The Many Worlds of the Quantum Multiverse | Space Time | PBS Digital Studios

The weird rules of
the subatomic world are very, very
different to those of the familiar
large-scale universe. A huge outstanding
question is when and why does the weirdness
of quantum mechanics give way to classical physics. One answer to this
question suggests that the entire universe is so
much weirder than we imagined, or should I say the multiverse. [MUSIC PLAYING] One of the strangest
features of the quantum description of reality is
the idea of superposition. We can’t describe the
most fundamental building blocks of our universe with
defined singular properties. Instead, they seem to
behave as probability clouds of all properties
they might have were we to try to measure them. Mathematically,
this is encapsulated in the wave function
of a quantum particle or system of particles. The best illustration
of why we need to describe the
quantum world this way is the famous
double-slit experiment. We did an episode on it. Check it out if you
aren’t familiar. But to summarize, a stream of
photons or electrons, or even molecules, travels
from some point to a detector screen
via pair of slits. These particles arrive
at the screen distributed like the interference
pattern you would expect from a simple wave. Quantum mechanics
very successfully predicts this result by
describing each particle’s journey as a superposition
of all possible trajectories. In other words, the
particle simultaneously takes all possible
paths, which means it passes through both slits. It tries out all histories
between launch and landing. And those many maybe
histories somehow interact with each
other to determine the most likely
final destination when a measurement is made. In a sense, different
possible superposed histories appear to converge
on one final outcome. But what causes
that convergence? In the original
Copenhagen interpretation of quantum mechanics,
the act of measurement was thought to collapse
possibility space into a single reality,
at least with respect to the measured property. It collapses the wave function. That collapse signifies the
transition between the quantum and classical realms. One of the founders of quantum
mechanics, Erwin Schrodinger, found this ridiculous. And he proposed his famous
Schrodinger’s cat thought experiment to highlight
the absurdity. It goes like this– a cat is in
a box with a flask of poison. A machine containing
a radioactive element is set to shatter the
flask in the event that the radioactive
element decays. If that happens, the cat dies. That radioactive decay is
a purely quantum process. And so until it’s
observed, it exists in a superposition of states. It has both decayed
and not decayed. But doesn’t that mean that
the entire macroscopic system attached to that quantum event
is also in superposition? If so, then the cat should be
simultaneously alive and dead until we open the box. But why can’t the cat collapse
its own wave function? And from its point of view,
is the physicist outside also a quantum blur until
the box is opened? And what about the entire
rest of the universe that’s not currently being observed
by physicists or cats? Many adherents to Copenhagen now
have a more sensible resolution to the paradox of
Schrodinger’s cat. It’s that quantum
superposition doesn’t extend to macroscopic scales. It disappears when different
quantum scale histories diverge. This is called decoherence. When the wave functions
describing quantum systems overlap sufficiently–
in other words, they are coherent– it’s
possible to get interference in the double-slit experiment
and spookily correlated quantum entanglement measurements. But when these systems interact
with their environment, coherence is lost and
parallel histories fall out of alignment. They can no longer
interact with each other. By the Copenhagen
interpretation, we might say that the universe
chooses the final outcome of all those histories. It doesn’t exactly
choose a single history. Instead, it chooses an end
result– say, particle location on a screen or cat
alive or deadness– based on those histories. If a larger number
of possible histories lead to a given
result, then it’s more likely that the universe
will select that outcome. The Copenhagen
interpretation says that this selection happens
in a fundamentally random way. The universe plays dice,
even if the dice are weighted towards certain results. It is what we would call a
nondeterministic interpretation because there’s no
underlying predictability behind the selection. However, there is
another way to interpret the transition between the
quantum and classical worlds. What if the wave
function never collapses? If we can imagine a cat in
a superposition of states, alive and dead, why
stop at the cat? What if the family
of possible states extends beyond the radioactive
decay, beyond the cat, and includes the observer and,
indeed, the entire universe, too. If we open the box and
find that the cat is alive, it’s because we’re part
of an entire quantum timeline in which
the radioactive decay and subsequent poisoning
never happened. But there’s an equally valid
timeline in which it did, and another version of
us experiencing that. This sounds outrageous, but it’s
a very serious interpretation of the mathematics
of quantum mechanics. It was proposed by Hugh
Everett in his 1957 PhD thesis entitled “The Theory of
the Universal Wave Function.” It’s come to be known as the
many worlds interpretation. To outline the idea without
killing so many cats, let’s talk about what
this means in the context of the double-slit experiment. The Copenhagen
