The Problem with Quantum Measurement

[@sjzara]

I really like that you get right down into the technicalities. You don't hand-wave away issues like so many physics popularisers.

[@SteelBlueVision]

Definitely and you don't appear to be biased towards a particular interpretation of QM and blind-sighted by its deficiencies.

[@voidisyinyangvoidisyinyang885]

Que the latest Sean Carroll promotional mass media mind control tour!

[@extradimension7356]

Yeah really good point. I'm so happy that my BS detector is no longer creating multiple (BS) universes every time I switch it on and make observations, now that Sabine Hossenfelder has straightened half of this out I can't wait to see the next video so I can really tell my detectors to knock it off...

[@robmorgan1214]

If you liked this you should check out her book. I found it refreshing. It like lee smolin's book gives people permission to think again. Group think is not thinking!

[@extradimension7356]

@@robmorgan1214 That sounds like a good plan, "We happy few' that work at the edge of photonics and related fields in a practical way need something from the pure-physics community to assure us that the lunatics have not taken over the asylum. Keeping things between the rails would be super helpful in respect of new discoveries of various phenomena that most physicists / mathematicians are not usually aware of or have practical experience of. Sabine Hossenfelder does a really good job of mopping up really bad names for things devised by notable physicist and explaining what "THEY" mean when they say "Holographic principal " and the like.

[@timjackson3954]

When I was a young physicist trying to get my head around these concepts, asking questions like "what actually happens to the wave function when it collapses", appeared to be taboo. In undergraduate class the response varied from "come and see me after the class" to "I don't know". And don't get me started on Copenhagen! It's lovely to see Sabine breaking the taboos and stating clearly what we know and what we don't, drawing a solid line around the limits of the various theories.

[@randomnobody660]

Has that changed in the past 3 years? Also "come see me after the class" seems a reasonable response if it's tangent to the material on the curriculum. Have you tried taking that offer?

[@dandymcgee]

@@randomnobody660 Yeah I agree, "come and see me after class" could be a great opportunity to discuss something really interesting with a professor who is also frustrated by his inability to teach the most interesting problems as part of his standard curriculum.

[@joshuacoppersmith]

The clarification of superposition and mixed state is pure gold. Thanks!

[@justchecking905]

I have just binge-watched several of your programs and find them extremely well done - your clear explanations, the grphics used, and your view of the unreliability of scientific objectivity are fantastic. With my background in physics and science I was able to immediately understand everything you presented. I look forward to watching more of them tomorrow. John D. German, retired scientist, engineer, and professor of physics.

[@mikecrafton]

Your videos are wonderful!! I love how you make your explanations make sense and are so clear and understandable even for those of us who are not professional scientists!! Thank you!! Always looking forward to your next video!!

[@baterickpatman]

Sabine, you never cease to amaze me.. after trying to pour through scientific articles that were over my head, doing useless Google searches to read uninformed incorrect answers, and everything in between, I found the best answer here. THANK YOU :) This is the best, most accessible to the "casual physicist" explanation of The Measurement Problem I've ever seen/heard!

[@peterh.1521]

Good explanation of the problem with quantum measurement by you Sabine. You make the difficult illustrative and easy to understand.

[@stevereal-]

It’s amazing how good you are at podcasts now. Total different vibe, energy, and ease of performance. You really are firing on all cylinders now. However, I love science and still look to you for my dose of physics. Once again, bravo of becoming a master presenter, performer, artist, podcaster and did I forget anything? 🤔 Yes of course! And top notch physicist! A+

[@quantumcat7673]

Bonjour Sabine, I appreciate more and more your (mini)lectures. I love your approach to physics. The only major drawback is that 6:56 min. of you is just a teaser for me. I would love something like one hour of your interesting lecture on a subject like string theory or any subject that you personally like. Sabine, I believe that I'm getting addicted to you and quite frankly I love it.

[@EffySalcedo]

It's easy to appreciate concise and outlined lectures becoz nowadays who has a lot of time to watch about a particular subject in branch of science? Probably thats an excellent idea to have parts of the whole series like a documentary. 👍

[@jonathandamonte174]

I bought your book about a week ago & just finished reading this chapter tonight when I saw this video just posted today. Great timing. Great book. Great video. Thanks!

[@Rospajother]

Great video, that has always perplexed me concerning the measurement of the interference when measuring it collapses it :)

[@Mobius3c273]

Sabine, you may not be liked in your field of expertise from the 'experts' but I have upmost respect for your true fundermental scientific principles. We need more scientists like you, scientists who are true to the scientific methods and not 'believers' or corrupted by funding. On the contrary Brian Keating is my least favourite... my impression..a believer who does not question the standard view. Dr Becky has a lovely personality too..however like Brian she too does not question aspects of theory that are obviously shakey. You are no.1 ❤ keep up the great work Sabine. I love the sprinkling of comedy too.😂 Love your channel x

[@hckytwn3192]

Would love for you to continue this Sabine... you left us hanging at the end!

[@deborahrosengarth5672]

Yes would you please?

[@nossocc]

Awesome, this is great. Its never been clear to me what constitutes a measurement and how it can be "outside" of quantum mechanics. Your topic seems to be addressing this issue. Looking forward to the next video :)

[@CaptainGuntu]

I love your channel so much. It's hard to comprehend everything you say, but I love trying, and thinking about these topics.

