True or fake news?
https://www.spacedocumentary.com/201...which.html?m=1
Sent from my iPhone using Tapatalk
True or fake news?
https://www.spacedocumentary.com/201...which.html?m=1
Sent from my iPhone using Tapatalk
Looks correct to me, but very old news.
EPR was a "paradox" intended to show that QM was incomplete in its description of reality. Einstein insisted on local realism, and was against what he saw as QM's "spooky action at a distance". But subsequent experiments testing EPR show that Einstein was wrong about local realism.
Grant Hutchison
The idea that "which" should only be used in non-restrictive relative clauses was cooked up by H.W. Fowler, pretty much out of thin air. He thought it would be nice if people used "which" and "that" to distinguish between non-restrictive and restrictive clauses - but no-one ever did that until Fowler brought it up as an option, and few people have bothered with it since.
Grant Hutchison
It's a thing. People still teach it, people still do it. I certainly do it, and I recall developing involuntary tooth-grinding while reading some of Peter Hamilton's early novels because he used restrictive "which" far too much.
It's just more of a stylistic choice than a grammatical error.
Grant Hutchison
That choice of a word is a trifle compared with the rampant grammar and syntax lapses throughout the article. Such an unprofessional-looking presentation makes me skeptical about its reliability. I realize that may be unfair, but I don't know enough about quantum entanglement and quantum theory in general to judge it on its merits.
From another article:
"Does "waterworld" will have life? Today we have numerous eyes in outer space to make discoveries, of course they are space telescopes. They helped us to discover many galaxies stars and planets present at very large distance."
This is the real joy of the internet: you do not need an editor in order to be published and widely read. You do not need an editor for anything. But you will look stupid.
Not news at all in what looks like English as a second language with incorrect statements about Einstein. A better description is on Wikipedia at EPR paradox. Einstein did not want to "prove quantum theory wrong". Einstein hoped to complete quantum theory to make it a "purely algebraic theory" or a hidden variables theory.
Actually I think it's pretty fair to say that Einstein wanted to prove quantum theory wrong, and the EPR paradox was an effort to do just that. The position was essentially, "did you folks realize that your theory is predicting something absurd," taking Schroedinger's cat paradox and keeping it at the level of experiments that can actually be done. As it turned out, experiments of the absurdly "spooky" result vindicated quantum mechanics-- starting about 50 years ago! Yes the experiments keep getting better, and every new update generates headlines just like this one, but no one is surprised any more. Grant is right-- it's true, but old news.
Not that the EPR paradox doesn't matter any more, though. In a remarkable irony that probably went completely unappreciated at the time, in the same year in 1935, Einstein and Rosen were involved in two completely separate papers-- the EPR paradox paper on quantum mechanics, and a paper on black holes, about "Einstein-Rosen bridges" between black holes and white holes. There are three very interesting aspects of these two papers:
1) they are both generally regarded as Eintein "misses", because he drew the wrong conclusion from the EPR paradox, and because there is no evidence that white holes exist,
2) at the time they were written, it is unlikely that either Einstein or Rosen saw any connection between them whatsoever, and
3) today many theorists regard the deep connection between them as the most profound discovery ever made by humanity, sometimes expressed in the cryptic equation "ER=EPR." A terse summary is given at https://en.wikipedia.org/wiki/ER%3DEPR, but the upshot of this conjecture is that instead of seeing entanglement as a kind of weird quirk that is so fragile it rarely has any significance, we should see it as the glue that holds all of reality together. Maybe it is like the glue on sticky notes-- allowing for both connectedness and dynamics.
Sit and ponder the irony of two great physicists, in the same year, writing one paper that says quantum mechanics can't be right because it's absurd, and another paper saying general relativity must be right because it is so darn beautiful and profound, all the while never realizing that the connection between the absurd and the profound might be the very beating heart of why reality works at all.
The wiki link provided does not work. Did you mean this?
https://en.wikipedia.org/wiki/EPR_paradox?wprov=sfti1
It works for me. It's not just EPR, it's EPR=ER.