interpretation tells us that the superposition
of particle trajectories, of histories, merges
into the single timeline of the observer’s reality. Many worlds says this
merging never happens. Those alternative
histories continue, and we find ourselves in
just one of those timelines. Which one? Well, they’re all
equally likely. But some look very
similar to each other. For example, many
histories lead to photons landing on the bright bands
of the interference pattern, and very few to the dark bands. We tend to find ourselves
in the more common families of histories. This is a pretty crazy notion. The many worlds interpretation
invites the idea that reality splits into
different branches every time quantum states diverge into
different possibilities– for example, at every particle
interaction everywhere in the universe. This would lead to an
unthinkably large number of alternate timelines
or worlds that contain all possible
realizations of this universe since the Big Bang. It seems extravagant to propose
uncountable eternally-branching universes just to get out of
collapsing a wave function. It’s like building
an entirely new house to avoid doing the dishes. But remember, the Copenhagen
interpretation itself proposes multiple worlds
in the superposition of paths or properties
of a quantum system. Both many worlds and Copenhagen
create alternate realities. It’s just that
Copenhagen merges them into a single timeline with
its wave function collapsed. The superposition of
states of many worlds can be thought of as
overlayed histories, slices of a universal
wave function that diverge from each other
as the universe evolves, but none ever vanish. Many worlds may, in fact, be
the more pure interpretation of the mathematics
of quantum mechanics because there’s nothing
in that math that requires the collapse
of the wave function. So many worlds is more
economical in the number of unsupported concepts it
adds to quantum mechanics, even if it isn’t particularly
economical in the number of universes it predicts. Now, Everett’s idea
wasn’t taken too seriously when it was first proposed. That may have been
in part because he wasn’t a well-known physicist. He was just a graduate student
who all but disappeared into military research
at the Pentagon right after graduation. But another point
of resistance must be the overwhelming
existential crisis induced by the idea of
near-infinite versions of one’s self. Many worlds may imply that
every possible version of you exists out there. You’re just the one who
happens to be experiencing this branch of reality. Every other possible
life path, including those branching in
different directions from every decision you ever
made, may be just as real. In fact, each may be
real in vast multitudes. There’s no more
evidence for many worlds than there is for other
mainstream interpretations of quantum mechanics. And it is somewhat
mainstream these days, with many noted physicists
being swayed by its parsimony, its economy of ideas. But it remains an
interpretation. And so although it is supported
by the incredibly successful mathematics of
quantum mechanics, it has not yet
added a prediction that might distinguish it
from other equally-supported interpretations. Nor is it complete
in its explanation. There are some
ideas about what’s really happening when these
neighboring coherent histories interact or why the
wave function translates to probabilities
the way it does. But they are far from
generally accepted. Unlike Copenhagen,
many worlds is a deterministic interpretation. Any given timeline is
a predictable chain of cause and effect. It explains the apparent
randomness of quantum mechanics with a sort of observer bias. All possibilities are
chosen at every junction, and we just happen to be
seeing the one that happened in the branch that we occupy. That adds a second possible
cause for philosophical unease. In a purely
deterministic universe, what happens to free will? If we’re going to make all
possible decisions anyway, why sweat any given choice? Well, sure. But of all those countless
future branches of reality, some are going to
be pretty amazing. Think of it as a choose
your own adventure, and steer this version
of you towards one of the more awesome many
world branches of space-time. Well, guys, do
you know who this? This is Dianna from Physics
Girl right here on Space Time. Hey, Dianna. It’s cool to be in space here. Yeah, it’s nice, right? One thing I love
about your show is all of the crazy awesome
experiments you do. They are so much fun. That thing with the water
vortexes blew my mind. You don’t do a lot of
experiments on your show. We could do experiments. OK. Well, then, I have
a challenge for you. I want to challenge you
to prove that the Earth is round using an experiment. Ooh. How long do I have? You’ve got a
year, starting now. Challenge accepted. One thing I really
like about Physics Girl is it explains complex stuff
in such understandable ways. I try. MATTHEW O’DOWD: But I’m a
kind of jargony kind of guy. I love those long,
sciencey words. But it’s hard to keep
track of them sometimes. So I have a challenge for you. OK. I would love you to do
an episode in which you explain the five most jargony
and commonly encountered modern physics words
in simple English. Done. But I want you to use
only the 1,000 most common words in the English
language to do that. That’s going to
be a little harder. Yeah. But challenge accepted. So keep watching PBS
Space Time to make sure that Matt follows up
with that challenge. And keep watching Physics
Girl because we’re going to hold you to that, Dianna. [MUSIC PLAYING]