[@reframer8250]

Frau Hossenfelder, vielen Dank für dieses Video!! Seite Jahren versuche ich das mit Leuten zu besprechen. Ich weiß nicht, ob ich immer an die falschen Leute geraten bin, aber Sie sind tatsächlich die erste, auf die ich treffe, die dieses einfache Problem verstanden zu haben scheint. Sie haben es perfekt formuliert, ich könnte es nicht besser. Die Inkompatibilität der beiden Prinzipien (bei Ihnen 1. und 3.) und die einfach Feststellung, dass ein Observer ebenfalls aus mikroskopischen Bestandteilen aufgebaut sein muss, die der Dynamik der Schrödinger Gleichung folgen (und damit 3. eben NICHT erfüllen können) liegen eigentlich auf der Hand. Dennoch habe ich in der Vergangenheit festgestellt, dass sich die Physikerwelt zum einen nicht dafür interessiert oder zum anderen teilweise das Problem einfach nicht versteht, was wirklich sehr frustrierend ist. Danke also nochmal für dieses Video! Jetzt fühle ich mich nicht mehr ganz so alleine^^ Und - halleluja - die eindeutige Aussage, dass Decoherence daran nichts ändert. Darauf werde auch ich immer verwiesen - und natürlich, es ist leicht, ein Problem einer Theorie mit einem Berg kompliziertem statistischen thermodynamischen Ballast zu überhäufen und dann zu sagen, das löst das Problem, es ist nur nicht direkt offensichtlich verständlich - natürlich. Das ist wie wenn ich ein Fake-Unternehmen mit irgendwelchen Zahlenrechnereien versuche schön zu rechnen. Das ändert nichts an dem Grundproblem, das das Unternehmen fake ist. Genauso ist es mit der Inkonsistenz der Quantenmechanik und der Dekohärenz.

[@anubhav21dec]

This issue has been bothering me since I joined college. It's agonizing. Thanks for seriously addressing this issue and not discarding it like some of the poppy physicists of the west.

[@SabineHossenfelder]

Happy to know I'm not the only one!

[@dankole307]

You got an attitude problem dude. Are you now the smartest man in the world? Congrats on your accomplishment.

[@dankole307]

@Vendicar Kahn How on earth do you get around the double slit experiment. Sure wave fronts behave with propagation in channels when exiting the slits. But shooting single photons at the same slits produce the same result. Thats the conundrum. Light behavior works like a wave no doubt. It works the same with individual photons. I can't site a reference off the top of my head but I know I've read it a couple times. If you can find evidence to dispute it let me know. I am retired for many years my instant recall is not what it was. I got other things to do tonight. Let me know what you find if you like. People helping people makes the world go round.

[@dankole307]

@Vendicar Kahn so shooting individual photons or electrons hasn't been done? Site a legit reference. Mapping electrons in beta decay is something we used decades ago. A distribution to determine effective ion chamber designs. Beta decay is well understood I think you know that. It tends to be noisey but consistent. Not precise but accurate. Aren't electrons photons? Yes they exhibit wave behavior no question. Aren't entangled electrons individual electron pairs? This stuff will drive one to drink and its cocktail hour. Cheers.

[@dankole307]

@Vendicar Kahn At this point I think we are talking past each other. Your quoting text book stuff which is just fine. I work in an applications where on the bottom is a source holder with some Promethium or Krypton 85. Beta/electrons are colluminated pass through thin windows travel a 0.5 inch air gap and enter an ion chamber that has a 800vdc charge to attract the negatively charged buggers. The electrons produce a tiny current that feeds into a high gain op amp with a gain of say 500 meg ohms. So shutter closed it reads zero vdc open gap say 8 vdc. The output is just a little noisey but through so adjustment in integration time we get adequate signal to noise ratio. Additional averaging through proprietary signal processing provides a response model capable of creating closed loop control to less than 1% of process. Is it a wave that creates the noisey opamp output or is it the nature of individual atoms producing the response model? Adding more curries does not produce a stronger signal it just makes it less noisey. In the last 50 years I would guess they have sold well over 5000 of these guages. Many repeat customers. We've used other forms of radiation transfer both reflective and transmission. Hopefully you can see my point of view. I am an engineer not a physicist. I have seen the Feyman diagram presentations. They also describe transfer of energy models. I am describing practical applications you are looking at a different set of variables. Good luck to you and yours. I think I've whipped this pony to death..

[@riadhalrabeh3783]

''The weight function doesn't correspond to something we can observe..'' This is the essence of the problem. The weight function is in a transformed space very much like the frequency domain is a transformed space of the time domain. The frequency spectrum of my voice does not resemble my voice at all, and it exists everywhere too. But when Fourier integral transforms it to the time domain, we get a single point of my voice, and this is the so called the wave function collapse. Thus the collapsed values are in real time and correspond to measurement, whereas the wave function is a 'material' frequency domain. My full praise to the channel.

[@amityaffliction4848]

Love your vids. Very informative 👍🏻

[@magnet2593]

It's marvelous how you clear so many things up in such a short time.

[@Jehannum2000]

I look forward to the future video where you explain your solution to these problems. I wonder what it will be. For me, the Transactional Interpretation answers these questions and ties it all together nicely: The Born Rule and the measurement problem are no longer such a mystery.

[@louisgauthier1889]

It's strange but I enjoy hearing you talk about things I don't quite understand. It's comforting knowing that you've figured it out and are trying to explain it to me. And it's the accent. You have a great physicist accent.

[@markostojiljkovic7100]

Ok... i need to rewatch this

[@TheAlison1456]

This is the best video I've seen on quantum mechanics. It explains the core problem of it in such a succinct and beautiful manner it's unbelievable. Other mediums just introduce philosophical or classical physics complications by providing an absurd interpretation or the wrong lens. I await the next video on this topic.

[@robertoiannucci4881]

Come for the music, stay for the physics.

[@galegreyson4196]

Since I am not a physics major and struggle to understand some aspects well, I especially appreciate your clear explanations and non-nonsense, logical approach to the material and science in general. I always enjoy your videos.

[@lepidoptera9337]

If you are listening to her you will never understand. She is simply talking nonsense here. It is theoretically extremely well understood what a measurement is. It is, BY DEFINITION, an irreversible energy transfer. The only problem here are theorists who are stuck at the kindergarten level of theory in which everything is reversible all the time. You can find such theorists in classical mechanics (they are only doing Hamiltonian mechanics on systems with finite phase space volumes) and in quantum mechanics (these are the ones who are talking about the "measurement problem"). Relativity provides a trivial solution to all of this and this was known since, at least, 1932.

[@galegreyson4196]

@@lepidoptera9337 Hi, thanks for your comment. I’m curious, what is your role in the field of physics, just to attempt to understand perspectives?

