politics version of academia.

solinent 7y ago

I think quantum mechanics is well-understood, the mathematics behind it provide us with excellent predictions. I think because at its core it is a probabilistic (or perhaps there are many worlds, but the implications are identical) theory--there is some inherent uncertainty in the predictions. This uncertainty builds up over time if left unmeasured, due to the chaotic nature of the system. We won't be able to result this uncertainty until we have more precise and accurate measurement devices. I was thinking, the only real way for us to progress was to get the results out of CERN we were expecting--either smaller particles or some detection method which allows us to peer even deeper into the atom. I think certain physicists are tired of the search for a unifying theory since it probably won't help us make better predictions. We need to get out there and get new empircal data.

tempguy9999 7y ago
I've no idea about nuffink, but > We need to get out there and get new empircal data. To do this it's necessary to formulate the right questions first, as gathered data (which are in effect, answers) provide no information alone. Edit: "provide no information alone" is a bit too strong. What I'm trying to say is more precise questions tend to produce more precise answers in normal discourse, I'm generalising that.
jdc 7y ago
Would higher precision of measurements help here?
- analog31 7y ago
  Certainly. Effects can show up as qualitatively new things such as a new kind of particle, but also as tiny discrepancies between theory and experiment. There might be interesting new physics in every digit that gets added to the fundamental constants, for instance.
chr1 7y ago
Quantum computers working (or not working) would be another important test for quantum mechanics. Because quantum computer with n qubits to work requires amplitudes to behave the way quantum mechanical equations predict to the precision of 1/2^n which for 256 bits is much larger than the precision amplitudes can be measured in principle (e.g. for a spin ~1/planck length)

whatshisface 7y ago

The idea that someone with equal ability to do calculations with both could understand Newtonian mechanics better than they understand quantum mechanics belies an extremely naive view of how easy it is to perceive the true metaphysics of classical mechanics. In fact, the metaphysics of classical mechanics remains unsettled even today, the only reason it seems like there isn't a lot of philosophical debates left to have is that it has fallen out of fashion. A brief conversation with any philosopher will reveal that nobody "understands" the basic essence of being or whatever you want to call it. In fact, if "understand" means "have direct sensation of the true nature of reality," or even "have some grasp of the true metaphysics," then nobody understands anything. To give a specific example, let's say you have a classical system with only three particles in the entire universe, and further let's say they are interacting via a conservative force. So, how many things are there in the universe? Is each particle communicating with the others to organize their movements? Then, there would be three things in the universe. Is there a potential field permeating all of space, into which the particles project their influence? That would be four things. Is there a "strand of force" connecting each particle to every other particle? Then, there would be six things. The debates in the paragraph above were alive and well in Newton's time. However they were philosophical debates, not physical debates, because the three suggestions I proposed (along with the other possibilities I didn't mention) are all mathematically equivalent and would lead to the same motion.

haecceity 7y ago
Do people understand causality?
- bsder 7y ago
  Causality is probably okay. Continuity? Not so much. The fact that we assume that the rules yesterday are the same as the rules today is one of those axioms that we simply have to accept in order to make progress.
- internet_user 7y ago
  Not sure why this is being downvoted?

nitwit005 7y ago

> Physicists don’t understand their own theory any better than a typical smartphone user understands what’s going on inside the device. This article seems to take a confused definition of "understand". Not admitting to a full and complete understanding is rather different from knowing nothing at all. And to give your typical smartphone user some credit, most of them probably have some idea of the concepts of radio waves and computers, even if they don't grasp the details.

titanomachy 7y ago
I think it's a somewhat legitimate comparison. The average person can use a smartphone but couldn't tell you much about why it works the way it does. They can accomplish all sorts of things with it but they have little insight of its internal structure. It's the same with Schroedinger's equation: I can use it just fine, and it's clearly a useful way of looking at the world, but I don't understand why reality is like that.

taneq 7y ago

"If you think you understand quantum mechanics, you don't understand quantum mechanics." - Richard P. Feynman

analog31 7y ago
A related comment from one of my physics profs: "You don't understand quantum mechanics, you just get used to it."
- jeffwass 7y ago
  Never heard that one before, but I love it.
  - platz 7y ago
    The original version is from Von Neumann John Von Neumann once said to Felix Smith, "Young man, in mathematics you don't understand things. You just get used to them."

mellosouls 7y ago

Despite the forthright title, it is worth noting that this is an Opinion piece in the NYT and there are other physicists who would be uncomfortable with the popularising tendency to woo-ify our most successful scientific theory.

