Comment response video for Understanding Quantum Mechanics
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- Опубликовано: 23 апр 2018
- In this video I cover the common misconceptions I saw in my last video- Understanding Quantum Mechanics.
In particular, I talked a lot about the measurement problem in this video. 
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Thanks a lot for taking the time to clarify what a "measurement" is in QM. Your examples were crystal clear.
What I get from this is that, essentially, a measurement is a form of interaction that disturbs a system to give us information about some of the system's parameters.
This really sheds a bright light into why QM keeps hammering that measurements alter the state of the system...I am slowly beginning to see the link with Entanglement and (somehow) Quantum tunneling now.
And yes, I can't wait to hear about QFT from you. It's obviously a different subject matter (i.e much bigger scales), but making all the connections when learning Physics really is an exhilarating experience! :)
Still one of the absolute best physics youtube channels out there! I'm very much looking forward to your future videos! :)
Amazing! I love your approach. Keep creating, please!
This is the most exciting Physics related series on the whole of RUclips. Thanks, waiting patiently for the main videos. Appreciate the homework too, though.
Thanks for another great video :)
Thanks for the video and explanations! Love your approach and mindset :)
I'm learning a lot on your channel. Thank you!
Awesome video! We need more motivated tutors like you!
Some of the best educational content I've seen.
You're great :)
About the gravity problem: I would answer the effect of a particle on the gravitational field is very negligible and thus gives away little to none information about its position / momentum.
you make great videos! that demonstrate the uncanniness of Quantum mechanics, FUNDAMENTALLY!
Love the video!, but i have one question what happens to the case of pilot waves when you measure the particle passing trough one of the doors, how do you explain the pattern not presenting interference using the pilot waves? Thanks for the videos and keep the good work.
There is interesting work by Sir Roger Penrose on the 1st question being posed here. It is known as one graviton criterion. Which says when the difference in mass distribution of two major alternatives among a series of superposition states (complex weighted) of a small particle (of quantum behaviour) with immediate surroundings , causing a difference in their gravitational field of the range 1/100 of Planck mass then the quantum linear superposition collapses yielding a classical measurement/ observation . Although this theory is very original it needs further work to be substantiated.
What I loved about this video is the remarkable skill of drawing and specifically showing the spacetime warps around each particle (be it an apple or a mote of dust)
Thank you so much LGU! That was very well explained, as usual, and makes sense to me with so many of the slit experiments I've read about being explicitly about information leakage rather than interaction, like the beloved quantum eraser, if I recall.
The gravity question was such a cliffhanger, though, and that's another one I find myself often wondering about! 😬 I'll be looking forward to your video addressing that. Not that anyone seems to totally understand gravity, but if disturbing an air molecule can lead to information leakage then wouldn't a gravitational perturbation also leak information about a particle? Perhaps that information is itself uncertain in a way, or has multiple possible interpretations?
Can't wait for the next episode!
Just stumbled on this interesting channel (ty google algorithm), these homework questions are going into very difficult and contentious topics but kudos for giving it a try! Something not said here but fundamental to measurement is that there needs to be an observer to finish it off. It’s not enough for information to leak from the ‘system’, the observer needs to get that information for a measurement to have occurred. If information just leaks (ie if the decoherence destroys the off diagonal elements of the density matrix in the measurement basis) one could describe the knowledge they have by a classic probability distribution, but they still haven’t done the measurement as they haven’t determined which of the possibilities has occurred. That last step is usually what people refer to as the measurement and there must be an observer to do it. I’ve seen authors refer to the first step (the non-unitary step) as a non-selective measurement and the second one (the non-linear projection onto the state corresponding to the measurement outcome) as a selective measurement to avoid confusion.
Thanks to you for the great video!
Have you ever attempted to navigate through the change management process at a place like IBM? We could look at the blinkenlights on the systems and even physically touch them to replace redundant hardware, or observe what's on the console. But strictly speaking, the moment we needed to login to the box we had to go through a nasty multi-week long change management process because the simple act of accessing a system would trigger it to deviate from steady state in order to write login data to the logs. Think about it this way, do the computer systems on a plane care that they are traveling through the outer space of our planet? Measurement is a change in state of the system, but a state change of the system is not synonymous with interaction.
I am loving this.
I will NOT do any of the homework. I will watch EVERY single one of your videos. And I do ENJOY the whiteboard approach. Cheers!
