How Decoherence Splits The Quantum Multiverse
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- เผยแพร่เมื่อ 23 ก.พ. 2020
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Why is it that we can see these multiple histories play out on the quantum scale, and why do lose sight of them on our macroscopic scale? Many physicists believe that the answer lies in a process known as quantum decoherence.
Hosted by Matt O'Dowd
Written by Matt O'Dowd
Graphics by Leonardo Scholzer, Yago Ballarini, & Pedro Osinski
Directed by: Andrew Kornhaber
Executive Producers: Eric Brown & Andrew Kornhaber
End Credits Music by J.R.S. Schattenberg: / @jrsschattenberg
Does conscious observation of a quantum system cause the wavefunction to collapse? The upshot is that more and more physicists think that consciousness - and even measurement - doesn’t directly cause wavefunction collapse. In fact probably there IS no clear Heisenberg cut. The collapse itself may be an illusion, and the alternate histories that the wavefunction represents may continue forever. The question then becomes: why is it that we can see these multiple histories play out on the quantum scale, and why do lose sight of them on our macroscopic scale? Many physicists believe that the answer lies in a process known as quantum decoherence.
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#space #quantummechanics #astrophysics
It's usually around the 7 minute mark when a certain wave function collapses and I can say with confidence that I don't get it.
Why does this comment speak to my soul?
lmao, I feel that
Haha
haha
You decohered an ability to get it! lol😊
Even early 20th century scientists would be blown away that we have this sort of information so incredibly accessible. This is the golden age for media like this and I hope it keeps going far into the future.
It's also the golden age for clickbait and fake news, nevertheless, this show remains true to its roots: quality, semi-understandable, and for the most part accurate knowledge spreading videos that actually teach you something legitimate.
@@scibanana3542 DUDE, DURING WWI FAKE NEWS WAS THE NEWS
@@scibanana3542 "for the most part accurate knowledge" lmfao that's the kind of claim you make without any examples or citations if you want to sound chickenshit or bitter, especially if your channel name sounds like a failed goofy science channel. Not saying you're lying... but the audience has no reason to believe you're telling the truth.
They had pop-sci books even then. It would be the technology itself that they'd be blown away by
Even after losing track of just how many times the double slit experiment has been explained on this channel and elsewhere in my life, even performed, I find it astounding I can still learn something new about it. Shows you well how there's always new physics which gives me hope :).
10:04 Oh God, the Eyeball-Brain Macintosh guy has multiplied.
I loved that image! Nightmare fuel!
You can hear when he starts winding up to say "space time" at the end.
i always hear that near the end of every sentence he says
yes it makes me so sad, it sucks when its over
Listening to him saying space-time it's the highlight of my week tbh
@@Catmomila totally.
"Something something something...
...
...
...
...of our
...
...space-time."
:D
@@davetoms1 yeah
I mourn the missed opportunity to say "I will attempt a coherent explanation."
Even big brains love dad jokes.
It so happens that any attenpt to find cohesion is itself decoherent, and therefore futile.
Glad they didn't do it, terrible pun
@Sebastian Henkins 🏺
I rather like the attempt to decoherently explain things.
This clears up so much! Decoherence should always be explained in pop sci when bringing up the double-slit experiment
But he doesn't understand decoherence
@@bionoetics5336 How not?
Currently all histories where I intuitively grasp this are being interfered with, apparently.
Get used to that with anything that has the word quantum
.
Destructively*
LOL
I wanted to take a break from studying Young’s Double-Slit Experiment but it seems that I was unable to escape my probable future.
Maybe your body needed something unrelated and your conscious mind assigned relation in post?
Thank you for planning to call Future Crimes, how are we about to help you
I hate you right now, for the science dad joke.
Forget everything you think to know about quantum mechanics and realise watching PBS Spacetime leads to an interference pattern in your studies.
.
This is by far the best "intuitive" explanation of quantum decoherence (and of the many worlds interpretation) I've seen so far. Thank you, amazing work!
It still boggles my mind, though. Does it mean that since we are already within one "slice" of the wave function, our lives are basically predetermined and we can't influence the future or does the "slice" of reality then keeps on branching out?
@@mabaker from 12:16 it seems reality keeps branching out. But I have a hard time with this as well!