100 thoughts on “The Many Worlds of the Quantum Multiverse | Space Time | PBS Digital Studios

  1. The Multiverse is impossible, if people knew etymology of words they would know that, they are confusing parallel Dimensions with parallel universes.

  2. I am a mathematics guy myself but i hope the analytical abilities will be suerly helpful to understand the equation of QED but i seriously lack physical intuition needed for the subject like QED , I THINK i should start to study these stuffs seriously

  3. I have viewed tiny clear bubbles traveling away from what I think were my thoughts , some of them were linked in a string arrangement . They traveled to a distance of 8 to 10 feet away from me and burst. They had interior rings , sometimes 2, sometimes 3. Sometimes dark centers. They seem to appear most when first waking up in the morning and sitting outside. For some strange unknown reason I connected them to thought process.

  4. Look at Matt getting flustered and crushing on physics girl 🤣

  5. I don't think spacetime every followed up with physics girl's challenge…

  6. We could wake up in a different universe each day and not know it

  7. Schrödinger's cat CAN be saved, groundbreaking new research

  8. What if there are two mutiversal "states/types" one being literally separate big bangs creating entirely new and infinite universes, but each universe experiences an infinite number of possible timelines

  9. If there's a version of me in a parallel universe, that looks like you, and does this show, and there's a version of me that looks like each person commenting in the thread…then maybe we are all the same person having many experiences at once. Hello other me's.


  10. There is no universe in which this video ends the way i would like it to.

  11. Seems like the many worlds interpretation is saying 1+1=3. Like, where did you get all of this extra energy to create an infinite amount of universes all of a sudden? Magic?

  12. There's no such thing as free will. Will always charges, but look out for him short changing you. 😨😨😨

  13. There is no evidence that I’m aware of that predicts that quantum properties should not be observed at human scale

  14. While quantum entanglement suggests a third party reality supporting the world as a cause, the idea that multiple universes coincide that supportive cause , is false. Even if a particle was to escape one universe and disappear into another universe, there would be some sort of time and space consumed by an alternative universe, that would fail to explain the instantaneous exchange of data between distant images of one particle's identity. If you escape this universe and leap into another world, you have to traverse that other world, and that would not account for an instantaneous behavior. So Multi Verse ideas are just evading the obvious fact that the escape of this Universe by a particle's behavior, must escape any other Universe as well to achieve the strange and spooky behavior of quantum physics.
    The use of Multi Verse theories is a avoidance of the principle fascination with what can only be called SUPERNATURAL causation . Leaping out of one Universe into a parallel Universe of a Multiverse theorem , does not justify the absence of time and space, it just substitutes the rates of conduct through one universe with the leaping over to another universe, which if familiar , consumes time and space according to that paradigm. You are only trying to evade confession that there is a supernatural origins to natural events.

  15. Could there be a direct connection or correlation between the results of double slit experiments, the many worlds theory, and the emergence theory? They all talk about a "consciousness" which somehow lies at the center of them all. But what is that consciousness that they are talking about? But before everything else, let me say that I am, as always, blown away by your videos.

  16. For me at least, MMW validates 'free will'.

    Every choice you could make but didn't still gets played out in some other world while the consequences of whatever choice(s( J did in fact make, are observed by 'me' ad infinitum.

    The fact is, MMW doesn't discount any choice I made since, regardless of whatever choice I made. Only the 'me' right 'here' pursuant to what ever choice that was was, has any real say about it.

    The rest are, from 'my' perspective, purely hypothetical anyway.

    I mean, even if I ran into another me, that's git nothing to do with the fact that 'I' still made the choices 'I' made.

    If anything, I'd be happuer knowing that whatever choices I couldn't/wouldn't/ didn't make get realized elsewhere.