I always enjoy your videos. I just wanted to suggest that the difference between interaction and measurement could be related to Bohr's description of irreversible amplification. An "interaction" could be described as a phase change in the wave function. A "measurement" involves the annihilation/creation process which alters both the real and imaginary components of the wavefunction (the leak to the environment). So we identify the location of annilation/creation of the photon / electron kick as the location of the photon (at least after the amplification of the electron). A soft measurement (or nudge) gives us less than 1 bit of information. An interaction is a soft measurement. Amplification through photo-electric process gives us 1 bit of information (a hard measurement), but we can't recover the original waveform. Just my toy theory...
YOUR BACK!!!!!!! we missed you xx
Reading this comment, I was hoping of a nice view of her back. Now I am disappointed.
"We're got a long way to go tough" - I have time and hop around a little while visiting.
Electrons behind the doors: "Come to us, it's cozy here."
Electron in front of the doors: "Why? Finally there is a little more space available and I don't crash into others."
I won't give the homework a go myself any time soon, but I do like to see these responses, it's very interesting.
Finally the measurement vs interaction debate finally hit me today. (It is sort of like the number of bits required to carry the interaction information = log1 if you get no useful information about the interaction) i hope.
Great video! I love the concept of homework followed by answers to the homework. It helps me think through the ideas even though i am studying this subject as a hobby :-) Please do continue with homework questions.
Question: If measurement amounts to information leaked, how does the particle know someone’s leaked it’s information and so it had better collapse?
Could you perhaps do a video to go through decoherence? I've watched a few but not all of your videos so I'm unsure if you've already covered it.
Your videos are a real joy btw.
Thanks for the great clarification! What still puzzles me though is the discontinuity between measured/non-measured. However, your description of information leakage seems more "continuous" to me, ie one can leak more or less information. Are there experiments where a quantum object is "half"-measured?
This is an excellent question, and the answer is very much yes! In fact, that's the answer to the gravity question- that it leaks some information, but not much and so doesn't totally collapse the wavefunction.
I really like your videos by the way!! They're fantastic :D So cool/weird for me to see you on my channel.
Tu parles français aussi alors?? Je ne l'aurais jamais deviné.
The so called discontinuity between measured and non measured is inherent in the collapse hypothesis. The salient problem is that there are two types of time evolution in quantum mechanics: Reversible (unitary) evolution of the wavefunction, and irreversible collapse of the wavefunction. The cause of the collapse, and indeed whether the collapse is even real, is part of the measurement problem of quantum mechanics. This is a deep and long standing problem that is as yet unsolved, and indeed may not even be solvable, as it crosses from physics to the philosophy of "reality".
As for the question about half measurements; there are what are called weak measurements, whereby a system is measured without being significantly disturbed. In this sense, the measurements can have an arbitrarily low probability of causing a collapse due to the very weak interaction, yet carry a very small amount of information. By doing this many times, statistical methods can reconstruct the measurement result without effectively collapsing the measured system's wavefunction.
The information leakage perspective delivered in this video does not actually solve the measurement problem. It is central to the phenomenon of decoherence that transitions a quantum system to a classical system, yet it doesn't solve the measurement problem, but rather sweeps it under the carpet.
@@LookingGlassUniverse So does the wave function partially collapse? if so how does that work?
What interpretation of QM do you lean most towards?
I'm thought the Heisenberg interpretation, but the more I learn about QM (especially QFT), the more the many world interpretation seems likely (but it doesn't make any sense!)
do you have links to the single electron double slit experiment papers ? In the case of one of the slits having a detector it's quite important to determine how much energy is exchanged from the electron and the detector
Your example from ~ 2:55 is interaction in quantum world, because this particle collapse wave function, and looking at chance of being in "two place at once" it change everything. Only not interactive observation is then object emit something, and we catch it, if we measure some field we interacting with it (in case of emitting, we interacting with only with emitted object).
PS as you explain later, not all interaction collapse wave function, so is not so simple, and we start see group of particle functioning as wave, is interesting effect, and I think it will lead to new discovery, maybe not in physics, but technology.
Thank you !!
I just found your videos, and I like them, even though I’m pretty familiar with quantum mechanics, I’ve watched most of your videos and learned some cool stuff. In a previous video, you addressed the issue of sending information faster than light, but I still have one question. What is wrong with using a pair of double slits to send information. Suppose Sally and Bob both have a pair of slits and Sally has a sensor on her slits. Sally turns her sensor on, and removes the interference pattern for both Bob and Sally. All Bob has to do is watch as the interference pattern appears and disappears.
In fact, the quantum eraser experiment doubles as a perfect instant communication device.
Thanks your video is amazing! I didn't quite understand your example of the particle that changes colour and the fact that it doesn't carry information because, to me, it carries the information that the particle is in the path/exists but not where it is located.
When your procrastination video gives you homework, that's when you know, you should get started on your own. XD love your vids anyway.
I'm your 82000th subscriber!
