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First Experimental Evidence That Time Is an Emergent Quantum Phenomenon 530

Posted by Unknown Lamer
from the quantum-machine-elves dept.
KentuckyFC writes "One of the great challenges in physics is to unite the theories of quantum mechanics and general relativity. But all attempts to do this all run into the famous 'problem of time' — the resulting equations describe a static universe in which nothing ever happens. In 1983, theoreticians showed how this could be solved if time is an emergent phenomenon based on entanglement, the phenomenon in which two quantum particles share the same existence. An external, god-like observer always sees no difference between these particles compared to an external objective clock. But an observer who measures one of the pair — and so becomes entangled with it--can immediately see how it evolves differently from its partner. So from the outside the universe appears static and unchanging, while objects that are entangled within it experience the maelstrom of change. Now quantum physicists have performed the first experimental test of this idea by measuring the evolution of a pair of entangled photons in two different ways. An external god-like observer sees no difference while an observer who measures one particle and becomes entangled with it does see the change. In other words, the experiment shows how time is an emergent phenomenon based on entanglement, in which case the contradiction between quantum mechanics and general relativity seems to melt away."
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First Experimental Evidence That Time Is an Emergent Quantum Phenomenon

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  • Hmm (Score:5, Insightful)

    by wenchmagnet (745079) on Wednesday October 23, 2013 @08:56AM (#45211271)

    First time I've seen no comments show up a few minutes into a Slashdot story going up.

    Are most other people, like me, scratching their heads and trying to wrap their minds around this? :)

    • Re:Hmm (Score:5, Insightful)

      by AbbyNormal (216235) on Wednesday October 23, 2013 @08:58AM (#45211281) Homepage

      You must be new here.

    • The summary mentions "God" or "Godlike" about three or four times. I think most people have figured out the "twist" in this particular quantum press release -- I mean experiment.

      • The aliens had to make us believe in gods so we'd eventually figure out how time works. "It was worth the price." - Darth Albright

      • Re:Hmm (Score:5, Funny)

        by msauve (701917) on Wednesday October 23, 2013 @09:15AM (#45211425)
        The headline should be really about the creation of a Godlike observer, which was a prerequisite for this experiment.
        • Re:Hmm (Score:5, Funny)

          by dbIII (701233) on Wednesday October 23, 2013 @09:27AM (#45211513)

          The headline should be really about the creation of a Godlike observer, which was a prerequisite for this experiment.

          Let's give Mr and Mrs Norris a bit of privacy for that one.

        • Re:Hmm (Score:5, Funny)

          by Andrewkov (140579) on Wednesday October 23, 2013 @11:01AM (#45212463)

          I'm a Godlike observer, but only when I have mod points.

          • Re: (Score:3, Funny)

            by Anonymous Coward

            And if you become entangled with one of the comments, your Godlike status disappears.

            Slashdot: 1; Quantum Mechanics: 0

          • by metlin (258108)

            As someone with mod points, I almost modded you -1 Troll for kicks, but my god-like powers of self-control kicked in.

            • As someone else with mod points, I almost modded you +1 Funny , but my god-like powers of commenting kicked in.

        • Re:Hmm (Score:5, Insightful)

          by pscottdv (676889) on Wednesday October 23, 2013 @11:10AM (#45212577)

          The theory requires no outside, God-like, observer, nor does it propose one. The point is that time is measured by "events" and "events" occur when the quantum states of two systems become entangled, but only to the systems that became entangled. To an "observer" that has not become entangled, a system is static and no event has occurred.

          In the Copenhagen interpretation, one would say that according to the entangled observer the "wavefunction has collapsed" whereas according to the unentangled observer, it hasn't.

          • Re:Hmm (Score:5, Interesting)

            by pz (113803) on Wednesday October 23, 2013 @01:37PM (#45214289) Journal

            If time is an emergent phenomenon, then how does the first event happen? If time does not yet exist, then there is no was to distinguish an event. By the parent's suggestion, time can only be propelled forward when already in motion, by the contribution of each new event. The very ideas of "first" and "new" presuppose the existence of time, and thus despite this likely significant scientific work, we continue to have a tautology until an instantiation somehow starts things off.