    Free will is a reactionary drlusion since we don't live in a vacuum and are affected by things wsy outaide our conscious awareness anyway, be it the quantum underpinnings of superposition to the decisions somebody/something we may or may not be awsre of.

    In my view, 'free will' is more after the fact anyway.

  17. Maybe the particle doesn't go through both slits. maybe the measurements and calculations of its position is already calculated coming from the future just like everything else. Now I got it.

  18. many worlds explains schizophrenia which is not a disease/disorder but a higher state of consciousness and being a multidimensional human being

  19. I thought the line at 11:02 was a sneaky segue for a ad. A missed opportunity to entice viewers into becoming a smarter self in their part of the multiverse.

  20. Maybe we should consider the possibility that both Copenhagen and the many worlds theories are right and wrong at the same time. Imagine a more organic construct.

    Multiple universes are created, but only when sufficient cumulative deviation occurs. I.e. if I choose one toothpaste or another, even though the potential for a butterfly effect sort of impact on the future exists, a new universe won't be created. Instead it will self correct by averaging the decisions of my counterparts in all currently existing timelines and imposing my most popular decision on all of us as a group. This is why we sometimes do things on an 'impulse'.

    However, when a sufficient number of individuals and/or factors are involved and the possible outcomes are too close to equally likely, then the universe is forced to split creating a new one.

    In this way we end up with many worlds, but not an absurd, nearly infinite number.

  21. That's the wizards explanations!! The trick is to jump in between those reality to the one that's the best for you !!!

  22. Matthew: Evaluates competing theories surrounding one of the most abstract subjects ever contemplated.
    Physics Girl: "Prove the earth is round."

  23. The many worlds interpretation was designed to preserve determinism in the face of infinite uncertainty in quantum physics (ie probability wave function – dbl slit experiment). The irony is that it has imploded under the weight of it's own declaration of determinism. It's logic has reacted to itself like it was it's own auto immune disease. MWI's "alternate worlds" conflict with it's deterministic foundations and it evaporated itself. Simply, if the universe was determined it wouldn't produce alternatives of itself. There wouldn't be probabilities in a determined universe to necessitate alternatives. Read David Albert's objections. It's all over but the yelling for the MWI.
    The math behind MWI is simply the extrapolation of the unrealized probabilities – what might have been… lol

  24. Sir Isaac Newtron: For every action there is an equal and opposite reaction.

    Quantum Mechanics: For every action there is an infinite number of reactions.

    It's kind of terrifying to know that there is an entire universe filled with nothing but my dopplegangers…

  25. that double-slit experiments is a real pandora box, everett's research paper is the catalyst

  26. Cats get picked on enough….gosh, next experiment let's use a mou…nevermind

  27. did you immediately check for the thumbs up ratio to see if the internet youtube experts approved and so the video is worth your time?

  28. I look forward to the day when we actually know for certain what the true nature of reality is, and the role that the observer has if any. There are just so many theories out there including the simulation/Virtual Reality theory?! Will we ever know 😉

  29. Is there a universe where Mario & Luigi are real? Is there a universe where Crash Bandicoot are real? Is there a universe where Ratchet and Clank are real? Is there a universe where Jak and Daxter are real?

  30. I thought of this theory completely all by myself and though I was the only person who was aware of it. Then as I was watching stranger things, Mr. Clark who was the science teacher, was talking about this same theory. I'm a little bummed out at how this theory was already discovered, but I still do think it is pretty surprising how I though of this theory all by myself when I was 14.

  31. 8:43 Maybe the many worlds are moments. The universe is coming into existence at every moment. Over and over again…the last moment creating the next and they seem all fluid and connected to us, but really it's a whole brand new universe.

  32. What if they are both right? What if the wave function collapses at first, but then a certain event forces it to fracture into branching realities? And both these then experience their different trajectories while collapsing the wave function of their respective realities until some event forces one or both into two realities. So on and so forth. The question then would be, the nature of the events that cause the fracture. What, origin, where, why, and how often. What if it's a specific kind of choice? A turnpoint? And if so, who is the choice coming from: each individual? An outside power? An alignment of both? (If an alignment, then what's the relationship: how long and strong And connected is the relationship, what's it's underlying principle?), why the event occurred, both the physical; and if it occurred from the alignment scenario: non physical reasons. And how often does the event occur and why.