platz 7y ago
This opinion piece is written by a well-known research professor at CalTech and sits behind Feynman's old desk. He's been extolling this exact message for years. I think he would say he's trying to de-woo QM by asking folks to think critically about it's principles He is not saying that the predictions that QM gives is wrong. He's a hard materialist and rejects the Copenhagen interpretation of QM (as many do who think intently about it) and prefers Many World's Interpretation, but admits there's more work to be done. He's saying in the article that folks should work on it. https://en.m.wikipedia.org/wiki/Sean_M._Carroll https://en.m.wikipedia.org/wiki/Sean_M._Carroll
- mellosouls 7y ago
  I'm well aware of the author's credentials, writings and views - and would have thought that being in a position of popular renown would have made him more cautious of playing to the crowd with titles that indicate mysticism is the acknowledged heart of the scientific project.
  - deleted 7y ago
    [deleted]
  - tim333 7y ago
    I'm not sure how you get from a title like "Even Physicists Don’t Understand Quantum Mechanics" to the "mysticism is the acknowledged heart of the scientific project" thing. The heart of science has been trying to figure out things we don't understand which is not the same as mysticism.
    - mellosouls 7y ago

russellbeattie 7y ago

I think the author (Sean Carroll - whose other books I've read and pre-prdered the one this article comes from) is trying to point out that we're at a stage where maybe we should regroup a bit and find better analogies for what's happening in the quantum world, which may lead to better understanding in the future. The mish-mash of crazy phenomena could be laid out a bit more logically than "wow, check out this insanity!" We need to kill Shrodinger's cat, stop yammering about entanglement, and stop talking about wave functions as if they're real things. There has to be better ways to describe this stuff. Personally, I think they should start with the nomenclature. It may have been amusing at first to call things strange and up and down and colored, etc. but at this point it's a mess, especially when it's now clear that many particles are just the same thing with varying energy levels. Also, while I'm on a rant, the double slit experiment is crap. It never shows the particle grouping pattern, just the interference pattern. They talk about measuring the photon at the slit, collapsing the wave function and creating a grouping as if by little ping-pong balls, but it's never demonstrated!

AstralStorm 7y ago
Stop BSing and run it with protons, electrons or neutrons. Measure charge distribution in the sensor, track paths in a bubble chamber, call it a day. De Broglie called from afterlife to check if people still run simple experiments.
tim333 7y ago
> They talk about measuring the photon at the slit, collapsing the wave function... but it's never demonstrated! I believe they have done real experiments, Feynman mentions doing it with electrons going through the slit and a light source to make a flash by the slit when the electron passes. If you use short enough wavelength light to tell which slit then the interference goes. But true it was done in a lab sometime, not as a popular demonstration.
mensetmanusman 7y ago
The double slit experiment has been repeated many times in single-particle (photon, etc.) mode. https://www.researchgate.net/figure/Esperimento-della-doppia-fenditura-effettuato-con-elettroni-Le-immagini-sono-prese-dopo_fig47_262251891 https://www.researchgate.net/figure/Esperimento-della-doppia... Here is data showing particle grouping patterns. This forms the basis of the many-particle interference pattern. If you put a detector near the slits to try to measure what passes through, then this pattern does not arise.

Jerry2 7y ago

Sean Carroll, the author, is a huge proponent and believer [1][1.1] in Many-Worlds Interpretation (MWI) interpretation of QM. MWI's basic idea is that the wavefunction is real and that there is no wavefunction collapse. Each time there's a decoherence, there's a universe split. Some physicists think this is pseudoscience or 'crackpottery' at best [2] since it can never be proven. A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value (if you assume it to be true, there's nothing that this belief 'buys' you). So when Carroll talks about 'physicists not understanding QM', he's just unhappy that most physicists don't share his view about QM and he's been known for trying to shame physicists for not sharing his view too. [3][3.1] [1] http://www.preposterousuniverse.com/blog/2014/06/30/why-the-many-worlds-formulation-of-quantum-mechanics-is-probably-correct/ http://www.preposterousuniverse.com/blog/2014/06/30/why-the-... [1.1] https://www.youtube.com/watch?v=HxgGYJ3OjM8 https://www.youtube.com/watch?v=HxgGYJ3OjM8 [2] https://motls.blogspot.com/2014/07/many-worlds-pseudoscience-again.html https://motls.blogspot.com/2014/07/many-worlds-pseudoscience... [3] http://www.preposterousuniverse.com/blog/2013/01/17/the-most-embarrassing-graph-in-modern-physics/ http://www.preposterousuniverse.com/blog/2013/01/17/the-most... [3.1] https://www.youtube.com/watch?v=ZacggH9wB7Y https://www.youtube.com/watch?v=ZacggH9wB7Y