            We are still, also, a long way away from understanding what causes wavefunction collapse, since the notion of observation is clearly ludicrous: there are no observers in the center of the sun, or on the far side of Jupiter, as two minor examples.

            • If time is an emergent phenomenon, then how does the first event happen?

              Funniest thing I have seen all day, and I watched the surgeon simulator video so that is saying something.

          • Re:Hmm (Score:5, Interesting)

            by Remus Shepherd (32833) <remus@panix.com> on Wednesday October 23, 2013 @01:43PM (#45214363) Homepage

            In the Copenhagen interpretation, one would say that according to the entangled observer the "wavefunction has collapsed" whereas according to the unentangled observer, it hasn't.

            I prefer the Copenhagen interpretation, but this experiment is also interesting if we use the Many-Worlds interpretation. Then the God-like outside observer sees every possible quantum state and all of its outcomes simultaneously, as if they all have already happened. That sounds to me like a recipe for strict determinism.

            • by alexgieg (948359)

              That sounds to me like a recipe for strict determinism.

              Many-World is in fact strictly deterministic. It's considered one of it's advantages as QM becomes just like everything else in Physics.

              Notice that strict determinism doesn't affect subjective free will. Instead of being a property of the world free will becomes a property of your internal representation of the world, pretty much like colors don't exist in the world, only in your brain, what evidently doesn't make them any less real for you and for anything you do based on them "being there".

    • Re: (Score:3, Funny)

      by Anonymous Coward

      Most of them are still trying to figure out the info on the relevant Wikipedia pages, ya know, so as not to sound too stupid when commenting here :-)

    • I find articles like this one to be the most interesting content that pops up here on Slashdot, even if I can't wrap my head around it.

      Equally fascinating: http://science.slashdot.org/story/13/09/14/1822201/study-our-3d-universe-could-have-originated-from-a-4d-black-hole [slashdot.org]

      Can these two ideas be conciled?
    • by Chrisq (894406)

      First time I've seen no comments show up a few minutes into a Slashdot story going up.

      Are most other people, like me, scratching their heads and trying to wrap their minds around this? :)

      No - time just came to a halt as the emergent digression of entangled pairs was affected by so many observers contemplating the fact.

    • Re:Hmm (Score:5, Informative)

      by hodet (620484) on Wednesday October 23, 2013 @09:29AM (#45211531)

      It's because the subject takes time to digest and respond to intelligently. As opposed to the usual "NSA is Monitoring My Brain" headline. It's nice to see this type of article, it's what brought me to slashdot so many years ago. I still come everyday hoping to see more stuff like this.

  • by MrKaos (858439)
    All this time travel stuff gives me a head ache!
  • First Post! (Score:5, Funny)

    by Fieryphoenix (1161565) on Wednesday October 23, 2013 @08:59AM (#45211293)
    But only from the point of view of an external god-like observer.
    • Indeed.... :-)

      Next time, just be faster!

    • Well...if the scientists can pretend to do it in an experiment.
      • Re:First Post! (Score:5, Insightful)

        by TopherC (412335) on Wednesday October 23, 2013 @11:47AM (#45212981)

        What I can't yet understand is how this experiment helps validate the theory of time as an emergent quantum phenomenon. It seems more like a demonstration than an experiment to me. What alternative theory is their experiment excluding?

        I'm a physicist but that doesn't mean I understand any of this QM stuff. I have a feeling this is a little like experimentally demonstrating Bell's inequality -- one can do experiments whose results are consistent with predictions of QM, and in ways that one might expect other general classes of theories to differ even though you don't have a specific alternative theory to exclude. Most experiments are like this really. But in the case of this time-entanglement experiment I really don't see room for alternative predictions. I think the paper's title acknowledges this: "Time from quantum entanglement: an experimental illustration" (my emphasis).

        I'm not saying that the experiment is in any way unhelpful or bad. It's a great idea, but I would not go so far as to say that this is "experimental evidence."

  • by sandytaru (1158959) on Wednesday October 23, 2013 @09:07AM (#45211347) Journal
    We need to start likening things to quantum physics. At this point rocket science is frikkin' easy compared to all this quantum stuff.

    Until quantum entangled particles gets harnessed into the faster than light communications they've talked about over the years, no one will really care anyway.
    • by MadRocketScientist (792254) on Wednesday October 23, 2013 @09:17AM (#45211437)

      We need to start likening things to quantum physics. At this point rocket science is frikkin' easy compared to all this quantum stuff.