[@lepidoptera9337]

@@galegreyson4196 I was an experimental high energy physicist. I have done trillions of quantum measurements while I was active. Not once was there a problem, either in the lab or in the theory. The theory even spells out explicitly for us what needs to happen to have a measurement outcome. It is very strange how many theorists seem to be completely blind to that element. That is the real mystery here... why otherwise reasonably smart people have such deep misconceptions about a nearly trivial topic. They can handle much more complicated stuff with ease, but when it comes to seeing the obvious they are blanking. ;-)

[@linusmlgtips2123]

​@@lepidoptera9337lmao you're an ignorant idiot

[@dillonkeller4477]

Your channel is a "diamond in the rough" as they say :)

[@fewwiggle]

Can you quantify that?

[@dillonkeller4477]

@@fewwiggle yes

[@dillonkeller4477]

@Madara Uchiwa Sure thing

[@foolo1]

Hi. Great video! There are a few popular science channels out there that have made videos recently, that seem to suggest that many-worlds solve the measurement problem. It seems to be a trending topic. You mentioned in the end of the video "What does it take to solve the measurement problem? We will talk about this some other time." I would love to see this update video.

[@tomschmidt381]

I to really enjoy these videos and have leaned a lot. Recently read Ms. Hossenfelder's book "Lost in Math." While I can't say I fully understand all the issues it was nice seeing someone attempt to explain why theoretical physics seems to be stuck. There is so much we know we don't know and yet very little progress has been made over the last few decades.

[@stevekeller7696]

I used to work around this stuff, at a charged particle accelerator facility (SLAC). I'm always impressed with someone who actually understands this stuff. I got A's through math and physics; professors praised me, but I barely had a clue. I enjoy this gal.

[@madderhat5852]

I understood everything except for the bit after " In this video..."😶

[@keppela1]

Ha ha, I made it to about 48 seconds, then it became completely incomprehensible.

[@johnpepin5373]

lol!!!

[@shawngraham3598]

Funny shite! Lol

[@Raging.Geekazoid]

Basically, quantum mechanics has a very nice formula that accurately describes how particles behave when they're just floating around and minding their own business. The problem is that nobody has the slightest idea what happens when they smash into large objects.

[@SB-pq9dd]

Hahahaha

[@DingbatToast]

Fabulous, clear, engaging and quite devoid of sensationalism. Probably because the topic discussed is sensational enough! Thank you Sabine

[@luisr5577]

*Please talk about the Wheeler-DeWitt Equation!* Is is more fundamental than Schöringer's Equation? Carroll argues that the absence of space in Schöringer's seems to imply that space is not fundamental. What implications (at least in principle) could be infered about the absence of time in the WD equation?

[@ivanfromunion3513]

When time is not time, time is space; when space is not space, it is time: when they are neither, they are gravity. There is no escaping "Spacetime"!

[@SabineHossenfelder]

The Wheeler-DeWitt Equation is really the Schrödinger equation, it's just that in General Relativity that brings in additional complications.

[@luisr5577]

@@ivanfromunion3513 In fact, there are many ways to get rid of spacetime. Sean Carroll's work leads to the conclusion that spacetime emerges from entangled information, Nima Arkani-Hamed also says that Spacetime is doomed and proposes the Amplituhedron, the Holographic Principle may be applied to the Universe itself. Wheeler's "It from the bit," Verlinde's "Emergent Gravity and the Dark Universe" and so on.

[@ivanfromunion3513]

And not a single prediction in sight... I suspect that is a no no.

[@luisr5577]

@@ivanfromunion3513 Or a yeah-yeah. Experiments with entangled photons by Anton Zeilinger and his collaborators have ruled out a large class of theories that claim that realism is true and locality is false. Also, Zeilinger's experimental tests' results suggest the falsification of Local Realism which is Empirically Adequate to emergent spacetime.

[@MaryAnnNytowl]

I am really glad I found your channel, Sabine! Between you, Anton, Kyle, Hank, the folks at Spacetime and SciShow, and Dr. Becky, I can get _anything_ explained in the entirety of science!

[@MaryAnnNytowl]

Oh, and the new debunker that's also now a Trig and slide rule teacher, ResearchFlatMoon, too!

[@RalphDratman]

A much-described measurement device from the history of quantum mechanics is the electron multiplier. In this device, an incoming electron is accelerated by an electric field. The accelerated electron hits a metal plate and knocks out a cascade of additional electrons, which all escape the plate and get accelerated by a second electric field. Those secondary electrons flow into the next multiplier stage. Eventually, after several stages of multiplication, a large number of electrons hits a final metal plate which thereby receives a macroscopically-measurable amount of charge. Each many-times-amplified clump of charge is electronically counted as a single incident electron -- the one electron that started all the cascades. Simplistically speaking, this whole apparatus has to obey the Schrodinger Equation, but in practice a great deal more physical and mathematical structure is necessary to describe it. Notably, time reversal symmetry is effectively lost when the electron being detected "falls" into the electron multiplier, accelerated by a macroscopic electric field. I think linearity also must somehow be effectively lost when the original electron is sucked into this irreversible cascade. I don't know the details, but I think the incident wave function (field) somehow gets completely drained away by the apparatus. Bohr, in his famous conversations with Einstein, emphasized the irreversibility of the measurement device, but did not elaborate on what the irreversibility implies. I have simply tried to hand-wave how that might affect the incoming wave function. I no doubt appear ridiculous in doing so, but I did want to pass along my thoughts after all these years of thinking about what Bohr was getting at when he talked about irreversibility in the measurement apparatus.

[@esonghori]

This was one of the clearest explanation of quantum measurement problem I found on the internet. Thanks.

[@docholiday8029]

Welcome back Sabine!

[@SabineHossenfelder]

Thanks... Still recovering from the jet lag, uh-oh :/

[@tekdragon]

I feel like I know JUST enough about theoretical physics to appreciate everything she says while also understanding I have no clue what most of that means, but at the same time, WANTING to understand it! I just discovered your channel and im subscribing. Sorry i'm late :D

[@sbkaggle5961]

Love the videos, especially the technical details, I was never taught these specifics in undergrad. just the basics. Please do more! Also if there are specific papers or books you can refer to for those who want to do further reading (like me) please let us know! Most of us are unaware which papers are important to read. Also what would be a suitable donation to support more videos? I am a student so I don't have much money...would $5 a month be good? Also if you can, please consider doing a MOOC!