There's also an interesting bit of explanation from Sean Caroll here: th-cam.com/video/ZacggH9wB7Y/w-d-xo.html
@@DaDoubleD Thanks,Pierre - I'll watch it. Cheers.
@@mabaker What is that supposed to mean? Both your actions and other processes lead to the different futures all of which contain you.
In other words:
“Your life is the sum of a remainder of an unbalanced equation inherent to the programming of the matrix. You are the eventuality of an anomaly, which despite my sincerest efforts I have been unable to eliminate from what is otherwise a harmony of mathematical precision. While it remains a burden assiduously avoided, it is not unexpected, and thus not beyond a measure of control. Which has led you, inexorably, here.”
ergo...
Ergo vis-a-vis Concordently
That's sounds like something agent smith would say. Are you Agent Smith?
@@anteconfig5391 Metatron dude... It's the Architect
Bullshit
This is the clearest as well as briefest explanation of the “ non-collapse “ of wave function I have ever heard! Well done! 👍
7:37 "Got it"
Yeah, I got it, I got ... s*** I lost it.
I am Tyler Durden's total lack of comprehension.
I am jacks total lack of surprise.
Also , i could understand this......but i don't wanna😂
This is the moment some greaseball gives you a raw jaw, so - duck.
@@lethalsub SLIDE
That was mental decoherence
Skip to tha Lou
"Got it? Sort of? Good!" Loving it. If you ever grow tired of the channel title, use this and be much more honest with your target audience!
I didn't understand anything after 9:30 but I'm legit crying because physics is so damn beautiful.
I am a physics undergrad. Because of the intense study load of college, I sometimes fail to appreciate the true beauty of physics. It gets depressing at times. Thank you for reminding me again why I have chosen to become a physicist.
It is the cascade of Quantum Entanglment that has to survive and produce an observable "deflection on the dials" on our measurement devices for us to distingush between "coherent" and "de-coherent" state of the measurement we are trying to perform.
I wish a coherence/decoherence interpretation of the "Delayed Choice Quantum Eraser" experiment was also included.
But if this is correct I think it does. What I believe he is saying is that the wave function does not actually collapse, just our ability observe it. So it appears to collapse from our perspective because of decoherence. You have to keep in mind that we are also within the wave function, so we only see the interference pattern because we are entangled with the wave function of the photon as it passes through both slits and interferes with itself. However, any sort of measurement of one of the slits causes a decoherence (or loss of entanglement) between the observer and the particles wave function through the measured slit. So the wave function does not actually collapse, only the loss of coherence (or entanglement) means that we can no longer see it because it is no longer in phase with our reality. We can only see measurement results that are entangled, or coherent, or in phase (so to speak) with our reality.
So it doesn't mater when our where the decoherence occurs. The wave function is still there, only we are out of phase with the measurement, so we no longer see the interference pattern, but in a sense it is still there. So if you could somehow observe across multiple decoherent phases, you would see that the interference pattern is still there, but we cannot because we are entangled with one particular coherent reality of the wave function, so for us the wave function/interference pattern appears to collapse.
At least this is what I interpreted from all this, it still seems pretty wild when you think about it, and only explains one small aspect of reality. It still doesn't explain anything about consciousness. If versions of us exist in infinite alternate realities branching off through wave function decoherence, causing other realities that we cannot perceive, realities where things are virtually the same and also very different, are those other selves also you? Are you only what your conscious mind can perceive? Or is our perception of reality an illusion?
If we are in essence patterns of information arranged in a specific way, if that pattern is repeating through infinite worlds within worlds, perhaps the idea that you exist as a finite being living a single existence is just an illusion of our limited perception. For example, say we were able to vaporize your entire body and then reconstruct an exact duplicate down to the last detail, and did it in less than a microsecond , so from your perception you would not even know it happened, are you still you? If not, how and why?
For that matter, if everything you are is a function of what the entire universe is doing at the point we perceive as here and now, are you just your body? It would seem that to is an illusion no?