Ok thank you. Entering the formula into wiki’s search bar brought it up.
I believe the idea behind ER=EPR is that the unification of quantum mechanics and general relativity has promise to help us understand what spacetime is. The great thing about physics is that it doesn't have to just take anything as given, we aren't forced to say that since we all perceive space and time, they must just be. In physics, we can look at space and time as consequences of something else, something more fundamental that explains, in some sense, why we perceive space and time in the first place. We might even conclude that both space and time are mental constructs that we build to make sense of the phenomena we perceive, so it is a kind of illusion that we actually perceive either space or time in and of itself, just as it is an illusion that the objects around us are single solid entities, or that baseballs really follow trajectories. We make sense of our surroundings using the space and time constructs of our minds, and physics allows us to understand why those constructs are successful, without actually taking space or time as a thing.
The core idea of ER=EPR is based around a duality, two things that look very different but are actually the same thing. The two things are how GR functions in anti-de Sitter space (AdS), and quantum field theories that are constrained to make the same predictions when using observers with different perspectives (CFT). The duality says that the behavior of the CFT on the boundary of the AdS mimics everything that happens in the AdS "bulk," which suggests that what we perceive as spacetime is actually just the boundary of a more profound set of "happenings." The connection with Einstein-Rosen bridges is that they pass through this "bulk", providing essentially invisible connections between things that may, for example, enforce entanglements that seem "spooky" to creatures (like us) who have no direct perception of this "bulk." The fragility of entanglements can be viewed as the reason our minds have never developed any intuition about them, and we have never needed to account for the bulk in our process of making sense of our perceptions, but its existence can help "explain," in a theoretically pleasing (and very difficult and currently speculative) manner, why our concept of spacetime works. We are, in a sense, like the ants that crawl on the surface of apples, who have no perception that there is an apple in there anywhere, as they have need only to perceive its surface-- until they break the skin and feast on the fruits of that interior.
This duality was never dreamt of as Einstein and Rosen were writing about GR solutions of bridges through this higher-dimensional bulk, and as Einstein and Rosen (with Podolsky) were also writing about the absurdity of a quantum theory that says correlations between experiments on particles can be enforced outside the normal limitations of cause and effect within the light cone. It was that cause and effect structure that Einstein labored so carefully to maintain in his theory of relativity, yet it seems that in the end he derived a theory that when applied in the anti-de Sitter space of Einstein's own cosmological constant, expresses a duality on its boundary that shatters those very same notions of local realism. Einstein may have birthed a theory that exhibits, and even helps explain, the exact spooky behavior he regarded as so abhorrent in quantum mechanics.
This irony goes deeper. Einstein originally expected spacetime to be flat, so suggested a cosmological constant to make that possible. When Hubble observed expansion, Einstein discarded his own constant, but after his death, the acceleration was discovered, requiring the return of the cosmological constant. This constant seems to have a value that makes spacetime flat again, but this flatness is only in the boundary of the "bulk" anti-de Sitter space, but the irony is that what you need to have an anti-de Sitter space is also Einstein's invention-- putting a cosmological constant into the vacuum. So as he was bashing entanglement as absurd in this EPR paper, he never dreamed that he had already furnished the two key pieces (anti de Sitter space and Einstein-Rosen bridges) to explain what entanglement actually is (and spacetime to boot).
Last edited by Ken G; 2019-Jul-08 at 12:34 AM.
very nice explanation, I hope you don't mind if I send that to friends who pester me about space time after a few wee drams.
sicut vis videre esto
When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
Originally Posted by Ken G
Actually, the anti-de Sitter space in question is not the space we inhabit, it is the "bulk", a higher dimension that the spacetime we inhabit is just the boundary of. It's a "holographic" model, where you regard the information carried by all processes within the bulk volume as being "read from" the boundary only, as if our senses were only able to penetrate the boundary but all the information is there anyway. The bulk can be anti-de Sitter, even if the boundary is flat (indeed, it predicts that the spacetime of our universe must be flat, as the boundary will be Minkowskian). The duality is a conformal field theory playing out on a Minkowskian boundary that is dual to the equations of GR in the anti-de Sitter "bulk".
