‘My complete answer to the late 19th century question ‘what is electrodynamics trying to tell us?’ would simply be this: ‘Fields in empty space have physical reality; the medium that supports them does not.’ Having thus removed the mystery from electrodynamics, let me immediately do the same for quantum mechanics: ‘Correlations have physical reality; that which they correlate does not.’ The first proposition probably sounded as bizarre to most late 19th century physicists as the second sounds to us today; I expect that the second will sound as boringly obvious to late 21st century physicists as the first sounds to us today. And that is all there is to it. The rest is commentary.’ Mermin D. What Is Quantum Mechanics Trying to Tell Us? Notes for a lecture given at the Symposium in Honor of Edward M. Purcell, Harvard University, October 18, 1997. Am. J. Phys. 1998; 66: 753-767. Quantum Physics Quantum physics - the world of the very small (or more strictly, the world of the very isolated) encompasses some bizarre theories – do not worry if they seem bonkers; they really are. Quantum theory is strange to all but the wisest of people, counter intuitive and impossibly difficult to explain in simple language. The ‘theory’ consists of a collection of ideas developed over the twentieth century. Some of its components are still not well understood and some of the bizarre behaviour it predicts flies in the face of ‘common sense’. Paul Dirac who was a Lucasian Professor of Mathematics at Cambridge University England (a predecessor of Steven Hawking) said: ‘there is hope that quantum mechanics will gradually lose its baffling quality... I have observed in teaching quantum mechanics, and also in learning it, that students go through an experience... The student begins by learning the tricks of the trade. He learns how to make calculations in quantum mechanics and get the right answers... it is comparatively painless. The second stage comes when the student begins to worry because he does not understand what he has been doing. He worries because he has no clear physical picture in his head... Then, unexpectedly, the third stage begins. The student suddenly says to himself, I understand quantum mechanics, or rather he says, I understand now that there isn’t anything to be understood...’ The atom is the building block of everything. How does it work? How do the electrons move inside it? Scientists at the beginning of the 20 th century had been pondering such questions for more than a decade, without getting anywhere. A Danish Physicist Niels Bohr had developed a series of equations that would in part predict electron behaviour in jumping from one orbit to another and back, releasing light in the process (predicting the orange colour seen when heating sodium in a flame for example). However, there seemed to be no reasonable force capable of guiding the electrons on Bohr’s strange orbits, and in his orbital leaps. Staying alone on Heligoland, an island in the North Sea, to escape seasonal pollen allergy, Werner Heisenberg resolved to explore radical ideas as an explanation. His ‘radical idea’ was to stop trying to find a new force or a new law of motion as explanations and base everything on quantities that are observable, considering the electron itself. He simply replaced the numbers in Bohr’s equations for orbits with tables or matrices of numbers accounting for every possible electron orbit. At the time Heisenberg said ‘At first, I was deeply alarmed. I had the feeling that I had gone beyond the surface of things and was beginning to see a strangely beautiful interior and felt dizzy at the thought that now I had to investigate this wealth of mathematical structures that Nature had so generously spread out before me’. The energy values calculated using the matrices of Heisenberg were precisely those hypothesised by Bohr and in effect, quantum physics was born. Ultimately it leads to two principles of quantum theory: firstly, information is finite and secondly, even when we have gathered maximum information about an object, it is still possible to learn something unexpected about it. The future is not determined by the past: the world is probabilistic. This general property of reality is called Heisenberg’s uncertainty principle. He showed that if the precision with which we have information on the position of something is ΔX, and the precision with which we have information on its speed (multiplied by its mass) is ΔP, the two precisions cannot both be arbitrarily good. They cannot both be too close to zero. Their product cannot be smaller than a minimum quantity (half the Planck constant). It applies to everything. An immediate consequence is granularity. Light, for instance, is made of photons or quanta of light, because portions of energy that were even more minute than this would violate the the first postulate. Teleportation Broadly speaking, Newton’s Law of Universal Gravitation is a perfectly good description of our everyday experiences; yet it is wrong. Much of physics is now explained in terms of General Relativity – the world of the very large and Quantum theory, yet we have not quite worked out how to bring the latter two worlds together – but we are getting close (although those who offer any such explanations are often