[@robmorgan1214]

If you've got an under grad science math or engineering background or feel comfortable with linear algebra calculus or probability and statistics, there are a few textbooks that are best for coming up to speed on the specifics IMHO (they are less likely to skip important steps that they assume we already should know). I'd recommend Griffiths intro to QM as a good jumping off point (assuming you're not already familiar with it)! It takes you through the usual toy model calculations and even works through the hydrogen atom in a way that's relatively self contained (you may need to reference a math book here or there to see things from a fresh perspective but it's rare with this guy). It covers commutation relations really well which is why we get the uncertainty stuff. It's explanation of perturbation theory is really good especially if you then immediately crack open Cohen and Tannoudji and read their take on dynamic perturbation theory. Finally he gets into the details of EPR/bell's theorem and explains the issue with his usual clarity. However, I also like Sakurai's discussion of EPR/Bell's. But Griffith's is where I'd start since he includes a good selection of worked examples and the solutions to many of his exercises can be found online... also Griffith's is a very slim volume given what it successfully covers compared to the others. To get a feel for the practical (how did we actually get here) side of things you should check out the original paper by plank. It's reprinted with commentary added in a book called The Discoveries by Alan Lightman. If you're interested in the human dimension you can't do wrong with Richard Rhodes' The Making of the Atomic Bomb most of which is really just the early history of quantum mechanics. Gets you a feel for how a group of unique minds worked together and assembled the majority of the puzzle we're still discussing today! After this read Sabine's book because it's nice to see how something used to work before trying to figure out why it's breaking down. She did a tremendous job writing it! It's why I'm here watching her videos.

[@sbkaggle5961]

@@robmorgan1214 thanks for the book recommendations

[@robmorgan1214]

@@sbkaggle5961 no problem. Hope you find them relevant!

[@alexdevisscher6784]

Great video about one of the most central problems in physics. I think that solving this problem will bring us close to fully understanding physics.

[@cipaisone]

we are still waiting for the sequel fo this video!

[@AlexHop1]

Great video--thanks for the great explanation of linearity and how it plays a role in the Measurement Problem.

[@ekklesiast]

"After you have made a measurement" Can someone explain what exactly IS "measurement"? How do you "measure" a wave function?

[@parthabanerjee1234]

The wave function (Ψ) describes a quantum system. Essentially, The wave function is a mathematical tool that can be used to describe the probability distribution for position, momentum, spin, energy, etc of a particle*. One does not measure a wave function itself. One measures the outcome probabilities (stated by the Borne Rule) which is described by the wave function. This sounds very abstract. So, let me give an analogy which might be of some help. There is a fly in your house in the middle of the night. You are sleeping and so you have no idea where the fly might be. The wave function of the fly states that there is a 10% chance that the fly is in the kitchen, 30% chance that it is in the bedroom, 40% chance that it is in the drawing-room and 20% chance that it is in the toilet. You wake up and see that the fly is in the bedroom. You made a measurement of the probability distribution of finding the fly somewhere in the house. The moment you made the measurement, the probability of finding the fly in the bedroom became 100% and 0% in the rest of the locations in the house. You see, you did not make the measurement of the wave function of the fly. You merely measured the probability of finding the fly which had a wave function associated with it which can tell you the probability distribution of the location of the fly. But there is a difference between this analogy and a quantum wave function. In this analogy, you can be sure even before you open your eyes that if the fly is in the bedroom, it cannot be in the kitchen. But in a quantum wave function, you would have to consider the absurdity that the fly is everywhere in the house until you have located it in the bedroom. Another absurdity in the quantum wave function, unlike in this analogy, is that there is no fly in the house. In the quantum world, the fly never existed. It happened to pop up the moment you saw it. *I used the term particle for the lack of a better word. I tend to use the term 'entity' instead of the term particle because I do not think that there exists something called a "particle".

[@kanucks9]

From my understanding, the whole point of this video was to describe why it is difficult to answer that question, and she says she will make a follow up video. Thus "the measurement problem"

[@parthabanerjee1234]

@@kanucks9 , it is normal to watch a video/read an article on the measurement problem and yet not understand it and ask the question that was asked. I have been in that loop for quite a while in the initial stage of my studying QM.

[@diegomontalvo9173]

@@parthabanerjee1234 why it does not exist particles?

[@parthabanerjee1234]

​@@diegomontalvo9173 , What exists or what is real is a philosophical question. Quantum Physics, especially the Copenhagen Interpretation does not deal with this philosophical question. We can say so and so thing exists only when it is macroscopic. You and I exist, the house exists, the fly in the house exists. But the same cannot be said either about the particle or the wave function associated with it. There is nothing real about the Schrödinger's probability wave function or the particle. The wave function is just a mathematical tool that can give you the amplitude of finding a particle in a location at a certain time. So, when you make a measurement what you detect is the density of probability in a location. This density of probability is what we call a particle. But there is really no particle in the conventional sense in that location. There is no ball-like solid or liquid thing over there. One might ask, what is this density of probability? One might ask, this density of probability is of what? And the answer would be, we don't know. Nobody knows. Quantum Physics is completely silent about it. It is very weird but that is how Quantum Physics is and that is why Quantum Physics is so interesting. What physicists call a particle is just an amplitude of a mathematical function and the point to note is that there is nothing real about a mathematical function or the amplitude of this mathematical function. So, the particle is not real and what is not real, cannot exist.

[@jamesdriscoll9405]

Very interesting and complex topic. Thank you for bringing it into focus. I am looking forward to hearing about Bose-Einstein condensates and Rydberg atoms, and how they fit in to quantum physics. Also QED in semiconductors would be very interesting.

[@tikke8511]

Simply, thank you very much again

[@rasimzeytunlu2936]

Your videos are so good that i dont know where to start for praising, so i will just write perfect👌 but i especially love your explanations on technical parts bcs most of the physicists are not even bother to explain the real deal of physics👏 i adore you

[@trevorgwelch7412]

" The most incomprehensible thing about the universe is that its comprehensible . " Einstien .

[@rwarren58]

There is no such person.

