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."
Re:Hmm (Score:5, Informative)
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:i wonder.. (Score:1, Informative)
Uhm, the speed of light isn't at all constant, no more than the speed of sound is. The speed of light changes depending on the medium it is in, just like everything else.
how can this be, slashdotters?
Because you utterly fail to understand what you're talking about. This behavior is also no different than sound. They behave identically.
If you turn on the flashlight while traveling at 0.5C the light would travel away from you at 1C anyway, making a difference of 0.5c and causing all sorts of blue shift. You (as are most people with a poor grasp of these physics because of some shitty analogy someone used to explain it to them) are making the common mistake that the person with the flashlight in hand would think the light is traveling at 1c away from him (total of 1.5c) but they wouldn't see any such thing.
And then there is time dilation, which makes it all work out.
Re:I think... (Score:5, Informative)
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? (Score:5, Informative)
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.
Re:i wonder.. (Score:5, Informative)
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 think... (Score:4, Informative)
Re: i wonder.. (Score:4, Informative)
You (as are most people with a poor grasp of these physics because of some shitty analogy someone used to explain it to them) are making the common mistake that the person with the flashlight in hand would think the light is traveling at 1c away from him (total of 1.5c) but they wouldn't see any such thing.
Yes they would see it traveling away at 1c - but the velocities don't sum like that. Due to time dilation, you're also experiencing time at a different rate than a stationary observer. The net effect is that you both see the light traveling at 1c.
To extend the analogy, suppose both people also have a stopwatch which starts timing at the exact moment when the person who's moving at 0.5c fires a pulse of light in the same direction as his movement. After the observer's stopwatch has reached 1 second, freeze everything and see where everyone is. The person who's moving at 0.5c has moved half the distance light travels in 1 second, obviously; about 149 896 km. The pulse of light has moved twice as far, about 299 792 km.
To the outside observer, the light has traveled 299 792 km in 1 second, i.e. it is moving at 1c.
The moving person, saw it travel only half as far relative to him - only 149 896 km - yet, because he's experiencing time at a different rate, his stopwatch has only ticked off 0.5 seconds. So from his perspective, the light has traveled 149 896 km in only 0.5 seconds, i.e. it is moving at 1c.
Re:i wonder.. (Score:4, Informative)
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?