The idea of molucules being in a closed system sounds a lot like entanglement, any thoughts on that or did I just point out something obvious?
I am still confused about the difference between measurement and interaction. I mean when electrons are travelling from source to the screen through the slits, there are air molecules in their way. And even if the electron double slit experiment is carried out in total vacuum in a completely closed box, there will still be infrared photons present in that box's volume due to temperature (Stefan's Law & E=hf gives significantly large number of infrared photons per unit volume inside the box). And further the quantum Foam (Heisenberg's uncertainty principle :-E & t pair) will be there to interact with the electrons. Then why these Interactions mentioned above do not collapse the wave function & why does it collapse when we try to "Measure " electrons position??
How about the results for placing the observer after (behind) the 2 slit before the electron hitting the screen? Is it the same results as observer before (in front of) the 2 slit?
Can't wait ffor the next ono !
Thanks a lot for the video.
Yes, what is the measurement was the question. But now it is "information leaking out". Unfortunately, I felt, "then, what is the information, and what does "leaking" means?" Is the information leaking the side effect of some particle interaction? At the end, in your explanation, some measurement device needs to interact with a particle, which carries some information. Then, this is back to the interaction to me.
So this answer is a kind of tautology to me. Something undefined words mapped to another undefined words. But, maybe this is I am not good at about physics... I have some feeling about position, motion, force, Newtonian physics terms. Does your "information" can be expressed by these Newton's words (please not use the ambiguous words, but a bit more mathematically)? After I watch your video, I am interested in this subject. But I feel I don't have enough knowledge to understand this. Though I would like to learn this. Do you have any suggestion where shall I start? I will try to learn it.
Thanks!
Hitoshi
Hey LGU! Love the videos! Fellow Cantabrigian here, what college are you in? :D
Regarding the color changing particle example. Wouldn't it already collapse to the option of the apple being to the left, as it turned purple after passing through it, therefore carrying away information? Wouldn't the situation has to be considered "measured" as soon as it passed through the first apple, rendering it irrelevant if at a later state it could be impossible to tell whether it was purple because of passing through the first or second one?
So does measurement require a human then? Since there needs to be something getting or interpreting the information?? And so also, if there was no air or light or anything "measuring" an apple going through the double slit, would it get an interference pattern..?
3:43 ..since the particle has changed the colour. Also it will not change its direction so from this we get to know that apple must be in the straight line between initial and final point of particle . So we got the information of particle position and hence its measurement. So why it is no measurement??
I think because you already knew that the apple is in one of those two positions (along the path taken by the particle), so when the fact that the particle changed color does not give us any new information.
could you please describe how weak measurements work and how to make one etc...
In the example you gave of interaction without measurement, with the object that changes the color of the particle, surely the presence of the object within the path of the particle is measured at least, even if its exact position along the particle's trajectory is unclear. Does this not count as a kind of measurement?
Ra ra ra! Keep it up! Your doing a fantastic job :-D
Thank you for the nice video! I am a dilletant on physics. I understood the difference of an interaction and a measurement. I´ve heard though that either a measurement or an interaction may cause the entanglement within a system. So the old belief that consciousness causes the wave collapse is just nonsense. Is that correct?
Yes. Measurement is irreversible energy transfer. It is that already in classical physics. We could, and should, have taught you that in high school. I apologize that we didn't. The high school system is still stuck in the 19th century as far as the teaching of math and physics is concerned. Until we get it into the 21st people will come out of there with lots of misconceptions about the world.
What happens if the same number of particles are fired over a much much longer period of time, so as to nullify the potential impact from past waves on the trajectory, which would presumably have dissipated after some time? Do we still get an interference pattern?
Thank you
Thank you for clarifying the way you physics in QM use the terms measurement and interaction.
It does leave me with some questions though. Say I threw a sliced apple with a paper banner attached to it through two open windows. One window with hidden variable bars horizontally and one window with the hidden variable bars vertically. Hitting the bars in the first window makes for an interaction that causes it to miss and not interact with the second open window. You don’t count the first change in attitude / colour as a measured leaked out change in position because you perceive (i.e. interpretation of an observation) the action as weird interaction. For you being an observation of changed attitude not a measurement of a changing position. Isn’t this the route of thought on having weird use of definitions? Leading the way to the root cause of quantum weirdness? Namely the way the instrument between the ears is taught to be used? Don’t different personality types perceive data differently? Urging a subconscious - i.e. weird - urge to feel a necessity to follow a way of use of incomplete data that can’t be made compatible with the formula of Bayes? Leading to sort of weird religious science? Doesn't any observed change that can be reproduced in a required accurate way need to be defined a measurement in any science? For doesn’t any science require all logic and mathematics to be consistent? Did you know that the brain works Bayesian completely for both deterministic as probabilistic problems? The latter, as QM, can’t do it deterministic. Wasn't Gödel thus wrong & Einstein correct?
