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-------------------- 2587 - STRING THEORY - and Quantum Mechanics ?
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- One particularly important quantity in quantum mechanics is the anomalous magnetic moment of the electron, has been measured to thirteen decimal places, in perfect agreement with theory. This accuracy is like having a watch that keeps perfect time to within a second in 300,000 years.
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- The quantum mechanics theory tells us about atoms and molecules, electrons and nuclei, quarks and leptons properties and their interactions in accurate detail. For example: The least well-known of the constants of nature, the gravitational constant G, is known to about 20 parts per million, which is something like knowing how much table salt is in a shaker to within a single grain.
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- Many of the features of the quantum world defy our everyday intuition about how objects ought to behave. Many properties are indeterminate until they’re measured, an inescapable ,but essential. They include the element of randomness, and correlations between objects that seem to defy sensible limits.
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- Why should everyone learn something about quantum mechanics? For the same reason that everyone should learn something about art, and music, and philosophy, and all the rest: because it shows the very best of what humanity
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- Ever since Einstein, scientists have also been scratching their heads about how to make sense of space and time. Before then, almost everybody thought Isaac Newton had figured it all out. Time flows equably without relation to anything external. Absolute space is also its own thing, always similar and immovable.
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- But Einstein’s theories turned Newton’s absolute space and time into a relativistic equations that merged space and time. It was a physics game changer. No longer did space and time provide a featureless backdrop for matter and energy.
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- Formerly independent and uniform, space and time became inseparable and variable. As Einstein showed in his general theory of relativity, matter and energy warped the space-time surrounding them. That simple truth explained gravity.
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- Newton’s apparent force of attraction became an illusion perpetrated by space-time geometry. It was the shape of space-time that dictated the motion of massive bodies, and, massive bodies determined space-time’s shape.
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- Verification of Einstein’s space-time revolution came a century ago, when an eclipse expedition confirmed his general theory’s prime prediction giving a precise amount of bending of light passing near the edge of a massive body, in this case the Sun.
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- Space-time and gravity must ultimately emerge from something else. Quantum mechanics describes the machinations of matter and energy on the atomic scale with unerring accuracy. Attempts to find coherent math that accommodates quantum weirdness with spacetime geometric gravity have yet to be discovered.
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- Progress has emerged from the theoretical study of alternate space-time geometries known as “anti de Sitter space“, is weirdly curved and tends to collapse on itself, rather than expanding as the universe we live in does.
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- Studies of anti de Sitter space suggest that the math describing gravity and space-time geometry can be equivalent to the math of quantum physics in a space of one less dimension. Think of a hologram, a flat, two-dimensional surface that incorporates a three-dimensional image.
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- In a similar way, perhaps the four-dimensional geometry of space-time could be encoded in the math of quantum physics operating in three-dimensions. Investigations along these lines have revealed a surprising possibility: Space-time itself may be generated by quantum physics by the phenomenon known as “quantum entanglement“.
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- “Entanglement” is a spooky connection linking particles separated even by great distances. If emitted from a common source, such particles remain entangled no matter how far they fly away from each other. If you measure a property, such as spin or polarization, for one of them, you then know what the result of the same measurement would be for the other.
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- But , before the measurement, those properties are not already determined, a counterintuitive fact verified by many experiments. It seems like the measurement at one place determines what the measurement will be at another far distant location.
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- That sounds like entangled particles must be able to communicate faster than light. Otherwise it’s impossible to imagine how one of them could know what was happening to the other across a vast space-time expanse.
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- How do entangled particles transcend the space-time gulf separating them? Perhaps the answer is they don’t have to because entanglement doesn’t happen in space-time. Entanglement creates space-time.
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- Physicists have produced theoretical evidence that networks of entangled quantum states weave the space-time fabric. These quantum states are often described as “qubits” , bits of quantum information like ordinary computer bits, but existing in a mix of 1 and 0, not simply either 1 or 0.
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- Entangled qubits create networks with geometry in space with an extra dimension beyond the number of dimensions that the qubits live in. So the quantum physics of qubits can then be equated to the geometry of a space with an extra dimension.