Eric Michel The concept of "you" is a construction of humanity. What characteristics defines a person are characteristics that we, as people, choose to be definitional, and we can change that definition if we want. That definition is also contingent on human circumstances. For example, this definition does not account for the event of a human body reanimating after 100 years, acquiring the same appearance that was had before death, and then acquiring the exact same personal-emotional traits had before death with memories. Why does it not account this event? Because this event has probably never happened, and it probably never will. If it has happened, then it has not been recorded down in history reliably, and even if it has happened, the observation that this does not consistently happen in this age is a reflection of the fact that this is simply not a situation plausible for the human circumstances. If it were normal for this type of occurrence to happen, then we probably would not be asking ourselves this question, because our definition, which would have adapted to those circumstances, would have a definite answer as to whether that constitutes the same person or not.
Besides, in the first place, this question is very loaded and relevant on a significantly more general context. Is any type of change at all the formation of a different person altogether? If I acquire a new memory, am I different me than before? Am I no longer that person, but a different one? What does it mean?
The colloquial usage of "you" can most adequately be described as a continuously changing sum of atomic states within a living thermodynamical system. Therefore, by this definition, if I get vaporized and reconstructed perfectly within a microsecond, then I am still the same me as before. Even if you could argue that this me stopped existing, this is not to say that this me did not start existing again.
@@angelmendez-rivera351 Alright, so you are saying that you are defined as a "construction of humanity with characteristics determined by circumstances" all of which is determined by our environment. What determines our environment? If you subscribe to a deterministic universe then it follows that your existence here and now was predetermined from the very moment of creation. So put in another way, as improbable as it may seem, you are literally a localized manifestation of the entire universe. As you put it, we can be described as "a continuously changing sum of atomic states within a living thermodynamical system" essentially a replicating pattern that in an infinite universe (or multiverse) is repeating infinitely throughout space and time. Therefore, the fact that you are a conscious being tells you something about the fundamental nature of the universe.
One question, in your definition of "you" you also said "What characteristics defines a person are characteristics that we, as people, choose to be definitional, and we can change that definition if we want." So does this mean you believe in the concept of free will? If you see yourself as a localized system that is a product of you environment (however you care to define that as genetics, society, general circumstances...) Every thought, feeling, and decision you make is predetermined by environmental cause and effect that can literally be traced back to the moment of creation.
This fact has been demonstrated with MRI functional brain testing where researchers can accurately predict what choice a subject will make up to four seconds before they consciously make a decision. This seems to indicate that your localized conscious experience is an illusion.
Some get very uncomfortable with this realization, believing that this makes them some sort of puppet being pushed around by a cold unconscious deterministic universe. However, the truth is, what it means is that you are far more than just your body/mind. You are having a conscious experience as a localized individual, but that is in fact an illusion. The real you is far more than that, only pretending you are not.
What does all this mean? well it does not change the reality of day to day life experience, but it does provide a common sense perspective regarding the ultimate nature of reality. Alan Watts explains all of this far better than I, here are a couple of short clips of his lectures that sum up the basic idea: th-cam.com/video/wU0PYcCsL6o/w-d-xo.html and th-cam.com/video/mMRrCYPxD0I/w-d-xo.html
This a full lecture without the somewhat annoying music background: th-cam.com/video/OAFH_nwqSHQ/w-d-xo.html
Eric Michel - Eric, I truly appreciate you breaking this down. I for one appreciated what you stated and wish I was quick to pick up this more easily! I also read your latest reply and I enjoy Alan Watts as well! Have a great day. Now if I could only have you break down all the other science and physics questions I have. Lol 😁 jk
@@sisu4134 Glad you liked it! Disclaimer: I am no physicist, just trying to make sense of it from a somewhat layman perspective. I like to post because it helps organize my thoughts and occasionally I even get some constructive feedback. So thanks for the kind words, I have to get back to working on my time machine, now where did I put those crystals ;)
*Who else think PBS Space Time is the best channel??*
At least that tiny chunk of the wavefunction we get to see from it, yes.
Isaac Arthur is the best, but Space Time is up there.
The Science Asylum is the best and fermilab
FirstRisingSouI you got that right bro
@@FirstRisingSouI I love Isaac, but I'm going to have to go with Kurzgesagt. I like their style.
10:05 and many more: I love the unique illustrations of Space Time and I love the show 🥰
The use of the action in detecting which slit the particle goes through as a decoherence mechanism (and hence the loss of interference pattern on the screen) is brilliant pedagogically. Keep it up.