considered crazy by their contemporaries). Our current gaps in understanding are expressed through terms such as ‘dark energy’ or ‘dark matter’. Do not be fooled by anyone who talks knowledgably about either of these; they are claiming expertise in ignorance! Einstein’s theory of General Relativity describes how matter distorts space-time and how distorted space-time, in turn, affects matter. Objects, like the Earth, fly freely under their own inertia through warped space-time following a curved path because it is the shortest route in that warped space- time. One of the interesting possibilities raised by quantum theory is ‘teleportation’. I know that is something much beloved by TV and films – all of which you might rightly suspect is nonsense. Except quantum theory is weird enough to accommodate it. Just not in the manner it is usually portrayed. Quantum teleportation is a technique for transferring quantum information from a sender at one location to a receiver some distance away. However, Quantum teleportation only transfers quantum information. Put all that aside for the moment. Let us suppose you had the ability to ‘teleport’ objects and people. With that, you would have intoxicating, addictive and absolute power. Imagine how it would make you behave? Well, I can tell you, not like it is currently portrayed in popular science fiction. As John Emerich Edward Dalberg-Acton, 1st Baron Acton, wrote to Mandell Creighton, Archbishop of the Church of England on April 5 th , 1887, ‘Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always bad men, even when they exercise influence and not authority: still more when you superadd the tendency or the certainty of corruption by authority. There is no worse heresy than that the office sanctifies the holder of it. That is the point at which . . . the end learns to justify the means.’ Imagine if you were not even a great man in the first place. The Speed of Light After detailed study of the motion of Jupiter’s moon Io, Ole Rømer concluded in 1676 that light travelled at a finite speed. In 1865, James Clerk Maxwell, building on the earlier work of Ampère, Coulomb and Faraday, proposed that light was an electromagnetic wave travelling at the speed (c) relative to some unconfirmed medium he called ‘aether’. Michelson-Morley’s experiments of 1887 failed to find this “aether” but unexpectedly demonstrated that light travelled at the same speed regardless of whether it was measured in the direction of the Earth’s motion or at right angles to it, completely contrary to classical physics and common sense at the time. In 1905, Einstein realised that Maxwell’s equations led to an apparent paradox in the laws of physics. They suggested that by catching up to a beam of light, a stationary electromagnetic wave could be seen – an impossibility. He also realised that the whole idea of aether as a medium for light to travel in was totally unnecessary. According to Einstein’s theory of special relativity, the speed of light (c) was the maximum speed at which all matter (and thus information) in the universe could travel. For many practical purposes, light (and other electromagnetic waves) appeared to propagate instantaneously but, over very long distances, its finite speed has a noticeable effect. For example, light from the stars left them many years previously. The speed of light is used to measure large distances to a high precision. As defined by the International Astronomical Union (IAU), a light-year is the distance light travelled in a vacuum in one Julian year (365.25 days). The term light-year is sometimes misinterpreted as a unit of time, but it is, of course, a unit of length – approximately nine trillion kilometres (or about six trillion miles). If you could travel at 30 million miles an hour, it would take 40 years to cover two light years. Since light started travelling at the big bang, just under 14 billion years ago, we cannot see any further than about 14 billion light-years (remember a light-year is a measure of distance not time). The amount of space encompassed by this journey of light is called the Hubble Volume and represents our observable universe. The observable universe includes 10 million superclusters, 25 billion galaxy groups, 350 billion large galaxies, 7 trillion dwarf galaxies and 30 billion trillion stars. So, how can the universe be 93 billion light-years wide if it is only 14 billion years old and nothing can travel faster than light? Observations of galactic redshift (the change in light’s wavelength when its source is moving away) reveal those objects three times more distant are moving three times faster relative to nearby galaxies. The farther we investigate space, the faster the galaxies are moving. They are moving so fast at these vast distances that they easily surpass the speed of light. While the theory of relativity states that objects cannot travel faster than the speed of light, it does not place any limits on space-time itself. Consequently, the galaxies (and any other objects in space) are not defying the ‘laws’ of physics by travelling through space faster than light. Instead, every portion of space-time is expanding. It is not even that the edges of space are flying outward but that space-time itself – the area between galaxies, stars, planets – is stretching. When the universe first came into existence approximately 14 billion years ago, space-time itself began expanding at speeds faster than the speed of light. This period, called inflation, is integral to explaining much more than the universe’s size. It also covers things like the homogeneous nature of space on a large scale and the conditions that existed during the first epoch. The universe transitioned from an infinitely dense and hot state into a vast area teeming with protons and neutrons – particles that eventually came together and forged the building blocks of all matter – within moments. After the initial inflation died down, the expansion slowed. Now, objects are being pulled apart by a process we do not understand and, in our ignorance, call dark energy. Black Holes, Wormholes and White Holes Neither wormholes nor black holes have yet been seen directly, although both follow inevitably from the General Theory of Relativity. There is indirect evidence, at least for black holes, including a recent photograph of the accretion disk around one. If the mass of the compressed remnant of a supernova exceeds about 3 to 4 solar masses, the core collapses completely into a gravitational singularity, a single point containing all the mass of the original star. The gravity in such a phenomenon is so strong that it overwhelms all other forces, to the extent that even light cannot escape from it, hence the name black hole. Although the singularity at the centre of a black hole is infinitely dense, the black hole itself is not necessarily huge and exerts no more gravitational pull on the objects around it than the original star from which it was formed. Any objects orbiting the original star that survived the supernova explosion continue to orbit the black hole. The black hole can grow by assimilating material, but that material must approach quite close to the black hole before being drawn in. The simplest type of black hole, in which the core does not rotate and just has a singularity and an event horizon, is known as a Schwarzschild black hole after the German physicist, Karl Schwarzschild. He pioneered much of the very early theory with Albert Einstein. In the late fifties, David Finkelstein published a paper, based on Einstein and Schwarzschild’s work, describing the idea of a “one-way membrane” which triggered a renewed interest in black hole theory. In the mid-sixties, Roger Penrose demonstrated that a gravitational collapse of a large dying star must result in a singularity where space-time cannot exist, and classical general relativity breaks down. In the late sixties, Penrose and Stephen Hawking applied a new mathematical model derived from Einstein's theory of General Relativity. This led to Hawking's proof of the first of several singularity theorems. Such theorems provided a set of conditions for the existence of a gravitational singularity in space-time and showed that, far from being mathematical curiosities, they were a common feature of general relativity. Space-time locality is one of the cornerstones of our present understanding of physics. ‘Locality’ implies the impossibility of sending signals faster than the speed of light. However, our understanding of locality is challenged both by quantum mechanics and general relativity. Quantum mechanics gives rise to Einstein-Podolsky-Rosen (EPR) correlations (entanglement). General Relativity allows solutions to the equations of motion that connect regions through relatively short “wormholes” or Einstein-Rosen bridges. At first sight, both entanglement and Einstein-Rosen bridges seem like strange violations of locality. However, classical quantum physics says in both cases that they do not provide mechanisms to propagate signals. Examination of a Penrose diagram of a two-sided black hole clearly shows that no signal can pass through a wormhole from one exterior region to the other. Imagine two black holes that are entangled to produce an Einstein- Rosen bridge. Bob is stationed at one and Alice at the other. As long as Bob and Alice stay outside their respective black hole event horizons, communication between them can only take place through exterior space – a long trip which cannot be short-circuited through the Einstein-Rosen bridge. Imagine that Alice has a quantum computer that controls her black hole. She hopes to send messages to Bob through the Einstein-Rosen bridge. However, Bob cannot receive the messages if he is outside the event horizon on his side although as soon as he passes through the event horizon he can. You might imagine that under certain conditions Bob and Alice could jump into their respective black holes and meet very soon after. However, Einstein-Rosen bridges are not traversable. As Bob jumps into the black hole, it shrinks as he approaches the singularity; the bridge closes, before he can get through. At the same instant, time evolves and the bridge stretches. Its length grows so fast that no signal can get through. Although it may seem a very complex, peculiar and perhaps counterintuitive object, a black hole can essentially be described by just three quantities: its mass, its angular momentum and its electrical charge. In 1974, Hawking showed that black holes thermally create and emit sub-atomic particles (now called Hawking radiation) until they exhaust their energy and evaporate completely. According to this theory, black holes are neither completely black nor last forever. He showed how the strong gravitational field around a black hole can affect the production of matching pairs of particles and anti-particles. This happens all the time in ‘empty’ space according to quantum theory. If the particles are created just outside the event horizon of a black hole, then it is possible that an electron may escape – observed as thermal radiation emitting from the black hole – while its antimatter equivalent, a positron, may fall back into the black hole. This is the mechanism through which a black hole gradually loses mass. It was one of the first expressions of a theory which synthesised, at least to some extent, quantum mechanics and general relativity. However, a corollary of this is the so-called “Information Paradox” or “Hawking Paradox”, whereby physical information (which roughly means the distinct identity and properties of particles going into a black hole) appears to be completely lost to the universe in contravention of the accepted laws of physics (referred to as the "law of conservation of information"). Hawking vigorously defended this paradox for almost 30 years. In 2004, he overturned his long-held belief that any “information” crossing the event horizon of a black hole is lost. He became convinced that black holes would eventually transmit, albeit in a garbled format (as we perceive it) information about all matter they had consumed. This is a complex area of theory and even Hawking struggled to communicate it, stating at one point, “The Euclidean path integral over all topologically trivial metrics can be done by time slicing and so is unitary when analytically continued to the Lorentzian”. It is theoretically possible to use such a concept as a tunnel or short-cut for high-speed space travel between distant points. However, a generally accepted property of wormholes is that they are inherently highly unstable and would probably collapse in a much shorter time than it would take to get through to the other side. Furthermore, even if it were possible to get a photon or other matter into the Einstein-Rosen bridge it would necessarily hit the singularity(s). A more massive object would have to travel faster than the speed of light to get through. Nevertheless, the prospect of a practical application of the theory remains a possibility. An alternative proposed solution to the accepted view is almost impossible to envisage or explain in an understandable way. Conformal Symmetry theory suggests that, as an object falls into a black hole, a copy of the information that makes it up is scrambled and distributed in two dimensions around the edge of the black hole. Furthermore, it suggests that a similar process occurs in the universe as a whole. This implies three-dimensional ‘reality’ is merely a holographic representation of alternate reality contained in two dimensions around the edge of the universe. Quantum Entanglement Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently of the others. In quantum mechanics, ‘spin’ is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons) and atomic nuclei. One notable feature of angular momentum is that it must be preserved – it cannot be lost. Entanglement means that if you observe the spin state of one of a pair of particles, you know that of the other, even when the particles are separated by a large distance. In other words, a quantum state is determined for the whole system. Entanglement has been demonstrated experimentally in photons, neutrinos, electrons, molecules and even small diamonds. Imagine two observers, Bob and Alice, who might be neighbours, or on different continents, even on different planets, observing a pair of particles, one with Bob and the other with Alice. ‘People have been asking how the particle with Alice somehow knew the proper spin state to be in, because presumably, before any measurement is made, they both can randomly select one of two spin states to be in. Was there any signal sent from Bob's particle to Alice's to tell it what spin state to be in? We have found no such signal, and if there is, it has been shown that it will have to travel significantly faster than c (the speed of light). No matter how far apart the two daughter particles are, they somehow will know just what state to be in once one of them is measured. This, boys and girls, is what we called quantum entanglement. The property of the quantum particles that we call ‘spin’ is entangled between these two particles. Once the value of the spin of one particle is determined, it automatically forces the other particles to be in a corresponding state to preserve the conservation law. But note that what is entangled is the property of the particle. It is the information about the property (spin) that is undergoing the so-called ‘quantum teleportation’. The particle itself did not get ‘teleported’ the way they ‘teleport’ things in Star Trek movies/TV series. It is the property, in other words, the information, about the object, that is entangled, not the entire object itself. So, in this example, the object doesn't jump around all over the place.’ ZapperZ Wednesday, April 22, 2015 http://physicsandphysicists.blogspot.co.uk/2015/04/quantum-entanglement-for- dummies.html Accessed 2021 Quantum Vacuum Drive The Unruh radiation is a strange phenomenon: an accelerating observer travelling through Minkowski space-time will observe a thermal spectrum of particle excitations. In other words, the background appears to be warm when viewed from an accelerating frame of reference. Minkowski space-time is a combination of three-dimensional Euclidean space and time into a four- dimensional manifold. A manifold is a topological space that is locally Euclidean. For example, any spherical object, Earth for instance, that is nearly flat on a small scale is a manifold. Unruh demonstrated theoretically that the notion of vacuum depends on the path of the observer through space-time. However, a ‘vacuum’ is not ‘empty space’, it is filled with the quantum fields that make up the universe. A vacuum is simply the lowest possible energy state of these fields. This phenomenon underpins the quantum vacuum thruster where thrust is produced by the momentum transfer of microwaves in a waveguide chamber of the drive. The cone shaped chamber allows Unruh radiation of a certain size at the large end but only a smaller wavelength at the other end, exerting an impact on photons. Nevertheless, how could such a device work? According to Einstein’s theory of special relativity, any object with rest mass gains relativistic mass as it increases momentum. Yet, photons never come to rest and cannot be considered to have resting mass and, without that, its mass cannot increase like relativistic masses (which is why light travels so quickly). This forms the basis of our ‘laws’ of physics that agree with experiments; photons have no relativistic mass and therefore no inertial mass. Bizarrely, however, photons do have momentum as demonstrated by the Compton Scattering experiments. The scattering of a photon by a charged particle (or microwave) results in a decrease in energy (increase in wavelength) of the photon. It is this change in momentum and the requirement to maintain overall momentum in the system that provides the energy to power the thruster. Even more oddly, if the shape of the chamber is reversed, the thrust itself can be reversed. Speeds in excess of 600,000 mph are theoretically possible from an engine that apparently has no fuel. The Multiverse The multiverse is a theory in which our universe is not the only one, rather many universes exist in parallel to each other. There is a range of constructs to describe the multiverse from level one to four. Consider a level one parallel universe. In such a model, space is so vast the rules of probability inevitably dictate other planets exactly like Earth will exist (in fact an infinite number). This construct relies on two assumptions: The universe is infinite. Within an infinite universe, every single possible configuration of particles we know of in the Hubble volume takes place multiple times. However, if such parallel universes do exist, reaching one would be impossible. Out with the Hubble volume, no information could ever be exchanged as it is beyond the speed of light, the absolute limitation of information transfer within the Hubble volume. Unless of course, you could transcend space time. Ship of Theseus The ship of Theseus, also known as Theseus's paradox, is a thought experiment that raises the question of whether an object having had its components replaced remains fundamentally the same object. The paradox was most notably considered by Plutarch in the late first century. ‘The ship wherein Theseus and the youth of Athens returned from Crete had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their places, in so much that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.’ Plutarch, Life of Theseus Plutarch questioned whether the ship would remain the same if it were entirely replaced, piece by piece. Centuries later, the philosopher Thomas Hobbes (1588-1679) introduced a further element to the conundrum; what would happen if the original planks were gathered up after they were replaced and used to build a second ship. He asked, ‘Which ship, if either, would be the original ship of Theseus?’ The Platonic Solids The ancient Greeks studied the Platonic solids extensively. Sources credit Pythagoras with their discovery. Other evidence suggests that he may have only been familiar with the tetrahedron, cube and icosahedron and that the discovery of the octahedron and dodecahedron belong to Theaetetus, a Greek mathematician and contemporary of Plato. Theaetetus gave a mathematical description of all five platonic solids and may have been responsible for the first known proof that no other convex regular polyhedra exist. The Platonic solids are prominent in the philosophy of Plato. He wrote about them in the dialogue Timaeus, a long monologue given by Timaeus of Locri, written about 360 BCE, in which he associated each of the four classical elements (earth, air, water and fire) with a regular solid. Earth was associated with the cube, air with the octahedron, water with the icosahedron and fire with the tetrahedron. Of the fifth Platonic solid, the dodecahedron, Plato obscurely remarked, ‘The gods used it for arranging the constellations on the whole heaven.’