So the particles are interacting and handful of them doesn't leak the information and some does right ?
Well, then how the (electron) knows whether the particle which interacted with it gonna leak the information? And how does the electron in that case knows that I(electron) have to act accordingly ? Because you see once the particle bounces off the electron, there is no way that it could know whether it(particle) is going to leak the information or not.
Interaction is interaction afterall( hence measurement! whether it leaks info or not) .so I think there's still a subtlety in what actually a measurement is?
I would love to see a more detailed explanation of what happens at the wall with the slits in the single or double slit experiment. In all explanations i have seen so far, the slit is always shown as a massiv object that does not consist of particles or waves. This has always been weired to me because it's shown as a non-quantum object in a quantum experiment. It is never shown how the electrons of the wall interact with the incoming wave.
I guess the particles that doesn't make it through the slit may perhaps have interacted with the wall by a collapse of the wave function, but that can't be true for those which go through the slit. Is the part of the wave that "hits" the electrons of the wall just reflected? Or does the wall "erase" that part of the wave, which would magically increasing the probability of the rest of the wave function from a distance?
I don't think the details of how the electron (or whatever) interacts with the wall are important.
Also, the "collapse of the wave function" does not mean that the object is destroyed or anything like that; it just means that it momentarily is reduced to one of its eigenstates.
How could the details of any part of the double slit experiment not be important?
Could You make a vídeo with Quantum field theory and It models for atoms, or in the perspective that all até fields, how eletric fields of the atom interact with another field tô do a covalent bound or others as ionic, hydrogen, van der walls...but ALL this in the quantum field, not Quantum mechanics only
Thank you - your efforts are very appreciated! The explanations seem pretty clear, but sometimes it's a little over-anthropomorphized, such as with the explanation regarding pilot wave theory and the double slit experiment. Though, I understand you're trying to convey the concept to a plethora of different levels of understanding at once.
+Chaosism
I, personally, think that Anthropomorphising these matters does a lot to help with conveying such theories to people who have a lot less affinity for them than what you or I have. In order to teach effectively, you have to make people be able to relate to whatever it is you're talking about. A little Anthropomorphisation can go a long way in doing that.
What I am curious about, though, is: what do you feel is the (potential) harm in Anthromorphisation of topics / objects / phenomena in Physics? Personally, I can't see any -- but that, after all, is what asking questions is for, right? To see if someone else may have valid perspectives on things that you, at present, lack. So that would be why I'm asking you about this now.
Ahsim Nreiziev
Oh, no doubt! Catering to how humans naturally think is pretty effective. I totally agree with "A little Anthropomorphisation can go a long way" but it can go overboard at times, is all I'm saying. For instance, my opinion is that it went a bit too far and muddled the explanation, particularly in the part in this video about pilot wave and the double slit experiment (too much "it wants", "it cares", "tells the electron", and whatnot). It's my mere opinion, though. :)
As far as harm goes, there is a potential for a highly anthropomorphized explanation to convey an idea of an actual agency, which is how terms like "the observer effect" and "natural selection" get completely misunderstood by some, like by assuming that consciousness is directly influencing the world or that "something" must be making that evolutionary selection (respectively). I'm not saying it's a huge problem, just that it's a potential. I've personally encountered both several times.
+Chaosism
_"As far as harm goes, there is a potential for a highly anthropomorphized explanation to convey an idea of an actual agency, which is how terms like "the observer effect" and "natural selection" get completely misunderstood by some, like by assuming that consciousness is directly influencing the world or that "something" must be making that evolutionary selection (respectively)."_
Fair enough. I had, indeed, not thought of that, and it is indeed a valid concern. But, like I said, that's why I ask! To compensate for any lapses in being able to understand a certain insight someone else may have.
Although, in this case, my personal assessment is that the level of Anthropomorphisation +Looking Glass Universe employs helps more than it hurts. But that's something we can (agree to) disagree on.
Ahsim Nreiziev
I sincerely appreciate this brief exchange and your pleasant tone. :)
+Chaosism
So do I! Both this conversation we've been having as your own pleasant tone.
I would say no measurement has been made if no information had been detected, but the semantic arguments tend to revolve around equivocating observations with interaction or measurement.
So, apparently you can do the double slit experiment with molecules 800+ atoms, but is there a hard limit ?
Is there any fundamental issue that theory says is not possible to overcome ? You know, similar for instance to the Heisenberg principle that puts a limit in how well you can know both position & momentum...
