from the my-teacup-affects-your-galaxy dept.
Many physicists believe that entanglement is the essence of quantum weirdness — and some now suspect that it may also be the essence of space-time geometry.
A successful unification of quantum mechanics and gravity has eluded physicists for nearly a century. Quantum mechanics governs the world of the small — the weird realm in which an atom or particle can be in many places at the same time, and can simultaneously spin both clockwise and anticlockwise. Gravity governs the Universe at large — from the fall of an apple to the motion of planets, stars and galaxies — and is described by Albert Einstein's general theory of relativity, announced 100 years ago this month. The theory holds that gravity is geometry: particles are deflected when they pass near a massive object not because they feel a force, said Einstein, but because space and time around the object are curved.
Both theories have been abundantly verified through experiment, yet the realities they describe seem utterly incompatible. And from the editors' standpoint, Van Raamsdonk's approach to resolving this incompatibility was strange. All that's needed, he asserted, is 'entanglement': the phenomenon that many physicists believe to be the ultimate in quantum weirdness. 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.
(Score: 3, Insightful) by N3Roaster on Monday November 30 2015, @05:04AM
Note to self: don't read the comments under stories like this.
Typica - Free software for coffee roasting professionals. [typica.us]
(Score: 1, Funny) by Anonymous Coward on Monday November 30 2015, @06:38AM
I scrolled down out of curiosity and yes, it looks like more than a few people need to get back on their meds, pronto.
(Score: 2) by PartTimeZombie on Tuesday December 01 2015, @01:30AM
I don't agree, those comments are awesome. Some of them almost make sense.
I'm going back to look for references to the Time Cube.
(Score: 0) by Anonymous Coward on Monday November 30 2015, @07:54AM
Can we get a mathematician to try and break down the math, and a quantum physicist to try and break down the concept?
(Score: 4, Insightful) by sjames on Monday November 30 2015, @08:32AM
The 50,000 foot overview: If two segments of space share no quantum entanglements, they are separate spaces (universes).
(Score: 0) by Anonymous Coward on Tuesday December 01 2015, @01:47AM
I think about it like this, but not sure if it's a good enough approximation. Imagine if we take the "3D minus one spacial dimension to better relate" analogy often used to explain universe expansion. You know, the one with the ants as approximations of 2D beings on the surface of a balloon who can't tell they are on a balloon because photons only travel on the surface?
Entangled particles can be viewed has having a strait elastic lines from one point on the balloon to another (passing INSIDE the balloon). It's like those rubbery "strings" you find in underwear. Such lines between the myriad particles in objects also create what we call "gravity". They pull things together like lots of elastic bands between the particles of two (mutually attracting) objects, and we observe this as gravity.
However, the analogy perhaps breaks down somewhat for objects nearly on opposite sides of the balloon. There's not enough of an angle to translate the pulling into sliding across the balloon's surface. But such distances are perhaps so great that maybe we cannot measure the "problem" itself. From the ant's perspective, if he/she could measure gravity between distant objects, it would appear that gravity falls off unexpectedly with distance.
Hmmm, maybe this is why it looks like we have an expanding universe: distance objects are flying apart faster than expected due to the (apparent) expansion of the universe, which is really just angle-weakened gravity. Maybe I'm just over-stretching the analogy (pun intended).
(Score: 0) by Anonymous Coward on Monday November 30 2015, @09:57AM
You don't need just a quantum physicist (I am a quantum physicist, but all my knowledge about quantum entanglement doesn't really help me to understand much about the stuff described in the article). I guess a quantum field theorist could tell you more.
(Score: 2) by Justin Case on Monday November 30 2015, @10:51AM
OK so there's a similarity here: entangled particles affect each other at a distance, and gravity affects things at a distance, both with no apparent "medium" to carry the "message" from one to the other.