      Sheldon Cooper would agree:

      Missy: Yup, I’m always bragging to my friends about my brother the rocket scientist.
      Sheldon: You tell people I’m a rocket scientist?
      Missy: Well yeah.
      Sheldon: I’m a theoretical physicist.
      Missy: What’s the difference?
      Sheldon: What’s the difference?
      Missy: Goodbye Shelly.
      Sheldon: My God! Why don’t you just tell them I’m a toll taker at the Golden Gate Bridge? Rocket scientist, how humiliating.


      On a related note, maybe it's time for me to change my username...

    • I blame KSP.

      Seriously, orbit physics is now part of a computer entertainment game.

      And yet, US children keep getting dumber on average, WTF?
      • by jandrese (485)
        Children have forever and always been getting dumber. People look at their kids and go "Damn, I wasn't that dumb when I was that age!"
        • by Amouth (879122) on Wednesday October 23, 2013 @10:59AM (#45212425)

          If you don't nurture them then yes they don't grow. You don't have to force things on them but rather encourage their natural want to learn.

          Now having a child (3 years old at the moment) i'm amazed at how quick they can learn, and feel sorry for children who's Parents don't interact with them and teach them. Too many parents want the schools to do everything for them, yet it is what they do outside of school which has the greatest impact to what they learn.

          We are lucky, we don't say "Damn, I wasn't that dumb when I was that age!" instead my wife and I both go "Damn, he is smart, smarter than either of us at that age." and as long as we keep constantly feed him new ideas and information and reinforce it he will continue to be smarter than we were or are.

          Again, just for the soapbox, the fact that children on average are getting "dumber" is completely the fault of their Parents.

          • by camperdave (969942) on Wednesday October 23, 2013 @11:18AM (#45212649) Journal
            Sadly, it's becoming well nigh impossible to find a decent chemistry set, electronics kit, meccano set, or even a generic Lego set. Everything is either excessively "safened" or themed to the point of monotony.
            • Well, we don't have those now (but they were already watered down - literaly, in the case of the chemistry set - by my time, are you sure you are not romanticizing it?), but now we have PCs, arduinos (or Pis if you need something faster), and 3D printers.

              Yeah, they are not the same thing, but I guess that's exactly the point.

            • by blueg3 (192743)

              People keep saying this.

              Amazon sells large boxes of generic Legos. It also sells the same electronics and chemistry kits I played with as a kid. Beyond that, it also sells actual lab equipment, chemical reagents, breadboards, soldering kits, and electronic components.

  • what exactly is the difference?
  • by Anonymous Coward on Wednesday October 23, 2013 @09:09AM (#45211371)

    From the outside, the universe looks like a photograph.

    I hope we're hanging on a nice wall.

  • For example, when I am hard at work, and my wife thinks I am goofing off...

  • is better than Out Of Time.
  • by Covalent (1001277) on Wednesday October 23, 2013 @09:24AM (#45211493)
    I read this essentially as saying that without an observer, time does not exist. Essentially, a "god-like" observer does not observe any change unless he or she becomes entangled in the universe he or she is observing. That universe, therefore, is without change, and therefore timeless. However, observers that are entangled within the universe (as we are), observe change and thus the universe (to them) has time.

    This sounds a fair bit like some of the effects of relativity (on the train the shots appear simultaneous...on the ground they do not).

    What is most intriguing to me, though, is that if the universe is both timeless (from the outside) and has time (from the inside), is it possible for us to gain the outside perspective (or any information about that timeless perspective). This shouldn't necessarily be impossible - we would need to not become entangled in the thing we are trying to observe (which we can easily do). Perhaps observing the surrounding universe would give unentangled information about the experiment in question, and thus give us a glimpse of the future?
    • by MozeeToby (1163751) on Wednesday October 23, 2013 @10:25AM (#45212069)

      Just keep in mind that an 'observer' does not mean a conscious entity. An observer, in the quantum mechanical sense, is more accurately an "interactor", as in anything that interacts with it. Which, when put into those terms, their thought process in this paper is much clearer: without interaction there is no way to determine if time has passed, if there's no way to tell if time is passing... it may as well not be.