This is by far the most understandable explanation of the double slit experiment I've ever heard! Thank you for finally making it make sense for me!
After a few months of watching, I finally catch up on the latest video. Quite a journey. The only problem now is I have to wait one week for a new video. Thank you for all these great videos.
Yep
The last few minutes I was thinking the whole time he would end the sentence with "Spacetime". Yeah I guess I have been conditioned...
Um Yeahhhhh
waiting for the drop
Buzzwords: standed, 'slice of', our, we.
Ivan Pavlov would be thrilled!
The most coherent explanation of wave functions I've ever heard. Good stuff!
This is the sort of layperson introduction to deeper delving that I find extremely helpful. Thank you!
This makes so much more sense than having specific rules for measurement.
You guys explain things so well! And I love your animated visuals. Have you done a demonstration of the double-slit experiment, with the variations you're talking about?
I would like to point out that this video’s script was so well written that i was able to understand everything that was being explained. In fact it was of such quality that i understood this topic better than i had understood pre algebra. And by no means am i saying that previous episodes were not well written; this one is just phenomenal. And thank you very much to the gentlemen on the screen, who obviously understands the topic very well, for articulating it in such a comprehensible manner.
Best explanation of the wave function I've ever heard. Well done!
So what about the *Delayed-choice quantum eraser* ?
illesizs this was my thought as well.
Yup, NOTHING EVER really "touches" it in the 1st place. Such Ideas are really reaching imo.
I second this! (or… well, fourtheenth it)
Simple. The system decoheres when you make the measurement that does the erasing.
There's nothing particularly special about the delayed-choice quantum eraser experiment from a quantum physics perspective. It gives exactly what the Schrodinger equation predicts should happen. The only reason people get so excited about it is because it looks spooky to our monkey brains.
@@FirstRisingSouI That sounds like a non-sequitur. As there is NOTHING intrinsic to the wave equation that predicts a "collapse" at ANY time anyway. & It is "spookier"(for lack of a better term) bc unless you assume a probabilistic natural rendering engine or a nearly infinite # of imaginary universes or something that is, for the time being anyway, still metaphysical, it very much appears retro-causal(as the current best descriptor).
I love Sean Carroll's, "Something Deeply Hidden" & and PBS SpaceTime!
Seriously thank you for your work, you convincingly answered a question i have asked my self for many years and partially caused me to study physics.
Best explanation of the wave function collapse I've heard yet. Thank you!
Yes! Thank you! (I'd love to insert a big "Steve Carell thank you gif" here.) Finally, a much better approach to the wave function collapse and the observer influence problem. I've always been puzzled with the general tendency to assume the experimental apparatus consisting of just the observed particle and the observer and nothing else. As if there is just a photon/electron/whatever doing some weird stunt and then suddenly everything is revealed to the experimenter, with nothing in between. As if the billions and billions of particles that are used to capture the event and relay and record the information are subject to a different, totally deterministic type of physics. All this while we know that even a perfect vacuum is not devoid of quantum weirdness. I think this overly simplistic approach has always been the crack from which all the kooky interpretations and exploitations have managed to slither through.
Ow. The neurons of my cerebral cortex just decoupled attempted to understand that.
That episode was easy to understand compared to some of their other ones lol
Don't hurt yourself kiddo science is not for everyone
@@everythingisamindgame9666 What's nice about this channel is its just hard core enough to interest actual science students, but approachable enough for people like me to mostly keep up.
@@MichaelMiller-rg6or Yep. Matt is doing an awesome job for several years now.
@@everythingisamindgame9666 science is for everyone, the only problem is that it will be more complicated to understand for some people than others (but not impossible though)
Fascinating. One of my favourite Space Time episodes ever - thanks!!
Best (possible?) explanation of coherence/decoherence I've ever heard! Excellent episode!
9:20 I just had a thought. In SR, spacelike events, or events that aren't causally related, can be in any order depending on which frame of reference you're in. I see something similar here. When we're not observing the wave, it's a spacelike event and so it doesn't matter which slit the photon went through, possibly even both. But when we try to observe the wave, we establish causality, and it now becomes a timelike event and so the photon can't go through both slits at once.
Makes me think of images rendering only when you look, in a game.