The entanglement message is said to be instantaneous (yeah I know it can't be used for FTL communication) but I've heard the theoretical speed of gravity is the speed of light. Why not also instantaneous? How do we know? I mean it would be hard to do an experiment. Since we don't even know what gravity is, much less have the ability to switch it off and on, we can't measure propagation time directly.
Thought experiment: if the sun was suddenly non-existent, you'd still see it in the sky for another 500 seconds or so (from memory) as the light continues to arrive. Would it take that same 500 seconds for the Earth to notice the end of the sun's gravity, and stop orbiting?
(Score: 2) by inertnet on Monday November 30 2015, @12:01PM
Just another layman here. I don't know about gravity, but I think that gravity 'should' travel at the speed of light. Because it would be a strange universe if the gravitational tug of galaxies would come from a different position than where we see them. Meaning if the tug comes from the current position instead of the past positions where those galaxies now appear to be.
TFA made me rethink properties of quantum particles. All objects in our 3D world have properties like position (coordinates), direction of movement, speed, mass, temperature and such. I know that quantum particles have other properties like spin, but the article made me wonder if they even have a position in 3D space, in the sense that our familiar objects do. I already believe that entangled particles don't have 'distance' to each other, they stay together as twins in their own realm even though in our 3D space they can be galaxies apart. At least that's how I try to get my head around these crazy, but fascinating ideas. TFA made that 'twin' idea even stronger for me.
(Score: 1, Informative) by Anonymous Coward on Monday November 30 2015, @01:34PM
There is no need for an entanglement message. You only need an instantaneous "transmission" if you try to describe the entangled state by an underlying essentially classical reality. Once you accept that quantum mechanics is not just the effective statistical description of an underlying classical reality, but is a fundamental theory in its own right that is not subject to the restrictions of classical physics, in particular the restriction that there's a fixed set of quantities which are well defined at any time and determine the results of observations of the system, the "spooky action at a distance" simply disappears, and you'll find that doing anything with one of the entangled particles does not in any way affect the other. Yes, you have correlations. But correlation does not imply causation. OK, but what about quantum teleportation? Well, there you do a measurement that involves the particle whose state is to be sent and one of the entangled particles, then send the measurement results to the other particle and use them to manipulate that other particle. Of course this implies an information transfer from one particle to the other; it's quite explicitly in the protocol. But it's certainly not spooky (you explicitly send it using a normal physical mechanism) and not faster than light (unless you've found some way to communicate FTL and use that for your teleportation scheme; but in that case the FTL is in that communication scheme, not in the entanglement).
(Score: 3, Informative) by stormwyrm on Monday November 30 2015, @02:32PM
Numquam ponenda est pluralitas sine necessitate.
(Score: 3, Interesting) by opinionated_science on Monday November 30 2015, @03:06PM
gravity is the deformation of space. This cannot happen faster than the speed of light (in a vacuum), which is what Einstein showed.
For an experiment to show this is true, read about the orbit of Mercury, and how it was finally explained.
The beauty of physics lies not in the equations that describe it. The beauty is the logic which when applied is so elegant to change ones world view...
(Score: 1) by dak664 on Monday November 30 2015, @05:36PM
The three dimensional speed has no physical meaning in special relativity, since it depends on each observer's rest frame. The proper concept is the space-time separation between events, which for the electromagnetic interaction is always zero. Maxwell's equations already showed this, with the spooky gauge invariance that mixed E and B fields and allowed using instantaneous or retarded potentials which point in different directions.
A zero event separation means there can be no in-between events, the the event is the "action" disappearing from spacetime A and appearing at spacetime B. The amplitude at B derived by summing over all possible paths of from A weighted by the distance and phase. We somehow perceive that as the action taking time to travel from A to B, the amount of time depending on our reference frame. But a person moving from A to B with velocity c would see that is is just one event.
Similarly for quantum machanics, where the generalized propagator (Green's function) is integrated along all paths to give the interaction probability. We now see that Maxwell's equations can be quantized into the mathematical entities called photons to become a simple example of quantum entanglement, and the gravitational "force" could be treated the same way, with analogous gauge invariant "gravitational induction" and fictitious gravitons.