  33. I would like to differ with your interpretation of pee-a-boo, as an actual issue in physics. You say that the child's happy reaction is based on a lack awareness of object permanence. While this is one aspect, it is a lesser aspect. The greater effect behind peek-a-boo is the causal impact of consciousness itself. This can be verified by varying the emotional quality of the sudden conscious interaction. If you emerge from behind closed hands as a screaming, threatening monster, the child will not be delighted. Point being that reducing this interaction to a question only of object existence is a basic limitation of adult physics classical, relativistic and quantum. Simply ignore the mind and its effects. A child does not have that intellectual contrivance as an option. One might contend that the act of observation and the subsequent collapse of the wave function is a recognition of an effect of consciousness. However, the wave function is only an equation, a mathematical construct. Its collapse is also an idea only and there is nothing in that idea that establishes it as a physical, causal factor. In general, symbolic representations in and of themselves while possibly predictive, are not causal. Nor do they demonstrate a direct effect of consciousness on matter or energy. Consciousness does have both direct and indirect effects on both matter and energy, consciousness itself being an evident form of energy, as the child's reaction shows us, but these effects are not made manifest through self-contained symbolic manipulations.

  34. “It’s like moving to a new house to avoid doing the dishes.”
    Actually it’s more like terraforming a whole solar system and filling each terraformed planet with residential super-skyscrapers… to avoid doing the dishes.

  35. OR it is ALL complete BULLSHIT no matter what you "believe"…..just totally untrustworthy silly ass presumption ….to rightly be REPENTED of?

  36. Him and physics girl should get together. They could do lot's of cool experiments.

  37. You pretty much put my thoughts into words for me… See my theory is the universe itself is one giant probability wave with all possible quantum states throughout the universe happening simultaneously and also all possible past present and future possible qauntam states are also happening simultaneously and all of the possible probability waves past present and future occupy the same space and time …. More simply put every possible outcome that has happened will happen or is happening is on a never ending loop repeating everywhere within the same spacetime

  38. More easily put all possible past present and future timeline all exist simultaneously and all exist with in the same space and same fraction of a second

  39. And what we expeairence is the most common and more likely set of possible outcomes… But I believe past and future outcomes an moments are ever changing and fluid that they can vary moment to moment especially over longer periods

  40. Sadly, I cannot steer myself to the best future outcome because… this meta universe will choose which universe I experience for me 🙁

  41. Does this mean that there's infinite versions of every tiny insignificant gesture or even physical movement I could make. Like me typing this at a different speed? Or having slightly different eye movements?

  42. I have a question; where are all these many universes located physically? I don’t think they are scattered in a large empty space like it’s usually depicted.

  43. The true meaning of this videos is what if humanity never went to war with each other what the world would look like today?

  44. 3:22 does this mean we are in gods simulation and nothing will "load" until we observe it?

  45. Couldn't the particle be affected by space/time itself? Einstein observed light bending around a star. Maybe the nature of space/time is fluid or vibrating. If this is the case, they should be able to shoot particles at a frequency that matches the vibrations of space/time to create a single outcome.

  46. Maybe multiverse is the reason why we have dreams and nightmares?

  47. Hey buddy! I hope you have a good day! Jesus Christ be with you!😊

  48. The many worlds guy just got scooped up by the Pentagon. No biggie. Nothing to Mandela disturbances.. I mean, see here.

  49. So is the many worlds approach ultimately a way for particles to determine how to best fit the action principle?
    If so, why can't they just continuously respond to the local field within some distance of themselves? Wouldn't that be simpler?

  50. 5:20. "Why stop at the cat?" A mindset of a serial killer or a quantum physicist.

  51. MWI Critics: If we live in a multiverse, there are a surplus of universes where unlikely outcomes continue to happen, like all coin tosses come up heads.

    Me: My toddler puts his shoes on the wrong feet 100% of the time, so…QED

  52. The real question is, if all this confirms that I'm living in a computer simulation, then why is the simulation giving away its secrets by way of these videos?

  53. They need to bring back or reboot the sliders tv show. But that show made the universe really different… there should be universe that is exactly the same as this or only different by one electron on the other side of the universe going left instead of right for all intent and purpose of you being home is meaningless.

  54. Maybe the right one is a mid point, where some universes can be merged for some reason, so there's not infinite universes, but a few to some many.