Well in the photons frame, it was only ever emitted and absorbed and is not hindered with space-like or time-like events such as an observer traveling at sub-light speeds.
Seems like this reality has me watching this video mere seconds after its uploaded
One of my favorite episodes of PBS Space Time yet! Our perception of the wave function’s collapse is merely that, our perception. It’s an illusion based on our position or “slice” within quantum space-time. An objective understanding has been deemed relative once again, just as was done to time a century ago. Leave it to a quantum understanding of things to ruin objectivity, even when we try to play by its rules.
Quantum harmony creates infinite possibility; its dissonance creates infinite perspectives.
Infinitely poetic.
He's very good and patient with explanation. Even the esoteric.
Very nicely presented.
Decoherance is a far more satisfying than than the whole vague observer thing. This was a great explanation for a layperson such as myself.
Is a double slit experiment usually performed in a vacuum? If not, why doesn’t interaction with gas cause immediate decoherence?
it's always in a vacuum. otherwise decoherence would take place.
Maybe it happens rarely. I mean the space is almost empty for the photons and the few ones that get to have interaction just make the result a little more blurry.
Assuming we are talking about transparent gas... well, photons don't interact with a transparent medium, that is why the medium is transparent.
FDDA THOMAS Thomas Young did it in a vacuum?
Stefan B that seems like a fair answer, though air obviously still scatters light a bit. But I guess enough photons don’t scatter, like the comment above just pointed out. Thanks!
Excellent description of the diffraction pattern in Young's Double Slit. Thank you
Wow, this is actually the first PBS Space Time video that I have been able to follow from beginning to end!
I just saw the film "Coherence," and in this science-fictional world, a group of eight friends having a reunion somehow get 'stuck' in the multiple realities of coherence, i.e. their multiple selves. It's a mind-bending story! But in a way, the resolution to that nightmarish coherence is in fact decoherence: where the lead character finds the reality she prefers, and violently replaces herself, who had occupied that reality. But to Matt's point at the end, the film suggests, in a rather sinister manner, that the nightmare hadn't ended and that she hadn't destroyed quantum coherence. Yikes!
Just watched this movie! That's a great way to describe how the plot follows the science we learn about in this video. Very cool! Makes me appreciate that movie even more.
Yes. That complete "all possibilities are thought through"-world view is exactly mine. Finally a logical and awe inspiring explanation. Thank you.
I feel like I've always known this and tried to explain the limits of understanding this experiment, and I'm happy to see it in a video. Good information!
Very well put. Demystifying collapse is super exciting. I hope you talk about Loschmidt's paradox, Unitarity, and the the potential arbitrary basis problem of the MWI.
Therapist: "South Park Matt O'Dowd isn't real. He can't hurt you"
South Park Matt O'Dowd: 2:25
That was fun, but silent movie Matt was my favorite. Complete with physical props in the background.
That is a thing?
What episode lol
Existence itself is scary, confusing, and interesting...
i love it! super crazy lol
Really interesting and different angle than I'm used to. I love time and how it inevitably provides new discoveries.
Sir, your message filled a gap in my study. Thank you for taking the time. Cheers
Wouldn't the fact that the atom configuration between the screen and our brain causes decoherence mean that the single probabilistic location that we "measure" depend on the atom configuration between the screen and the brain of the observer?
But different observers, who have different circuitry and configuration, agree upon the location. How can that be?
this. how can different observers see the same thing and not their own version.
Because you will be on the same decohered branch of the wavefunction. Each decohered branch will have its own set of observers.
Vampyricon does that mean fate exists?
quantum is smaller than atomic, much smaller.
@@fredricknietzsche7316 No, atoms exhibit quantum behavior.
Young's double slit experiment is a really nice example to use for decoherence! Suprsingly I understood this video pretty well (probably because the experiment and physics vocab is taught in high school haha) Maybe this topic of coherence vs decoherence could go more in depth if we examine how one reality can be subjective to different observers in that same reality. I wonder if there can be a reality where the wave function is objective for all observers before the function is collapsed.
Nope something like that will never happen for us to observe sorry
"Maybe this topic of coherence vs decoherence could go more in depth if we examine how one reality can be subjective to different observers in that same reality."
That won't happen, because the wavefunction will have entangled with the environment long before you and other observers observe the results.