  • i wonder.. (Score:3, Interesting)

    by Connie_Lingus (317691) on Wednesday October 23, 2013 @09:32AM (#45211549) Homepage

    ...how this is related to the fact that the speed of light is the only true (known) constant in the universe.

    for example...you are on a train going 50 km/hr north...you throw a ball 30 km/hr north and the ball is now going 30 km/hr north relative to you and 80 km/hr to a stationary observer...standard stuff.

    BUT...you are on a light beam going 0.5c (half the speed of light) with a flashlight in your hand...you turn on the light...how fast is that light coming out of your flashlight going relative to you and our stationary observer?

    well...relative to you its going...the speed of light...to the observer?

    this is where it all gets weird...to the observer its going..the speed of light!

    how can this be, slashdotters?

    • Re:i wonder.. (Score:5, Informative)

      by thrich81 (1357561) on Wednesday October 23, 2013 @10:27AM (#45212091)

      There are other physical constants, too. The charge of the electron for one and Plank's constant for another. The reality of a 'physical constant' is that it is just a ratio of one measured quantity in the observed Universe to another measured quantity that is always the same, so is sort of a conversion factor between physical observables which are somehow tightly related (not a great explanation, I know).
        As for your light from the flashlight story -- there is no easy explanation because the easy explanations all depend on things behaving as we have grown up observing and internally modeling them in our low energy, slow speed existence. The explanation is just that at high relative speeds between observers the measurements of time and distance mix into each other such that each observer will always observe a light beam (in a vacuum) to be at 1.0c no matter what the speed of its source. A slightly deeper explanation is that time and 3 dimensional space form a four dimensional manifold (fancy name for something which local coordinates can be mapped to a flat space) in which the mix of time and space dimensions depends on the motion of the observer (actually reference frame of the observer). Relativistic effects are beyond the classical existence we model in heads growing up and so require math to take us beyond intuitive notions, that's about all I've got on the issue.

    • Re:i wonder.. (Score:5, Interesting)

      by tonywestonuk (261622) on Wednesday October 23, 2013 @10:38AM (#45212209)

      Speed is Distance / Time.

      Your watch measures time, so you can use it to calculate how fast the light comes out of your torch by timing how long it takes to travel a distance, and you have a meter stick to measure just that.

      When you are traveling fast, your watch slows down, and your meter rule gets shorter. However you don't notice this, as your own internal body's clock slows, and you yourself gets shorter in exactly the same proportions. But, when you measure the speed of light, coming out of the torch, now with your slower watch, and shorter meter stick, everything just adds up and you calculate the light to be traveling at the speed of light, EVEN THOUGH, the light, relative to you is now traveling just .5c.

      The person you have just passed sees your watch, and meter rule, and thinks you've made a mistake, because your rule is longer and your watch ticks slower. He sees you measuring the speed of light coming from your torch. To him, he sees the light is coming out of your torch at .5c, but can see you (inaccurately) measuring it....and working it out to be 1c because you've measured it over a shorter distance using a slower watch.

      When he measures the speed of the light coming out of your torch passing him, he also works it out to be going at light speed.

      So there you go. There is no paradox. Light is going at the same speed regardless of if you are moving or not. The only difference is that your movement causes things like slowdown of time, and length change, which means that you are unable to calculate the "proper" relative speed of light, which would be .5c.......any attempt at measuring it, always comes out at 1c.

      OR.....the more usual way of putting it is just make the speed of light constant, regardless of your speed, and alter the other things such as time, and length, to make your speed calculations always come to 1c.

    • Re:i wonder.. (Score:4, Informative)

      by wonkey_monkey (2592601) on Wednesday October 23, 2013 @11:05AM (#45212507) Homepage

      how can this be, slashdotters?

      It just is. Best not to think about it.

      (the following has turned into far more of a ramble than I first expected. I hope at least some of it makes sense)

      But, if you must, it helps me to remember that the only absolute is spacetime. How you divide that up into space and time is dependent on your path through it.

      If you were asked to divide a field into a coordinate grid, you might choose an arbitrary direction and then divide it up left-right and forward-backward from there. Someone else might face a different a direction and do the same thing - a different grid, but also a perfectly valid way to divide up the field.