Awesome video, big fan :-)
Aww, thank you so much!
I'm very very interested in your research, can you say something more about it? Quantum computers?
A question on the Pilot wave theory in the context of the double slit experiment. In the Pilot wave theory, the initial conditions determine the trajectories of particles. So, in a double slit experiment, can one prepare the particles to have a particular direction from their emission source, so that ALL the particles go through only one of the slits? The emerging pattern on a plate after the slits should show NO interference pattern. Such an experiment should demonstrate the validity of the Pilot wave interpretation, over the Copenhagen interpretation.
So, is this possible? Maybe at a super low temperature?
Very nice question! But actually, what's crazy is that, you wouldn't get no interference. Instead you'd get the interference pattern, but only half of it. The other half will just be empty. The reason you get interference regardless is because even if the particle itself goes through just one door, the wavefunction still goes through both in BM!
Do a video on cellular automaton interpretation of qm
Well done about the (mythical) QFT unicorn! It is too much of a walled garden that is all-things to all adherents.
Part of the slit problem is that (almost) no one ever considers that the slit objects can also be converted to waves, leaving the 'particle' as the solidus. In many ways it make those `pilot waves` look sensible.
It's the slits that radiate, and the particle then has a 4-d existence on those/that wave that projects the diffraction pattern, based in the infinitesimal inexactness of it's initial conditions.
The radiating slit view also hints at the 'it's all relative' thought experiment that we move the slits and wall toward the static localised source 'particle' and then see how it's collision products are distributed. In the end it's a logicians rabbit hole at the Mad Hatter's tea party (cf Looking Glass Universe ;-)
Why are you telling all of us that you don't understand quantum mechanics? We don't care. ;-)
@lepidoptera9337 maybe I do understand that duality is a mathematical concept, so all objects can be waves and waves can be objects.
The "real" problem is people's perceptions aren't the one-sided reality we tend to think they are.
The slits are just Fourier optics (just, just, ..) etc.
@@philipoakley5498 I do understand physics. What I don't understand is your endless need for my attention. ;-)
I loved the format of this video. Very enjoyable. I would love to see more like it.
For me, the strangeness quantum mechanics indicates that there are some fundamental principals that are missing from the picture. You don't see this sort of mess in classical physics. The excuse is that QM deals with particles where classical physics deals with macroscopic objects, but that is a terrible answer since it leads exactly nowhere. It is a cop out, nothing more.
Yes there is an obvious difference between the two but the fact that since the idea of QM was first brought to light, there still is no real consensus on what is going on; as the double-slit experiment clearly shows.
I was chided in another video for pointing about how science is good at measuring a process and terrible at giving us the reason the process exists in the first place. I was compared to a five year old and should just accept that there is no why. That is where we are at today in science? The why is the most fundamental question we can answer because it is the basis for everything. If we really understood why the double-slit experiment behaves the way it does, how many other answers would that reveal? Plenty you can be sure. The process exists, so there has to be a reason for the why. The universe is complicated but it isn't arbitrary.
I personally feel that until science can start to answer the why question we are simply going to have hundreds of ideas and no real answers. Just like we have today.
_"The excuse is that QM deals with particles where classical physics deals with macroscopic objects, but that is a terrible answer since it leads exactly nowhere. It is a cop out, nothing more."_
It's not an excuse and it's not a cop out; it is a fundamental fact of nature. As the video points out, macroscopic objects can be under continuous observation. Microscopic object (meaning quantum objects) can't be, and this is the reason for the weirdness of QM. Quantum objects cannot be, in principle, be observed between observations, and so we can't say anything about what they are up to while not observed. We can run the experiment again, adding new observations, such as a detector on one of the slits, but there must still be times when the electron (or whatever) is unobserved.
It is a fundamental error to assume that there is some underlying "reality" that the measurements only partially reveal. The truth is that we cannot, in principle, know anything that can't be measured. More than that, though. If we can't, in principle, measure something, then it isn't real.
We do understand the double-slit experiment: when the electron is not observed, the results of the experiment are as they would be if the electron did everything that it possibly could do. It doesn't "really" do everything, though; it doesn't "really" do anything; there is no "really".
That may make some people uncomfortable, but nature is under no obligation to make us feel good.
Michael Sommers Haha. Right out of the textbook. Just what I expected actually. No the experiment isn't understood at all and so far there isn't a good explanation as to why it behaves the way it does.
Just because you don't like or understand the explanation does not mean that it doesn't exist or that it doesn't explain.
Tell me, do you believe in the luminiferous ether? If you don't, why do you believe that there is some unobservable "reality" underlying the quantum world?
