Entanglement lets the measurement of one particle
instantaneously determine the state of a partner
particle, no matter how far away it may be — even
on the other side of the Milky Way.
If I have a bag of coins, and I take out all of the copper coins, it's not very mysterious that the bag now contains only silver coins, no matter whether I hide it under my bed, or in the freezer, or hang it out the window.
Yes, all the copper coins are now absent from the bag, forcing it into an all silver state, and I can know this, without even looking at the bag. I take the bag, and I drive it across town. I hide it under a rock. I go home. I think about the bag under the rock. I can instantaneously know that the bag contains only silver coins, even though it's across town, hidden under a rock. Instantaneous. I determine the state of the bag. With my mind. Just by thinking. Even across town. So amazing.
Why do journalists and scientists so deeply covet the seeming appearance of the arcane?
So the real problem isn't that "when one is up, then the other will magically be up too." That could be accomplished with local hidden variables (e.g. shared seeds on a PRNG, or your examples).
The real problem is that when you measure A in the "up" direction, and then B in the "10 degrees east of up" direction, then B seems to know that you measured A in the "up" direction.
That is to say: B's probability distribution as a function of the direction its being measured is correlated to the direction that A is measured. There's no way to construct an "A-independent" probability distribution of B's results for arbitrary directions. The probabilities won't sum to 1 and still match experimental results.
It's unfortunate that "A up" therefore "B up" is a degenerate case of this reality where classicality actually works, because it leads to confusion.
(Also the reason you can't use this magic to communicate FTL is that you can only ask one yes/no question of each particle, and because B's probability distribution is distorted in a symmetric way based upon A's measurement, you're still going to get a 50/50 response for yes/no questions asked of random entangled particles)
Feel free to comment, as I paste this on every misunderstanding of Bell's Theorem here, and I edit to make more clear each time.
The key difference between a bag of coins and a microscopic quantum system is that the contents of the bag before being observed is unknown, whereas the quantum state is actually indeterminate. By observing one entangled particle, you force the other to also take on a definite state. Read up on Bell's inequality for the experimental justification of this idea.
By observing one entangled particle, you force the
other to also take on a definite state.
Not knowing which placement has been done, you put one bag in your freezer, and drive across town with the other bag.
Then you ask yourself the question, or perform an experiment to tell you, "Which bag did the cat put all the coins in?", at which point you open the bag and find it full of coins or empty, determining the state of the bag you have, and the state of the bag in your freezer at home.
No problem, huh?
Except, if you'd asked a different question, or performed a different experiment, to tell you "Which bag contains all the copper coins, and which contains the silver coins?" - you would have still got a valid response, and found the bag either full of copper or silver coins, again determining the state of the other bag at home.
That's the nature of entanglement. Without knowing the state, the nature of the question you ask of one particle will determine what sort of answer you get, in a way that instantaneously affects the bag at home too. i.e. someone opening your freezer just after you ask your question will see the other bag in a consistent state with the bag you have.
That's why it's so gorram weird.
http://physics.stackexchange.com/questions/3158/why-is-quant...
http://physics.stackexchange.com/questions/126622/quantum-en...
Either you believe the state exists but is unknown, and
cannot be known until measured,
or, you believe that you know the state does not exist,
and materializes upon measurement.
If you're satisfied that their might be multiple past states which could all produce the same result, determining the current state, then you can safely ignore these semantic debates, about whether there is a concrete-but-unknown value, or whether the present value remains uninitialized and undefined.
https://www.youtube.com/watch?v=PSYXt3Xu3xI
I'm not a physicist, but he seems to be invoking similar ideas to Raamsdonk: that spacetime and gravity are emergent properties that boil down to entanglement somehow. But the loop quantum gravity people have been saying something like that for ages. And Stephen Wolfram and Konrad Zuse etc. And we have people like Lubos Motl on the other hand to ridicule all of the above.
Anyone able to give a big picture overview of what's been happening the last few years in this somewhat rarefied world? Who are we, the intelligent lay public, to trust?
The most interesting (to me, at any rate) bit of this article are susskind's observations on computational complexity. As a precocious undergrad I put forward the idea that gravity and time dilation were the same thing, and both stemmed from the universe needing a constant amount of "time" to compute the interrelations between the particles in a volume of space - and if there were more particles more time would be needed as the graph of particle interactions would grow non-linearly - and therefore time "slows down" in a matter (information) dense area of spacetime.