[@stormtrooper9404]

Sabine,if you ever read this.Please consider a (mini) series of videos covering topics alike.Interpretations and foundation of QM.Am very interested in learning about different approaches,but as a layman(prof. of literature) I can’t read physic papers and understand it on my own. You,as an expert in these fields are very good at explaining such a hard topics.More so,unlike other (mainstream)populisers/physics,you are not afraid to tackle this kind of topics,critique and give your personal oppinions.Which I highly regard! Keep up the good job... and keep singing! ;)

[@Skukkix23]

Great camera and composition this time!

[@SabineHossenfelder]

Thanks for the feedback!

[@altafvhora]

By virtue of my limited knowledge and education Perhaps I will not be able to understand and wrap my mind around but still I love to watch her vdos as she seems so authentic and seriously knowledgeable on the subject. Thank you for sharing all the knowledge. It's priceless! 👍🙏

[@xdrxt799]

What about Bohmian mechanics?

[@ivanfromunion3513]

They perhaps got Bohred?

[@aqu9923]

I watched this once again. It is one of the best explanations on the topic. However I have to adjust the playback speed to 75% whenever listening to Sabine 😂!

[@max_mel1]

My dice just collaps to 6.

[@davidarenard]

Are there models in macroscopic physics where the equations are not known to be derived from more elementary ones (microscopic physics)? Navier-Stokes in fluid mechanics for instance, can they be deduced from statistical mechanics ? Or is it always the case that when we have a good macroscopic theory with nice equations, they are consequences of the fundamental ones+statistics? (I am not a physicist as you can guess from this naive question)

[@DavidporthouseCoUk]

Asking about the Navier-Stokes equations is anything but naive. There we can model viscosity in a computer simulation as the Brownian motion of vorticity, as proposed by Alexandre Chorin, using the computer's random number generator. Adding Brownian motion to Euler's equation has the side effect of turning it into a Navier-Stokes equation, which is a different equation. Such side effects are prohibited in quantum mechanics, and yet we still need to make use of a random number generator. There are two things we can do. One is to say that the Schrodinger equation describes an oscillation in one way to travel faster than light, and we can add orthogonal tachyonic Brownian motion in the other way to travel faster than light. Another is to say that the Schrodinger equation is meaningless for objects heavier than the Planck mass, so we can just replace it with classical Brownian motion in order to maintain an Uncertainty Principle (this is influenced by Reinhold Furth). I am thinking of starting with simulations which investigate the interaction between the second way and the Dirac equation. I may look at the first way after that. I think we will need both ways in the future, which may offend fans of Occam's Razor, but I am a fan of using polynomial-time algorithms. I would emphasise that this is a practical subject despite the language that I use. My simulations can fail to work.

[@Art.ASMR-You2]

Listening, okay looking at your videos appreciate it thanks

[@whippetfun]

Clearest explanation of the measurement problem on KZbin.

[@UFCPR]

These videos are above my paygrade! :-D

[@ivanfromunion3513]

Given your profile photo... Buy cheaper cereals! 🤣🤣🤣

[@josephjohnson3738]

Best definition is gobbledegook.

[@BlaineCraner]

This channel needs more publicity.

[@Max-od7fb]

I really enjoyed this video. Thank you!

[@waynemcnab9496]

Excellent video, and I just finished your book. I couldn't put it down. It also was excellent. Mutually exclusive belief systems, be that in areas of science or religion, do not take into account that solution can come out of what at the time may seem to be totally ridiculous trains of thought. Any idea has value when it starts a path of different thinking. Conformity does not bring about change. Thanks again for the book, wonderful..

[@SabineHossenfelder]

Thanks for the feedback, happy to hear you liked it!

[@malekmannai9445]

what is the name of the book?

[@waynemcnab9496]

Lost in Math

[@ryanlyle9201]

The more I measure this channel, the less I actually know.

[@---ls5kx]

Ryan Lyle That's the spirit.. the more you know, the more you know, that you don't know

[@josephjohnson3738]

@ritemoelaw_books83 Or just accept the gobblegook being layer on thick. They are afraid to discuss that which is not coming from their accepted belief camp. Terrified of it, in fact.

[@jd-yo2is]

That's the dunning kruger effect leaving your body

[@0815-j3s]

What does it mean to say: "You have to update the wave function after measurement to 100%"? My understanding was that the wave function^2 is a probability density and the measurement is a realization of a random variable.

[@ronlong2400]

Wow! I really enjoy what I can understand, but my brain yells surrender after about 2 minutes. Thank you.

[@w1darr]

Sabine really does a great job with here channel, and I really appreciate how she approaches current 'way' of doing science with a critical (Not sure whether its the correct word actually, i mean 'kritisch') and highlights potential or real problems. I recently read 'a mathematical universe' by Max Tegmark, and he seems to be a proponent of solving the measurement problem the decoherence way (albeit I am not sure since I don't really understand this stuff well ;) . Wouldn't it actually suffice to show that in a complex system like all the things we encounter in our normal life (a teapot, which consists of, I don't know how many gazillions of quantum objects of some sort interacting) the interactions of those partial systems renders the possibilities for all the states of the compound system to become zero but for one single state? I mean, then we would indeed never experience a teapot being in some kind of superposition. If I understand the video correctly, the problem here is that there might be several possible states, in which the teapot could actually be in, and the selection of the 'actual' state would still be a mystery - and the teapot arbitrarily jumping around - which we never see. But what if the interaction of all the partial systems would force all compound states but one to assume possibility zero, and only one with possibility 1? These possiblities should be calculatable from the compound wave function, and if this turns out to render only 1 state being possible with chance 1, and all others impossible, then this state would be predetermined, there would be no 'randomness' leak from the partial quantum systems into 'world' , as the single possible state would be mathematically determined? On the other side, the explanation of Sabine somehow seems to indicate something more fundamentally wrong with this approach - and I am not able to grasp it.

[@santerisatama5409]

Please note that "01" and "10" are not palindromes, but "" and ">

[@frodejensen8968]

Could you explain the difference between a measurement (say someone looking at an interference pattern) and an interaction (say a photon hitting a screen)? It seems odd to link wavefunction collapse with measurement and not interaction. Unless we have no idea why the wavefunction collapses. And no ability to test it, because it would collapse the wavefunction. EDIT: As a layman, I was kept sleepless by this yesterday. My best bet is: Interaction is where the edges meet in a Feynman diagram. Measurement is what happens in an interaction where information escapes the wavefunction, causing it to collapse. Maybe a wildly incorrect guess, but it lead to a lot more thoughts, as I dozed off.