This is terrific. Can't wait for more episodes!
This is definitely a video I will have to watch multiple times to begin to understand. Ty for the videos and always
Hey I finally turned on notifications for this channel! Feels good.
Noetherfications.
Going to watch this video a couple more times to get a better grasp of the concept, but this was explained really well.
Very interesting! I have the feeling, that you are really savvy about what you are talking about. I definitely have to relook the video tomorrow, when it is not that late as now^^
"Got it?"
"Sort of...?"
...was waiting for the 3rd option - the wavelength path of history reaching my brain where I am lost.
Love the show!
2:25 now I want southpark space time
No you don't! XD
I'm in a superposition of wanting and not wanting Southpark Space Time.
Sometimes, Matt is mid-sentence and my brain yells at me “I know, that sentence’s gonna end in ‘… in space time.’” and then it doesn’t. :(
Around 12:00 is the most excellent explanation of many realities I've ever heard. Great video.
That is SUCH a good explanation.
Truly you have made this VERY understandable.
I'd say your explanation is even better than anything I've heard from Sean Caroll (and that's saying a lot)
The laws of quantum mechanics say this is the best channel on youtube.
I want to begin by saying that I really love the work of this channel and the explanations that are provided. I'd just like to ask a few questions about the previous video-
It was said (if I understood it correctly) that when the electron hits the detector after passing both slits its wave function interacts with the wave functions of the electrons of the detector and a superposition describing each detector electron as simultaneously excited and not-excited. I wanted to ask if some of the electrons on the detector are more likely to be excited in this state, or put more clearly, are some electrons 'more excited than they are non-excited' in this superposition?
Also, it was said that the electron is described as a wave function, a function similar to a wave that assigns or describes the probability of the electron being present at each point of space. I've also heard that the
fundamental particles are each consequent of quantum fields. The value of each quantum field at each point in space is the energy of the quantum field at that point (I think), and where the energy of the field is high it manifests as a particle. As the energy of the field becomes close to zero, definite particles are not found.
So is this the same thing as the wave function? Does the distribution of energy of the electron over each point in space as described by the field manifest as the probability of finding the electron at each of those points as described in the wave function? The greater the energy of the electron field at a point is the probability of the consequent electron being formed there more? Are energy and probability the same thing on those scales?
Sorry for writing so much and rambling on my questions. I really love your videos!
I only vaguely understand, but I get a sense that the implications of this may be profound. I am excited and moved by the nature of the universe implied by this theory.
Thanks for entangling my brain with a very coherent explanation of a complex subject
You've got those wave-blobs coming straight out of the barrier wall between the slits. That has totally thrown me. Hang on, I think I've got it.
I recall there were experiments where they "destroyed" the measurements after they were made and were able to maintain coherence. Does this mean that the experiments somehow removed the offset that would normally cause decoherence?
Yeah I remember hearing about the same experiment. I believe that it was resolved simply, as long as the Which Way information ultimately remained unknown, coherence was maintained..
I think that's as close to metaphysics as physics can get.
What happened to the measurement?
the quantum eraser?
Because they weren't proper measurements as in "some observer entangled with the environment looks at it". It was a pseudo-measurement, where the quantum system was entangled with another quantum system. The combined system can then be manipulated. The destruction of the pseudo-measurement is simply another manipulation of a quantum system.
This was the best explanation of quantum decoherence I've ever heard. Touché!
Thanks for this chapter, it clarifies many things!
What about objective collapse theories, specifically Sir Roger Penrose's "Objective Reduction" extension?
The idea that the wavefunction actually does collapse, and by means of an actual mechanism with an actually describable timing makes a whole lot more sense to me than the many-worlds nonsense. Penrose described it as "gravitizing" quantum mechanics. It's the idea the spacetime itself is also being forced into a superposition that begins to accumulate more and more energy (which is accelerated by entanglement of intially separate wavefunctions within the environment) until the product of the entangling wavefunction's lifetime, t, and its energy, E(g), reaches Planck's reduced constant, h-bar. Or in other words, a wavefunction will grow until such time as the h-bar/E(g) threshold is reached.
I like to think of it as the universe bubbling with wavefunctions that entangle and ultimately "pop" according to that energy threshold, and that the macroscopic "classical" world we see is the ongoing totality of those pops.