Michael Sommers Wow. I guess name calling and putting words in my mouth I never said is the best you can do huh? Have a nice day.
What name did I call you? What words did I put in your mouth? I guess the best you can do is make stuff up. I'll ask again: do you believe in the luminiferous ether?
Could you point to some readings that talk about the "information leakage"? The books on my shelves don't talk about that; they are just too old (as in, from before you were born). Thanks.
9:16 proves that, Heisenberg notwithstanding, it is possible to come to a 100% accurate conclusion. We most certainly ARE.
not we, I. :P
Does Decoherence theory solve the measurement problem? Decoherence by the environment, by gravity, by an observer or detector device?
Lightening.
Thank you for clearing up the distinction between interaction and measurement. It's an interesting concept because the idea of "information leaking" is weird. If door A. is open and not being measured, but door B. is open and is being measured, then is it true by the concept of leaking that things that go through door A. are not being measured or is the measurement happening due to lack of interaction with the measuring device on door B?
DeadLink 404 that's weird because you wouldn't expect information leaking to happen when a measurement doesn't happen. It seems like a sort of chicken and egg thing, did the particle path or the measurement happen first?
It is weird! And true, evidently. measurements do seem to have faster than light (nonlocal) effects.
can you name any papers or other sources that talk about what is e measurement and what isn’t and why?
Any locality event, such as speaking some words or having a measurement done causes the localization of that information that was previously undefined and also increases the amount of defined information stored in the Universe. The quantity of information never lessens, as information does not disappear. The amount of information in the Universe increases since the big bang as a result of the newly defined information starting from the indeterminate quantum nature at every instant; emerging out of randomness to take its place in a measurement that will outline some pattern. Prior to measurement, its pure and stochastic randomness has no meaning. For this to happen, a thinking construction to make sense is required. Measurements of quantum localizations increase the quantity of information that we are able to obtain about the random quantum states of reality.
Could you do a video on how quantum mechanics describe a macroscopic system? For example, if an apple is moving back and forth on a spring, does it have discrete energy levels? When i look at the apple is that a measurement causing its wavefunction to collapse? If its wavefunction collapses, then why does the apple still move?
Yes, it has discrete energy levels. The proof for that is the (modified) Planck spectrum that the apple and spring system radiate in form of electromagnetic radiation. There is no such thing as wave function collapse. That's just a meme preferred by those who don't understand quantum mechanics.
What about the delayed eraser quantum experiment?
What I can't get my head around is the fact that in the delayed eraser experiment the particles that produce the interference pattern interact with the measuring devices as well. The difference is that their paths are being scrambled and the information about what slit they went through is lost. But they are still interacting with the measuring devices. Therefore it can't be a simple interaction with a classical object that collapses the wave function. There needs to be actual information about the particle leaking out in the environment. But why would information in itself be so crucial? And doesn't it seem to indicate consciousness does in fact play a role, since consciousness is the only thing that could receive said information? Can someone clarify this?
A hand!
what would happen in a tripple slit experiment where you measure only one of the three slits?
The leaked information isn't complete in this case.
See this paper: arxiv.org/abs/0811.2068
I've seen this experiment, they block the light to see the different patterns. I was talking about an experiment where they don't block any light, but they measure whether the light passes through a slit, and they only measure one slit.
All measurements involve interactions, even if not directly on the particle we are being informed about (weak measurements). But not all interactions give us the information we are looking for. We know the color changing particle hit an apple, but not where the apple is. It seems to me "information" is more fundamental with "measurement" being perhaps some undefinable anthropocentric goobly-goop.
So what if apple would be in the perfect space in the perfect vacuum with no interactions from the outside, meaning no possible thing carrying away the information about it? It is macroscopic, and yet we can still represent it as a compound object of a multitude of molecules. Should it behave in a quantum way? Why / Why not? What if it was a single DNA string (i.e. a single molecule)? What if it was a cat (without box nor poison)?
why is measurement only related to position? if for example the weird interaction with the color was so that it only turns a certain color if it interacts with a very specific object, you have some information about if it happened or not, and i would call that some degree of measurement (in a wordy way though, not a ''scientific'' measuring)
"Measurements" can/are interpreted as spacetime existence because it's compiled by Quantum Computation of modulated timing into the properties/relationships aspects of integrated coexistence at .dt here now. Ie depends on word usage (derived from quantum duality) of the difference between the activity and the result of a measurement, cause-effect.
Therefore it's technically not only Interaction, it's connected universally in a multiplicity of measurable/observable relationships. (Relativistic => pure-math relative-timing condensation-coordination numberness like 1+1=2?)
You can make an absolutely legitimate case (confined by zero-infinity flat-space-time omnidirectional-dimensional cause-effect = Quantum Logic) for "Measurement" as self-defining pulse-evolution Interaction, here-now-forever.