[@jaydeepvipradas8606]

I guess measurement is observation of interaction. Interaction can continue without measurement. When measured at specific time, measurement shows state of interaction. At quantum level, measurement or observation changes interaction, and seems like that's wave collapse. I like to think analogy as, everything is interacting like water wave ripples, but when observed or measured, things become solid ice like, due to measurement process. State of ripples gets frozen, yielding probability 1. Not sure if analogy is applicable.

[@pansepot1490]

Jaydeep Vipradas, nice analogy.

[@ivanfromunion3513]

"Could you explain the difference between a measurement (say someone looking at an interference pattern) and an interaction (say a photon hitting a screen)?" The first clause and aside don't apply: if no one EVER looked at the two-slit interference pattern it would still be there because it's a property of the universe, from which you originated. You can't claim ownership of it nor that it reproduces "your" thought patterns. That is not how it works. On the contrary: you are bound to it. The first clause and aside also don't apply because you are mixing verbs: verb "to be" is not the same as verb "to acquire a photon" and isn't remotely connected to verb "to acquire a photon, process it, and give the output to humanity for my eternal glory". So you are mixing infinity CLASSES. As for "action": it has no thoughts. It has already taken the decision. It's completely blind. That is upside down from regular understanding, of course. As it should be. Interaction, on the other hand, has thoughts as it has a.........nother "you" involved in the "action". That is an ordinal/cardinal war I don't wish to get involved with again because I already took my survival decision and I don't care how many people die for my survival. What that is supposed to mean is that you are comparing apples and oranges: looking at an interference pattern has nothing to do with measurement. (Not yet.) Whereas... second clause: a photon hitting a screen is an interaction or an action? Is "action" that which is done to you or that which you do to others? Either you "killed" (verb of your choice goes here, chose well, my child) your future axe murderer or you didn't, there is no middle ground. If you didn't you are dead and I am talking to your ghost and YOUR future ended, and if you did... good for you because I did plenty of that too. (I am still on verb to be, in case it's not transparent, translucent, iridescent, fluorescent, and non-refractive yet.)

[@amedeofilippi6336]

In my opinion at microscopic level it can be that measurement can also be an interaction. Maybe I am ignorant but never could understand the superposition explained with Schroedinger cat in the closed box. In my opinion the cat is awake or sleeping in any moment but not in both status.we just can’t know until we open the box.

[@zemm9003]

Measurement does not have a precise definition. It is some magical process that collapses the wave function. It is that simple.

[@ps200306]

Fabulous vid, Sabine. Had to watch it twice. Finally, I understand what decoherence is and why it doesn't make the measurement problem go away. I'd seen the term bandied about for years and wondered why physicists weren't saying it had plugged all the holes. So, decoherence doesn't solve it, Many Worlds doesn't solve it, Bohmian mechanics doesn't seem to add anything, what's left? ... I hope you're going to say "superdeterminism" and give us a video!

[@alexleung842]

What's the problem you see with Bohmian Mechanics?

[@lisakeitel3957]

Waiting for part 2...

[@MlSTA_GREEN]

Was looking for some info on Von Neumann. Quantum Decoherence was a surprise, but a welcome one. Good video!

[@lepidoptera9337]

You can find his book online. It basically already treats an early form of decoherence way before anybody else caught on. Not that decoherence buys you anything. The actually correct explanation is also in von Neumann's book, though. Pay extra attention to chapter six.

[@chrihipp]

Like it, but what a cliffhanger! C‘mon this is unfair.

[@billlewis8295]

Okay, so in which video do you describe your solution to the measurement problem? Thanks!

[@lezhilo772]

A student asked about the measurement problem and tried to interpret the wavefunction with what sounded like the neo-Copenhagen interpretation you mentioned. My argument against it went like this: if the wavefunction really only corresponds to information that observers know, then consider electrons going through a double slit towards a screen and two observers(A&B). Observer A does not measure the electrons' position, so to A, the electrons' wavefunctions do not collapse, and a double-slit interference pattern forms at the screen. Observer B measures the electrons' position, so he has gained information about the electrons' positions. The electrons' wavefunctions collapse and the double-slit interference pattern is destroyed. Thus we arrive at a contradiction: if two observers possess different information, then quantum mechanics predict contradictory screen patterns according to the neo-Copenhagen interpretation in the presence of observers having different information. Is my understanding of neo-Copenhagen interpretation correct?

[@PauloConstantino167]

Forget the damn cat. I can't bear these scientists that can't talk about QM without mentioning the damn cat.

[@Teleleco_do_ifood]

Agreed. Schrödinger used that cat as a reducto ad absurd rethoric argument exemplifying how things in quantum scale didn't happen in the classic scale. And everybody uses it as if it is the ultimate building block of the universe

[@Teleleco_do_ifood]

@Vendicar Kahn The cat having contiousness or being sentient is meaningless. the superpositin state is something very difficult to achieve even for subatomic particles (the quantum computer from IBM for instance can only sustain superposition of electron spin for about 0.5 milliseconds because every photon absorved, compton effect or thermal energy exchange is an "observer"). A cat in a box would never experience such superposition. Schrödinger knew that. His question was "Why?". Where's the limit of something collapsing the wave function or not? And Many worlds interpretation doesn't solve this problem, decoherence solves only part of this problem.

[@MindinViolet]

On a fundamental level, the universe is made of cats.

[@charlesgantz5865]

I can see my cat, and I'm still not sure if it's alive or dead.

[@Darkanight]

I can barely wait to see you in Genoa... I came 5 days earlier because I thought it was on the 24th... 😆 just a little afraid because i could not reserve a seat in advance... and I bought the ticket as soon as you posted that travel update... but, since you're so good at what you do, it's only understandable that so many people want to see you. :) thank you for the great work!