What really got me gunned down was then going on to argue that this suggested a simulated universe, running in a substrate.
Either way, interesting to see someone else who actually has some clout having similar ideas.
To me, the language here is important. Both simulation and computation imply (to me) a tool and a user of the tool. Even a broader interpretation of computation as, umm, the efficient transfer of precise information through spacetime in certain shapes (which is easily providable by our understanding of physics today) requires an observer to extract the computation from the otherwise non-semantic system.
It definitely makes sense to think of the universe as a projection of a higher dimension, or a holograph, or however you want to look at it, but that's a far cry from implying a simulation.
EDIT: hologram -> holograph
I wonder if the trick about this is not really to find a true explanation but the right perspective and more and more simulation seems to be a very valuable perspective to put on this.
Disclaimer — I am not a physicist so apologies if my question is stupid.
Anyway, the part that I know, and which is well established, is that there seems to be a correspondence between a d+1 dimensional quantum gravity theories, and d dimensional quantum field theories (e.g the standard model). A while ago this was still purely conjecture, but Maldacena showed that this correspondence was true (under certain conditions) for an AdS space with a conformal field theory on its boundary. As far as I know this is now pretty well established, most of the discussion seems to be on how much it can be generalized.
From my (limited) understanding it seems that (in AdS/CFT) entangled particles tend to correspond to strings traversing from one part of the boundary, through the bulk, to another part of the boundary, the space the string travels through then forms a tube like object. This gives a link between entanglement and geometry, since these tubes exist if and only if the two points on the boundary are connected.
I think it isn't disputed that this happens for AdS/CFT, but whether something similar is true for our universe is debatable. If however it turns out that the holographic principle does hold in general then that would imply that our universe somehow corresponds to a 2+1 dimensional field theory, where entanglement of this field theory is responsible for the fact that our space-time is connected.
[1] https://scholar.google.no/scholar?cluster=132568844183140142...
Can anyone explain to me why it can't simply be a force? If you accept that gravity is caused by energy and not mass (which is obviously the case), then I see no reason a photon can not experience a force.
So what is the reason to insist it's geometry?
And related to that, I still have never seen an explanation of how geometry is supposed to cause something to start moving without a force. Explaining how it deflects something, I get. How does it start moving in the first place?
The only explanation I've gotten is that things are always moving - through time, and the geometry just transfers some of that motion into physical motion. But that explanation is very very very lacking since all things do not move through time at the same rate (because of the various types of time dilation that are possible), yet the gravitational force is identical.
The crucial concept is Newton's first law (objects continue on their trajectory if a force is not applied). The straight lines in the 4D spacetime (geodesics) - the lines that an object would follow if no force is applied - correspond to the paths that look as if a gravitational force is applied.
- The surface of the earth is a 2 dimensional positive curved space. To see this, draw a triangle with corners on the north pole, on the equator near Somalia and on the equator in Equador. The resulting triangle has a sum of all corners > 180 degrees.
- In a negative curved space, the sum would be less than 180 degrees. In a flat space, it is equal to 180 degrees.
- Another way to see the curvature of the surface of the earth is to observe that it's impossible to draw 2 parallel lines that do not intersect.
- The 2D torus (e.q. the surface of a donut) is flat. Test it with triangles.
- The towers of the Verrazano–Narrows Bridge are wider at their top than at their base. This has nothing to do with the earth have a positive curvature. Test it with a torus.
- 3D space is nearly always flat in the universe, especially at the surface of our planet.
- 4D space-time is not remotely flat. If I throw up a ball, it will come down. This is due the mass of the earth curving its surrounding 4D space-time. The straight line for a ball in the curved space-time looks like the ball changes directions and comes down in our flat 3D space.
- If you try to find the triangle of a sphere with the biggest sum of corners, you'll discover that the outside and inside of a triangle are interchangeable. We've entered the field of topology now and this has nothing to do with its curvature.
This is the crucial point that many discussions overlook. The concept of "curvature of space" is obvious nonsense because curvature is measured with respect to space. For space itself to curve implies the existence of meta-space (and as many nested metaspaces as you like). But "spacetime" does not work like "space", and there actually is no metaspace. Talking about "space" curving or expanding is unnecessarily confusing.
It could be a force - if someone finds a theory that describes all the observational data. They haven't.
The reason to insist geometry is that general relativity manages to predict extremely accurately the result of all gravitational experiments/observations as of 2015. In science, prediction comes before explanation, meaning if you have to accept whatever explanation the best predictive theory offers and not vice versa.