If the color changing particle goes through an object and does not change course, but only color, information is still leaked, as we can determine that the object has been on the particle's path. Am I wrong?
In regard to the color-changing particle, wouldn't it still have measured the apple since it would be carrying away information about the apple between the apple's first possible position and its second possible position?
Disparaging Cheers no because it would take the same time to get through the apple no matter where it is. If the particle takes 5 seconds to finish the path and one second to get through the apple, its the same thing saying 5s+1s (the apple is in the 2nd position) or 1s+5s (the apple is in the first position)
Disparaging Cheers Im only talking about one apple and how it wouldn't matter where we put it because the outcome would be the same, the time it would take for the particle to reach the measuring device ( basically you don't know when the particle changes colour according to the experiment because the whole thing is hidden from view!) Think of a light ray traveling 5 meters from a source to a measuring device. Now cover the whole distance between the source and the measuring device with a cover. If you have put a filter to make the light green at some point in those 5 meters, you cant know where it is because the outcome doesnt change. If you put the filter 1 meter between the source and the measuring device, it would be the same as putting it 3 meters in, since the light comes out green at the end anyways.
Disparaging Cheers By the way your 2 apple assumption about information erasing is a great idea and sounds right
At the very least, the change in color shows that there is an apple somewhere nearby, which is a measurement of sorts.
So if the actual pattern of a single slit has multiple bumps, I assume it is still true that if you add together those two patterns of each single slit you do not get the same pattern as the double slit, right?
No, we don't. What causes these patterns is NOT the "addition of light". It isn't like that in classical wave theory, either. We simply can't teach the subtleties of boundary value problems for linear partial differential equations at the high school level and that is why people who do not, at least, take undergrad physics AND are paying extraordinarily close attention to the details of the solution theory are struggling to understand the physics of waves. I didn't understand it in the physics lectures, either. I took a class on numerical solutions to PDEs and the mathematics professor who gave that class was the one who illuminated the actual mechanism for me. If I hadn't been interested in numerical math at the time I would probably still be "in the dark" about the physics of waves, even as a physics PhD.
I absolutely love this video (except for the outsourcing 😉) because what is explained is explained very clear and easy to understand. You did a good job at this one.
What if we observe the point at which the weird hypothetical thing changes color?
Recently, I read somewhere that pilot waves failed to reproduce double slit results.
Does that mean bohemian mechanics doesn't hold true now ?
I read somewhere... where?
@@haushofer100 www.quantamagazine.org/famous-experiment-dooms-pilot-wave-alternative-to-quantum-weirdness-20181011/#:~:text=By%20Natalie%20Wolchover&text=Oil%20droplets%20guided%20by%20%E2%80%9Cpilot,exists%20a%20single%2C%20concrete%20reality.
It feels like information should be regarded as a first class entity just like energy or momentum
I have recently been enjoying your videos; however one thing that bothers me in this type of description is the finality with which these types of experiments are described. The measurement occurs and, the wave collapses, superposition ceases. But that is not the end of the story. The event is over and the particle is once again in a superposition. It is no longer being measured(leaking information). Particles are constantly interacting (collapsing the wave function) then not interacting and back to that non-observed state.
It is like a room with a strobe light where you only see snapshots and of events and infer what is happening when it is not observable.
Thank you for the thought provoking content.
I love you
Here is a question Mithuna...The weird hypothetical thing you are referring to changes color when it comes into contact with our object, as you put it. Would that not tell us precisely where our object is? In other words, if we were to observe the thing moving, we know it hit the object precisely when it changed color. As an example, let's say we have a curtain and behind that curtain could either be the object or nothing. We don't know...all we see is the curtain. If the weird hypothetical thing passes behind the curtain and comes out the other side it will change color if our object is there but will stay the same color if not. In this way, we know whether or not our object is behind the curtain by observing the color of the weird hypothetical thing as it comes out from behind. In other words, it appears (to me) that the weird hypothetical thing does, indeed, carry information about what is behind the curtain by changing color (or not) as it passes behind it. Am I wrong?
Now I'm really confused. Please help.
Starting at 7:30 you say that there is more than one blob. Does that imply that there is interference with one only slit?
I never heard this before. Even in the Feynman lectures he says there is only one blob. I'm confused by this. What am I missing here?
I believe that is just due to diffraction caused by the slit; it isn't a quantum effect (except to the extent that particles have wave-nature in QM).
If it is due to diffraction then the single slit still demonstrates that light is a wave and not a particle. If a photon or electron is a particle then there would be no diffraction. So how does this demonstrate the particle nature then?