      So it is, sort of, with spacetime. But we don't choose our direction - instead it depends on our motion. If you're moving relative to another person, a bit of what they'd call space overlaps with a bit of what you'd call time, just as in the field where a bit of what they might call left-right overlaps with what you call forward-backward. There's a negative sign in the equations somewhere that puts the brakes on things though, and means you can't accelerate to the speed of light relative to anyone else without expending an infinite amount of energy. In Greg Egan's Clockwork Rocket series, the negative sign acts is switched with a positive one, so it's more like the easy-to-imagine field, and by accelerating one can completely swap what your home-bound friend would call time for a spatial dimension. Once they have accelerated enough, the travelling explorers can continue to experience time while none at all passes on their home planet. I think the implication is that by accelerating yet further, one could easily travel back in time. In fact, the danger in the story is from objects - quite possibly another otherwise perfectly ordinary solar system - travelling at right angles to the protagonist's home system - effectively at infinite speed.

      The next brain-melting thing to consider is that, perhaps, everything moves at the speed of light - not through space, but through spacetime. But because most of the stuff we're familiar with - the Earth, the stars, etc - shares roughly the same path through spacetime, we don't experience it like that. All of our speed is taken up with travel into the future. We could swap a bit of it for travel through space if we accelerate. Without relativity, you could expect to travel for ten years there-and-back-again and find that ten years have passed at home. If you consider the simple field "swap" situation, you might conclude that by swapping some of your travel through time for travel through space, you'd find yourself less far into the future when you got back. But then that niggly negative sign comes into play - it makes me think of time as sort of 1/space - which means you actually find yourself more far into the future when you get back. Hence the twin paradox, where you find your Earth-bound friends have aged more than you have.

      In the case of the photon, which uses up all of it's speed travelling through space, no time ever passes for it.

      Any questions? No? Good. I'm off to catch up on the few hours of sleep I missed last night. Does it show?

  • Here's a perfectly stupid question that probably does a good job of highlighting how little I know about this topic: So they are saying time is an emergent property that occurs when only one particle out of a entangled pair is observed. Does this mean that all objects in our universe must therefore be composed of particles that are somehow entangled with other particles located elsewhere (since all of the objects that we observe appear to be subject to time)? Even when we perform measurements at a particl

  • by rgbatduke (1231380) <rgb AT phy DOT duke DOT edu> on Wednesday October 23, 2013 @10:49AM (#45212305) Homepage

    Most of this has been known and stated fairly clearly in the quantum theory of open systems for some time now. The Nakajima-Zwanzig (generalized master) Equation is derived based on the assumption of a "universal" quantum description that is partitioned into "system" and "everything else", with a projection of all dynamics from everything else onto the system variables. The universe is, of course, completely deterministic, but entropy (and hence "time" as an arrow) enters the system from the incomplete information available on the system "bath", everything else.

    The proper treatment of this completely eliminates the common quantum "paradoxes" such as Schrodinger's Cat because one can clearly see where one makes an incorrect assumption about the possibility of quantum entanglement of the cat and the microscopic decay process independent of "everything else". The entire "system" consisting of cat and box is coupled to the rest of the Universe and the apparently "purely random" decay that creates the supposedly tangled state that is resolved by opening the box is continuously resolved because the box and all of its contents is already tangled, so to speak, with everything else. It also helps to properly view and include time-reversibility in the description and not treat the quantum process of measurement non-relativistically and semi-classically. The same thing is true of the EPR paradox -- if it is treated relativistically there can obviously be no such thing as wavefunction collapse per se with some sort of transluminal communication of phase information, because the time reversal of this process makes no sense at all. The GME resolves this entirely because it correctly describes the infusion of classical entropy in a measurement process from the bath in an e.g. thermodynamic state within e.g. the random phase approximation.