acqq 7y ago
In the article, there is a statement: "Empirically minded physicists have realized that the phenomenon of measurement can be directly probed by sufficiently subtle experiments." Then please write about these probes, and not just the rant that "nobody understands." The public doesn't have to worry (and we don't have to read) about the "interpretations" until there is a specific proposition of how to do such probe an the experiment can be constructed and performed. He writes "students who demonstrate an interest in the topic are gently but firmly — maybe not so gently — steered away, sometimes with an admonishment to “Shut up and calculate!”." My answer to this article would be, to theoretical physicists: "shut up and construct an experiment that can be performed." As long as there's no practical difference (in the sense that any experiment that can be imagined can demonstrate it) there's just no physics there. So yes... "shut up and calculate."
- 7y ago

deleted 7y ago

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scotty79 7y ago

I think the problem is that people have trouble shedding the illusion that particles are small balls on 3d billiard table. If they accepted that the wave function with all it's weirdness is the particle they colud get a better feel for quantum mechanics. Funny thing is that Schrodinger equation that describes how wave function evolves simplifies to classical movement equation if you consider "pointlike" wave function. https://en.m.wikipedia.org/wiki/Ehrenfest_theorem https://en.m.wikipedia.org/wiki/Ehrenfest_theorem There's no need for thinking that there's a collapse of the wave function and then some little ball pops up that's governed by different equation. The equation is the same. Just a lot od terms can be simplified if wave fuction is small and sharp. Just like there is no collapse when you slow down from relativistic speed even though you can now skip relativistic terms in equations and still get mostly correct result.

millstone 7y ago
How did you conclude that there's no need for thinking that there's a collapse of the wavefunction? How does wavefunction collapse arise from the Schrodinger equation?
- scotty79 7y ago
  https://en.m.wikipedia.org/wiki/Ehrenfest_theorem https://en.m.wikipedia.org/wiki/Ehrenfest_theorem Basically classical mechanics is just Schrodinger equation for sharp, small wave functions. So you don't need to think that due to measurement classical particle pops up out of fuzzy thing that the wave function is. Instead you can think instead that due to measurement wavefunction itself reshapes to be really narrow and sharp but it still obeys same shrodinger equation. Just now thanks to sharpness you can simplify the equation a lot so it becomes classical motion equations.
  - username90 7y ago
    An integral part of quantum mechanics is the actual discrete states, ie the eigen values which it probabilistically chooses during a wave function collapse. Hence it doesn't behave like a wave, also it doesn't behave like a particle, it behaves like a mix of both. That is quantum mechanics and we don't fully understand the maths of it yet, ie when do these waves behave like particles and when do they behave like waves ie when do the wave function collapse?

keypusher 7y ago

> If you think you understand quantum mechanics then you don't understand quantum mechanics. Richard Feynman

mayankkaizen 7y ago
This is the third time I'm reading this quote here.

GistNoesis 7y ago

Time to grab your tinfoil hat. Of course physicists don't understand Quantum Mechanics, it has been classified in 1964. Before that time we didn't really have the computational resources to use the alternate model efficiently. You've got to remember we are talking about the technology which make nukes. What if the physics world was as simple as the one we teach in high school, a simple classical world with a twist. In the 1950s there were even science kits for kids with Uranium. We were on the track towards a world with clean infinite energy. Clean, yes, because the first fusion bomb had just been tested, and fusion technology was just around the corner. Then the cold war paranoia made everything change. The Vietnam War brought what ifs ? What if the know how was so simple that any Vietcong could build a nuke ? What if one of those damn pacifists decided to make one at home ? They gathered a few people from Los Alamos to seek council. The tale has it that it was Von Neumann that put the final nail in the coffin of the green world utopia. With machines using its architecture, it would, before a few decades, be simple for everyone to simulate everything from chemistry to atom bombs. It was simply not acceptable. They devised a plan to make sure that was not going to happen. The beauty of science is that once you accept a false result, you can easily disprove the true theories. Then it's just a question of smoke and mirrors (should I say vapor chambers, and single particle detectors ?). Control the experiment results by making sure the experimenters know the theory it needs to prove. That's how in 1964, a crackpot physicist made the world non-local. It was such a success to attract young new people to the field, that those who knew better played along. Of course since then smart people saw through the veil and are thankful for the elders' wisdom to not free the dragon.

Bombthecat 7y ago
I can't follow, what do you recht to say? That quantum physics doesn't exist?
beders 7y ago
" it has been classified in 1964" oh, and math too? All over the world? Seriously...
- GistNoesis 7y ago

droptablemain 7y ago

"If you think you understand quantum mechanics, you don't understand quantum mechanics." - Richard Feynman

wozer 7y ago

You can read about the newer theory mentioned (but not explained) in the article here: https://en.m.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory https://en.m.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%8...

jvanderbot 7y ago

Isn't this a tautology? It's the same with all probanalistic descriptions of a phenomenon, isnt it? You can use probability to model all kinds of things that you cannot (yet) directly model, cannot observe, and do not understand. It seems natural that it's a way to describe a system not well understood. Isn't many worlds what you get when you interpret the Randomized Model as Truth?