There are further ironies here. String theory was devised as a new way to understand gravity by making it look like a quantum field theory, but the duality means that the gravity we already have, GR, was equivalent to a quantum field theory all along, just on the boundary of the bulk rather than in the space itself. What makes this particularly ironic is that the problem with field theories is they are often nonperturbative, meaning that you need to include some potentially infinite number of processes that all contribute to the result, and you can't do that. But with the duality, any theory playing out on small scales with strong coupling is dual to a theory that plays out on large scales with weak coupling, that is easier to compute. So in the main practical applications of the AdS/CFT duality (which is still speculative but has found applications anyway), it is actually the solutions of GR that are being used to understand applications of field theory, even though string theory was invented to accomplish the exact opposite!
Last edited by Ken G; 2019-Jul-09 at 01:35 AM.
(Just hopefully clarifying things a little more here):
De Sitter space is curved spacetime continuum with positive curvature, (meaning the angles of a triangle > 180 degrees).
Anti de Sitter Space (AdS) however has a negative curvature, (meaning the angles of a triangle > 180 degrees). It has similar properties to the interior of say, a spherical box, but the spherical ‘wall’ exerts a repulsive force which is so strong, (due to the curvature), that if it contained an almost universe sized black hole (BH) for eg, the BH couldn’t evaporate (via Hawking Radiation - HR), because the repulsive force would push the HR back into the BH. Clocks run extremely fast out towards the walls (or boundary .. or cosmic horizon) of the AdS spacetime .. and it would also be extremely hot.
AdS can also have a variety of dimensions (any number of spatial, but usually only one time dimension).
The main thing to notice here is that the boundary wall (or cosmic horizon) of AdS is basically impenetrable .. so the idea that everything inside the spherical box of AdS space can be described by bits of information stored in pixels on its walls (as per what the Holographic Principle purports), takes another step towards having at least theoretical support from the AdS spacetime (negative curvature) model.
The CFT/duality discovery revealed that a ‘flatland’ universe of 2 spatial+1 time dimension that includes Quantum Chromodynamics (QCD) but not gravity, was mathematically equivalent to our 'normal' 3 spatial + 1 time dimensional universe with gravity. It was then found that this was caused by the distortion of the AdS space. The generalisation that followed was: therefore a 3 dimensional universe with gravity is mathematically equivalent to a 2 dimensional quantum description (ie: informational) 'hologram' expressed at the boundary (or cosmic horizon) of that universe.
It's the other line that needs correction. In flat Euclidean space, the angles of a triangle add to 180 degrees. In space with a positive curvature, the sum of the angles is greater than 180 degrees. And in space with a negative curvature, the sum of the angles is less than 180 degrees.
(Note that this means that the "inside" of a sphere is not a good example of negative curvature. The "inside of a sphere" has the same curvature as the "outside of a sphere". For negative curvature, you actually need a different shape entirely.)
Conserve energy. Commute with the Hamiltonian.
Oops .. yep you're right. Just a typo. Thanks for the correction.
Meh .. its an analogy and its more intended to serve the purpose of picturing an AdS observable universe and how it behaves in connection with its interesting application of enclosing a BH. The analogy isn't strictly about distinguishing between negative and positive curvatures .. (although I acknowledge that was the topic of Strange's original query).Originally Posted by Grey
Yep .. twas a typo.
I found the notion of 'the bulk' of a model universe having a different dimensionality to its outer regions (the CH), as somewhat confusing (which was the purpose of my post). The Holographic Principle's main outcome of viewing a universe's 'enclosed' quantum information at a remotely located Cosmological Horizon of only 2 dimensions, doesn't really justify saying that the dimensionality of that universe has to change at that outer region 'where we reside'. There is no need to change the dimensions of an any universe in order to conceptualise the HP. An AdS (3+1) universe provides a model which more or less realises the concept of the HP, because it forms an impenetrable barrier (due to the extreme curvature at its CH).
I guess the issue is more about where the physical significance emerges in such discussions ..