First Experimental Evidence That Time Is an Emergent Quantum Phenomenon 530
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."
Instead of likening things to rocket science (Score:5, Interesting)
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.
What I got from the article: (Score:4, Interesting)
From the outside, the universe looks like a photograph.
I hope we're hanging on a nice wall.
Time is dependent on observation? (Score:4, Interesting)
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?
Re:god-like vs. measuring observer (Score:5, Interesting)
A god-like observer can observe without interacting. Back in reality every observation is an interaction.
i wonder.. (Score:3, Interesting)
...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:Time is dependent on observation? (Score:2, Interesting)
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.
It's even sillier than that. From TF Abstract:
We implement this mechanism using an entangled state of the polarization of two photons, one of which is used as a clock to gauge the evolution of the second: an "internal" observer that becomes correlated with the clock photon sees the other system evolve, while an "external" observer that only observes global properties of the two photons can prove it is static.
So, surprise, an outside observer who can only access invariant quantities of the 'toy universe; (so that the interaction is 'non-entangling', meaning it's not breaking the existing entanglement[*]) will observe ... invariant quantities. Well, I'll be damned! It's the chicken that emerged from an egg that emerged from a chicken! Emergence ahoy!
[*'Nevermind the question of how that 'go-like' outside-the-universe observer interacts with the Universe.
The thing is, not everything that's been pushed into arxiv is publishable quality (hence their attempt with the endorsing system). Wake me up if this toy thing gets peer-review approval for publishing. If it ever does, I'll write a competing article stating that time emerges from symmetry breaking and sidestep this whole fancy-pants 'entanglement' label (should have a better shot at being published imho)
So... Parmenides was right after all? (Score:2, Interesting)
This sounds a lot like what he was saying 2500 years ago.
From Wikipedia:
In "the way of truth" (a part of the poem), he explains how reality (coined as "what-is") is one, change is impossible, and existence is timeless, uniform, necessary, and unchanging. In "the way of opinion," he explains the world of appearances, in which one's sensory faculties lead to conceptions which are false and deceitful.
Re:i wonder.. (Score:5, Interesting)
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.
Generalized Master Equation... (Score:5, Interesting)
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
Candidate for "god-like observer" (Score:3, Interesting)
--Thomas
Sometimes, this is almost too easy.
Re:god-like vs. measuring observer (Score:4, Interesting)
A god-like observer can observe without interacting. Back in reality every observation is an interaction.
OK ... then what the heck is scientific about speculating about something that by definition either doesn't exist or can't practically participate in the experiment?
Are you kidding? Godlike observation - to observe things exactly as they are without interfering in the outcome - is the goal of all science.
Re:Hmm (Score:5, Interesting)
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.
Re:Hmm (Score:5, Interesting)
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.
Re:Instead of likening things to rocket science (Score:4, Interesting)
And don't forget the joy of pouring over the counter muriatic acid on aluminum foil, how easy it is to make a surprisingly potent explosive out of over the counter batteries and hydrogen peroxide, how much one can learn about orbital and collision dynamics playing Angry Birds Space, and the fact that kids now have nearly instant access to all of human thought and knowledge not actively covered by copyright (and summarized access to much of that!).
What they lose from not building a crystal radio or tinkering with cars (that have grown so complex that they are sadly no longer particularly tinkerable) they gain building a functional social network and tinkering with electronic devices that were pure science fiction for the first half of my life. To the extent that complexity of environment stimulates growth of intelligence as a possible partial explanation of the Flynn effect (and more, there are other metrics) children today grow up in very complex environments and do different things within it than we did.
It is thus silly to judge one generation in terms of the metrics of a previous one, especially a previous one that grew up in an entirely different political/historical context. Most of us would truly suck at stalking a deer armed only with a bow we made ourselves using nothing but a stone knife and arrows tipped with arrowheads we chipped out of river rocks. Most of us would simply die if we were dumped into the wild to survive a winter. We are therefore idiots by the standards of, say, 12,000 years ago. I suspect most of us would struggle with political dynamics from the feudal era and would rapidly find ourselves enslaved or hung if dropped into the world 1000 years ago. My own kids don't appreciate the stresses associated with growing up in the middle of a cold war that meant that every day there was a finite chance of the world of the survivors of a nuclear exchange regressing 1000 years overnight. I struggle to appreciate the stresses THEY experience growing up in a world that increasingly concentrates power in a hidden class of elites that have turned government into theater and that manipulate world-spanning conflicts between insane mythologies or hypothesized world-spanning disasters into excuses for concentrating ever more wealth and power in the hands of a criminal class that grew rich on laundered money in my lifetime.
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