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- The geometry created by the entangled qubits may very well obey the equations from Einstein’s general relativity that describe motion due to gravity. A geometry with the right properties built from entanglement has to obey the gravitational equations of motion.
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- Still, it remains to be shown that the clues found in toy universes with extra dimensions will lead to the true story for the ordinary space-time in which real physicists strut and fret. Nobody really knows exactly what quantum processes in the real world would be responsible for weaving space-time’s fabric.
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- String theory aims to address these various theoretical conundrums; the most fundamental of which is how gravity works for tiny objects like electrons and photons. General relativity describes gravity as a reaction of large objects, like planets, to curved regions of space, but theoretical physicists think gravity should ultimately behave more like magnetism, refrigerator magnets stick because their particles are swapping photons with the magnet’s particles.
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- Of the four forces in nature, only gravity lacks this description from the perspective of small particles. Theorists can predict what a gravity particle should look like, but when they try to calculate what happens when two "gravitons" smash together, they get an infinite amount of energy packed into a small space. This is a sure sign that the math is missing something.
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- One possible solution, which theorists borrowed from nuclear physicists in the 1970s, is to get rid of the problematic, point-like graviton particles. Strings, and only strings, can collide and rebound cleanly without implying physically impossible infinities.
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- String theory turns the page on the standard description of the universe by replacing all matter and force particles with just one element: Tiny vibrating strings that twist and turn in complicated ways that, from our perspective, look like particles.
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- A string of a particular length striking a particular note gains the properties of a photon, and another string folded and vibrating with a different frequency plays the role of a quark, and so on. In addition to taming gravity, the framework proved attractive for its potential to explain so-called fundamental constants like the electron's mass.
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- But that initial simplicity turned out to come at the cost of unexpected complexity. string math didn't work in the familiar four dimensions, three of space and one of time. It needed six additional dimensions for a total of 10 visible only to the little strings, much as a power line looks like a 1D line to birds flying far overhead but a 3D cylinder to an ant crawling on the wire.
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- A more fundamental theory emerges that the five string theories each represented an approximation of a more fundamental, 11-dimensional theory in a particular situation, much as how Einstein’s space- and time-bending theories of relativity match Newton’s description of objects moving at normal speeds.
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- The novel theory called M-theory, remains as a placeholder with no official meaning except to be the parent theory that would describe absolutely everything.
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- “Entropy” refers to the number of ways that you can arrange the parts of a system, but without being able to see into the impenetrable depths of a black hole, no one knows what type of particles might lie inside, or what arrangements they can take.
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- In the 1970s Stephen Hawking showed how to calculate the entropy, suggesting that black holes have some sort of internal structure. Most attempts to describe the black hole’s makeup fall short, but tallying the configurations of hypothetical strings does the trick.
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- The string framework still faces many challenges, however: It produces an impossible number of ways to fold up the extra dimensions that all seem to fit the broad features of the Standard Model of particle physics, with little hope of distinguishing which is the right one.
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- All of those models rely on an equivalence between force particles and matter particles called “super symmetry” that, like the extra dimensions, we don't observe in our world. The models also don't seem to describe an expanding universe.
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- Modern string theory connects mathematical dots. Regardless of how string theory's “Theory of Everything” evolves, its legacy as a productive research program may be assured on mathematical merit alone. The five string theories were shadows of a single parent theory, they highlighted connections called dualities, which have proven to be a major contribution to mathematics and physics.
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- A “duality” is an abstract, mathematical relationship between two situations that look different, but can be translated from one to the other. For example: a bird hologram on a credit card. Is it 2D or 3D? In a physical sense the sticker is flat, but in a visual sense the image has depth. Both descriptions agree that the hologram contains a bird.
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- It is implausible that humans stumbled by accident on to such an incredible structure as string theory that sheds so much light on established physical theories, and also on so many different branches of mathematics. Maybe it will be part of regular course curriculum in the near future?
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- January 16, 2020 2587
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--------------------- Thursday, January 16, 2020 --------------------
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