First Experimental Evidence That Time Is an Emergent Quantum Phenomenon

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."

Comments

Hmm

[wenchmagnet]

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

[Cryacin]

You see, the story had not yet been entangled, so to the outside observer, there was no change.

Re:Hmm

[msauve]

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

Re:Hmm

[hodet]

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.

Re:Hmm

[cold fjord]

Dude, most people here have big enough egos as it is without referring to them as "god like," even if you do it indirectly.

Re:Hmm

[Andrewkov]

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

Re:Hmm

[pscottdv]

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

[pz]

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

[Remus Shepherd]

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:Hmm

[taiwanjohn]

I can appreciate the "get off my lawn" sentiment as much as the next guy, but honestly I don't feel the /. experience has degraded that much since the old days. Is it different now from when I joined 15 years ago? Yeah, sure. But so am I. So's the world.... So what?

The thing I find consistent about /. and which keeps me coming back here is that I know I'll (almost) always find something interesting here, often something very interesting and/or enlightening. Sure, I may occasionally bitch and moan about the dupes and the mods, etc., but when I see a story that looks interesting and has a "healthy" discussion going, I'm pretty confident that reading that discussion will give me some new insights or information that I hadn't heard of before. Offhand, I can't think of many other "popular" websites I could say the same about.

First Post!

[Fieryphoenix]

But only from the point of view of an external god-like observer.

Re:First Post!

[TopherC]

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."

Instead of likening things to rocket science

[sandytaru]

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.

Re:Instead of likening things to rocket science

[MadRocketScientist]

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...

Re:Instead of likening things to rocket science

[Amouth]

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.

Re:Time

[Cryacin]

At least this time they're not pointing loaded guns at cats.

Re:god-like vs. measuring observer

[lxs]

A god-like observer can observe without interacting. Back in reality every observation is an interaction.

Re:Time

[DeathToBill]

Time is an illusion. Lunch time doubly so.

Re:I think...

[LateArthurDent]

After reading a lot on this is that sometimes an issue becomes a problem without reason.

Now, time is ONLY a man made measure - a measure between events. Nature/the universe doesn't know what time is nor cares about it. It is only us humans that need to try to explain time dilation and various other 'time issues' to make the maths work. Remove time, and I bet it will balance these equations.

Time cannot run backwards,as there is no such thing as time except in the human brain and the human concept of measuring changes.

Nature doesn't care about time? Tell that to the laws of thermodynamics. Entropy only goes one way.

If you watch a video of a ball rolling on a desk, you can't tell just by the video whether time has been reversed. The physics governing that motion don't care about time. If you watch a video of an egg being shattered, you'll know when the video is reversed. You know all the contents of the egg can't spontaneously get back together as time moves forward. That would be going to a much more well-ordered state.

Also, the GPS device you use to triangulate your position and navigate to your destination? Well, consider that relativity tells us that the satellites zooming up above us have slower ticking clocks. They're actually moving through time slower than you are, and our current GPS accuracy wouldn't be achievable if we didn't take that into account.

Re:Time is dependent on observation?

[MozeeToby]

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.

Find a new measuring place

[Galaga88]

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.

Re:Time

[RMingin]

"Time, we know, is relative. You can travel light years through the stars and back, and if you do it at the speed of light then, when you return, you may have aged mere seconds while your twin brother or sister will have aged twenty, thirty, forty or however many years it is, depending on how far you traveled. This will come to you as a profound shock, particularly if you didn't know you had a twin brother or sister."