I suggest all entanglement involves that zero event separation with fictitious particles mediating the interaction, and the only spooky part is how we perceive one event as two different ones.
(Score: 0) by Anonymous Coward on Tuesday December 01 2015, @09:02AM
That's a too strong statement. While speed indeed depends on the rest frame, the relative speed of two objects does not. That relative speed is related to the Minkowski equivalent to the angle between the four-velocity vectors. A space analogy would be that terms like "left" and "right" depend on the orientation of the observer (and thus are not meaningful concepts in space geometry), but that does not mean that the concept of direction is not physical; that concept is described by the angles between vectors, and that angle is the same in all orientations (while "left" and "right" depend on the orientThe proper concept is the space-time separation between events, which for the electromagnetic interaction is always zero.
Geometry is not only distance, but also angles. Especially important in the context of this article, which concerns conformal field theory: That's a case where only angles matter, while distances can be changed freely (apart from the sign, of course) through the conformal symmetry.
The electromagnetic potentials are mathematical tools that are helpful in describing the electromagnetic field (because they are more easy to handle mathematically). They are, however, not physical fields; the physical fields are the electric and magnetic fields, which are explicitly local.
Anyway, even the potentials are local in the Lorenz gauge. There's nothing in Maywell's equations forbidding you to fix the gauge to the Lorentz gauge. Note that to quantize the electromagnetic field, you have to do gauge fixing; however normally the gauge is fixed to Coulomb gauge, as that gives a much easier to handle mathematical description, at the cost of apparent(!) nonlocality (the "nonlocality" is of course only ion the potentials, not in the fields, and the actual observables are all perfectly local). Note that the locality/nonlocality I'm speaking of here is not to be confused with the entanglement-related nonlocality which is an inherent feature of quantum physics (and thus appears in every quantum theory, including quantum electrodynamics), but is completely unrelated to Maxwell's equations (which, I repeat, are perfectly local).
"Spooky gauge invariance" is about as spooky as the "superluminal speed" of a star that was many light years left from me, until I turned around so that suddenly it is many light years right of me. Of course the star's position did not change; my description of it did change. And similarly, the gauge transformation doesn't change the physical fields, it just describes the used description of those fields.
A zero event Minkowski distance does not mean anything like that; indeed, there are very clearly events between two different events with light-like separation (i.e. zero Minkowski distance). Note that the Minkowski metric is more properly named a pseudo metric, exactly because zero "distance" does not imply same place.
No, anything travelling with velocity c will not see anything.
(Score: 1) by khallow on Monday November 30 2015, @01:13PM
For field theories, a key aspect is that actual observable features of the field theory are actually operators over the fields with particular algebraic properties. He notes an observation over the class of space-times that comes from studying pairwise interactions (mathematically via "correlation functions" [wikipedia.org] with the operators applied in turn and integrated over the entire space) of certain operators with information about the underlying space-time (namely, there is a single location attached to the operator). Here, two such operators interact with the interaction proportional to some exponential decay function of the distance between the two operators. These interactions are the "entanglement". Two operators in different universes would have infinite distance and hence, zero interaction.
This can be worked in reverse. If you have a collection of operators which you know have the above spatial content and you happen to be able to calculate the pairwise correlation functions, then you can reconstruct the underlying space-time. First, you can calculate the length between operator objects (really, it may be doable by calculating for a single object which varies with space-time by doing the pairwise correlation function of the object with itself at different positions) by calculating the pairwise correlation functions and determining the length from that (once you've determined the decay exponent). It is a feature of space-time that knowing the distances between your points in space time is enough to determine the shape of the space time even in the absence of a coordinate system.
So I think the idea here is that if one starts with a quantum system with time, a class of operators that vary smoothly in the quantum space, and a pairwise correlation function calculation on those operators, then one can construct one (or more) space-times without having any explicit space-time representation present.