  55. Schrödinger`s daughter, once asked, why her father used a cat to potentially be killed, she answered: "My father just doesn't like cats!"

  56. I feel fucking scared.
    This was thoroughly unsettling…

  57. Matt O'Dowd you are an absolute gem! "Choose your own adventure"–what a wonderful way to sum up how I feel about the possible implications of MWI!

  58. The only thing that really bothers me about this theory. How would you explain the splitting of dimentions when the universe hits a junction? And what determines wich one we(you) will keep living?
    It seems weird that there is an infinite growth in different worlds…

  59. There's a world where this theory doesn't exist and a world where it is confirmed, assuming it is true and there's a physical way to prove it in at least one of the worlds. Though if it can be proven, it's probably been proven in many.

  60. Is an observer really necessary ? Has this been shown in a laboratory with reproducible results.

  61. Serious question here.
    If there is an infinite number of universes with an infinite number of possibilities then what if in another universe parallel universes are proven to not exist ?

  62. You're a bit quick to follow the divergence of human decisions into different universes. That would require the decisionmaking to be a quantumevent being on a superposition with another possible decision, which is most certains not the case.

  63. This is a question that I have regarding experiments like this.

    We know that the mirror parody from left and right is broken once we involve the strong nuclear force. I believe it is the strong force. In one of his books Kip Thorne describes an experiment where this was proven. I believe Strontium 90 was brought to near absolute 0 and barraged with neutrons or alpha particles. Any rate the resulting experimental observation showed that no matter which way you sent the particles in the particles sent off from the collision always went in one direction to the right.

    This meant that the mirror parity assumption was broken. This says that whatever you see in the mirror can be duplicated. Here whether you shot the particle from your direction or the direction 180 degrees opposite the particles given off always went to the right. I believe it was the right I am not 100% sure I remember forgive me.

    Professor Thorne said this was due to the fact that the particular interaction being tested was based on the strong nuclear force. It may have been the weak force again forgive me I cannot remember 100%. So the conclusion was that although there is a mirror parity between interactions using the electromagnetic force, this was not so for the nuclear force in question.

    So anyway this gets to my question regarding this experiment. Thinking about this and remembering what Thorne explained above it occurs to me that we can only observe the universe through the electromagnetic spectrum. The other forces even gravity affect us but we only experience their effect on the electromagnetic spectrum.

    Certainly light is electromagnetic but force as we experience is as well. Most of matter is empty space and atoms can pass through each other and very rarely are their collisions. The reason when we touch a wood table for instance that we feel solid matter and are stopped from phasing through it is that the electromagnetic fields in the atoms repel each other. So when we touch something what we feel is the effect of electromagnetic force the matter creates.

    Given this are we not essentially handicapped in our observations and especially when it comes to the observation of the quantum world and individual particles where the strong and weak nuclear forces play a much greater role in deciding the outcome of a result.

    We talk of the particle packet of electromagnetic waves being made of all possibilities and affected by the interactions of other particles in some spooky fashion. However is this so or is this only what we see and observe because we only see with a sense based on one force. If we had eyes that could see in the strong force or ears that could hear in the weak force or a field sense like a shark has that sensed the vibrations of gravity would we not have more information?

    Is it not possible that something is going on with the other three forces of the universe that would cut through the confusion of quantum physics and give us a clearer picture that made more sense?

    Just some thoughts! Please let me know what you think!

  64. There are not separate physical worlds. Quantum fields contain quantum states, which are like empty shelves, places to put things like energy, momentum, electrons.

  65. I wonder if when we die we just slip into another universe but we'll never know. Unless something goes a little funky like people who experience past lives. Considering the video I don't believe at all that it's out of the question.

  66. Whats interesting is navigating the multiverse! Yes it is possible to do so given you know the signs. The nature of the signs are given in hints as to what it asks for. Many times it is asking you to correct something where you're at. This is so you can navigate to other realms or possibilities. BTW you already do this in various ways , you just don't know it! Have you ever gone back to close a closet door in your home which popped open? Stopped to pick up a piece of litter on the ground? Been delayed in traffic for no apparent reason? This is called reordering the universe and it may only apply to you and other multiverses. Course this is only my theory and cannot be proven. Our inclinations are much more complex than any mathematical equations I am afraid-lol.

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