It also happens to neatly solve the measurement problem, which is nice. ^_^
In my opinion, the idea that the wavefunction never collapses, but only appears to because of decoherence, doesn't make any less sense than anything else in quantum mechanics. If we accept that systems on a small scale can be in a superposition of multiple possibilities, I would hardly call it nonsense to say that this can probably happen on a large scale as well, especially when that's perfectly consistent with all our observations, and it's what the math predicts unless you specifically add in something to make the wavefunction collapse at some time. So basically, I think that given what we already know, the decoherence hypothesis is more parsimonious than any theory which posits collapse, since wavefunction collapse is just an extra assumption that isn't needed to explain the data.
I do like interpretations like the one you mentioned, though, precisely because they actually do allow for ways to test whether the wavefunction collapses, as opposed to the plain Copenhagen interpretation, which says that the wavefunction collapses with no explanation of how or when. Maybe in the future, we will be able to test these interpretations and find out if the wavefunction really does collapse in the way they describe.
Really interesting stuff! Thanks for sharing it!
Well, are you willing to give up causality and information conservation? If so, feel free to believe collapse theories.
Many worlds isn't nonsense unless the whole concept of superposition is nonsense. The idea that the wave function doesn't collapse is unfalsifiable, but a necessary corollary of that fact is that wave function collapse is similarly unfalsifiable. Superposition is just a feature of quantum mechanics. The idea that it doesn't stop at some point shouldn't be treated like bizarre nonsense when the observational outcomes are identical between that and interpretations where we handwave away superposition arbitrarily.
The benefit of some real collapse theories like Penroses' is that they actually do propose that quantum mechanics stops working at some point, so there is the possibility of running real tests. The problem is that mosts of the tests would be super expensive, and the only motivation is investigating something that a lot of physicists don't treat as overly important.
@@plasmaballin There's still an extra assumption in MWI, though it's also present in Copenhagen in an equally ad-hoc way; we have to assume that the probability that we'll find ourselves in a given branch follows the Born rule. You almost have to say that reality is just denser in some places than others.
10:12 Please put this image on a t-shirt
Nicely done. I first came across this type of explanation of decoherence while reading Murray Gell-Mann's book: "The Quark and the Jaguar". It was on a sunny summer's evening and I was sitting on some grass outside a cinema waiting for a movie. Three women wondered up and asked me what I was reading. I attempted a bumbling explanation but their eyes clouded over, they smiled regretfully and wandered away. A really great book but it has no pulling power.
Excellent exposition on a very “entangled” subject … Thanks! … 👍🏽👏🏽
Every time I see the double slit experiment I ask myself: What happens if one of the Slits has different forms or surfaces?
If a slit has a surface that can detect the path the particle takes, there is no waveform, it either goes through one slit or the other like a particle. For different forms, you just change the interference pattern.
This is actually something you can try at home if you want to play with it. It's a bit tricky to do, but all it takes is a laser pointer, some electrical tape, an exacto knife and a really steady hand.
If you mean different surface toplogies like a beveled corner on one but not the other. It will still have an interference pattern, the shape just might be different.
you know you can do this experiment yourself, right? Take a pointer laser and a piece of wire (or string, it doesn't need to be conductive, just not transparent. tape the wire so it covers in the middle of the laser. boom, you will see the interference pattern.
I believe Eidetic Ex answered your question correctly.
The "slits" don't have to be the same size or shape, you'd still get an interference pattern, albeit it might be shaped a bit differently.
And like others have suggested, it's cheap and quick to pull this off at home - here's a link for ya (th-cam.com/video/OUj0gt3h9Tk/w-d-xo.html).
True
I tried using the title to woo a girl I fancied. I 'll never make that mistake again. In all and every universe.
This channel keeps getting more and more in-depth.. I feel like we're just around the corner from solving the meaning of life soon...
This explanation makes so much more sense than the Kopenhagen one.
And it goes in line with the fact that it's so hard to isolate quantum computers to keep the entanglement from disturbance.
New T-Shirt:
Decoherence has occurred.
On the back: it has not
Of course you know that it would have to have more than two arm holes and one each of body and neck holes.
More like T-coherance AMIRIGHT?