TL;DR: Starting from a peculiar entanglement relation that was derived from some toy physics models, this guy asks "what if we go the other way and start with the entanglement relations?" Then he shows we may be able to construct from that entanglement information one or more physics models which happen to result in the entanglement relations.
The practical application of this is both the stated intent of unifying quantum mechanics and general relativity, but also to describe general relativity's space-time as an emergent property of a quantum system with time which doesn't have explicit space-time. A side effect is that this may substantially increase the size of the can of worms that is the anthropomorphic principle. The construction may result in a large number of distinct space-times from which we have to choose the right one for us.
(Score: 0) by Anonymous Coward on Monday November 30 2015, @01:54PM
I believe you mean the anthropic principle. [wikipedia.org] An anthropomorphic [wikipedia.org] principle would probably imply animism. [wikipedia.org]
(Score: 1) by khallow on Monday November 30 2015, @07:33PM
(Score: 2) by buswolley on Monday November 30 2015, @06:22PM
I wish I had the knowledge to understand whether you just made things up very cleverly or actually know a thing or two. Bravo.
subicular junctures
(Score: 1) by khallow on Monday November 30 2015, @07:58PM
In April 2010, the journal sent him a rejection — with a referee’s report implying that Van Raamsdonk, a physicist at the University of British Columbia in Vancouver, was a crackpot.
His next submission, to General Relativity and Gravitation, fared little better: the referee’s report was scathing, and the journal’s editor asked for a complete rewrite.
Even the experts have trouble with this. I haven't looked through the other dozen or so papers that Van Raamsdonk appears to have coauthored on the subject, so there might be a better explanation of this stuff. But I do see some warning signs. First, his "entanglement" is a very specific form of entanglement. The "spooky action at a distance" things, which gets so much airtime here, aren't the same entanglements as the ones he claims lead to gravitation and space-time. Second, I see no way currently to come up with the space-time structure from a quantum system that doesn't already explicitly have it. There is a lot of ground to cover and a lot of existence proofs and consistency checks that will need to be met.
(Score: 2) by inertnet on Monday November 30 2015, @11:12PM
It looks a bit like the chicken and egg problem, or what are causes and what are effects. It seems to me that Van Raamsdonk looked at the problem from such a completely different angle (almost literally) that the referee got lost right away.
I don't know if this is related but I guess it is, some time ago there was a news item claiming that the universe is possibly a projection, similar to a hologram. Was that about the same or similar theories as discussed in the article?
(Score: 0) by Anonymous Coward on Monday November 30 2015, @04:18PM
Maldacena’s research had led him to consider the relationship between two seemingly different model universes. One is a cosmos similar to our own. Although it neither expands nor contracts, it has three dimensions, is filled with quantum particles and obeys Einstein’s equations of gravity. Known as anti-de Sitter space (AdS), it is commonly referred to as the bulk. The other model is also filled with elementary particles, but it has one dimension fewer and doesn’t recognize gravity. Commonly known as the boundary, it is a mathematically defined membrane that lies an infinite distance from any given point in the bulk, yet completely encloses it, much like the 2D surface of a balloon enclosing a 3D volume of air.
So, he basically starts with, "Imagine a perfectly spherical Universe..." The entire time I was expected mention of a frictionless vacuum full of perfectly spherical cows.
(Score: 1) by angst_ridden_hipster on Monday November 30 2015, @10:56PM
In Quantum, "spin" is a name for an attribute, but it is not what we think of as spinning like a top. It has nothing to do with rotation other than the equations work out similar to the angular momentum of a spinning object in the macroscopic domain.
</pedantic>
Eloi, Eloi, lema sabachtani?
www.fogbound.net
(Score: 0) by Anonymous Coward on Tuesday December 01 2015, @09:14AM
That's not true. It is transformed like a pseudovector under space rotations, and thus takes part in the conservation of angular momentum through Noether's theorem.
What is true is that it does not imply something actually spinning. But it has much more relations to rotation than just a superficial mathematical similarity.