    Personally, I think the Nakajima-Zwanzig treatment and master equations are one of the most neglected areas of quantum theory, often completely untaught in graduate-level quantum series. It is one of the better ways to rigorously derive things like spontaneous emission and in the process explain a lot of things about the process that are otherwise mysterious, such as how "exponential decay" arises from the coupling of a two-level quantum emitter to a multimode bath (and how it does NOT occur if one, for example, couples a two-level quantum emitter to a single field mode). Loudon has a nice discussion of this point, and Agarwal describes the application of the GME to spontaneous emission including radiative shift. The outcome of this approach in quantum mechanics is often to transform exponential processes that typically move one out of the basis one begins in almost instantly (entanglement) to projective dynamics within the basis and with e.g. discrete dynamical transitions replacing cats that are half dead or half alive in an entangled state, a Langevin approach where the actual system really does either kill the cat or doesn't, at a particular time, with the correct probability distribution for an ensemble of diabolical cat-killing engines, because the rest of the Universe always functions as a "measuring apparatus" -- one cannot "disentangle" the cat, the poison, the radioactive source from the Universe by merely putting it in a box, and at the instant of the cat's death the future time evolution of the entire Universe is unique to this and only this outcome.

    You can see some small part of the malaise that infects the terminology of quantum theory in the phrase above: "An external god-like observer sees no difference" -- the hardest single thing one has to deal with when correctly considering the quantum description of the Universe is the notion that there is no outside, most especially no outside from which the inside can be "seen". Seeing is the exchange of information, mediated by a field interaction. The Universe cannot possibly be "seen from the outside" because if the "outside" in question can see it at all, it is a part of it. It cannot

    • " The universe is, of course, completely deterministic, but entropy (and hence "time" as an arrow) enters the system from the incomplete information available on the system "bath", everything else."

      Saying that the universe is "completely deterministic" is rather disingenuous, considering the fairly huge amount of evidence to the contrary.

      "The proper treatment of this completely eliminates the common quantum "paradoxes" such as Schrodinger's Cat because one can clearly see where one makes an incorrect assumption about the possibility of quantum entanglement of the cat and the microscopic decay process independent of "everything else". The entire "system" consisting of cat and box is coupled to the rest of the Universe and the apparently "purely random" decay that creates the supposedly tangled state that is resolved by opening the box is continuously resolved because the box and all of its contents is already tangled, so to speak, with everything else."

      You take the Schrodinger's Cat "paradox" far to literally. Old Ernst intended it as a thought experiment, not a real one. And in that experiment, the contents of the box were presumed to be "disconnected" from the rest of the universe... any form of entanglement whatsoever. Your argument relies on re-defining the whole problem to fit your explanation. (Readers should

      • by adonoman (624929)
        Out of genuine curiosity, can you point me to evidence showing the universe is non-deterministic? I'm not sure how one would go about making that kind of observation.
  • by Empiric (675968) on Wednesday October 23, 2013 @10:55AM (#45212385) Homepage
    Jesus said: If they say to you: Whence have you come?, say to them: We have come from the light, the place where the light came into being of itself. It [established itself], and it revealed itself in their image. If they say to you: Who are you?, say: We are his sons, and we are the elect of the living Father. If they ask you: What is the sign of your Father in you?, say to them: It is movement and rest.

    --Thomas

    Sometimes, this is almost too easy.
  • by MobyDisk (75490) on Wednesday October 23, 2013 @11:07AM (#45212531) Homepage

    If a tree falls in the forest and no one observes it, how long did it take to fall?

  • by Galaga88 (148206) on Wednesday October 23, 2013 @11:14AM (#45212609)

    The problem is that they keep formulating and performing these measurements where the scientists work.

    Everybody knows time doesn't pass at work. If they'd re-run the experiment under a rainbow or with a beautiful woman they'd find that time passes far too quickly in fact.

  • by technomom (444378) on Wednesday October 23, 2013 @12:08PM (#45213219)

    Step 1. Become Godlike ....

  • by WaffleMonster (969671) on Wednesday October 23, 2013 @01:47PM (#45214417)

    In this case, the observer cannot detect any difference between the photons without becoming entangled with one or the other. And if there is no difference, the system appears static. In other words, time does not emerge.

    This is the kind of in your face bullshit I have come to expect from a certain crowd of attention whores who regularly abuse terms like phase velocity and negative absolute temperatures to attract undue attention to their Sci-Fi ish ramblings which in reality are quite mundane.

    Why yes dude you can't make a measurement without effecting what is being measured... newsflash from a century ago.

    Since you can't measure something without changing it... you make the following jaw dropping assumption "And if there is no difference" to get to your assumption..

    "the system appears static. In other words, time does not emerge."

    "In other words" if you ASSume there is no difference time does not emerge.

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