The observer(s) has a quantum connection to the system (on the macro scale). Quantum decoherence seems to be the solution to Einstein's question: If there is no one to see the moon, does it exist? I some times think that there are people on this planet living in a different reality than me (ie flat Earth proponets)?
I would argue it does exist, that the moon itself "sees" itself.
Quantum Decoherence has nothing to do with a sapient observer in macroscale. Its going to happen regardless.
This is the best video ever on this channel - if measured by how much I learned in the 15 minutes.
Came for answers, I'm leaving with more questions. Thank you pbs
Somewhere.. there's a Universe where I could speak coherently on this subject.
But this ain't it.
My brain feels heavy. I saw too many photons
Do wave functions have observable, cumulative mass?
No but photons have momentum, so your neck could literally get tired from watching a video (you'd be immolated long before then, but oh well)
A wave function is just a description of possible positions of the particle, its simultaneously in multiple places when it isn't interacting, but once it interacts with something, ie hits the wall, then its mass becomes real and measurable
Fundamentally the wave function itself cant be measured because measuring it collapses the function into the particle, we can just get around that by forcing random interaction and extrapolating the wave function that way.
This is such an incredible episode, it bugs me that this doesn't have more views...
Awesome explanation as always!
Thx
*_...the transition between quantum and 'macro' is like the sum of a series of normal-distributions: close-up their tops seem to merge to an almost flattened sinewave, but spread-out they're separate smooth bumps..._*
This is the first video I saw that explains quantum decoherence in so simple terms that everyone can understand it. Everyone.
Love this videos, thanks PBS guys.
Exceptionally well worded talk!
"The hypothetical angle of the dangle is directly inversely proportional to the heat of the beat in a vacuum ²" -Dr.Prof. Cornwallis the Great
Now I clearly understand how decoherence splits my brain.
The version of me that gets this explanation must be in another universe. 😅
I don't know much about physics, but usually I can piece together bits I remember from college along with what I know from computer science / programming to kind of follow along lol. The way this was explained reminds me of how "branch prediction" works in CPU design/programming. Basically there's a function/program execution running that encounters a conditional/decision point or "branch". The calculation to resolve which branching path to take is costly, and in order to prevent the system/program from stalling a "guess" is made based on branching algorithms and patterns and execution continues (we have a general idea of what path execution will take, but not sure till the calculation resolves). When the calculation resolves, if the correct guess was made the function has already gone ahead, if wrong the system must then backtrack to take the correct branch. This can be done with some degree of parallelism, but even modern computers can only handle a few simultaneous branching paths efficiently because of possible subsequent branching and resource consumption.
If I recall correctly, this is one of the areas where quantum computing is mentioned / would benefit as well; instead of having to do this branch prediction and correction when wrong, an equivalent execution/program in quantum computer would resolve or otherwise represent all possible branches and we'd just pluck the result from the collapsed path we were interested in (or something, quantum computing wasn't something they talked about much in undergrad CS lol).
Wow!! That explanation was perfect for my understanding 👌
So we're not really observing, we're actually absorbing
Like the difference between looking at food and eating food, right?
True. Re. photons we absorb them with our eyes and then process the resulting data into a coherent version of reality.
so, how does this explain the delayed choice experiment?
also, is it me or there are two writers of the scripts? one that talks as if he/she wants us to understand (this episode) and one that does not (the previous episode)?
No one understands the consciousness interpretation of QM. People only pretend like they do because they want quantum superpowers.
It does not: you need General Relativity to explain the DCQE experiment. Photons experience no time (no time happens, nor space even, at the speed of light, all is here and now for them), QM fails because it is "time-dependent" (i.e. too dampened in obsolete Newtonian ideas such as linear time).
@@LuisAldamiz linear time is far from obsolete. it may be incomplete, but i dont think any other phenomenon is more experimentally verified.
@@LuisAldamiz Wouldn't this mean that DCQE would not work with any particle that has mass?
@@Woffenhorst - My limited understanding is that it would work differently but I haven't calculated at which parameters it would stop working, probably at great distances only, depending on the mass (and thus speed) of the studied particle. My thoughts reach as far as that only.
Excellent episode! Thank you!
OMG , Finally a complete episode that I not only make sense of but I truly understand, today is going to be a Good Day 😊😉😊