Everything is a wave. Electrons. Photons. Everything. But they are highly localized waves, or wave packets, that can sometimes seem to act as particles would act if there were such things as particles.
Wow, you've set the new trend! Until now everyone saw apple with the context of gravity. But now you've connected apple with double slit experiment and quantum mechanics.
link to deBroglie video?
If A interacts with B, it carries an information about B because if B wasn't there A would not have interacted. B was on the trajectory of A. Am I wrong ? I suspect that measurement implies intent and is therefore a meta-physical concept.
what if measuring a particle is to get it entangled with yourself in some way?
From my understanding, this is the main theory, not to solve the measurement problem, but to describe what happens. It's called decoherence. The particle gets entangled with the detector, then when you try to get the information from the detector, you necessary have to open up the system, because information needs to ride on the back of matter/energy. At some point in that von Neumann chain the collapse happens.
If it is an electron, how can a guiding wave go faster than the electron and tell him where to go at the same time ? wouldn't it be faster than light ?
It would be faster than light, "nonlocal". Alain Aspect and other experimentalists have figured out that if guide waves affect the situation, then they must act faster than light (or perhaps through an unseen dimesion, or other such improbable thing): en.wikipedia.org/wiki/Bell_test_experiments
Hey, your probably not going to see this, but figured might as well ask anyway. How does QM mesh with any future information a hypothetically living observer that has passed the event horizon of a black hole will see? That is, there seems (to me at any rate, but I'm not particularly intelligent) to be a causal conflict between the future information our observer sees, and non-deterministic takes on QM. Is this even a coherent question?
You answer to the "paradox" of Bohmian mechanics where when 2 doors are opened, the interference pattern shows up. However, what is this theory's response to the fact that when you measure the electron, the interference pattern completely disappears and becomes totally normal? Because, ok, the photon measuring the position of the particule does interact with it, although how does the electron's trajectory "rectify" itself to become as if only one door was open? And would this trajectory change if the measure was done slightly farer from the two doors?
Furthermore, the interference pattern disappears when we send photons to check a door even if the electrons pass through the other door. I understand that the pilot-wave of the photons may have an influence on the electrons passing through the other doors, although how is it that the pattern is so regular in the latter case?
Is it just me, or are getting a Hackdashery for quantum mechanics?
In the tiny bit of QFT I've had the opportunity to teach myself, I've so-far found no answers to the more bizarre aspects of QM. That is, QFT seems to be mute on subjects like wave-function collapse and entanglement - it seems to sweep these issues under the rug, as if they don't exist.
Though I'd love to be mistaken about this. So if QFT has something to say about these, and I just haven't come across it yet, then I'd be happy if someone could point me in the right direction.
As Tim Maudlin has said to me (via personal communication): “the reason some people say that QFT meshes with relativity is because of the no-signalling theorem. You can't use QFT to send superluminal signals because of the Equal Time Commutation Relations. So if you (falsely) believe that all relativity does is rule out superluminal signalling, then you mistakenly think that QFT must be consistent with Relativity. But that is just an error. Of course, you can't superluminally signal using Bohm's theory either, but (as is noted) that does not mean it is simple to make the theory Relativistically invariant. In fact, in a straightforward sense, you can't. But if Bohm's theory appears to be in conflict with standard QFT in that the former cannot obviously be made Relativistic and the latter can, why pay any attention to Bohm? Because Bohm actually solves the measurement problem and standard QFT does not. Solving the measurement problem is exactly where the non-locality of Bohm's theory comes up, and hence the necessity to make any non-locality Relativistic. QFT does not even face this problem and hence faces no difficulties with its solution to the measurement problem: it does not have such a solution."
Jean Bricmont says similarly: “The predictions of quantum field theory are extremely impressive, but contrary to received opinion, it is not true that there exists a fully relatvistic quantum theory. After all, such a theory should include (as one of its approximations) the results of EPR-Bell experiments. But that would require a relativistic treatment of the collapse postulate, and such a treatment simply does not exist. Moreover, one would encounter enormous difficulties if one tried to formulate it. The reason why few people worry about this…is probably just that the implications of EPR and Bell concerning the nonlocality of the world have not been fully grasped.” Jean Bricmont, Making Sense of Quantum Mechanics
(Springer, 2016), pp. 172.
If you're interested in neo-Lorentzian approach to this (neo-Lorentzian STR is empirically equivalent to Einstein-Minkowski STR) and unifying it with QFT see, Einstein, Relativity, and Absolute Simultaneity, Ed. William Lane Craig and Quentin Smith. For issues concerning QM and STR see: Tim Maudlin, Quantum Non-locality and Relativity (3rd Edition).