[@EffySalcedo]

Ok I have to say I'm a person with simple tastes, I see a cat, I click 😽

[@TorstenSeemann]

Dead cats included?

[@ulflyng]

Congrats, you just killed a cat

[@jamesruscheinski8602]

Can the observation from the measuring device take over the probability from the wave function? With the measurement by the device the probability has shifted to the observation (classical) away from the wave function (quantum) which is now separate? Upon measurement by the device, could there be two probabilities, one for the classical observation (100% probability) and another for the wave function (quantum probability distribution adding up to 1)?

[@shinymike4301]

Sometimes I talk to the wave function of my wonderful Grandmother, passed on many years ago.

[@ChiDraconis]

The «those who have passed» can actually do just that but is astounding if you develope a cogent sentient «wave» that is capable of decision making and responding we get an eerie feeling;

[@sanjosemike3137]

ShinyMike The information that was your Grandmother can never be destroyed. It is conserved, just as you will be after you too die, or rather, pass into a different state. Sanjosemike (no longer in CA)

[@phillipneal8194]

Thank you very much for all your videos. I have learned some new ideas and some old ideas have been cleared up ...a bit.

[@timhallas4275]

The problem is: those "things" aren't really there at all. everything is a field. there's nothing here but a sensory experience.

[@abhijeetbhagat100]

why there is field

[@timhallas4275]

@@abhijeetbhagat100 why is there anything? is a better question.

[@abhijeetbhagat100]

@@timhallas4275 may be we will never found this question answer

[@timhallas4275]

@@abhijeetbhagat100 But I already know the answer, don't you?

[@abhijeetbhagat100]

@@timhallas4275 yeh i know that you are god

[@greggor07]

Thank you Dr. Hossenfelder, firstly for writing your book, which had a profound effect on me, it hit really close to home. And secondly, for doing this, for getting down to the nitty-gritty in such a concise manner. Honestly, the latest book by Sean Carroll and the entire "Everettian" arrogant, hand waving attitude, is infuriating, lol! They (the Many Worlds Interpretation proponents) "take the wave function seriously"...smh.

[@NothingMaster]

Love the new dress; it’s highly distractive in unmeasurable ways.

[@malekmannai9445]

It gives a quantum sensation, I think it fits :P

[@岡安一壽-g2y]

I appreciate this video. I think all that is needed is the wave equation and Born's rule. What actually exists are particles. Particles follow the rules of waves. We only feel that waves exist when there are many particles. If we compare particles to cars, the rules of waves are traffic rules. Maxwell derived the equation of electromagnetic waves under the condition that there is no electric charge or current. Without charge or current, we cannot observe photons. I support Born's rule, Schrödinger's judgment, and Feynman's idea.

[@schmetterling4477]

There are no particles. There are only people who don't understand physics. ;-)

[@岡安一壽-g2y]

@@schmetterling4477 Am I one of the people ?

[@schmetterling4477]

@@岡安一壽-g2y That depends on whether you can learn or not. Physics frequently requires adaptive thinking. It took me years to learn that. I also went in with very clear ideas of how nature was supposed to work. Most of those ideas turned out to be wrong and I had to abandon them one after another and replace them with ideas that work much better. I am fine now. The process only took 30 or 40 years or so and will be ongoing until death or Alzheimer's will part me from a working mind. Let me put it this way: if you can ask whether you might be the problem if your description of nature doesn't match nature very well or if it seems overly convoluted, then you still have a shot at understanding physics, eventually. If you can't ask that question and give an honest affirmative answer, then, I am afraid, the goddess of physics will not shine on you. The simple fact is that nobody has ever seen a particle (as in tiny classical object with a center of mass coordinate that follows a classical path). That's just a very bad way of thinking about nature. A much better way is thinking in symmetries. Time translation symmetry causes energy conservation. Spatial translation symmetry causes momentum conservation. Symmetry under rotation causes angular momentum conservation. All of these conserved quantities belong to systems. They don't belong to tiny little objects. Where do the waves come from, then? They are literally generated by the complex exponential function acting on one of the infinitesimal generators of the translational and rotational Lie groups.

[@岡安一壽-g2y]

@@schmetterling4477 "nobody has ever seen a particles" Is that true? I was told that a very weak light source can emit photons one by one, and these photons can be observed on a screen. Is that a lie? I'm very surprised.

[@schmetterling4477]

@@岡安一壽-g2y A photon is not a particle. It's a quantum of energy. It doesn't have position and path. It doesn't exist independently of an emission or absorption process.

[@lol2Dlol]

If you aren't a teacher, I think you should be. I feel like I really understand the subject after every one of your videos. Thank you for making these.

[@leonardgibney2997]

You're a better man than me Gunga Din.

[@grahamgillard3722]

I get the impression she is a teacher. The way she first tells what she is about to explain - she sets the scene, then she explains what she explains, then she tells us what she has just explained. Very like a teacher.

[@merlin5by533]

Still the best, Sabine. Could you delve into the Wave Function collapse? I am intrigued by the possible interaction of the Wave with any form of the old concept of the Aether, including the quantum virtual particles in empty space.

[@marcusbeau]

human reset 2 31, gets up and walks down hall to the measurement postulate class, sit back down, from being lost in a hallway with no class and only an ai, 4:55 first time ive been lost in your classes but back into place at 621 interference, biological and non biolgical

[@primovid]

Best description I've seen...Thx!

[@raghu45]

Your line of argument is very clear, even to laymen like me. I get it that at the particle level what we have is really its Functional representation. We know the metaphysics of particles and so their physics gets limited by the states their Formulations allow. Finally, any better reformulation to include your three postulates, especially the measurement (post facto) state.