Well, its has been explained - you just haven't gone through the right books. There are two answers, which I will simplify. One, the Big Bang threw everything all over the place and now masses are moving so as to reach the state of minimum energy. Two, there are 3 other forces in the universe which can cause masses to move. For example you can use electromagnetic forces during the combustion of rocket fuel to send a satellite in space. The satellite then moves in orbit because of the geometry of spacetime. Same when stars explode - this involves all three forces.
I'm going to be a little picky about your choice of language here.
It seems to me that, at least that your are predicting randomly, you can't possible make predictions with a good model, that is, a good explanation.
In other words, there's no such thing as "spooky action at a distance", because with particles joined by a wormhole there is no distance between them?
Remember the correspondence principle will still be in play; future quantum theories will still have to limit out to what we know today, because the QM of today is arguably the most rigorously tested theory in humanity's history, by number of significant digits. FTL communication still will have all of the problems conventional relativity says it will, for all the same reasons.
Entanglement has suggested for a long time that there may (in clumsy English words) be some sort of "real reality" that isn't necessarily constrained by what we think of as space and time. In fact even relativity looked at in a certain manner has suggested this; you can travel from any point in the universe to any other, barring black holes, along null spacetime intervals. Null spacetime intervals have no distinction between the points in them, because they all come out the same 0 in the metric measurement. I wouldn't expect that any of this new math is going to change anything; it may explain where the constraints of space and time come from, but explaining the constraints doesn't mean that the explanation will come with a way to get around them!
In fact my personal observation is that the fundamental limits of space and time have been getting stronger as we learn more about physics, not weaker; a mathematically rigorous derivation of the fundamental speed-of-light limit from a "more fundamental" level of reality locks the door even tighter, it doesn't open it.
No. No! No!!! This meme has really got to die. A measurement of one entangled particle does NOTHING to the other particle. Its state is exactly the same as it was before. In fact, the whole concept of "before" and "after" a remote measurement doesn't even make sense because it depends on your frame of reference!
And I didn't say the state of the particle was already determined. It wasn't. Yes, of course superpositions are real. Yes, of course the Bell inequalities are violated. Yes, this eliminates all local hidden variables theories. Yes, it seems like this necessarily leads to the conclusion that there is spooky action at a distance. But that's wrong. To see why, read the paper or watch the video.
The correct story is that measurement and entanglement are the same physical phenomenon. The creation of an EPR pair is the first step in any measurement process. The correlations in EPR measurements derive from exactly the same physical process as the correlations in "ordinary" measurements (I put "ordinary" in scare quotes because, as I said, even "ordinary" measurements start with the creation of an EPR pair). When you "measure" the two halves of an EPR pair what you are really doing is performing two measurements on whatever system produced the EPR pair to begin with. When you look at it that way it is not at all surprising that the measurements should be correlated.
For more details see:
Yeah, it does, amongst other things. Unfortunately in that context two of its meanings (to discover & to decide) could have been appicable.
There are two unifications that need to happen. One is the unification of the strong force with electro-weak force(the unified version of electromagnatic force and weak force). The other is gravity with the unification of the three forces.
As far as I understand, this work is concentrating on the second unification, and not the same. Though it might open the door for the first one too. Someone closer to this area should comment.
Rotation of Earth around Sun is just a process, there is no time in it apart from the mind of an external observer. Similarly with any so called "atomic clocks" or any other physical process, including so called expansion of the Universe.
Time, of course, could be derived as a concept from an observable change (a process) by mind, but this does not imply its physical existence, like it is with what we call physical forces.
Space is more subtle, but it is also require an observer and at least two particles related via this or that set of forces.
Two random Photons share nothing, and without an observer there is neither space nor time among them.
Mathematics does not imply existence of described abstraction.
Western philosophy, so far, succeed in separating these concepts as being a priory which is perfectly reasonable, considering that any sensory input which is subsequently used to train and condition our mind is coming serialized by out sense organ, so, for a mind, which is a result of conditioning by the senses, the notion of succession is a priory. Conditioning by shared physical environment gives us cycles, so the notion of a cycle is also a priory. Succession days into nights in the environment and ageing of other people's bodies gives us notion of a continuous change. But change is not time.
Eastern philosophy (and modern cognitive neuroscience) would suggest that this a priory is related to our minds, not to photons or forces. So?