[@davidwilkie9551]

Excellent presentation. (Nearly understood the circumstances?) Under the circumstances of eternal temporal Superposition-point Singularity positioning, where the Calculus of instantaneous pulses in periodic wave-envelopes of e-Pi-i resonance imaging, this explanation is probably as good as it gets or needs to be in the continuous creation cause-effect resonance conditions of uncertain wave-particle location repeatability. From which follows:The measurement problem is like using a Thermometer without a Spectrometer to analyse the density and intensity of amplitude and frequency modulation, with the expectation that the emissions and absorbtion lines are composed of "discrete" particles, when actually they are fuzzy approximations of Logarithmic Time Superposition-point Singularity functionality. (Mathologer demonstrates how an arbitary choice of terms in the sequences of transcendental e and Pi as numerical series, combine to form real-time "analog" numbers)

[@lennarthoekveen9339]

Thanks for adding the little tiger to the thumbnail, it really made my attempt at understanding all this feel a little less daunting :)

[@peach8352]

Thank you so much for your videos! While the human brain has incredible ability to generate intuitive leaps which have led to many discoveries and changed scientific dogma, too many scientists conveniently ignore facts when they contradict their desired outcomes, political views, or popular opinion. Please keep up the great work, and stay disciplined!

[@WJohnson1043]

Collapsing wave function! Sounds plausible but doesn't it depend on how the wave function is defined? For instance, we all know that when a dice is thrown the probability of getting a particular number is one-sixth. After throwing and getting a number, does the probability of getting that number change to one? I don't think so. To my mind probable events are by definition in the future, so probability takes on a different meaning for past and present events. Have I missed something?

[@mason4295]

Thank you for another concise video!

[@theceohq]

Arm-chair physics enthusiast here: I can't believe that it took that many years after learning about quantum theory that I only "understand" the difference between decoherence and the measurement postulate. Danke Sabine!

[@schmetterling4477]

I can't believe that you think that you understand. Decoherence has nothing to do with measurement. ;-)

[@theceohq]

@@schmetterling4477 Isn’t that literally what I wrote?

[@schmetterling4477]

@@theceohq You wrote that you understand. I very much doubt that. ;-)

[@theceohq]

@@schmetterling4477 You have to read the full sentence, friend; I am clearly stating I had conflated those, not that I understand them individually. Even that realization is marked by using the word “understand” by using quotation deliberately. But it does feel good making strangers on the internet feel dumb rather than understanding intent, I reckon?

[@schmetterling4477]

@@theceohq Is it dumb that people who can't play baseball themselves talk about baseball on the internet? Absolutely. I never do that because I hardly know which end of the bat to hold. Now replace "baseball" with "physics"... why should the statement not be just as true? :-)

[@Carvin0]

I have a PhD in Physics (40-odd years ago). I have used quantum mechanics at a practical level, but I have never really understood it. It's not the "strangeness" vs classical mechanics that's the problem - I'm OK with abstraction. Instead there seems to be a fundamental logical disconnect, or incompleteness, in the theory that frequently gets swept under the rug by complicated obfuscation. Thanks for expounding on this.

[@ptyxs]

Have a look at the book "Making sense of Quantum Mechanics, by Jean Bricmont, 2016.

[@DavidporthouseCoUk]

Look in the mirror, and you may notice that you are in Brownian motion on the scale of Planck's constant, which is what quantum mechanics is for any object with a Compton wavelength less than the Planck length. Your very presence is like poison for the Dirac wave packet, and causes it to collapse at random. This is amenable to computer simulation. I completed my PhD in 1983 on computational fluid mechanics based upon the Brownian motion of vorticity, and have always been interested in doing something similar for quantum mechanics. It's taken me 38 years to see the obvious.

[@allenrussell1947]

Layman question, how do we know that observing changes the observed if we cannot know it's state before observing it?

[@massecl]

A measurement projects the state to a state for which the result of this measurement has probability 1. We know by performing the same measurement and getting always the same result. An example is the measure of the position in a bubble chamber. We get a track because the state has been projected onto a localised state.

[@allenrussell1947]

@@massecl but what was the state before the measurement?

[@massecl]

@@allenrussell1947 We know the state simply by making a measurement. Then every further measurement of the same type gives the same result. But if we make a different measurement, there is a different result for each particle.

[@allenrussell1947]

@@massecl Sorry if I sound dense, but I realize that, at the time of measurement we have a state. But how can we know the state of the object before the measurement? Maybe I am expecting it to be intuitive but to say that taking a measurement affects the state of the object observed implies that we know the state of that object prior to the measurement but, as we have not yet observed the object, how can that be so?

[@bhobba]

We cant directly measure a state, but we can prepare a state so we know exactly what it is.

[@captainyt1177]

Fantastic please make a video on wormhole and time travel

[@joaogabriellucas1865]

Finally an honest comment about the decoherence solution! And made by a science person. But why is this insistence in the decoherence solution so common these days? It appears that some people fear the outcoming conclusions derived from the impossibility of this solution... Thank you so much

[@haimbenavraham1502]

Wonderful and lucid, but I'm going to replay it a few times before I go to sleep. Like ' ring a ring a rosey, they all fall down'.

[@Jehannum2000]

Maybe you will dream the answer!

[@davidmoon3776]

When you say towards the end that the attempt to reinterpret the “wave function as merely [an] encoding [of] the knowledge that an observer has about the state of the system” necessarily means that “you are implicitly assuming that the behaviours of detectors is incompatible with the behaviour of the particles that make up the observers or detectors,” and that it therefore “requires that you explain when and how this distinction is to be made” - is it fair to say that this is a scientific formulation of what many philosophers call the mind body problem?

[@rayh7264]

Just found your channel and it’s great. Thank you. Brisbane Australia.

[@blueckaym]

I'm interested in the Born Rule (that squaring of the wave-function gives you the probability). It seems like a key step in applying QM, but from what I know even Born added it in his 1926 paper just as a footnote.

[@schmetterling4477]

There was a lot of confusion back then, even though in hindsight all of this is pretty trivial. QM is an ensemble theory. Unitary evolution preserves the total number of systems in the ensemble, i.e. the total probability between initial and final state. The square of the magnitude of the wave function is NOT a physical quantity. The theory does, indeed, not predict any physical quantity, at all. What it predicts are probability distributions (probabilities don't exist in nature, only frequencies do) for the outcomes of measurement setups that are being described by the spectra of projection operators. The square of the magnitude of the wave function is merely the result of that operation for the unity operator (which does not have a direct physical meaning, either, because the interpretation of the result depends on the basis of the representation of the wave function). There is still an awful lot of confusion about all of this out there among lay people and physicists who haven't really studied the theory in detail but think they know enough about it and these internet videos are not helping.